Lithium Battery Design for Catamaran

We have decided to install lithium batteries. We have also decided which Lithium batteries we are going to buy. We have consulted an electrical engineer who has installed lithium batteries on their boat. I have prepared a circuit diagram below. We would really appreciate design input in relation to any flaws or improvements.

 

I think I'd get rid of Sw5 and replace it with a battery combiner diode such a Victron BCD 402. As drawn, Sw 4 wiring needs to be good for 1000 amps not the 50 amps the BCD requires.

A sketch of the boat's general arrangement and mechanical arrangement would help.

 

Thanks so much for taking the time to give feedback. I am looking into the Victron BCD 402 - thanks for the heads up. I have attached the "as is" drawing showing a single engine battery starting both engines (I think that is what you are referring to as the general arrangement and mechanical arrangement. The new design has two starter batteries. The current design has a few flaws that we are correcting at the same time as installing lithium.

In terms of key loads - we have a 1000W windlass, washing machine (always run at less than 400W across whole cycle off the 2kW inverter). Watermaker (100W only). Freezer (100W max normally). Fridge (less than 100W). No generator and have only needed to run engine 6 times to charge batteries in 2 years of cruising (at anchor not marinas). Don't use shore power. Currently have 400Ah lead acid and 100Ah starter.

 

Do you have a fire suppression plan for the battery.

 

If I'm reading it right you plan to charge the 400Ah battery from two 50A alternators via a 30A battery to batttery charger. That is a lot of wasted potential, you charge at under 0.1C. No problem if you don't need to rapidly charge the batteries, but an odd choice.

The Sterling protection device is superfluous, it does nothing since your lithiums are not connected directly to the alternators. If you keep lead acid starting batteries in the loop they would act as load buffers even if the lithiums were connected directly to them. They only make sense if you set up the system the other way around, with the lithiums directly connected to the alternators and the starting batteries on the B2B charger.

 

Yes the existing schematic does show the 400Ah battery from two 50A alternators via a 30A battery to battery charger. And yes I agree a lot of wasted energy, but we have only used the engines to charge the house battery 6 times in 2 years of cruising - we have 1.3Kw of solar. We sail almost all of the time apart from coming into and leaving some anchorages and we very rarely use both engines otherwise. We did think of a second battery to battery charger to increase the amps to 60A (30A from each alternator) from both alternators but trying to keep costs down. I would value your input on a cost effective better way of doing this?

That is a really good point about the Sterling Alternator Protection device. We could keep them in as a cheap insurance policy in case the starter switch was turned off rather than pulling the stop cord which has happened a couple of times already - would they work under this circumstance?

 

We don't have one planned apart from fitting smoke alarms in the engine bays and perhaps by the Lipo batteries. We have already got a dry powder fire extinguisher and plenty of water

 

The Sterling devices will do something only if you run the alternators without the starting battery connected and the B2B charger quits or the BMS disconnects the Lithiums from the charger. Otherwise they are wasted money.

If you don't run the engines then your setup can make sense. It is a question of money, what is cheaper, the B2B charger or two external regulators with field limiting capability for the alternators and diode isolators for the starting batteries.
Adding a second B2B is possible but makes no sense.

 

Really like your approach... trying to reduce the cost rather than recommending expensive devices

 

Already have a diode isolator installed so thinking it would make for a cheap solution. Been looking for external regulators with field limiting capability online and can't find any. Found a site showing how to make you own but I think opening up the regulators is a bit beyond my level of knowledge.

 

All Balmar regulators are capable of field limiting, they call it the "Belt Load Manager". You compare the prices, two Balmar regulators, two diode isolators (one for each starting battery) vs one B2B.

Why would I recommend expensive devices? You stated your use case so the responses should be tailored to it.

 

Questions:
1. If you don't use shore power why do you have an AC charger?
2. You do not really plan to use the Invac DuoVolt wired as shown do you? Maybe not at all?
3. How often do you actually use the engines? Once a week or once a month?

 

1) The shore charger came with the boat and could come in handy if we have to leave the boat.
2) I don't have an instruction manual for the Invac DuoVolt and can't find one online. Is there an issue with the proposed wiring? Could you point out the problem?
3) We have used the engines for about 6 hours in 2 years of cruising. We do incidentally charge when we come into an anchorage or leave an anchorage.

Thanks for the heads up on the belt load manager - just what I was looking for. I will compare the costs.

You have been a great help already...very much appreciated.

