New angle on using truck alternator to charge lifepo4 house battery bank

[Pauhar1]

I have a Lance truck camper that comes with an 8 ga wire connected to the trucks alternator/battery. Lance does this to allow the DC refrigerator to run while driving and to help,charge the batteries. I now have a 500 ah bank and it needs more power coming in. While a dc to dc charger would be optimal I have another option, my truck has a 20 amp outlet at the rear bumper literally 3 ft from the shore power connection for the camper. So…..
1. Could I manufacture a pigtail which would connect the power outlet of the truck to the camper and charge through the campers converter just as if I was plugged in?
And 2. Would I need to do anything different with the factory wiring harness from the existing 8 ga wire?

 

[HRTKD]

Is the 20 amp outlet a 120 vac outlet? If so, I would go the easy route and connect to that outlet. However, the camper's shore power input is likely expecting 30 amps. The OEM converter may try to exceed the available 20 amps.

Any direct DC circuit from the truck to the camper may need to be throttled using a DC-DC charger. Otherwise, it will try to pull too many amps, more than the 8 gauge wire and any fuses can handle.

 

[datdude]

Any direct DC circuit from the truck to the camper may need to be throttled using a DC-DC charger. Otherwise, it will try to pull too many amps, more than the 8 gauge wire and any fuses can handle.

I hear this a lot, but I just don't see this happening IRL. Has anyone really ever seen this happen through the 7-pin? I am quite skeptical.

 

[time2roll]

Why manufacture a pigtail?

Get a pack of two for $10 on amazon. https://www.amazon.com/Cable-Matters-2-Pack-Adapter-TT-30R/dp/B084D6JK4J

 

[IMSITTINGINYOURCHAIR]

basically, the batteries will accept as much current as they can when at a lower state of charge, at 500ah capacity that can be quite a lot and will likely be more than the wire is rated to handle. dc to dc controller would allow you to use all of the capacity of the wire without blowing the fuse or setting the harness on fire.

 

[HRTKD]

I hear this a lot, but I just don't see this happening IRL. Has anyone really ever seen this happen through the 7-pin? I am quite skeptical.

The only "throttling" through the 7-pin connection is the small wires. Try to charge a depleted, large Ah, LiFePO4 battery long enough and you're likely to blow the fuse, burn up the relay or smoke the wires. I would not rely on the small wires to limit the charge.

 

[Pauhar1]

Thanks for the input guys. I’ll install a dc to dc.

 

[Zwy]

I have a Lance truck camper that comes with an 8 ga wire connected to the trucks alternator/battery. Lance does this to allow the DC refrigerator to run while driving and to help,charge the batteries. I now have a 500 ah bank and it needs more power coming in.

What battery chemistry?

While a dc to dc charger would be optimal I have another option, my truck has a 20 amp outlet at the rear bumper literally 3 ft from the shore power connection for the camper. So…..
1. Could I manufacture a pigtail which would connect the power outlet of the truck to the camper and charge through the campers converter just as if I was plugged in?

I do on my truck camper but don't use the converter but run AC power thru the Growatt AIO inverter. I can adjust charge rate thru the inverter.

Here's my truck camper setup

Not yet, remember this is 24V system, not 48V. I haven't had any time to use the camper since last August. Battery is turned off when it sits. I'll get around to it when I get time to use the camper, was busy this past winter working on my house system, then once it was all installed, I had the...

diysolarforum.com

And 2. Would I need to do anything different with the factory wiring harness from the existing 8 ga wire?

Again, what battery chemistry?

 

[datdude]

The only "throttling" through the 7-pin connection is the small wires. Try to charge a depleted, large Ah, LiFePO4 battery long enough and you're likely to blow the fuse, burn up the relay or smoke the wires. I would not rely on the small wires to limit the charge.

Yet here I have been driving a couple of years without any of that happening with LFP batteries. Small in my case is 10g, but it is factory. However, I do not have a large battery at only 2x100ah. I believe that likely represents at or above the majority of campers out there by the numbers.

 

[HRTKD]

There's a story out on YouTube of one of the "influencers" in the truck camper genre. I think he had a bank of Battleborn batteries, somewhere north of 400 amps. His truck had an OEM alternator setup with a spec of ~390 amps. Charging the Battleborns burned up the alternators. Not right away, but it didn't take years either. I don't remember the name of the YT channel, otherwise I would provide a link.

There's enough risk in direct alternator charging that, in my opinion, it isn't worth it. A DC-DC charger is the safe solution.

 

[0truck0]

Yes, good choice to use dc-dc.

Yes, I too burned out a 135 amp alternator trying to run a propane fridge on DC while driving. IDK that amperage, but it was fine the first day and on second day went out. The driving battery slowly faded and I ended up running the generator all day to give DC power to the driving battery so I could keep going. The alternator bolts were seized up and the motor mounts broke getting alt off the vehicle. had to just put new one in with broken threads to the vehicle. Quite a long process. Good news is it worked til the day a foreign driver totaled the vehicle. You don't want to burn out your alternator, ever, is just not worth the risk. Dont do janky things to your vehicle to save a few bucks. Use the Dc-DC charger, they are not that expensive.

For those reading.... Usually a 20 amp model is plenty, and I would nnot want to rely on vehicle to recharge completely dead RV batteries. Get solar or use a generator at this point. vehicle is great to keep batts topped off while driving.

 

[Pauhar1]

Sorry guys I’ve been out of service driving back from Alaska. Zwy the batteries are LiFePO4. Thanks again everyone!

 

[Bananaman321]

I hear this a lot, but I just don't see this happening IRL. Has anyone really ever seen this happen through the 7-pin? I am quite skeptical.

You're absolutely right its total BS you'd be lucky to get much over 10 amps to flow through even with a discharged 4s LFP battery regardless the size of it.

I have tested this myself with two paralleled partially discharged 100 amp hour LFP batteries and only had 8 amps flowing with the engine running.

If you're planning on charging LFP batteries the 7 pin connector (comparable to 120w give or take of solar with vehicle running) is most likely not the answer unless you're going to be doing a whole lot of driving (more than 10 hours per 12v 100hr) much better solution would be a DC to DC Converter, an inverter + charger or a small solar panel/charge controller setup at least 100w.

The 7-pin connector's aux terminal itself is generally rated at 20 to 30 amps and is most likely relay switched with B+ ignition on check your vehicle's owner manual to be sure. But you may only get 8-9dcv when loaded to neer max capacity due to vehicle's conductor size / length.
That being said even with a DC to DC Converter used through the 7 pin connector you would most likely not get neer 300 watts before blowing the fuse or kicking the DC to DC Converter out on low voltage.