How are people charging Li/LA hybrid setups?

[FlyingScot]

Alternator to Argofet Isolator to both house and starter batteries.

[Rohan]

I avoided all the complications here. I have 2 battery banks and flip back and forth.

I have one AGM battery on bank one as my start/motoring battery, and 4x LiFePO4 on bank two as my house bank.

When motoring the alternator only charges the battery I'm selected to, while on shore power the battery charger charges both. So when motoring, I select the LA battery, and while anchored or on shore power I select the Lithium bank. I never leave both on together. I also set my battery charger to the "gel" setting so that it's slightly lower voltage for both, so they won't overcharge.

[Ryban]

Is it a dumb idea to incorporate another DC-to-DC charger to allow the alternator to also charge the LFP bank (albeit at a lower rate)? It adds incremental cost and complexity.

I sketched up a schematic of the planned system below.

I want to retain the ability to use the start battery as a back-up battery bank if there's an issue with the LFP bank, or we need to take the LFP bank offline for maintenance. This is the purpose of the first 1/2 selector switch.

The second 1/2 selector switch will determine which DC-to-DC charger is in use. Normally, and as-drawn, the LFP bank is charging the Star bank as-needed. However, if running the engine to charge batteries, the 1/2 switch can be switched, which will connect the + of the start bank to the input of the second DC-to-DC charger (and disconnect the output of the first DC-to-DC charger), thus providing alternator output to the LFP bank.

Since we will probably only be using the alternator to charge the house bank infrequently, I feel like the compromise of lower charge rate is acceptable here.

But maybe this is a really dumb idea.

Also: Can a DC-to-DC charger provide power to the start bank from the MPPT chargers if the LFP battery is disconnected/removed from the system? Just thinking of corner cases.

[OS2Dude]

Most LFP battery BMSes can not take the in-rush current required to start a decent sized engine, so people keep the LA start battery. If you have an alternator with a regulator that can handle LFP, then charging the LFP directly from the alternator with a DC-DC back to the start LA is most efficient. ALT to LA to DC-DC- to LFP works but is not as efficient.

I am switching from a single bank consisting of two 98Ah AGM batteries (Start & House) to a 300Ah LFP house and separate AGM start. House batteries will have solar as the primary charge source, the start will use the ALT. (It's a sailboat, so I don't use the motor much.) My array is currently two 175W panels, but I am adding two 115 bi-facial panels as well. In the event that solar is not enough, I also purchased a shore power charger for the LFP.

[dreuge]

There are many reasonable solutions. I considered a DC/DC converter but was turned off by the limitations and cost. Like you, I already had an ACR (BlueSeas ACRsi) and I have a 120A alternator. Because of the higher LiFePO4 voltage, the ACR would always be above the combine threshold. I called BlueSeas and was told that one could control the ARC by placing a switch in the ACR ground wire. Switching on/off the ARC ground wire controls the ACR's internal relay on/off.
Use your ACR!

Simply connect your alternator charging wire to the ARC terminal with your LA start battery and connect your LiFePO4 house battery to the other ARC terminal and control the ACR by the ground switch. I first installed a simple Push/Pull switch in the ACR ground line. This works well but relies on manual operation. I later added a smart switch in parallel (can use either switch) which I DIY built for $20 using Arduino. The Arduino smart switch is powered from the engine key switch and controls when to combine the batteries. It has a built in delay timer, and I added 2 thermo probes for monitoring the alternator (high temps) and the LiFePO4 (low 32F). I have a write up of this on my blog which includes photos, electronic diagram, and Arduino code: https://svjohannarose.blogspot.com/2...m-w-solar.html. It's been working fine with my 560AH LiFePO4 systems for over 3 years.

[TPG]

Our Lifepo4 house bank gets charged by solar + regulated/protected alternators directly. Then I am using DC-DC chargers to charge SLA start batts.

When there's not enough sun or I don't want to run the engines, I can charge my house bank via shore power or Honda generator.

I use all Victron equipment except for the batts and solar panels.

This system works great for me, and can't imagine ever going back to the "old school" setup I had on my last boat.

[Amazing Grace]

I'm in the process of changing out my AGM system to Li and Pb combination. The route I've chosen is using Clark's Battery Bank Manager. I know there are lots of differing opinions on this, but I think it's worth checking out.

https://www.youtube.com/watch?v=VZSr6o5fLHE

[Artey]

Originally Posted by dreuge

There are many reasonable solutions. I considered a DC/DC converter but was turned off by the limitations and cost. Like you, I already had an ACR (BlueSeas ACRsi) and I have a 120A alternator. Because of the higher LiFePO4 voltage, the ACR would always be above the combine threshold. I called BlueSeas and was told that one could control the ARC by placing a switch in the ACR ground wire. Switching on/off the ARC ground wire controls the ACR's internal relay on/off.
Use your ACR!

