The boat for which we are designing the system in this lesson is used mostly for day sailing, so we can assume that, apart from a night at anchor from time to time, we will have a shore power connection pretty much every evening.
Let's explore how we would plan such a system by developing a circuit diagram and also discuss components that allow us to implement the wiring. Here is what the final circuit diagram will look like:
You can access the complete diagram of this example in easyEDA here:
(Or you can download it in PDF-format.)
Grouping the Loads
Before we start drawing the diagram, we have to find a meaningful way to group our loads and decide for each group whether it will be protected by a circuit breaker in the switch panel, by a fuse, or by a standalone circuit breaker.
We chose to assign the loads in the Boat Electrics Planner for our simple example boat to the following groups:
We chose the Prefix G for groups that are protected by panel breakers and F for loads that are protected by a fuse.
The somewhat arbitrary numbering of the fuses is because we actually use the numbers of the fuses in the circuit diagram and we have already used the lower numbers for the main fuses.
In the Sheet "DC groups", the groups will be summarized and we can give them a name (ideally one that later corresponds to the label on the switch panel):
We made a choice to use a separate circuit breaker for the radio and the other navigation equipment at the chart table, so that at least one of the two remains functional should a fault occur downstream of the panel in one of the conductors.
It is a good idea to use a unique ID composed of a prefix and a number for both loads and groups. This helps us identify the component in the circuit diagram and we can also use this on the labels for our conductors to indicate to which device or component the other end of a conductor is connected. In easyEDA, the upper text label of a component is reserved for such a unique ID and you will get an error message if you try to assign a duplicate label in your circuit diagram.
Charging
In our example, a multi-step shorepower charger charges the house bank whenever we have a shorepower connection and also keeps the cranking battery in a full state of charge. A good option for such a setup would be the Victron - Blue Smart IP22 Charger 12/30(3). This model delivers 30 amps which get distributed among three outputs. We only use two of these outputs.
Since our boat is connected to shorepower more or less every night, we don't have to worry too much about sophisticated charging systems underway. As a result we will keep the standard alternator. Its main job is to top up the cranking battery after an engine start at sea but it also provides some energy for the house bank when we are motoring for an extended period of time.
In this example, as the alternator is never used as a major charging source, we use split charging diodes. However, remembering what we learned in the lesson on charging circuits, we either choose a model that compensates for the voltage drop (such as the Victron Argodiode) or use a FET-based battery isolator (such as the Victron ArgoFET; the FETs minimize the voltage drop):
Batteries
The energy consumption in amp-hours between recharge periods for our simple example boat according to the Boat Electrics Planner is the following for the different scenarios:
We want to use gel cell batteries, so we use the Mid Capacity Rule and plan on 180Ah of battery capacity. This corresponds roughly to the recommendation according to the Mid Capacity Rule by the Boat Electrics Planner:
Because batteries in this capacity range are heavy and bulky, we choose to install two 90Ah-batteries in parallel:
Main Switches
Both the main battery bank and the cranking battery should have a main switch (battery isolation switch) to disconnect them (S1 & S2). This is important for situations when we want to work on the system or if a serious problem arises.
Requirements for Battery Isolation Switches
According to the ABYC, a battery is not required to have an isolation switch if the CCA rating is below 800 CCA or its capacity is below 100Ah. In this case the paralleled batteries will need a switch but the cranking battery may not (depending on its size). We still think it is a good idea to add a switch to each battery bank.
The two devices in our system that bypass these main switches are the battery monitor, because it has to be constantly powered up in order not to forget the state of charge of the battery, and the charging device. According to the ABYC and ISO, this is okay, see also this note.
The power draw of modern battery monitors is so low that it is not a problem to leave them connected to a battery for an extended period of time. (The Victron BMV 712 Smart, for example, only draws 0.7 amp-hours per month in standby mode.)
However, for an extended winter layup you might want to consider disconnecting it from the battery posts, depending on its power consumption in standby mode and the battery capacity.
For a layup, an easy way to make sure that no parasitic loads can drain the battery is to simply disconnect the negative battery conductor from its post.
Battery Monitoring
The cost of battery monitors has gone down significantly in recent years, so there really is no reason not to install one even on simple installations. Especially if we are in any case doing a rewiring job. For our example we choose a modern model where the shunt contains all the measuring electronics and transfers the data to the display unit via a data cable. This simplifies the wiring. (For example the Victron BMV 712 Smart.) The battery monitor will keep track of the state of charge of the house bank and also sense the voltage of the starter battery.
We have represented the data cable in green. The shunt needs to be powered via the main battery bank and also has a second conductor to measure the voltage of the cranking battery. The voltage sensing conductors are connected directly to the positive battery posts and therefore must be protected by a fuse (this fuse is typically already integrated in the conductor).
(Main) Fuses
For the house batteries we need a main fuse (F1). We leave the task of determining the rated amps until later after we have determined conductor sizes. But we should figure out the fuse location and fuse type at this stage of the process.
The cranking battery is not required to have a fuse, although depending on your situation, and how well you can physically protect the cranking conductor, it might be advisable to install one. If this is done it will almost certainly need to be technically oversized in order to prevent nuisance blowing (see also our lesson on Overcurrent Protection).
Michael once had a bad experience with an accidentally blown 500A fuse that prevented him from restarting his engine when he badly needed it!
For these main fuses, MRBF-fuses, which can be attached directly to the battery terminal, come in handy. If other fuses are used, not directly attached to the battery terminal, to comply with the ABYC and ISO standards we will need additional protective sheathing on the conductor between the battery and the fuse. Whatever fuse is used needs to have a high-enough ampere interrupting capacity (AIC) rating to handle the highest potential short circuit current from the batteries (again, see our lesson on Overcurrent Protection).
In addition to the main battery fuse, we have to add lower rated fuses to protect any smaller positive conductor going to the switch panel, and to any loads, such as charging sources, that are connected directly to the battery. We can use separate in-line fuse holders or, and depending on the situation this might be the easier and cheaper option, a fuse block.
In our example we chose the SafetyHub 150 from Blue Sea, which has the advantage of providing slots for both high-current fuses (MIDI / AMI) and standard ATO fuses and in addition has a busbar to connect the negative conductors to circuit ground.
