Boat Electrics 101 - Safe & Reliable DC Systems

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Boat Electrics

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In this course you will learn everything you need to know about DC systems on boats. Beginning with the basics about current, voltage and resistance, we teach you how to (re-)do all DC wiring on your boat, complying to ISO and ABYC standards.

Boat Electrics 101 - Safe & Reliable DC Systems

3 Lessons

A quick welcome and introduction of your teachers and a few words on who this course is for and what to expect.

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Get an overview on the contents of this course and the underlying standards.

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In this lesson we will cover some dangers and necessary safety precautions to keep in mind before working on your system.

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6 Lessons

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What is electricity and what happens when a current flows? We take a quick look at the behavior of electrons inside metallic conductors.

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Learn all you need to know about voltage, the equivalent to pressure in electrical systems.

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Ohm's law allows you to calculate how resistance affects voltage given a certain current and vice versa.

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Power the product of voltage and current. With two examples you will learn how to calculate the power draw of an appliance.

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A quick recap on everything we have learned so far.

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Test your knowledge with a quiz!

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Learn why it is important to be able to read and draw circuit diagrams.

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In this lesson you learn the symbols for wires and conductors and and their connections.

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What is ground/earth and how is it represented in circuit diagrams?

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Get to know the basic symbols for switches and buttons and learn how relays and solenoids work.

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Get to know the symbols for resistors and learn about the most common type of resistor on board: the shunt.

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How are fuses and circuit breakers represented in circuit diagrams?

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Coils mostly occur on boats within transformers. Here you will learn about their basic function and how to represent them.

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In this lesson you will get to know a few more symbols for common components in a boat's electrical system.

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In the final lesson of the module, you will learn how the components in boat electrics are connected in parallel and in series and how this affects battery capacity and voltage.

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Test your knowledge with a Quiz!

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Learn about different types of conductors and which ones are suitable for use on boats.

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Learn what conductor colors you can use for what purpose and how to properly label your wiring.

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Learn how to choose the proper size for a cable with respect to ampacity and voltage drop.

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It is crucial for the system's safety to establish proper connections. In this lesson you will learn how to install terminals in a professional manner.

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Proper connections of terminals to bus bars and consumers are vital. Here you learn what makes a professional connection.

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In order to prevent fires due to overcurrents and short circuits, protective measures are absolutely crucial. In this lesson you will learn how to choose fuses and circuit breakers and where to install them.

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Learn the proper way to install conductors in order to protect them from chafing and physical stress

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In this lesson we will apply what we have learned in this module to the special case of high output alternators. As we will see, there are quite a lot of things to consider.

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Here we show a few more examples of good or bad installations and also what happens in case of a short circuit if no adequate OCP is installed.

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Test your knowledge with a Quiz!

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12 Lessons

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Get an overview on what to expect in this important module.

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Even though they operate at relatively low voltages, there are significant dangers when dealing with batteries. In this lesson we cover the required safety measures.

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In this lesson you will get an overview on the chemistry inside a battery and how lead acid batteries work.

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Here we go more into the details of the internal construction and discuss the differences between cranking and deep cycle batteries.

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Now it's time to look at different types of lead acid batteries, such as wet cell, AGM, gel-cell and some new innovations.

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Learn about the crucial difference between amp-hour and watt-hour efficiency and how to evaluate batteries based on this.

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What do the common ratings found batteries (nominal voltage, nominal capacity and cold cranking amp) mean?

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In this lesson you will learn what the most common reasons for battery failure or reduced lifespan are and how to avoid them.

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Learn how to maximize battery life when installing batteries in serial or parallel.

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This lesson will help you decide how much battery capacity you really need for reliable operation and optimal battery lifespan.

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Learn how to properly install your battery bank and how to maintain it in order to optimize its performance.

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Test your knowledge with a Quiz!

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Learn about the most common failure modes with lead acid batteries so mistakes can be avoided.

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Through the analogy of a water tank with semi-permeable membranes we explain why it takes a long time to completely top off a lead acid battery.

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Learn what an IUoU profile is and how the bulk, absorption and float phases increase battery life.

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Learn strategies to reduce charging times and engine hours while at the same time increasing your battery's lifespan.