Simply connect your alternator charging wire to the ARC terminal with your LA start battery and connect your LiFePO4 house battery to the other ARC terminal and control the ACR by the ground switch. I first installed a simple Push/Pull switch in the ACR ground line. This works well but relies on manual operation. I later added a smart switch in parallel (can use either switch) which I DIY built for $20 using Arduino. The Arduino smart switch is powered from the engine key switch and controls when to combine the batteries. It has a built in delay timer, and I added 2 thermo probes for monitoring the alternator (high temps) and the LiFePO4 (low 32F). I have a write up of this on my blog which includes photos, electronic diagram, and Arduino code: https://svjohannarose.blogspot.com/2...m-w-solar.html. It's been working fine with my 560AH LiFePO4 systems for over 3 years.

Way to use your noggin! I really like this as a fairly low cost solution. Thanks for sharing!

[Pete7]

Originally Posted by Rohan

I avoided all the complications here. I have 2 battery banks and flip back and forth.

I have one AGM battery on bank one as my start/motoring battery, and 4x LiFePO4 on bank two as my house bank.

When motoring the alternator only charges the battery I'm selected to, while on shore power the battery charger charges both. So when motoring, I select the LA battery, and while anchored or on shore power I select the Lithium bank. I never leave both on together. I also set my battery charger to the "gel" setting so that it's slightly lower voltage for both, so they won't overcharge.

Make sure you don't float charge LifePO4 using a gel setting. That would be very bad for the LifePO4. They should be charged and then the charge stopped.

[Pete7]

Originally Posted by Ryban

Is it a dumb idea to incorporate another DC-to-DC charger to allow the alternator to also charge the LFP bank (albeit at a lower rate)? It adds incremental cost and complexity.

I think you are over thinking it. Remember the KISS principle. By all means carry a spare but not wired like that with two DC>DC chargers operating in opposite directions.

With an electric galley we carry a spare inverter and a spare double hob unit. We have a LA battery in parallel with the LFP house bank just in case. We can remove one solar panel and continue on 50% quite happily for a while.

[Texasvlad]

Originally Posted by Ryban

Is it a dumb idea to incorporate another DC-to-DC charger to allow the alternator to also charge the LFP bank (albeit at a lower rate)? It adds incremental cost and complexity.

I sketched up a schematic of the planned system below.

I want to retain the ability to use the start battery as a back-up battery bank if there's an issue with the LFP bank, or we need to take the LFP bank offline for maintenance. This is the purpose of the first 1/2 selector switch.

The second 1/2 selector switch will determine which DC-to-DC charger is in use. Normally, and as-drawn, the LFP bank is charging the Star bank as-needed. However, if running the engine to charge batteries, the 1/2 switch can be switched, which will connect the + of the start bank to the input of the second DC-to-DC charger (and disconnect the output of the first DC-to-DC charger), thus providing alternator output to the LFP bank.

Since we will probably only be using the alternator to charge the house bank infrequently, I feel like the compromise of lower charge rate is acceptable here.

But maybe this is a really dumb idea.

Also: Can a DC-to-DC charger provide power to the start bank from the MPPT chargers if the LFP battery is disconnected/removed from the system? Just thinking of corner cases.

Ryban,
I like your sketch. I have even saved it to my disk to use when I will upgrade my banks. But some question: Would you put the fuse in between engine and battery bank or add some manual disconnector to be able to disconnect engine circuit from power source for emergency or engine maintenance?

[Rohan]

Originally Posted by Pete7

Make sure you don't float charge LifePO4 using a gel setting. That would be very bad for the LifePO4. They should be charged and then the charge stopped.

I'm not worried about that, since I also have solar hooked up to the Li batteries only, with its own charge controller at Li battery setting.

And it hardly would ever apply anyway, because I rarely use the battery charger, since solar provides well more than enough power while I'm away from the boat.

I still have my old AGM batteries. When I sell the boat, I'll probably reset everything back to all AGMs, so the next owner won't have to worry about these complications.

[Ryban]

Originally Posted by Pete7

I think you are over thinking it. Remember the KISS principle. By all means carry a spare but not wired like that with two DC>DC chargers operating in opposite directions.

Assuming your alternator is connected to your LA bank, do you ever find you need to charge your LFP batteries from the LA/Alternator side, and if so, how do you achieve this without the second DC-to-DC, or other complex schemes.

[Rohan]

Originally Posted by Ryban

Assuming your alternator is connected to your LA bank, do you ever find you need to charge your LFP batteries from the LA/Alternator side, and if so, how do you achieve this without the second DC-to-DC, or other complex schemes.

I'm not the one you are asking, but other people have hooked up temperature limiters and other devices to allow the LFP batteries to be safely charged from the alternator.

In the future, I hope manufacturers will include LFP batteries as a setting on the alternator itself.

[W5PAD]

When I switched to LiFePo for my house bank I kept the LA start battery. To charge it I installed a time delay relay that's activated when the engine is started and connects the start battery to the house bank for 30+ minutes. I also have the ability to manually connected them if needed. I fell this is sufficient because I look at my LA start battery as if it's in a car. Does a car have a 3 stage charger? In a car it would last 4-5 years without 3 stage charging. Since the start battery is relatively inexpensive, any shortening in life by not having 3 stage charging is compensated by not having the expense of a 3 stage charger. I've had this setup for 10 years and have only replace the start battery once in that time.