How are people charging Li/LA hybrid setups?

[Ryban]

I see a lot of talk about people keeping lead acid around for their start bank, and switching to LiFePO4 for the house bank, but I'm still a little confused on how people are charging these setups efficiently, given the different requirements of the chemistries.

Are people using DC-DC chargers for each bank, or manually switching between the banks to top up the start bank as needed?

Currently I have an ACR in my all lead acid setup so I never have to think about it, but I will be switching to Lithium soon.

I like the idea of just switching everything to Lithium, but people seem to have strong opinions about that.

[Tin Tin]

If you are going to keep your standard internally regulated alternator (eg Hitachi), then some people install a Victron DC - DC charger between the house bank and the start/alternator. This is to protect the alternator from running too hot at full blast as the LifePo4 bank sucks as much amps as it can whilst in bulk stage. So the DC DC charger is really a buffer to the LifePO4 bank. The alternator will still charge the start battery. The AMps fed to the house bank is limited by the charger (most commonly 30A) although 50A models now available. The charger can have settings changed such as cut in/out voltages to suit the situation and usually have a remote on off option.

[mvweebles]

225A (12v) Balmar externally regulated alternator de-rated to around 150A charging a 600Ah LFP house battery bank; then a 30A Victron DC-DC from the house bank to charge three Group 31 FLA start batteries for engine start, generator start, thruster, and windlass. Works okay. Took a bit of tweaking to get the settings right on the DC-DC, and I'm still not 100% pleased with the settings, but good enough.

[mcarthur]

Since our house is 48V, there's few 48-12 DCDC that are chargers (as distinct to converters). So we'll be using a 100/20 or 100/30 MPPT from Victron to charge the 12v from the 48v.

[Ryban]

I guess I'm still a little confused though. Are people essentially building their charging infrastructure around their LFP house banks (e.g. all solar/wind/alternator power being configured for and directed to) and then using DC-DC chargers from the LFP bank to charge the LA bank?

Or just having the alternator be directly connected to the start bank, and to the LFP bank through a DC-DC charger, but no the other charge sources?

Or is it a combination of the above.

[NorthCoastJoe]

[QUOTE=Ryban;3868538]I guess I'm still a little confused though. Are people essentially building their charging infrastructure around their LFP house banks (e.g. all solar/wind/alternator power being configured for and directed to) and then using DC-DC chargers from the LFP bank to charge the LA bank?

Yes. That is the right way to do it. The big bank gets it all then feeds the smaller FLA battery.

[team karst]

Originally Posted by NorthCoastJoe

Yes. That is the right way to do it. The big bank gets it all then feeds the smaller FLA battery.

No; its the large Li bank that has the potential for overheating the stock alternator. So the DC to DC output is the house and insures a limited amount of AMPS. Of course the inverse is possible with enough controls on an externally regulated alternator.

[Pete7]

Originally Posted by NorthCoastJoe

Yes. That is the right way to do it. The big bank gets it all then feeds the smaller FLA battery.

Surely this depends on what the primary charging system is. Alternator, then yes, but if solar is the primary perhaps not. We only use the alternator occasionally to add a bit of umph to the LFP house bank so for us, alternator to start battery and DC>DC charger to LFP. This also meets our LFP suppliers instructions, might be useful if insurance ever questions it.

There is another way and that is the long wire route. Alternator to LFP with a long wire, say 25mm x 4m. Run engine at speed and checking temperature ensure it doesn't overheat. Once the length is correctly providing enough resistance that's it done. Cheap and cheerful, little to go wrong. Drip feed small charge back to engine start battery with a switch.

[Ryban]

Originally Posted by Pete7

Surely this depends on what the primary charging system is. Alternator, then yes, but if solar is the primary perhaps not. We only use the alternator occasionally to add a bit of umph to the LFP house bank so for us, alternator to start battery and DC>DC charger to LFP. This also meets our LFP suppliers instructions, might be useful if insurance ever questions it.

This is the solution that seems to make the most sense to me, too. We will not be using the alternator to charge the batteries except when needed (e.g. extended periods of cloudy weather, or an issue with the solar system). This also seems to be the simpler solution in my case, as it won't require a change to the alternator, or additional devices to ensure the alternator is safe while charging the LFP bank.

I also found this article that I wish I had found before asking my question, but maybe someone else will find it useful:
https://www.yachtingmonthly.com/gear...atteries-89782

[flightlead404]

Originally Posted by Ryban

I guess I'm still a little confused though. Are people essentially building their charging infrastructure around their LFP house banks (e.g. all solar/wind/alternator power being configured for and directed to) and then using DC-DC chargers from the LFP bank to charge the LA bank?

Or just having the alternator be directly connected to the start bank, and to the LFP bank through a DC-DC charger, but no the other charge sources?

Or is it a combination of the above.

For me, the answer to that first question is yes, its built around the charging requirements of the LiFePO4 batteries as those are the ones that need special charging requirements, can shut off based on the BMS, get the most use and therefore require the most charging, and are much larger AHr.