The alternator and the feeder conductor to the switch panel are connected to the MIDI / AMI fuses (F5 and F6) and the loads/groups for which we choose a fuse as the OCP device (F9, F10, F14) are connected to the smaller ATO fuses. Note that for individual loads you have to check the maximum amperage for single circuits for which the fuse block is rated, and also the maximum sum of the loads for the fuse block as a whole.
Level of Detail in Circuit Diagrams
Note that in general circuit diagrams are supposed to be an abstract representation of the system. In theory we only need the basic symbols introduced in the module on Components and Circuit Diagrams.
However, in order to make it easier to understand the actual installation on the boat, we have chosen to represent common components such as fuse blocks, switch panels, and bus bars as items in the circuit diagram.
We have added these to our BoatHowTo component library in easyEDA, so feel free to use them also for your own diagrams.
Panels & Switches
We have only 8 groups of loads that we choose to put behind a circuit breaker in the switch panel. So we can select a model with 8 switches, such as this one:
Depending on the situation and if we plan to extend the system in the future, it might be a good idea to use a panel with one or two extra circuit breakers that are left empty for future use.
Most of the better switch panels have LED lights included that indicate if a switch is closed, in which case they also need a connection to ground. This is something that is easy to forget when planning your wiring. We will talk more about negative conductors and connections to ground later.
Individual Switches for Loads in Groups
We may also want to add individual switches to loads that are grouped together. A typical example would be cabin lights. Depending on the model, individual lights may have a switch right at the light. In such a case it is up to you if you want to add it to the diagram or leave it out. It might add unnecessary clutter to the drawing. In our example, we omitted these individual switches.
We added an extra switch to the USB plug, because for the model we used we could measure a current draw of over 20 mA in standby mode:
This does not sound like much, but it would draw almost 15 amp-hours out of the battery over a month! So we want to be able to turn it off whenever we leave the boat. Other models are better in this respect and draw less than 1 mA in standby mode which is below one amp-hour per month. Be sure to check/measure the energy consumption in standby mode for any device that is connected to the battery via a fuse without a separate switch.
For the bilge pump, we chose to add a single pole, double throw switch (S3): Switched in one direction (‘auto’), the float switch S4 is powered up so that every time the bilge water level rises the pump is turned on. In the other direction (‘manual’), the switch is a momentary type, which is to say it can only be held on against a spring pressure. When held on, a circuit is powered up which bypasses the float switch to turn on the bilge pump. This way the bilge pump can be tested without water in the bilges to make sure it is still operational. In the neutral position, the bilge pump is turned off.
Another situation where we could have used a SPDT switch is between the navigation lights (Group 1) and the anchor light (Group 3). Wired this way, it is not possible to accidentally leave the anchor light on at the same time as the navigation lights and vice versa and we would have also saved a breaker on the switch panel.
The connections between multiple loads in a group can be carried out by one of the methods we talked about in the last lesson. In the circuit diagram, you can either use the abstract representation with a dot or else be more specific and add a bus bar from our library as a separate component (or create your own specific component in easyEDA).
Negative Conductors & Circuit Ground
In our example, we have only drawn the positive conductors and used the ground symbol as a shortcut for the negative ones. Remember that this does not mean that we can use the hull of a metal boat as the conductor!
Each negative connection has to be connected with appropriately sized conductors (of at least the same size as the positive conductors) to the point we define as the common ground or circuit ground.
In a typical installation, the negative conductors are connected to bus bars that are located in the same location as the positive distribution points. The busbars in turn are wired to a DC Main Negative busbar or, on simple boats like this one, the engine block, which is then connected to the negative terminals of the batteries. There is a connection from the DC Main Negative busbar or engine block to earth ground (source ground) via a keel bolt or some other underwater metal. The exception is boats with an isolated ground DC system (what the ISO calls a 'fully insulated two-wire DC system') which we will discuss in our Advanced Marine Electrics course.
If you want to show all the conductors on your boat and have enough space on the sheet, you can of course also draw the negative conductors. An example of what this might look like is this (older) wiring diagram of Jan's boat (the descriptions are in German but you should be able to get the general idea):
An older version of the circuit diagram of Jan's boat that includes the negative conductors. Click on the image to download a PDF of the diagram.
Add-on vs. Rewire
At this point we have a detailed design with all the core pieces for an electrical system that will meet the needs of a specific boatowner in a particular boat. Let’s assume the implementation will require significant changes to an existing boat, even a new one. Now we must go back to Module 4 to calculate conductor sizes, determine if existing busbars have sufficient ampacity, modify or add overcurrent protection as necessary, and think about all the other aspects of the changes that will be made to the boat’s wiring. A failure to adequately upgrade the boat’s wiring harness will result in poor performance and quite possibly an unsafe system. It takes only one weak link to create a fire risk!
With older boats that have wiring harnesses which were designed to handle significantly lower-energy lifestyles than what people expect today, and on which the wiring is now an untidy mess with nothing labeled, very often the smartest thing to do is to strip out the existing wiring and start again. However, it should also be recognized that the resulting high cost of installing a new electrical system is rarely, if ever, reflected in the value of the boat when it comes time to sell it. The benefit is going to be in terms of the improved onboard lifestyle in the interim so you had better plan on keeping and using the boat for a while!
Sizing the Conductors & Fuses
Now we have a good idea of the general setup, know which loads are grouped together, and also have the length of the conductors from the loads to the main distribution point(s). It is time to determine the required conductor sizes to limit voltage drop and to assure sufficient ampacity for the expected loads.
For this we use our filled-out Boat Electrics Planner and the wire size calculator (depending on your location either the ISO or the ABYC version).
We need to plug the conductor length, the amps and the other settings regarding conductor type and whether it runs through an engine compartment and any bundling considerations into the calculator for every single circuit on our boat. This will likely result in a variety of different conductor sizes which means we will have to buy a number of different conductors. Of course, we can always reduce the number by 'oversizing' the conductors to some loads, but we can never undersize them. (Once you get a feel for this, you may not need to do the calculations for every single load as they are often similar and with similar conductor lengths. But please do not get sloppy at this point and undersize any conductors!)
