Charging LiFePO4 Batteries via 7-Pin Connector: Safe and Effective?

[whawahwa]

I'm about to pull the trigger on a used Coleman 202rd. The inspector noted the existing lead-acid battery likely needs replaced

I'd like to replace it with a 320AH LiFePo4, it sounds like the converter will handle it, but what about the charging from the truck towing it (I think through the 7-pin connector)? I'm reading conflicting information. Do I need to put some kind of gizmo between the connector and the he battery?

 

[whawahwa]

according to chat GPT I should add 20A DC-DC charger between the 7-pin connector and the charger (and a 30A circuit breaker between those?)
something like: VEVOR Lithium Battery Charger 12V - 250W DC-DC AGM & GEL

 

[chrisski]

I recommend you ask these questions on DIYsolarforum.com

That has been talked about on that forum.

The dc to dc converter may not be needed.

I have a 24 VDC lithium battery on my trailer and use a 24 VDC to 12 VDC converter. The 7 pin 12 volt has not been modded with a converter between 7 pin 12 volt and the 24 VDC to 12 VDC converter.

 

[dsol]

Agree you should consult experts but the give or take the 12 volts output by your tow vehicle will likely be fine while under tow. For long term charging and maintenance you need a lithium compatible converter that uses the proper charging protocol.

 

[leisuresolar@gmail.com]

I'm about to pull the trigger on a used Coleman 202rd. The inspector noted the existing lead-acid battery likely needs replaced

I'd like to replace it with a 320AH LiFePo4, it sounds like the converter will handle it, but what about the charging from the truck towing it (I think through the 7-pin connector)? I'm reading conflicting information. Do I need to put some kind of gizmo between the connector and the he battery?

Depending on your tow vehicle, your alternator may or may not make enough voltage to charge a LiFePO4 battery through the 7 way plug. Older alternators (pre 2012-2014) usually went to 14.5V and stayed there. That would charge a lithium battery. Newer "smart" alternators turn the voltage down based on various criteria, such as time or temperature etc. These will not charge a lithium battery. Typically we use a DC-DC isolator that converts your alternator voltage to a lithium profile, limits the current to 10A, and shuts off when your engine shuts off. Occasionally we use an 18A DC-DC, but that will sometimes overload the alternator fuse and blow it.

There are a couple of myths:
1) LiFePo4 can accept so much charge so fast they will burn up your alternator. False! The charge line is fused at 30A, that will blow long before your alternator gets hot.
2) LiFePO4 batteries can back charge, damaging your tow vehicle. False! LiFePO4 batteries typically are charged to 14.5V, that will not damage your tow vehicle battery.

 

[whawahwa]

The more I look into it, the more I'm convinced that with the regular 7-pin you will not fry/damage anything, but you will also put in very little juice, like a couple of amps, so the trickle charge will be slow, don't expect your battery to be ready to run your RV over ight after a couple hours on the road.

Smart alternators may not charge well/at-all as you point out, but won't damage anything.

Having higher gauge wiring (to Anderson connectors) or wiring inside a driveable could out strain on the alternator because there is a whole lot less resistance between the alternator and the battery under charge

The battery I'm looking at has Bluetooth and will show you instant amps going into it, so I should be able to quickly verify in in the trickle charge situation.

I can then decide whether to add a DC-DC charger.

 

[whawahwa]

The more I look into it, the more I'm convinced that with the regular 7-pin you will not fry/damage anything, but you will also put in very little juice, like a couple of amps, so the trickle charge will be slow, don't expect your battery to be ready to run your RV over ight after a couple hours on the road.

Smart alternators may not charge well/at-all as you point out, but won't damage anything.

Having higher gauge wiring (to Anderson connectors) or wiring inside a driveable could out strain on the alternator because there is a whole lot less resistance between the alternator and the battery under charge

The battery I'm looking at has Bluetooth and will show you instant amps going into it, so I should be able to quickly verify in in the trickle

 

[videoarizona]

I've been charging my 200amp lithium from from GMC truck's 7 pin for 2 years now. No issues. I get from 5 to 8 amps to my battery measured with an installed Victron shunt, depending upon the state of charge of the lithium. I moved my battery inside closer to the power center which eliminated half the long run from the 7 pin to the battery. I know the voltage coming out of the alternator will not fully charged my lithium but it does come close.
By the way, my truck battery died on the road and wouldn't start the truck. While I was waiting for a tow truck, I went and looked at the shunt reading on my phone. It was showing a minus 4.4 amps. What? The fridge and the gas detector were all the that was on. It dawned on me since voltage always flows to the lower source, I was trickle charging my truck battery!
Sure enough, after about an hour, I turned the key and the truck just barely started. (Tow truck never showed). So yea, an added bonus. In time, your lithium will backflow through the 7 pin and charge your truck because the lithium voltage is higher than the lead acid in the truck. Was an interesting discovery!