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Learn what to look for when choosing a battery charger, an alternator or when planning on installing renewable energy sources.

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Learn about different ways to charge multiple battery banks from a single power source.

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Learn about the importance (and challenges) of proper battery monitoring.

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A quick recap on what we have learned so far in this module.

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Test your knowledge with a Quiz!

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In this lesson we introduce the BoatHowTo Boat Electrics Planner which will help us to determine the energy balance on our boat

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In this lesson, we will look at all loads on the boat and determine their energy consumption for different scenarios.

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To store the energy between charge interval, we have to carefully design our battery banks. In this lesson we look at various options for batteries depending on our calculations from the previous two lessons.

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Now we look at the supply side and determine the available charging sources such as shorepower chargers, alternators and renewable energy sources and their required output to keep up with our energy needs.

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Test your knowledge with a Quiz!

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We start the module with a brief introduction of our three example boats.

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In this lesson we get to know a free, web-based tool for the creation of circuit diagrams.

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Before we get started with our examples, we examine various options for grouping loads and discuss practical limitations, in particular when it comes to older boats.

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We go in detail over the planning of the rewiring of our first example boat, a modest cabin cruiser for weekend getaways.

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In this lesson we plan the wiring of a more complex cruising boat, with systems that you can find on many medium-sized production boats today.

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In our third example, we use everything we learned in this course to plan the complete rewiring of a full-fledged offshore sailboat with a lot of complex, state-of-the-art systems aboard.

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In this final lesson of the course, we leave you with a few final remarks. If you made it this far, congratulations! Now you should be able to assess, repair and extend your own system in a safe and reliable way and even be able to do a complete (re-)wiring job.

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About the teacher

Jan C. Athenstädt

Dr. Jan Athenstädt guides you through the lessons of this course. The course content has been developed in a joint effort with the most renowned experts on boat electrics from both sides of the Atlantic: Nigel Calder and Michael Herrmann.

  • Dear Jan,

    I was wondering if you could clarify something for me.

    I have installed a battery monitor on my 26-foot sailboat (thank you for the advice on that). My electric panel has 6 main switches than turn on and off six different circuits: one for instruments, one for cabin lights, one for nav lights and so on…

    Obviously, with all the main switches off, the battery monitor reads 0 Amps. However, I noticed that when I turn switch number 2 on, the one that controls all the electrics inside the cabin (apart for the nav instruments), but I have nothing turned on, the battery monitor still shows a consumption of 0.4 Amps. This switch turns on/off the circuit that feeds the cabin lighting (LED lighting), the freshwater pump, the bilge pump and little bit more. But with everything off, the battery monitor is showing a usage of 0.4 Amp.

    When switch number 2 is on but all the loads that feeds are off there is a “little consumption” from:
    – A couple of pilot lights in the panel, the size of the tip of a pen, that tell me that the circuit is on, and that the main battery switch is on.
    – The analog fuel tank gauge and its light are on.
    – The freshwater pump only comes on when I turn the tap on. Does the pump consume any electricity when there is no water running?
    – A pilot light on the FM radio on standby.

    Do you think all of that could account for the 0.4Amps?

    The thing that makes me think that there could be something wrong is this: when I turn any of the cabin lights (LEDs) on, the battery monitor does not show an increase in Amps being used! It stays at 0.4A. The same when I turn it off.

    Do you think there could be something wrong? Any suggestions will be very welcome.

    Thank you very much.

    By the way, John Neal’s lecture is a fantastic idea. Please bring more people like him, with tons of experience.

    • Hi Bonito,

      Without knowing the exact brands of your components, it’s hard to tell how much they consume in standby mode. What you can do is this:
      Disconnect all components from the circuit breaker, turn it on and off (to check for the load of the indication light) and then connect them one at a time and check your monitor battery monitor (of course with all other loads off). This should help you find the culprit pretty soon. While you’re on the boat and charging regularly, 0.4A is not such a big deal. But you definitely want to get rid of this load when you leave the boat…

      Let us know if you managed to isolate the consumer!

      Best
      Jan

      • Thank you Jan. I don’t understand my electric installation very well but I will try to disconnect each one of the loads one by one and see how the battery monitor reading changes. Thank you very much.