Feeder Conductors for Groups
If the distribution of your groups takes place at multiple points in your boat (for example, you have a distribution point in the front cabin where the cabin lights are attached) you can enter the length of the feeder conductor for the group in the "DC groups" sheet. The load for this conductor will be the aggregate load of the lights. It must be sized and overcurrent protected appropriately. If the same size conductors are used for the individual loads (e.g., the lights) no additional overcurrent protection is required, but if the conductors are down-sized additional overcurrent protection will likely be required unless the amp-rating of the OCP device on the feeder conductor is reduced to protect the smaller conductors (this can often be done without nuisance tripping).
Just make sure to use the total conductor length (i.e., the length of the feeder conductor to the distribution point plus the length of the conductor to the load) for your voltage drop calculations. This can become quite complicated, especially if the size of the feeder conductor is different from the individual conductors to the loads (for example, the feeder conductor from the batteries to the main panel on a boat). Your best bet will be to size the conductors conservatively so you are on the safe side when it comes to voltage drop.
Remember that whenever you reduce the conductor size for a downstream conductor, the amp rating of any existing OCP must not exceed the ampacity of the smaller conductor. If it does, you have to insert another fuse or circuit breaker at the connection point of the smaller conductor.
Typically it makes sense to choose one or two conductor sizes that exceed the required size for most of the circuits on the boat and to buy these sizes in bulk. This is not only cheaper but it also limits the amount of stock you have to carry if you want to be able to extend or fix the system on the go. These conductor sizes should be sufficient to meet the requirements for voltage drop (<10% for normal loads and <3% for essential loads) with an ampacity above the tripping amperage of the circuit breakers or fuses that are protecting the conductors.
Depending on the size of your boat and your loads, these common conductor sizes will probably be in the range of 1.5 mm² to 2.5 mm² (AWG 16-14 in the U.S.). This will keep voltage drop at bay for most smaller boats and the ampacity will be high enough for the circuit breakers typically used in switch panels (usually these are rated anywhere between 5 and 20 amps).
You also don’t want the size of these conductors to be unnecessarily large because you will have a hard time fitting them in cable trunks and connecting them to the switches in the panel.
In most cases, it makes sense to use duplex cables. You can cut back the outer insulating sheath at each end to separate the conductors and connect to both a busbar and the terminal block at the distribution point. But it is also possible (and sometimes easier) to use a separate conductor for positive and negative, but in this case the positive and negative conductors to individual loads should be run together. (Also, make sure they have an appropriate and consistent color scheme - see this lesson.)
There will probably be some loads that require larger conductors, in particular those that are not connected to the switch panel but run on their own fuse or circuit breaker. Charging devices are a common candidate for these larger conductors. Once again, it might make sense to choose a "standard" conductor size that is large enough for most cases. It does not hurt to oversize the conductors (as long as they fit the cable trunks and connections on the devices and connection points). The corresponding fuses or circuit breakers need to be sized to not exceed the conductors' ampacity. In practice you might want to use smaller fuses or circuit breakers if the loads are expected to be limited.
For the conductors from the batteries to the main distribution point (in this case, the Safety-Hub) and the starter motor, we probably need a third, larger conductor size. Here you should also keep in mind potential future expansions of the system, such as inverters or other high load devices. You can't oversize battery conductors, so it might make sense to use one size larger than calculated. Keep in mind that the amps of all loads will flow through these conductors, including safety relevant equipment.
For feeder conductors, the ABYC requires the voltage drop to be kept below 3% for the sum of all loads which may be turned on at the same time (which is what we calculated as Peak Load in our Boat Electrics Planner).
There is a more complicated and detailed load calculation method described by the ABYC which may be more appropriate for boats with extensive electrical systems. We describe this in our Advanced Marine Electrics lesson on Digital Switching.
The main fuse has to be sized to not blow, should the peak load ever occur, but in any event must not have a rating that exceeds the ampacity of the main conductor. If the peak load is higher than this, the conductor size needs to be increased.
For most small and medium sized boats, we should be able to do the complete wiring with as few as three different conductor sizes. Some conductors may be oversized, but in the end this is likely to be the cheaper and easier option as opposed to optimizing every conductor: You can buy the conductors in bulk and you will have fewer small leftover pieces when you cut them to the right length. Plus you only need a limited variety of terminals and tools for installing them.
In our example of the simple boat, our cable supplier is a European marine chandler who offers conductors with an insulation temperature rating of 90° Celsius (note that most U.S. chandlers stock 105°C cables). Based on this, and with the ISO version of the calculator, we came up with the following conductor sizes for our example boat:
Small Conductor Size
We use 1.5 mm² as the standard size for all loads that are connected to the switch panel and the fuse block. According to the ISO, the ampacity of these conductors is 21 amps when they are not run in the engine room or in a bundle. In our example, none of the conductors run in an engine room, but the ones coming from the switch panel are going to be bundled for part of the cable run. So we have to use the derating factor for bundles which, in the case of DC circuits, for the ISO is 0.7 if three or more current-carrying conductors are bundled together whereas for the ABYC, the derating currently occurs with two or more DC conductors (the ABYC is discussing harmonizing this with the ISO so this may change; if these were AC circuits, for both the ISO and ABYC there are additional de-rating factors for bundles with higher numbers of conductors). We find that even with the de-rating, the ampacity is well above the maximum 10A circuit breaker in our panel. We will get the same result if we use equivalent U.S. AWG conductor sizes.
Medium Conductor Size
We use 10 mm² as the standard size for medium conductors. We use this conductor size to connect the alternator to the battery isolation diodes and the diodes to the cranking battery and the SafetyHub. We also use this size of conductor for our feeder cable to the switch panel. The ampacity is 70 amps if not bundled, so we are fine with the choice of fuses indicated in the wiring diagram. Given conductor lengths from the chargers to the batteries that are below 4 meters, we find the voltage drop is below 3 percent for the anticipated charging amps and for the feeder conductor to the SafetyHub.
