How many Amps to Trailer via 7 Pin Connector

[WRH]

I'm upgrading my trailer to an LiFePO4 battery that can suck 50 AMPs if left to it's own desires. I'd planned on installing a DC to DC charger to limit how much it sucks from the truck (2019 Ram 1500 Bighorn w/ Tow package). I'm thinking maybe 10 amps tops is what the truck is wired/set up for?

Questions:

1. Do these trucks have something to limit the draw (besides a fuse)? If I didn't use a DC to DC charger would I suck the life out of my truck / blow the fuse every time?
2. How many amps are they geared to feed my trailer as we are cruising down the road?

Lead acid vs lithium is like a baby suckling compared to a grown man chugging a beer. I don't want the trailer drinking all my beer....

Any ideas and suggestions are helpful! Maybe the new trucks electronics just take care of everything for me... not sure. I know since I'm doing it, there is nothing in my trailer to limit it. I'm running the wire straight to the battery....

Thanks!

 

[Zeronet]

I have 2 Battle Born 100 ah LiFePo4 batteries in my travel trailer, mounted in the pass thru storage area in the front.

When towing, my truck puts out a max of 15 amps through the 7 pin. I’ve seen as low as 8 amps, but 12-15 is more common.

I think it varies with the difference in voltage of the trailer batteries and the voltage the truck alternator is maintaining. The greater the difference in voltage, the more amps get moved. My truck maintains a high voltage (14.2+) after a cold start. But after running for a while (an hour?) it will settle to about 13.8, so less amps going to the trailer batteries.

When the truck isn’t running, the 7pin power is still energized, so the lithium’s try to charge the truck battery which tends to have a lower resting voltage.

I don’t have any experience with a dc to dc charger, so can’t help you there.

Let me know if you have more questions.

 

[cj7]

The power lead is fused at 30a.

Very unlikely even a well-discharged 100ah Li is going to draw that. Given a discharged Li battery at 11vdc, and a charging circuit at 14.4, you’d be hard pressed to get even a low internal resistance battery to draw 30a.

I replaced my 30a fuse with a circuit breaker, so I could use a mini winch off the trailer plug.



The pic is from the drivers side door. The CB is mounted in an existing hole in the dashboard brace, with the on/off/reset toggle accessible by reaching under the dash while in the drivers seat. Made a harness to the fuse holder (shown top left). After the pic, covered the terminals with electrical tape.

Works well for the winch (rated 45a peak draw) and trailer, which has 460ah lead acid battery bank directly connected to the 12v circuit. A solar panel and controller keep the battery bank topped up, but after a winter night with her heated blanket, the RV gens or truck do put some current back in.

Given the wire gauge in the 7pin receptacle harness, I would not go any bigger. My worst case use case is short duration peak amps, which the wiring and connectors in that circuit can handle.

So, I’d guess you will be fine directly connecting the trailer with the Li battery. But a toggleable CB comes in handy when you want to leave the RV plugged in, but have the RV isolated from the truck.

 

[Richard320]

This is an interesting question.

I know the truck has a 30A fuse. That doesn't mean you'll get the full 30 at the trailer battery. That said, I have no idea what the resistance of a Lithium battery is. If it's real low, then the current is going to be real high, and may pop the fuse.

If this were my trailer, I think I'd go in near the trailer battery and install a 20A circuit breaker and a diode in the charging line. That way, you won't be blowing the truck fuse and you also won't be sending voltage from the trailer to the truck.

 

[dannymcd]

Your worst case scenario is a dead lifepo4 (11.2v) and a running truck (14v), and that could pull 60a+ in theory. My camper has dual batteries and I also considered doing this but for me I don't boondock, I don't even run the camper for long periods on battery, or need to rely on the batteries, so for me it's a waste of money, and running a LFP4 in my track car to save 20# it's like having a Tesla, the car is plugged into a trickle charger when it's parked.

 

[Bob Limited]

Sort of related so rather than starting a new thread... I have a 2020 Limited and would like to run a 7.5 amp washdown pump in the bed of the truck so I can spray my trailer breaks with fresh water after launching.
Rather than running a dedicated wire from the battery, would it be possible to wire the pump on a 7 pin and just plug it into the lights socket when needed or will this blow a fuse or somehow damage the circuit?

 

[Richard320]

Sort of related so rather than starting a new thread... I have a 2020 Limited and would like to run a 7.5 amp washdown pump in the bed of the truck so I can spray my trailer breaks with fresh water after launching.
Rather than running a dedicated wire from the battery, would it be possible to wire the pump on a 7 pin and just plug it into the lights socket when needed or will this blow a fuse or somehow damage the circuit?

That would be super easy to do. The 7 pin has B+ and Ground, so you're set. If the pump you buy has a 12V plug, check this. 7 way to lighter plugs!

 

[Bob Limited]

That would be super easy to do. The 7 pin has B+ and Ground, so you're set. If the pump you buy has a 12V plug, check this. 7 way to lighter plugs!

Interesting idea but I have a spare 7 pin round so I'll probably just wire it straight to that. Do all the wires leading to that plug outlet all carry the same amperage? Any idea what the max amps it would handle?

 

[Richard320]

Interesting idea but I have a spare 7 pin round so I'll probably just wire it straight to that. Do all the wires leading to that plug outlet all carry the same amperage? Any idea what the max amps it would handle?

I have no clue. The B+/trailer charging line has a 30A fuse. You can probably figure the rest out reading through New 5th-Gen 1500 Fuse / Relay / Circuit Breaker Diagrams & Documentation

 

[kapinallinen2]

Interesting idea but I have a spare 7 pin round so I'll probably just wire it straight to that. Do all the wires leading to that plug outlet all carry the same amperage? Any idea what the max amps it would handle?

Everything else is fused at 20 amps.

 

[mtjag]

Everything else is fused at 20 amps.

So, with the eTorque, there is no change in the amperage going to the travel trailer than with a normal alternator? In other words, I won't need to change anything to start towing with an eTorque?

 

[Richard320]

So, with the eTorque, there is no change in the amperage going to the travel trailer than with a normal alternator? In other words, I won't need to change anything to start towing with an eTorque?

That is correct.