Special Considerations for Charging LiFePO Batteries

Braintrust,

I am replacing my house bank (24v) to LiFePO. The bank charges from both a dedicated battery charger and the alternator from the port engine. What have those of you who have switched to LiFePO done to modify your charging system (alternator and battery charger)?

Thanks in advance for your input!

Never mind.

I am doing that right now. I have a 120 amp Balmar alternator that will just charge the house bank. I have a 60 amp Promariner that will be dedicated to the lithium house bank. Sounds pretty much like your setup. .

For best results LFP batteries need a charger that peaks at 14.4-14.6 for best results. If you use a conventional three step charger it will usually peak out at a lower voltage which won't charge the last 10% or so, but otherwise works ok.

So for best results you need an alternator/regulator and a shore power charger that can be set for these parameters.

If your alternator has an external regulator usually a Balmar you can switch it out with their new one with standard LFP parameters or set up an older one yourself for these parameters and do the same with your shore power charger. But like I say all of this changeout only affects the last 10% of LFP charging.

David

Thanks for the feedback!

The internet is a dangerous place but read that there may be an issue of overheating the alternator and David confirmed that conventional chargers pump only 13.xx into the bank.

ComoDave - I bought the same batteries from Costco that you purchased (Lion Energy). Cannot believe how light those batteries are!

After I started this thread, came across this from Victron:

https://www.victronenergy.com/blog/2019/10/07/careful-alternator-charging-lithium/

I guess there may be some more bits to purchase and install.

I love that the terminals come off so I could use bus bars instead of cables.

I asked Balmar about the BMS turning the batteries off and damaging the alternator. They told me to use an alternator protection device. I got one from Compass Marine and will be installing it when I put the engine back in.

There are two alternator protection issues mentioned above when using LFP batteries:

Comodave noted above that the BMS will shut off the battery and potentially damage the alternator. This isn't like turning the 1,2,all, off switch to off. You still have the house loads connected to absorb the alternator output. The only way the BMS might be an issue is if you were charging the house bank and there was no load connected. But that diode is always good to have in place.

The other issue is overloading the alternator since LFP batteries can pull a lot of current. Use Balmar's alternator temp probe which will cut output in half if it gets too hot.

David

Your batteries should have the specifications for what the charge profile needs to be. If your existing alternator/charge devices can't be set to those specifications, they should be replaced or modified to do so. For the alternator, an external regulator that can sense alternator temperature and reduce output if the alternator gets hot is useful.

The alternator protection device by Sterling Power is designed to absorb an alternator created voltage spike if the internal BMS on your batteries decides to disconnect suddenly. Not sure if that same device has any useful effect on solar charge controllers that might be pumping a lot of amps in during a disconnect event.