  • Hi Nigel & Jan. Im working my way through these excellent courses and thought that if I get a feedback idea I should put it somewhere before I forget it!
    During the lessons I have asked a number of questions and received superb answers. Would it be possible to somehow link a subscriber’s questions and answers so they could pull them all into one place without having to go into each lesson comments section? Secondly, have you thought about grouping themed questions and answers from subscribers into an FAQ section as a resource? You could end up with a great knowledge repository to enhance the site. Best wishes Steve

    • Hi Steve,
      This is a very good idea! And in a way, that is also prette aligned with what we are currently working on. Nigel just went through all the content and updated the lecture notes based on feedback and comments we got. We will put the updated version online in the coming week. So many of the topics in the comment section will now also be addressed in the lecture notes.
      And once we are done with the Diesel course, we will also incorporate them into a re-recorded version of the videos (this will take a while though).
      In addition, we plan to discuss some of the questions in greater detail in the next “season” of our “Ask-the-expert” series on YouTube (https://youtube.com/playlist?list=PLAmFyqTkF7VnylrYEgNN32f-m73nXLgEe&feature=shares).
      Cheers
      Jan

  • Hello, I am trying to sort out a charging design for a newly installed Bow Thruster and its battery bank on our sailboat. This bank will also supply power to the electric windlass.

    The thruster/windlass bank consists of two new 12v 100ah AGM batteries wired in parallel. The Bow Thruster bank will also supply power to the electric windlass. The Bow Thruster package came with a Victron BtB 18A charger that only charges while motoring via the start battery.

    The boat start battery is AGM and the house bank is 2 300 ah Lithium batteries in parallel. The boat has two high output alternators that are externally regulated with Balmar regulators (MC614 and MC618). One of these alternators charges the starting battery and then two 30 A BtB chargers in parallel charge the Lithium bank.

    The yard installing the thruster has designed it so that the thruster/windlass bank is charged from the AGM start battery while motoring using Victron 18 A BtB charger.

    I’m concerned that the thruster/windlas battery bank may not fully charge during short motoring times, shortening the battery life. Is this a concern?

    I’m also concerned that the BtB 18 A charger will be too limited to charge the Bow Thruster Bank after using the windlass.

    I’m considering redesigning as follows: Connect the 2nd high output alternator (with its own regulator) to the thruster/windlass bank to enable quick full charging of the bank. Also charge the thruster/windlass bank via the Victron 18A BtB charger conncected to our 600ah Lithium house bank that is charged via a 1000 Watt solar array. I have a spare Victron 18A BtB that could be placed in power supply mode to step the voltage up from Lithium resting 13.8v to AGM required voltage and to account for any voltage drop going from house bank cockpit area to thruster bank 7m or 24′ away.

    Any thoughts on the options? Or suggestions?

    Thanks in advance and I love the course. Looking forward to the advanced course.
    Stacy

    • Stacy,

      There is quite a bit to unpack here! Fundamentally, pretty much all the electrical work on the boat will be done by the 600Ah lithium-ion house bank so most of the charging energy needs to go here. You have two high output alternators but you did not state their outputs. Let’s assume for discussion purposes 150A. Let’s say we applied them both to the house bank and the engine is running fast enough to get them to full output, and they are putting out their rated output (none of these assumptions are likely to be correct). We could, in theory, be seeing 300A into a 600Ah battery pack so that’s a charge rate of 0.5C so another piece of information we need is the maximum acceptable charge rate. As you can see, there is currently quite a bit of missing critical information!

      Let’s turn to the cranking battery. Feeding it with a high output alternator with a pass-through capability to the house bank of 60A (the two 30A BtoB chargers) is likely under utilizing the high output alternator. Assuming this is just a cranking battery (i.e., no other loads attached to it) It would be better to apply the high output alternator to the house bank and charge the cranking battery via one of the BtoB chargers. If you are worried about the BtoB charger failing and the cranking battery going dead, figure out some emergency paralleling, which could be as simple as a set of jumper cables, or as fancy as a redundant BtoB charger.

