converting RV to lifepo4 questions

[mnman14]

I'm new to the lifepo4 world and have a few questions that I'm finding conflicting information on. I found your forum via Will's YouTube videos and you seem like a knowledgeable bunch so maybe you can provide clarification.

In my RV the house battery has 3 charging sources: A PowerMax PM3 110 to 12v converter/charger, a Renogy Wanderer 30A solar charger, and the alternator on the engine. I purchased the Chins 100AH lifepo4 battery to replace the single house battery.

for the converter, my understanding is I should set it to fixed mode between 13.8 and 14.2 Volts, figured I'd just use 14.0, and the battery's internal BMS should take it from there. The chins documentation states:
The setting method of MPPT and inverter of 12.8V lithium iron phosphate battery pack is as follows:
Charging
Charging Limit Voltage: 14.2V
Over Voltage Disconnect Voltage: 14.6V
Over Voltage Reconnect Voltage: 13.8V
Float Charging Voltage: 13.8V

for the solar it seems straightforward that I just choose the lithium setting. I currently only have one portable 100w panel I put out when boondocking but I'm considering roof mounting more (especially if I have to take the alternator offline)

My big confusion is the alternator. I'll be keeping the engine battery lead acid. There is some sort of oil-pressure disconnect that isolates the two batteries when the engine isn't running but when the engine is running it does charge the house battery. There is also an emergency start solenoid that connects the two when a button on the dash is pushed. I've read some places that I should either buy a 12v to 12v charger or disconnect the charging circuit to save the alternator and battery. But others say it's fine to leave it as is and they've done so for years without problems. I'd like to understand the issues and benefits of each approach.

I appreciate your insights.

 

[fmeili1]

I've done such a conversion and it's always a good idea to put a DC/DC converter/charger between the alternator and the lithium battery! The charging current of a nearly empty lithium battery will overload your alternator - don't try it! Also such a converter uses the correct charging profile for lithium batteries. I left the solenoid and it's emergency start button installed, even if you loose the possibility to jump start the engine from the house battery. I've installed a "Victron Orion-Tr Smart 12|12-30" DC/DC converter/charger. It works great, but you need to left enough space around this unit for passive cooling, because it gets really hot.
Because you'll loose the jump start possibility, always carry a jump start cable with you

 

[sunshine_eggo]

I'm new to the lifepo4 world and have a few questions that I'm finding conflicting information on. I found your forum via Will's YouTube videos and you seem like a knowledgeable bunch so maybe you can provide clarification.

In my RV the house battery has 3 charging sources: A PowerMax PM3 110 to 12v converter/charger, a Renogy Wanderer 30A solar charger, and the alternator on the engine. I purchased the Chins 100AH lifepo4 battery to replace the single house battery.

PM3-LK unit with 3 stage vs. constant voltage operation via switch with voltage pot adjustable (I have 3 of them)?

for the converter, my understanding is I should set it to fixed mode between 13.8 and 14.2 Volts, figured I'd just use 14.0, and the battery's internal BMS should take it from there.

Understanding is incomplete. 1) The PM3 in the 3 stage mode can be a very effective converter. 2) You NEVER let the BMS be a part of routine charge/discharge operations. This can wear the BMS out.

The biggest issue with RV converters is the wiring that causes excessive voltage drop. This is exacerbated with Lithium.

Recommend you leave it in 3 stage mode with bulk pot set to 14.6V with no load applied. Evaluate if that gets you fully charged.

Also matters grid vs. generator. If charging with generator, constant voltage mode set to 14.6V. Monitor voltage and cut off when 14.4V is reached AT battery terminals.

The chins documentation states:
The setting method of MPPT and inverter of 12.8V lithium iron phosphate battery pack is as follows:
Charging
Charging Limit Voltage: 14.2V
Over Voltage Disconnect Voltage: 14.6V
Over Voltage Reconnect Voltage: 13.8V
Float Charging Voltage: 13.8V

for the solar it seems straightforward that I just choose the lithium setting. I currently only have one portable 100w panel I put out when boondocking but I'm considering roof mounting more (especially if I have to take the alternator offline).

If the Renogy can be set to a user mode, that's better.

The PM3 can be se

My big confusion is the alternator. I'll be keeping the engine battery lead acid. There is some sort of oil-pressure disconnect that isolates the two batteries when the engine isn't running but when the engine is running it does charge the house battery. There is also an emergency start solenoid that connects the two when a button on the dash is pushed. I've read some places that I should either buy a 12v to 12v charger or disconnect the charging circuit to save the alternator and battery. But others say it's fine to leave it as is and they've done so for years without problems. I'd like to understand the issues and benefits of each approach.

Again, it goes back mostly to wiring. If the wiring between the alternator and the battery produces a substantial voltage drop, this will protect the alternator. This is why those that don't use DC-DC chargers don't blow up their alternator, OR their alternators are "smart" and will regulate (reduce) their output based on temperature. LFP takes on the bulk of it's charge below 13.8V (at the terminals) and doesn't spike to peak voltage until the last 15-30 minutes of charge. This means the alternator can be run at max output for an extended period.