 

1. The chargers manufacturer is gone. No info about how it functions and what it's settings are. As far as I know there where 2 models, 15A and 30A.
2. Problems with your wiring: only the latest and greatest and most expensive multi battery chargers can actually deliver different profiles to the individual batteries. All others use the same profile for all, the better ones can do intelligent load splitting (sensing how much A to send to each battery). Combining Lithium and lead acid on the same charger means you must find a lead acid battery with the same charghing voltages as your lithiums and use intelligent load splitting. Lastly, it does not make sense to connect a "dumb" charger directly to the lithiums when you have a dedicated B2B charger for them. In your current configuration the charger charges the lithiums both via the B2B and directly (unless you disconnect the B2B).
3. Using lithiums on shore power is different from using lead acid. The recommended procedure is to disconnect them from all charghing sources after you run them down to 50% capacity. The onboard DC systems then run from a regulated DC power supply. Some chargers can do that, and that is why you don't connect the charger directly to the batteries, you use a separate busbar for charge sources (and another for discharge sources).
4. I did not ask for the total hours of engine operation, but the frequency of using them. That's because your starting batteries are charged solely by the alternators (the B2B is only one way), but they do require to be kept healthy, and running the engines 10 minutes every other week is not going to do it.

Possible solutions:
1. You keep the current charger. If you are lucky it is a 30A model and can act as a regulated power source. You only run it with disconnected lithiums. If you want to use it to charge the lithiums you do it via the B2B and disconnect the charger from the boats discharge bus beforehand.
2. You exchange the charger for something programable with custom profiles. For the proposed wiring scheme one of the latest and greatest. Otherwise same as 1, but with a charger that is actually programable for either the starter or lithium batteries and is sure to run the boats DC loads.
3. You use a regulated DC power supply instead of a charger, just to run your DC loads at the dock. With human supervision it can also be used for charging batteries.
4. If you use the engines as infrequently as I suppose you do, you would do well to arrange for the starting batteries health. This could be a small B2B charger feeding from the lithium bank, or you could use dedicated small solar panels with regulators.

If you ask what I would do, I would fit a 10W-20W solar panel on each starting battery, regardless of how the rest of the system turns out. Then I would use either a charger or a DC power supply to run the DC loads, and I would choose a modern unit that can accept 90-280V, 50 and 60Hz.

 

Ditto the start batteries. I would just add a couple little $10 PWM solar chargers run to the starter batteries. I also agree that for the time being, de-integrating the LiFePo4 batts from all other systems would be preferable. Any crossovers should be governed by simple break-before-make switches or switchgear contactors, with protected access to those controls.

If you design the system for discrete components, you can always elect to go with integrated components if you choose. But if you do it the other way around and can't find a replacement for a broken integrated component, you're stuck not being able to work around the problem with common parts. This is mostly a matter of adhering to best practices as far as wiring goes, and allowing for enough of a footprint to accommodate everything as a discrete component.

I suggest splitting your schematic into separate starter battery and LiFePo4 schematics. As far as your lead starter battery 12 volt schematic goes, try to show all the sources at the top - alternators, shore chargers, solar controllers - arranged port and starboard as appropriate. Show the batteries, isolation switches, fuses, and terminal boards in the middle. Show all load distributions on the bottom - inverters, starters, B2B charger, pumps, engine electronics and instrumentation, fuse panels, and any load that can be switched to LiFePo4. Show every contactor and switch (including engine key switches, push to start switches, engine heaters, battery isolation, and load source switches). Show all fuses on the 12 volt buss. Identify and show any circuits such as bilge pump #1, security system, etc connected directly to a starter battery terminal.

Then draw a separate schematic for the LiFePo4 system. Show sources at the top - solar, B2B, shore charger. Show battery, BMS, and terminal boards in the middle. Show loads at the bottom. Show all fuses, switches and contactors on the LiFePo4 buss. From the perspective of normal operations, consider the LiFePo4 as different/isolated from the starter batteries as the AC system needs to be.

Use a common reference system for any switches and contacts that appear on both sheets. And ask yourself why they are really needed. Accidental back-feeding needs to be avoided by design.

Consider how you want to connect the negative side of the two 12 volt systems. I'd probably only connect them at the single bonding point to earth.

Forget about chassis bonding for now, just show positive and negative battery wires. Don't use a ground symbol for battery negative. Show the entire negative buss.

So normally, you would have 3 main fuse panels protecting loads - 60 cycle, 50 cycle, and 12V DC. On the source side of these, you would have have selector switch panels for 60 cycle AC - Shore or generator (mains); 60 cycle AC - Mains or inverter; DC source select - Lead or LiFePo4. But you can choose to not have the AC source switches if you just want to run all your AC loads off the inverters or to hard wire the distribution separately.