Large Conductor Size
For the main battery cables and the cranking circuit, we opt for 25 mm² conductors. The ampacity is above 100 amps even when run in an engine compartment. And for conductor runs up to 5 meters, the voltage drop will remain below 3% even at 100 amps. So for our small boat, this is definitely large enough. For the cranking circuit of a small engine, this is likely also a reasonable size, but here you should double check the engine manual to see if this is sufficient.
With all this information in hand, we can add up the required lengths of conductors and place an order at our marine chandler together with the other supplies.
The Boat Electrics Planner automatically adds up the total conductor runs for each conductor size that you entered for the loads. You can also enter additional conductors (for example the ones to the charging devices) in the “Settings” sheet:
If you go back to the "Results" sheet, you will get this list of required conductor lengths:
This is the total required length of conductors for all the loads of all batteries and groups plus what you set in the "Settings" sheet. If you use duplex cable for the smaller conductors, you can divide this number by 2. You still have to figure out how much of what color you will need for the larger conductors. When you place your order it is always a good idea to buy extra lengths.
When you install the conductors, make sure to work according to the principles and rules we described in the module on conductor selection and installation.
In the next lesson, we will extend what we learned here by exploring a slightly more evolved example: our medium sized example boat.
Could you discuss using 2 wires for large amp loads on long runs? (Eg, bow thruster) How does one determine the fuse size?
Hi Jim,
You can find some information regarding this in the lesson on OCP ( https://boathowto.com/course/ocp/ ):
“The ABYC addresses this as follows: the conductors must be the same length, they must be bundled together, and the OCP must have an amp rating no higher than the ampacity of an individual conductor– in other words, you can’t parallel two conductors and then double the amp rating of the OCP on the circuit. By limiting the OCP amp rating to the ampacity of a single conductor, if a paralleled conductor becomes disconnected and the full circuit current goes through a single conductor there is still no way the single conductor will melt down.”
Does this make sense or do you mean something else?
Best
Jan
It makes sense safety-wise. I suppose this is why 24v is so popular and even 48v is used on the Integrel system. (I should probably replace the doubled battery and generator wires on my DeSoto (6v positive ground) and find some thicker cables!)
I was hoping to avoid mixing voltages on my project but it looks like there’s good reason for the necessary complexity for high power consumers. I will need to revise my plan.
Thanks
Yes, indeed. Especially for larger boats (typically above 45 feet), it may make sense to have a 24 Volt system (or run some devices on 24 Volts) to keep voltage drop at bay…
I believe there is an error in the text describing the conductors connected to the Safety Hub fuse block. I think that in “…and the loads/groups for which we chose a fuse as the OCP device (F9, F10, F4) are connected to the smaller ATO fuses…”, F14 should be substituted for F4.
You are absolutely right! Thanks for pointing that out, I fixed it now…
Excellent program. Thank you.
After working my way through to the sample boats a couple of times, I am still unsure how to wire the negative ground conductors for my project. I have a 12v 300ah house system with a fridge as a creature comfort. I live in Canada and although solar is helpful it can be difficult to get enough solar energy on less than ideal days to run the fridge with other devices needed. Also running engines is frowned upon where I sail on the Great Lakes.
I have a lithium iron battery that I want to use as a secondary energy source for the days my house bank is not keeping up (It would have its own solar charging). I wanted to have an ‘on off on’ switch so I could switch from the house bank to the Li battery. I believe I understand the positive wiring, fusing and wire sizing. On the negative side I have a a negative buss in my drawing that will be used to connect the negative wires from the fridge switch, 12v & USB charging outlets and or space for a couple of future devices but am unsure if and how I should wire the negative/ground. Would I wire from the Lithium negative buss bar to the central ground point on the engine where the other bank is connected? Or is there another way this should be wired? With two separate battery banks and different battery types, I want to fully understand the correct way to wire this small project. I have gone through the course and can’t seem to fully confirm how to correctly set this up. Your clarity on the situation is very much appreciated. Thank you!
Wendy, if I understand this correctly, you want to be able to run your fridge and maybe some other loads from the lithium bank by switching a switch which at the same time disconnects the normal house bank? In this case, you would need a selector switch before the positive bus bar leading to the loads you want to power with the alternative battery. The negative poles of both batteries should be connected to the common ground point with large enough cables to handle the amps of your overcurrent protection (OCP). And of course, you need properly sized OCP (main fuse) on both batteries. Especially for the lithium bank, your main fuse should also have a very high Ampere Interrupt Capability (AIC).
Thank you so much for your helpful reply. You are Pretty close. The switch would just to disconnect the fridge circuit from the main house bank power when I switch the switch to the lithium backup bank. The only device turned off on the house bank is the fridge. Any other circuits on the lithium bank would work independently. FYI the boat is a Bavaria 32 so u have an idea of what’s there now.
Fusing the + conductors
I’m planning on a T fuse that is calculated for the size of the + conductor that would run from the Li battery to a safety hub like fuse box for convenience and space savings. I am still deciding to add a main switch after the main fuse.
Selector switch
You mentioned the selector switch is located before the bus bar(safety hub)…to me that sounds like u mean upstream between the battery main fuse and the bus bar/ hub. I had thought the selector switch for the fridge to switch from one bank to the other would be downstream or after the bus bar / hub in a location that was convent for the original wiring from the house bank to be incorporated into the switch.
Common ground point
Thank you for the information on the ground connection point. As the engine block is the main ground for the original boat battery banks, if I understand correctly the back up Li bank can be added to the same connection at the engine block.
Note: The house bank wiring is complete and fused with its OCP. I had not planned on changing it unless there is a need.
Li bank conductor size
I will Calculate the correct conductor size that works for the positive and negative conductor runs. Distance from the Positive battery post to the hub with the fuse should be approx 12 to 18”. The Neg ground starts at the neg. battery post to the shunt and then to get to the engine ground point via….?
A. Run a conductor to the engine ground point with a second conductor to the neg bus bar/ hub off the battery – post
B. a conductor from the battery neg post to a separate bus bar that goes to the engine ground point and the hub hub
C. To the hub and from it to the engine ground point.
I always thought the neg wiring was the simple part….
Sorry for the long winded comment. Your guidance is very helpful.