      Let’s look at the bow thruster battery bank. Let’s assume a powerful thruster with a 300A draw running for a total of 30 seconds (multiple shorter bursts). That’s 2.5Ah. Let’s assume the windlass pulls 150A and you are struggling to get the anchor up and you run the windlass for a total of 10 minutes. That’s 25 Ah. So, worst case we are looking at 27.5 Ah. You have 200Ah of thruster bank capacity so that’s less than a 15% depth of discharge – the batteries can handle this without requiring any additional charging while operating the thruster and windlass. So we can recharge these batteries at our leisure.

      Your AGM batteries are around 85% efficient so we’ll round that up to 33Ah when it comes time to recharge. Feeding one of the high output alternators to the bow thruster bank will require large conductors and will largely be a waste of its capabilities. Once again, it would be better to feed the alternator to the house batteries and put a BtoB charger between the house bank and the thruster bank. The 18A BtoB charger will be more than adequate – it will have all day to catch up with the infrequent thruster and windlass use.

      The combination of the lithium-ion battery bank, two high output alternators, and a large solar array is potentially a really powerful DC system. You need to figure out how best to optimize it. Generally speaking, this is best done by focusing on the house battery bank as the core of the system and then figuring out how to maintain other peripheral battery banks rather than focusing on these other banks.

      Nigel

      • Hi Nigel,

        Thanks for the response. You were right that I left off quite a bit of information. Our “new to us” boat (a 2003 Caliber 40 LRC SE) came to us with a lithium house bank that was installed by an ABYC certified tech in Grenada. However, in our survey we learned that the small alternator was overheating (later learned it was burned up). That started us down a path to investigate the entire installation.

        Here’s what we have:
        The Yanmar 4JH4E 50 hp engine has a small case older Ample 125 amp alternator and a large case frame Ample 200 amp alternator (twin v belt). From the factory, we learned from the wiring diagrams that the alternators were regulated by a regulator that could regulate both alternators (as long as they were connected to lead acid or AGM batteries). The previous owner thought that the large case alternator charged the house bank and the small case alternator charged the starter battery. That is what he told the installer of the Lithium bank. However, upon our investigation of the wiring diagrams we learned that both alternators were connected to the house bank. We believe this is why the small alternator had burned up. The boat had a significant amount of solar (~800 watts) and we believe the Lithium had been primarily charged by the solar and maybe that is why the small alternator had not previously burned up. Both of these alternators while old have been rebuilt and not used yet after the rebuild.

        The Grenada installer put in two 300 amp hour Kilovault 3600 HLX+ 12 volt batteries in parallel as the house bank. He added a Balmar MC614 regulator for the Kilovault bank. The Kilovault batteries have an internal BMS and a CAN Bus communication port. Kilovault is still working on the CAN Bus communication and it is NOT supported at the moment. The Kilovalult has a maximum discharge current of 200 amp, maximum charge current of 200 amp, the BMS will disconnect if the current exceeds 500 amp for 3 sec. The C rating is 1.5.

        We are concerned about the inability of the Kilovault to communicate externally and the risks of charging it with an alternator. For example, we cannot use the features of a Wakespeed with its ability to communicate with the BMS and shut the alternator(s) down in the event of a problem with the Lithium bank. The only way that we can protect the alternator from the BMS disconnecting is by using a temperature sensor on the (alternator/battery) and by installing Balmars Alternator Protector APM-12 modules. However, I am not sure the Alternator protector will adequately protect the alternators. We were not comfortable with this, so we decided to change the design.
        We plan to:
        Install a new 100 ah starter battery – Deka 27 M

        Have the large frame alternator regulated by a Balmar MC618 regulator and charge the Starter battery.

        Use a switch rated at 10A placed in the ignition wire of the small alternator and leave open so the Balmar MC614 controlling the small frame alternator will not energize and the small alternator will just free spin and not generate electricity (and does not overheat) Note: The engine water pump is run off the pulley on the small alternator so we want to keep the small alternator in place and not have to redesign those belts). There may be an idler or tensioner pulley that might be able to be sourced but have not gone down that path yet.

        Use two 30 amp DC to DC chargers to charge from the starter battery to the Lithium house bank.

        We agree with you that we are not being able to take full advantage of the lithium battery’s high charge acceptance rate, but we viewed it is a tradeoff to us to ensure that the alternator is not exposed to a possible Lithium BMS shutdown. Do you think we are overly concerned about this?

