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Charging FLA or AGM from a LiFePO4 battery?

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OffRoadRN

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I put a 100ah LFP battering in a box with a 12v fuse panel to run my dometic fridge while car camping. I attached the basic wiring diagram below. The main way I charge it is with a battery tender via SAE outlet. If I put a sae connection on my travel trailers non lithium battery, will the lithium battery charge it ok, or do I need some sort of dc to dc converter?

Thanks!
 

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A direct connect to the non-Lithium battery will charge the non-Lithium battery all the time. Is that what you want? Or do you want the non-Lithium to charge only when the Lithium is being charged?

I would want some isolation there so that if the LiFePO4 battery is drawn down to a certain level, charging of the non-Lithium battery stops.
 
HRTKD said:
A direct connect to the non-Lithium battery will charge the non-Lithium battery all the time. Is that what you want? Or do you want the non-Lithium to charge only when the Lithium is being charged?

I would want some isolation there so that if the LiFePO4 battery is drawn down to a certain level, charging of the non-Lithium battery stops.
Click to expand...
I want to charge the non lithium battery. So just look up a simple isolator and that will make sure the flow of charging stays LFP —-> FLA and won’t reverse when the LFP is discharged?
 
A simple isolator will charge until the LiFePO4 battery is dead. I meant something like a programmable DC-DC charger that you can set a voltage floor on. It continues to charge until the source battery is at X volts, then it stops.

Plus, with a DC-DC charger, instead of an isolator, you can set the charge profile you want.
 
Oh ok. Any suggestions for a dc-dc charger? Will discharging the source battery until it is dead harm the cells? I thought it was ok to do that with lithium?
 
It's not ideal to discharge lithium completly, a Victron Orion battery to battery charger has programmable start and end charge voltage thresholds for the source battery.
If you directly connect the lithium battery to the trailers battery, it won't charge significantly as the voltage difference is too low. What it will do is to power the trailer DC loads from the lithium battery without taking power from the lead battery, until the lithium drops to around 20%SOC.

Orion-Tr Smart DC-DC Charger Non-Isolated - Victron Energy

The Orion-Tr Smart DC-DC charger is a professional DC to DC adaptive 3-stage charger with built-in Bluetooth. For use in dual battery systems in...
www.victronenergy.com www.victronenergy.com
 
mikefitz said:
It's not ideal to discharge lithium completly, a Victron Orion battery to battery charger has programmable start and end charge voltage thresholds for the source battery.
If you directly connect the lithium battery to the trailers battery, it won't charge significantly as the voltage difference is too low. What it will do is to power the trailer DC loads from the lithium battery without taking power from the lead battery, until the lithium drops to around 20%SOC.

Orion-Tr Smart DC-DC Charger Non-Isolated - Victron Energy

The Orion-Tr Smart DC-DC charger is a professional DC to DC adaptive 3-stage charger with built-in Bluetooth. For use in dual battery systems in...
www.victronenergy.com www.victronenergy.com
Click to expand...
Thanks for the info. I don’t want to invest much money into this since I am going to be upgrading my rv batteries to lithium soon anyway. I’ll probably just hold off until then
 
OffRoadRN said:
Oh ok. Any suggestions for a dc-dc charger? Will discharging the source battery until it is dead harm the cells? I thought it was ok to do that with lithium?
Click to expand...
No, you don't want to take it down to zero. Not if you want a long life for the battery. A good BMS won't let you take it down too far.

I was thinking of a Victron Orion-Tr Smart DC-DC Charger Isolated. REDARC is another option.

I don't have the Orion in my camper, so I don't have any experience with it.
 
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