Hi Wendy,
I hope you understand that we cannot do a complete planning here in the comments, and it is hard to judge if your wiring is correct from this text. So if there are things you are unsure about, please check with a marine technician first before you plug it in. That said, let me quickly try to answer your questions:
If the fridge is the only thing you want to power from your lithium-ion bank, then you can put the selector switch anywhere close to the fridge. Make sure that it is a switch that first disconnects one battery before it connects to the other one and that it cannot be set to “both”. Otherwise you might have very high currents between the batteries that will immediately blow your fuses.
Regarding the ground connection: In a typical installation, you would have a large bus bar, where all main negative conductors come together. This is what you define as common ground point. Between this and the battery you place your shunt. The common ground point then also has to be connected to your engine or a keel bolt for example.
I hope this made things a bit clearer. We will take a note of this and try to explain this in a bit more detail in our next revision of the course content.
Best
Jan
Thanks very much for clarifying and your patience. That was quite helpful towards understanding the common ground point.
Take care,
Wendy
I would like to change the old ferroresonant battery charger I have for the Victron IP22 model you mention. My boat has 30A shore power wired into a distribution panel with a reverse polarity breaker and two branch circuits. The Victron charger has a plug, is it acceptable to simply plug it into a 120V outlet? This is how my current charger is set up. Or should the charger be hard wired?
Thanks!
Mike and Alison,
In general, battery chargers should be hard-wired. However, there is a specific exception in the ABYC standards for ‘pre-wired battery chargers’ – i.e., with the plug installed – which covers what you want to do.
Since we are on the topic of battery chargers there are some other standards-related issues worth raising but which are not relevant to your installation. Sometimes a battery charger is the only AC device on a boat. In this case you can run a shorepower cord directly to a pre-wired battery charger without having to install a shorepower inlet, double-pole main breaker, and other components required in AC systems.
If a battery charger a metal case, the ABYC requires an external connection for a DC grounding conductor that is run to the boat’s common ground point. This conductor can be ‘be one size smaller than the minimum size conductor required for the DC current – carrying conductors providing the overcurrent protection device in the DC positive conductor is rated no greater than 135% of the ampacity of the DC grounding conductor and the conductor is no smaller than 16 AWG.’ Note that this DC grounding wire is separate from the positive and negative connections to the battery charger, and also the AC grounding wire which will be part of the AC cabling.
The idea here is that if there is a fault from the DC side to the case it will be carried back to DC negative via this conductor. To do this in the case of a serious fault the conductor must be large enough to not melt down (hence at least 16 AWG and no more than one size under the positive and negative conductors to the battery charger). The amp rating of the overcurrent protection on the positive conductor to the battery charger must be no more than 135% of the ampacity of this DC grounding conductor so that the overcurrent protection will be activated before the grounding conductor melts down.
Because omitting this DC grounding conductor has no impact on performance in normal circumstances, it is frequently omitted from installations, which are then technically non-compliant with the ABYC standards. Even if installed, it is often undersized.
The ABYC has various requirements designed to ensure secure mounting of a battery charger away from potential gassing, and sulfuric acid fumes, from lead-acid batteries.
The ABYC requires testing by an independent laboratory to ensure compliance with its A-31 standard.
Nigel
Excellent information! Thanks very much,
Mike
Great course!
My question: you recommend a 12/30 battery charger for a 180A AGM battery house bank. Regarding the higher charging possibilities with AGM batteries, wouldn’t it be better to a use a charger with higher loading capacity?
Martin
Thanks Martin!
It depends a bit on the situation. If there is no minimum charge rate requirements by the battery manufacturer, a shorepower charger with a 0.15-0.2C rate should be fine for most applications when shorepower is available for reasonable lengths of time. Unless you only make short pit stops at the dock (or have extensive DC loads that use up a large part of the charging current), you should be fine with such a charger.
Jan
Thanks for the information
Martin
Jan and Nigel,
First, I would like to thank you for an outstanding class. The module sequence is great and the material is thorough and concise.
While I understand most of the concepts, I’m obviously missing something because I still have some basic questions regarding the simple boat wiring schematic.
Question #1 – I thought that the alternator output gets wired directly to the house bank? In the schematic it appears that the alternator output goes to the Blue Seas Safety Hub first and can then feed all of the other loads connected to that hub. Shouldn’t the hub be powered from the battery? What am I missing?
Question #2 – Up and to the left of the battery monitor there is an unlabeled fuse. What is the purpose of this fuse?
Dave,
Thanks for the compliment! These are good questions and we should probably mention this in the next iteration of the course.
Regarding Question #1: We could indeed also have wired the alternator directly to the house bank (with an appropriate fuse of course). However, if you think about it, it does not make a difference (if you neglect any resistance in the wires). The safety-hub is connected to the battery and as such, the alternator as well. If there are any loads on the safety hub while the alternator is running, a part of the electrons might flow directly to the loads instead of the battery, but in sum it does not make any difference. So instead of installing a separate fuse holder to directly wire the alternator to the house bank, we can simply use a free connection at the safety-hub.
Regarding Question #2: The fuse protects the voltage sensing wire to the battery monitor. We did not label it as these fuse are typically already integrated in the cable. At least for the model we chose in this example, this is the case.
Hope this made things a bit clearer.
Best
Jan
In a note you say “For a layup, an easy way to make sure that no parasitic loads can drain the battery is to simply disconnect the negative battery cable from its post”.
We have 640W of rigid solar panels on top of an arch at the stern. For winter layup would it be better to leave these panels exposed so they in effect ‘trickle charge’ our 875Ah AGM house bank, or would it be better to have them covered when we shrink wrap and disconnect the battery bank at the negative post?
Another good question. It depends on the time of the layup and whether your solar charge controller has an appropriate charging regime with a float voltage that exactly matches the recommendations of your battery manufacturer. If this is the case and your installation is properly done, I see no problem with leaving the panels connected. I do this on my boat as well when I’m gone for a few weeks. On the other hand, if you have quality AGMs and they are fully charged, it should be no problem to completely disconnect them for a few months, especially in cold climates. And then you are on the safe side and don’t have to trust your charge controller or their installation.