Victron 70+1 skylla charger has 70 amps output for the lithium and like 3a trickle charger for the start battery.

standard internally regulated alternator charges the start battery and dc-dc charger charges the lithium from that, protects against alt overheat and bms shutdown issues

solar charges house only.

[NorthCoastJoe]

Everything I have read says to run the alternator to the larger battery or bank of batteries. From there you need a dc dc charger for the start battery. Should not be that complicated.

[Cari Laut]

Our set up may not work for everyone, but we have a 24v LI house bank with a high output alt, and a separate 12v alt feeding the 12v AGM start battery.

[pbiJim]

There is no one size fits all best solution. There are several issues to consider & different possible ways of attenuating each issue. Depending on the priorities on the individual boat, different answers may be best for different people.

Lithium batteries have a BMS that can disconnect them on short notice & if they are the only battery connected to a running alternator, the alternator gets blown out. This can be dealt with by using a special BMS with a pre trip warning that lets you kill the field to the alternator before the bank drops out, but not every dock side wrench spinner who may work on the boat will understand that system. The more common option, is just to use a lead battery across the alternator.

Lithium batteries run at a slightly higher voltage than lead batteries, have different charge curve preferences, don’t like to sit full all the time, don’t like to cold charge, don’t like to be run hot, have a very high acceptance rate,. & really don’t like to be over charged. Since they are so different from lead batteries, putting them directly in parallel with lead is not a good idea. There are different ways that they can be isolated.

These days, most people seem to charge one bank directly, & use a dc to dc charger to feed the other. Be aware that a dc to dc converter is different from a dc to dc charger. Be aware that both come in isolated & non isolated ground configurations. If you don’t know the differences & why they exist, you are not the guy who should be setting up the system.

Another option is to use an old school battery isolator that is simply a collection of really big diodes in a box with some big heat sinks & a few terminal posts to connect battery cables to. This prevents back feed from one bank to another & lets bulk charging go to all banks at the same time, but does not give separate curves for each bank. The lead, being lower voltage, will often charge to full first. The lithium will still suck up lots of amps. The lack of separate charging curves makes this a poor choice if the motor is run all the time. If the motor is only used now & then, and a solar system then tops things off, you can probably get away with it. In this configuration, if the BMS drops out, the lead is still effectively across the alternator & it doesn’t go pop. In this configuration, you can have separate solar controllers for each bank and each of them can have whatever curve that banks wants to see.

Alternators can only put out so much before they cry. A big lead bank will beat them up as much as a moderately sized lithium bank. Amps are amps. There are different ways of dealing with this. You can use an external regulator that allows you to compensate for temperature, or lets you manually set a current limit. You could also put a larger diameter drive pulley on the alternator so that it spins more slowly & doesn’t try to generate as much power. That is cheaper, but gives you reduced performance at low RPM.

If I felt like writing a few more pages, I could give several other options, but I’m not in the mood to write that much at this time.


It all starts with the question - what does my battery manufacturer say that the proper way to charge there batteries is?

[OldManMirage]

So my set-up is slightly out of the norm, but what I have done is to keep my systems separate.

I started with 2 golf cart batteries as my house bank, and a group 27 LA as my "backup" starter battery. I had 2 - 100watt panels going through a dual controller that fed both banks as needed. I still have my stock 35amp alternator, it fed the golf cart batts.

Now I have added 4 - 100AH lithium batteries, and upgraded my solar controller. The golf cart batteries are still there and they are now my start battery/reserve bank. Its 230AH of power there so I saw no reason to remove them - they'll probably last for 5 or 6 more years and I'll likely never have to worry about starting my engine. The alternator still charges this bank. It is essentially a separate system on its own.

The lithium is charged by my panels which are wired in series now. The controller is a Victron SmartSolar 75/15 MPPT. It has a bluetooth app and works fantastic !

Both banks are wired to a Off/1/Both/2 battery selector switch, so I COULD combine them if I ever need to. But this is the only cross connection between the 2 banks.

I did NOT want to add the complexity of DC-DC chargers and upgrading the alternator in order to charge the lithium house bank from the engine. Mainly because with my fuel capacity I don't see this as being viable when cruising long term. With this set-up I can do it in an emergency situation.

So now I feel I have a very solid, simple and reliable system. So far it is proving itself very well. My two last videos on my YouTube channel have a little more info, FWIW. NOT pushing the channel, just putting it out there. Sometimes visuals help.

[goeasy123]

We have a 20 year old 12VDC LA based system and a new big LiFePO4 powerstation. The powerstations MPPT is permanently connected to the LA load/charge buss through a programmable 200A VSR.


When the LA is 0.1V below absorbtion the VSR connects the powerstation. At the end of the day when the PV drops to 12.7V the VSR disconnects the powerstation.


There's a 15 minute delay before power-on to prevent the VSR from retriggering when the buss voltage goes up as the powerstation is off-loaded.