Charging lithium-ion trailer batteries while towing

[JGF]

As stated above, although the potential exists for damaging the alternator I have never heard of it happening.

The only way a wire limits a load is by its resistance to the current flow. Enough resistance (pushing more amps than the wire can handle) results in the wire burning up. One way to limit current flow but not the recommended method. A better way is to have the DC-DC charger control the charging current.

The 7-connector wire to the trailer provides only a trickle charge - 3-4 amps. If the batteries are fully charged this may be enough. If not, the DC-DC charger, wired properly, will provide up to its rated capacity. In my case, 30 amps.

Remember also your vehicle's charging system is designed to keep its battery charged. LiFePO4 batteries charge at a higher voltage. Again, a DC-DC charger will step up the voltage from the vehicle to properly, and completely, charge the trailer's batteries.

Hope this helps.

Thank you for your prompt reply. This thread has been very helpful to me. Looks like I'll be looking into a DC to DC charger! Oh, by the way, how are the Weize LiFePo4 batteries working out?

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[JonB]

Oh, by the way, how are the Weize LiFePo4 batteries working out?

Excellent. Spent four weeks boondocking out at the RV rally in Quartzite, AZ in January. Charged with 200 watts of solar; batteries handled everything, including heat, propane frig, lights, water pump, etc. Pretty much stayed above 13.0 volts all the time.

 

[T-Wrecks]

The 7-connector wire to the trailer provides only a trickle charge - 3-4 amps. If the batteries are fully charged this may be enough. If not, the DC-DC charger, wired properly, will provide up to its rated capacity. In my case, 30 amps.

Remember also your vehicle's charging system is designed to keep its battery charged. LiFePO4 batteries charge at a higher voltage. Again, a DC-DC charger will step up the voltage from the vehicle to properly, and completely, charge the trailer's batteries.

Hope this helps.

I've seen elsewhere the 7-pin provides 30 amps. It has a 30a fuse and a 6 gauge wire so are you sure about the trickle charge? If that's true is there any harm to using the 30a Victron with the 7 pin to charge Li battery other than a slow charge rate?

 

[JonB]

I've seen elsewhere the 7-pin provides 30 amps. It has a 30a fuse and a 6 gauge wire so are you sure about the trickle charge? If that's true is there any harm to using the 30a Victron with the 7 pin to charge Li battery other than a slow charge rate?

I looked through the chart of fuses for my 2019 Ranger and could not find one marked trailer battery charging. There were ones for lights, turn signals, brakes and something called "trailer module" but that's all. I've poked around in the harness and never found anything as heavy as 6 gauge wire.

Despite Ford's advertising the Rangers as tow vehicles they did not include a factory electric brake controller, either as standard or optional equipment. If they didn't include that I doubt they set up the Rangers to do heavy-duty charging of trailer batteries.

Victron's specific directions are to wire its DC-DC charger directly to the tow vehicle's battery and not anywhere in its wiring harness.

Given all of that, I'll stick with my prior assessment of the existing trailer wiring and wiring the DC-DC charger directly to the battery.

 

[Grumpaw]

I looked through the chart of fuses for my 2019 Ranger and could not find one marked trailer battery charging. There were ones for lights, turn signals, brakes and something called "trailer module" but that's all. I've poked around in the harness and never found anything as heavy as 6 gauge wire.

Despite Ford's advertising the Rangers as tow vehicles they did not include a factory electric brake controller, either as standard or optional equipment. If they didn't include that I doubt they set up the Rangers to do heavy-duty charging of trailer batteries.

Victron's specific directions are to wire its DC-DC charger directly to the tow vehicle's battery and not anywhere in its wiring harness.

Given all of that, I'll stick with my prior assessment of the existing trailer wiring and wiring the DC-DC charger directly to the battery.

All 7 pin trailer plugs come with/are equipped with an "Aux 12 Volt Charging Pin"....looking into the female plug (on the truck) it is the top right pin and is a red wire. It is an industry standard position and wire color.
It is usually/traditionally 10 gauge wire. The other 6 wires are usually 12 gauge.
It supplies power from the trucks electrical system to the trailer to charge the trailers battery.
As far as the Ranger listed as capable of towing but not equipped with a brake system....until just a few years ago no truck came with a "factory brake" set up....we all had to buy not only the brake set up, but the plug and wire and do it ourselves. The Ranger is the first truck I have bought that came with the 7pin/4 pin receptacle from the factory....all my past, except for motor homes, I had to equip and wire myself.

 

[T-Wrecks]

Despite Ford's advertising the Rangers as tow vehicles they did not include a factory electric brake controller, either as standard or optional equipment. If they didn't include that I doubt they set up the Rangers to do heavy-duty charging of trailer batteries.

My camper trailer has electric brakes, are you saying they don't work? 2019 XLT with tow.

I'm not interested in heavy duty charging, just keeping the Li topped off when on the road and maybe running a refrigerated cooler. So will the 7 pin power work in slow charging mode with a 20a DC-DC charger?

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