Hi, I hope you can help me understand the installation of the BMV 712 Smart monitor. My understanding is that all negative loads must pass through the shunt. The quick install guide is pretty straightforward however could you help me understand the negative side of the setup.
My system consists of a house bank (two T105 6V batteries wired in series) and a start battery. I have a solar panel as well as a DC charger for use with shore power.
Do I connect the negative battery terminal of the house bank to the “Battery Only” side of the shunt and then connect all other negative conductors ( DC panel, solar panel, DC charger, start battery, alternator??, starter??) to a bus bar and then connect the bus bar to the “Load and Charger” side of the shunt as well as the engine block?
The current setup has the alternator, starter and DC panel negatives all connected to the engine block. The solar to the house battery and DC charger connected to the start battery which is connected to the engine block.
Thanks and looking forward to more courses in the future!!
The way you describe the setup is correct. The idea of the Shunt is to measure all incoming and outgoing current of the house battery. In order to do this, you have to place the shunt between its negative pole and the boat’s common ground system where all other loads and chargers come together. Even though your current setup does the job, it might be a good idea to “clean it up” a bit by installing a negative busbar where everything comes together and then connect this to the engine block with a single conductor (that is large enough to handle the cranking current).
Thanks, that what I was thinking. My boat ( new to me ) is almost the same as your simple boat described above. Your easyEDA diagram is an excellent template to reference to clean up my boat’s wiring.
A question about the alternator, I have a 120 amp alternator going to a diode and then voltage regulator. I was thinking about swapping out the diode and regulator for the Victron Argofet Isolator to simplify the system, would this make sense? Could I expect better performance from the Victron Argofet than the older diode & regulator or would it simply be a cleaner (less conductors) install?
This depends a lot on the type of the alternator. I would check this with the manufacturer. If the controller has a voltage sensor directly on the battery, there is a good chance that the alternator’s output will be compensated for the voltage drop on the diodes. In this case, you will not gain much by the argofet. (Besides maybe a slight gain in efficiency.) You can also measure the absorption voltage at the batteries during the final stages of charging and see if this corresponds to the recommendations of the battery manufacturer.
Ok thanks , I’ll do that.
As I work through my boat’s wiring I’m finding it very similar to your simple boat example so that’s super helpful, thanks! I’m slowly changing (correcting) my system to look like yours. Looking at the schematic you have fuse F2 60A located between the Alternator and Starter Motor, downstream of the cranking switch. Is this fuse sized differently than the one in the Safety Hub which shows 50A? For my boat with a 120amp alternator would I size up to a 150A fuse ( using 2AWG conductors) to prevent a nuisance blow and ruining the alternator?
Thanks
Mike & Alison,
Thanks for your question. There is actually no particular reason for one fuse being 60 and the other 50 A. Their rating has to be below the max rating of the alternator’s output. And of course lower than the ampacity of the conductor.
So your plan with the 150A fuse for the 120A alternator is a good one, as long as the conductor has an ampacity above 150A. According to our calculator, this is the case for a 2AWG cable in an engine room if it has a temperature rating of 105C. In this case you’re all set!
Jan
Great thank you!
Regarding the location of the fuse in the diode to starter circuit, is the fuse placed near the diode to protect the conductor from alternator output or near the switch to protect the conductor from battery output? We have two sources of power in this case.
Mike
This is a very interesting question. In theory (at least according to ISO standards) you would also have to put a fuse on the alternator side (even before the diodes). The ABYC is more relaxed here (which makes sense in my opinion): If the alternator can not produce more amps than the ampacity of the conductor, there is no way it can melt it down. We have some more details on this topic in this lesson: https://boathowto.com/course/case-study-high-output-alternators/
Jan
Jan thanks for pointing me to that lesson, I just reviewed it and it was and excellent, answered my questions fully.
Mike
Just a general comment about the lesson and the comments above – both excellent. After finishing the lesson (and reading the lecture notes) I had 4 questions. Each and every one was well asked and clearly answered in the Q&A above, thank you all.
Hi Mark,
Thanks a lot for this feedback! This is exactly the idea for the comment section. And then if we ever record a second iteration of the course, we will incorporate all this into the lessons. So we are thankful for every single comment we get.
Best
Jan
Hi Jan! So, we’re figuring out the fusing on the positive side for the cranking battery. We want to fuse it, but understand the potential for a nuisance blow can be a headache. What are your thoughts on installing a fuse, but also connecting a switch which would bypass the fuse in the case of a nuisance blow? The switch could be left in the off position, but if the fuse blows and there are no safety hazards, can be switched on to again have access to the cranking battery power.
Hi Kristina,
Nothing speaks against putting a switch in parallel to a fuse if this gives you more peace of mind. On the other hand, if a seriously oversized fuse (like a 300A slow blow fuse) blows when trying to crank the engine, there is probably some issue with your engine. It is highly unlikely that it will crank with the bypassed fuse. After the fuse was blown and you try to crank it through your emergency switch, make sure to closely monitor all parts of the cranking circuit as there is the risk of a dead short somewhere.
A cheaper and simpler alternative to the switch would be to have a short piece of heavy duty jumper cable ready that you can clip to both ends of the fuse terminal in such a case.
Best
Jan
Makes sense, thank you!
Hi
I’m getting towards the final stages (I hope!) of planning my boats rewire. I have a twin alternator set up with one high output Alt for the house banks. I’m considering how to connect the alternator feed to the house banks. Should I connect through a fused BS Safety Hub 150 after the main switch or bypass this main switch and go direct to the main battery positive busbar?
This is a rewire job and the previous setup had a Powerline Solid State Battery Isolator which the alternator feed was connected to and then onto the house batteries.
Great course BTW and TIA.
Al.
Alistair,
With respect to fusing, the fuse issue is strictly one of conductor ampacity. If there is a fuse between the battery bank and the alternators that has a low enough amp rating to protect the conductors from the alternators there is no need for additional fusing but if the conductor from either alternator is not adequately protected then additional fusing is required at, or very close to, the point at which that smaller conductor connects to the battery end of the wiring. How that fuse is installed – through a Safety Hub or some other mechanism – is simply a matter of convenience.