        We are wondering whether we should just replace the Kilovault batteries with batteries that have CAN Bus communication and then invest in a Wakespeed 500 to regulate the alternator and communicate with the BMS. We’d be more comfortable using the large frame alternator to charge the lithium bank because we could use a Wakespeed to monitor. We could also consider replacing the large frame alternator with a more efficient alternator like the Balmar XT-50 which is a small frame but per Balmar designed to charge Lithium batteries. It would of course be a big investment, but we wonder if we are just spinning our wheels trying to overcome the lack of CAN Bus communication with the Kilovault batteries.

        Thanks,
        Stacy

        • Stacy,

          The bottom line here is you will have a significant amount of underutilized alternator capability with what you are proposing. I think you need to step back a bit and look at the energy requirements of your desired lifestyle, and how to minimize the engine run times necessary to do this. If this can be done with the combination of the solar and the proposed alternator setup, then you are good to go, but if this is going to require, for example, extended battery charging at anchor then you should rethink and figure out how to optimize the resources available to you. This, of course, also involves an estimate of the cost and work involved in reconfiguring things. Part of this comes down to how hard you will work the li-ion batteries, the ambient environment in which they will be operating, and as a result the likelihood of a BMS disconnect. If a disconnect is highly unlikely, some of your fears go away. So, I think we still need more information!!

          Nigel

        • Hi Stacy, you didn’t ask for another classmate’s amateur opinion, but I’ll offer it anyway! Regarding your concerns about alternator charging house vs starter with a “dumb” regulator: have you considered using an ARGOFET isolator to simultaneously charge the house and cranking banks? In the event of a BMS shut down in your house bank, my understanding is that the transient voltage spike from the alternator will be absorbed by the cranking bank’s AGMs. With an APM-12 you have additional protection. The downside is that you’ll perpetually slightly undercharge your cranking bank, but you can either accept some lifecycle shortening or use a B2B charger or small solar panel configured to an optimum AGM charging profile.

          That’s how my system is set up and so far so good. And it’s not just my own hare brained idea – this design is outlined by Rod Collins in his Lithium Drop-In Batteries article.

          Perhaps this is also touched on in the BoatHowTo Advanced course on Lithium systems, but I haven’t got that far yet.

          If Nigel, Jan, or Michael think this a bad idea then I hope they’ll set me straight!

          • Thanks Nigel and Will. I actually came across two items that we are now incorporating to address my concerns. One is the ARCO Zeus regulator to regulate the alternator to charge the Lithium. It has two shunts one for the Alternator and one for the battery bank to measure and then control the field current in the alternator. The other is the argofet to link the Lithium and AGm as you described (I did see that in Rod’s article!) and we are coupling that with a btb charger that we already own to get the AGM charge profile for the Starter. We have all the equipment, now we just need to install. In the meantime we are installing a new failsafe galvanic isolator. preinstallation testing began today. More research ensues….!

  • “Dear Jan, I keep seeing – including in the course’s cover image – that a strip fuse is mounted directly on the battery pole, and a battery switch is attached to it. How do I implement this combination or a variant with an MRBF fuse in practice? I would need a short piece of a busbar with two holes (or something similar) to connect the fuse and the battery disconnect switch. I haven’t found such connectors in the relevant shops (at least not ones that are explicitly intended for this purpose). Or do the two parts have to be connected via a cable? This would be significantly more effort (cable with cable lugs and the disconnect switch would need to be mounted somewhere if it’s not attached to the battery pole.
    Kind regards, Willi”

    • Hi Willi,
      This is actually a pretty good question. The image was made by our now-retired co-founder Michael for illustrative purposes and I must admit that I have not seen such a setup in practice yet.
      There are battery switches that you can directly clamp to a battery pole, but they do look a bit “flimsy” and I would not use them for anything else than maybe a starter battery. And then you would still need to put the fuse somewhere. You may be able to attach a normal switch to an MRBF fuse holder with a short home-made copper busbar, but then you would have to be very careful not to put too much stress on the battery pole. So if this is in any way possible, I would run a short cable from the MRBF fuse holder to a switch that’s firmly installed somewhere next to the battery case.
      Best
      Jan

      • Dear Jan, thank you very much for your prompt and comprehensive reply. I will install the switch firmly and solve the issue with a short cable.
        Best regards, Willi

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