Lithium replacement.

I used 305Ah EVE cells,JK-B2A8S20P 200A BMS and Victron DC to DC chargers. If anyone would like the details let me know.

Did you change or upgrade the alternator?

Why do you have 2 dc-dc chargers?  Are they running in parallel?

Did you change the ACR or other battery divider?

What happens if the BMS shuts off the battery?

Do you have a bow thruster?

What amperage dc-dc charger are you using?

I’d love to see your wiring diagram.

I have two Lithium banks but haven’t installed them yet.  I feel like I’m over thinking it…

Hi. 

I’ll try and go through each point. I can’t do a wiring diagram at the moment but you may not need one. 

I already had a 120A alternator so didn’t need to upgrade. 

The two DC-DC chargers are paralleled to provide charging up to 60A each can provide 30A, this is about a hard as I would like to push the alternator on a continuous basis. It’s more than adequate for the time we run on engine to recharge. It’s not the cheapest solution but saves a lot of pain changing the alternator charging regime.

The ACR isn’t needed as the DC-DC chargers have an engine on detection feature and the default settings seem to work just fine charging the start battery. They are user configurable if needed. 

The BMS will shut off the battery on low voltage but with lithium’s this is at a point where they are almost depleted. However, there is an override for this on the BMS app. For over voltage the BMS will disable charging while allowing discharge so not an issue. The BMS is rated at 200A so I don’t anticipate this being an issue as I’ve monitored the current draw over several years and only exceeded this a few times momentarily with a stalled windlass. The overcurrent can be configured to trigger after x seconds so these states won’t shut down the battery. If it does it resets after x (configurable) seconds in any case. I’ve been extremely impressed with the config options. 

We do have a bow thruster and this has a factory DC - DC charger. It appears to work fine with the lithium’s even with the higher steady state voltage and not noticed any significant draw but I’ve not actually measured it yet. 

In essence, after much tracing the wiring diagrams, all that we needed to do was disconnect the feed from the alternator/start battery from the ACR, connect this into the DC-DC chargers and connect the output from them to the main bus bar. At that point the ACR is redundant. 

I already had a shunt but the BMS has this function as well. 

Hope this helps. 

I really like this approach and I'm planning on copying it.

It seems much more elegant than all the changes I had planned on doing with mods to the alternator, charge divider, etc.

My only question - how would I wire up the Victron charger/inverter that I have?

My belief is that it's one set of wires to the house battery bus at this point - when the mains are plugged in it acts as a charger, so theoretically you could put that connection on the other side of your DC-DC chargers and they would handle the LiFePO4 charge profile, no? 

However if you do that, then when you want to run the inverter, the DC-DC chargers won't pull power from the LiFePO4 bank, only the starter battery, correct?

If you leave the charger/inverter wired directly to the house battery, then you won't be charging the starter battery, since the DC-DC charger only works in one direction (i think), and you have the issue of an incorrect charge profile as you noted (if you can't reconfigure the charger).  What happens if you start the engine while still plugged in?

How are you charging the starter battery with shore power in this setup?  Do you need another DC-DC charger pointed the other way?  Would that work? 

I actually have two batteries each with their own 200A BMS, so I believe that it should work ok.

I noticed while reading the manual that the charger has a second output for a starter battery, so I can probably just use that.

The main issue is that it doesn’t seem to have a setting for the primary battery chemistry to be LFP, so I’ll have to see if I can change the configuration somewhat.

The boat is typically on shore power when docked, so I want to ensure the charging is correct for the LFP when plugged in…