With respect to the battery switch, typically alternators that are wired to house banks (i.e. not back to the starter motor solenoid) are connected downstream of the battery switch (i.e. on the load side and not the battery side). The ABYC has a short list of circuits that can be connected upstream of the battery switch and it does not include alternators. However, we now run the risk of open circuiting the alternators if the switch is turned off with the engine running so the switch needs to be clearly labeled ‘DO NOT TURN OFF WITH THE ENGINE RUNNING’.
Nigel
Hi Nigel. Thanks for your quick reply. Fully understand the fusing matter now. Regarding the house alternator, is it ok to connect it directly to the up stream side of the main house switch itself or is best practice to go to a busbar or a BS 150 after the main switch?
Depending on the complexity of the installation, the main switch is fine so long as there are no more than 4 connections.
I am struggling with understanding the capacity calculation for the various battery types in the Simple Boat example above.
For the Lead Acid/Gel batteries, I get to the same capacities applying the mid capacity rule, under the assumption that the worst case also means discharging 60% (as opposed to 30% for normal case).
For AGM, I get the same normal use capacity (53.1 * 2), but I do not know how to get to the 149 Ah worst case.
And for Lithium I do not get to the same figures when applying the factor 1.4.
The spreadsheets show factors of 0,5 (normal) and 0.65 (worst) for AGM, and 0.7 (normal) and 0.8(worst) for Lithium. Can you please explain what these factor represent?
Thanks
Hi Hellmut,
I’m not sure where you get the 149 Ah worst case from. In my spreadsheet it shows 109.6 Ah worst case loads for the simple boat.
The factors in the spreadsheet you are referring to are the percentage of useable energy. So for example 0.65 in the worst case comes from the idea that we would assume 65% of useable capacity for AGM in a worst case scenario. (“For high quality AGMs, we assume a state of charge of 85% at the beginning of the discharge cycle, due to their higher charge acceptance rate. Thus we end up with 65% of usable capacity, which would be about 230 Ah of battery capacity for 150 Ah of worst-case requirements.”, see the lecture notes here: https://boathowto.com/course/energy-storage/
Hope this helps.
Best
Jan
Hi Jan, thank you very much for the explanation. It clarified the calculation for me, and I also found, that I was struggling with it because of the slightly different energy consumption figures in the spreadsheet vs the tables shown in the course (where I got the 149 Ah worst case for AGM from).
Thanks for pointing that out, I think the reference is still linking to an older version of the spreadsheet. I will put it on my ToDo-List to fix this…
Jan
There is a connection between the alternator isolator and the main backbone of the house circuits. This backbone could easily draw more than the 50 amp OCP / fuse that is connected. Shouldn’t the isolator be connected directly to the house batteries, i.e. between F1 & F4?
Great course, I’m learning a lot!
Thanks Kieran.
It depends on the maximum output of the alternator. For the example we assume an alternator with no more than 50A output. If you have a larger alternator, you would need to adjust the rating of the fuses (and of course also the cross sectional area of the conductors!). If your conductor to the battery isolator has an ampacity of 100A (taking into account potential bundling and of course the increased ambient temperature in the engine room), it would be protected by F1. So in this case you could indeed bypass the fuse block and connect it between F1 and F4. But only in this case! We talk about that in more detail in our alternator case study lesson.
Hi Jan & Nigel, thanks for the great course.
I am about to rewire my steel boat and came across the switch panel series from Philippi labeled “Panel STV XXX-2p”. I do not completely understand the difference between normal switch panels. How do I wire these double pole switches and why should I use them on a steel boat?
Besides this, can I adopt this simple boat example on my steel boat, or should I change anything else?
Best,
Helena
Hi Helena,
A fully insulated system with two-pole circuit breakers is usually only used on aluminum boats, because these are particularly vulnerable to the risks of stray current corrosion. On a steel boat I would not hesitate to install a normal, grounded, DC system, just like the one we describe in the lessons. So yes, you can adopt the simple example and use the 1p version of the Philippi panels.
Best
Jan
Thank you 🙂
Hello, I had a question regarding the use of MRBF on batteries. When on the Blue Sea website the fuse itself is rated as ignition protected but the standard terminal block you’d find attached to a battery is not rated as ignition protected. If this is true then I’m not sure the proper use of these fuses as then they would technically not be rated for use in engine compartments for gasoline engine boats to my understanding. If it was a diesel engine then this would be allowable except my thinking would lead me to wonder then about the venting of lead acid batteries since non-ignition protected items shouldn’t be in that environment either. That would then leave the usage acceptable for lithium except they do not have a high enough AIC rating and at that point a MRBF should be swapped for an ANL or T-fuse.
I work in the marine electrical field and generally find myself using ANL, MIDI or T-Fuse for batteries but after going through this course thought MRBF might be a good swap in certain circumstances but then I began thinking about the aforementioned train of thought.
Any insight would be greatly appreciated. Thanks!
Easton,
The ignition protection requirements apply to specific spaces and devices. As such, if we have a space that requires ignition protection (e.g., the engine compartment for a gasoline engine) then we need ignition protected devices and in so far as an MRBF fuse meets the ignition protection requirements it can be used irrespective of the issues that you raise related to other equipment attached to the battery posts. The benefit of the MRBF is, of course, it puts the overcurrent protection directly at the source of power.
The MRBF becomes the Main DC Fuse (i.e., the one closest to the battery) and as such requires an appropriate AIC rating. If this AIC rating is exceeded, the fuse is technically no longer ignition protected. Because of the potentially enormous short circuit currents with lithium-ion batteries, MRBF fuses are not appropriate in many lithium-ion installations, and neither are MEGA, and often also not ANL. We have to go to Class T (or NH in Europe).
Something else that is frequently not realized is that the AIC rating of a fuse is at a specific voltage. Let’s say it is 12 volts. If the system voltage is doubled (e.g., to 24v) the AIC rating is cut more-or-less in half, and if the voltage is quadrupled (e.g., to 48v) the AIC rating is cut more-or-less to a quarter. For example, the 100A MRBF on the Ble Sea Systems website has an AIC rating of 10k amps @ 14v, 5k amps at 32v, and 2k amps at 58v (the absorption voltage of most lead-acid and li-ion 48v battery banks).
When it comes to ignition protection and AIC ratings for fuses it is important to read the small print!
Nigel
Hi Jan & Nigel,
Thank you for such an enjoyable informative course.
As part of the re-wire I had planned to use both a NASA BM2 Battery Monitor (Rated at 200A) and a 1-2-Both Isolation Switch.
The switch would not be for control of charging just for emergency engine starting.
However looking at Jan’s Schematic for Ahora I realised that if the selection was made to start the engine using solely the leisure battery (not both) then the return current from the starter motor would pass through the shunt causing it to overload.
Is my thinking correct?
If so I would purchase a third battery isolation switch and connect it as an emergency parallel switch.
I prefer the isolation switch for its ability to bypass a completely failed engine battery although I suppose if needed it could be manually disconnected instead.
Thank you
Reviewing my comment..
I think my last sentence is in error.
Disconnecting a faulty starter battery then using the parallel switch would also overload the shunt?
Therefore in the situation of a faulty/damaged starter battery (not low charge) it would be better to remove disconnect the positive lead at the battery terminal and then use + and – jumper cables to bypass the shunt?
Timothy,
The shunt is essentially a dumb piece of metal which induces a miniscule voltage drop in the circuit. The meter converts this voltage drop into an amp reading. Within reason, if you exceed the rated amperage of the shunt it is not going to damage the shunt and the display will likely momentarily just max out at 200A.
With the 1,2, BOTH switch, if you are in the BOTH position the current back to the batteries will in any case be shared, so not all will be flowing through the shunt. If you are in the house battery position you need to ensure that the negative path conductors from the engine back to the house battery are at least as large as the positive conductor to the starter motor.
So, no need to be disconnecting conductors and don’t worry about the shunt!
Nigel
Hi Nigel,
Thank you, this is very helpful.
Hi Jan and Nigel,
I’m learning so much. I have a more complex boat than the simple boat model, but this module raises a question for me in relation to my current system.
My boat is a 42′ steel blue water cruiser from 1986 (Feltz Skorpion II). Lots of additions and rewiring by previous owners that I am trying to resolve (lots of wiring with speaker wire, and no fuses anywhere.) One of the first things that I did as I transition to a full isolated ground with correct wire sizes and types, as well as OCP on positive and negative sides, is to add an isolation transformer. I did this because of stray current concerns for my boat and family as well as other boats and swimmer’s safety.
In this module you have included battery isolators. Does my isolation transformer take the place of these devices?
Thanks for making this course so understandable. I have signed up for the diesel course too, which I’m quite excited about.
Hi Robert,
No, a battery isolator (in German also called “Trenndiode”) is only used to distribute the charging current of an alternator to two or more battery banks. I think you may have confused this with a galvanic isolator, which looks a bit similar and who is supposed to do the same job as an isolation transformer.
The isolation transformer is used at the shorepower inlet (in the AC circuit) to create a new source of power on the boat to which the grounding conductor is attached. This is there to prevent corrosion through the grounding conductor. If you want to learn more about isolation transformers (and their cheaper, but less reliable alternative, galvanic isolators), check out our modules on AC systems and Corrosion in our Advanced Marine Electrics program.
Hope this helps!
Cheers
Jan
I was just watching the tear down of a high end 460Ah 12V LiFePo4 battery. It was IP 67 rated, had a removable lid on the case, and under the lid, inside the battery, was a user replaceable Class T fuse.
This may become more common in the future.
Jan,
I’m in Module 8 Case Studies: lesson 4 “simple Boat” (i loved every minute of all these video’s) at 21:38 of the video’s a statement was made the chandlery has conductors for 90 c then you switch to the ampacity table an reference the 105 c cable for an ampacity of 25. I think you might of meant the 90 c cable with an ampacity rating of 21?
This is a small point (if I’m right). Just thought I would put my 2 cents in.
our sailboats.
corvette 32′ 1986 -2008
Hunter 45DS 2008 – still.
I’m finding this fascinating because we have faced 75% of the challenges that have been spoken about.
and thank you for your works
Best Regards,
Tony Fuller
Ottawa, Canada.
Hi Tony,
Great catch, thanks a lot for pointing this out! You are right, the conductors have a rating of only 21 amps. I will take a not of this for the next revision of the video!
Thanks a lot for the compliments for the course, we are very glad to hear that it’s helpful!
Jan
Hello Jan and Nigel,
Thank you for the great course. I am learning a lot and enjoying myself. The case studies are great since now it all comes together and it also shows where my knowledge is lacking.
I am still struggle with determining the rate of the fuses. I understand how the determine the fuse rating when I know the equipment specification (e.g. the VHF radio). Using the length of the cables, the bundle size, voltage drop etc.
Where I struggle is how to determine the size of the fuse that protects a distribution point. In case of the simple boat example: how do you rate for F5? You picked a 50A fuse, but Switch Panel SP1 can draw 80A (8x10A). I am clearly missing something.
On my own boat I have two Fuse Blocks (with each 8 positions) set in series. I have no problem with determining the fuse ratings for the individual loads, but I am not sure how to calculate the rating of the fuse to protect both Fuse Blocks. Currently there is no fuse.
These two Fuse Blocks are again wired in series with a BlueSea Circuit Breaker Switch Panel which gets its power from the Battery Bank. Again no fuse at the Battery Bank. Now I have the same question/problem as the Fuse Blocks.
Best regards,
Christoph
Hi Christoph,
The minimum size of feeder conductors and the size of their fuses gets calculated based on the worst-case total load of all the devices behind the fuse. The goal is that the fuse does not blow under normal conditions of maximum load. E.g. if all devices behind the switch panel or fuse block are on at the same time.
To determine this maximum load, just add up the amps of the devices downstream of the (main) fuse. This will most likely less than the sum of the ratings of fuses / circuit breakers downstream of the fuse, because these are rated to protect the conductors and thus have a higher amp-rating than what the devices actually consume.
Does this make sense?
Best
Jan
Hi Jan,
Yes, this makes sense. Thank you for the clarification.
Best regards,
Christoph