Charging Truck Camper batteries via 120v from truck

[ripperj]

I figured this must have come up, but search didn't find much.

I have a truck camper on a 2500 Crew Cab truck. It's a lot of big wire to get from my truck alternator/ battery back to the camper bank.


I have a Magnum charger/inverter in the camper, 88 percent efficient. A typical 2000 watt pure sine inverter is even better, 90 percent.

Besides the upfront 25 percent hit, what am I missing if I put a 2000 watt inverter in the truck and run 120 to the charger in the camper. I could run 12 Guage wire, use regular twist locks, and on the plus side I would have a big inverter in the truck.
Most research I have seen(on expo and else where) says I wound see huge charge currents with a small bank anyway.

My typical MO will be leaving the house at 100% battery. I really only need to run the ARB 50 qt in the camper when driving. (I thought about running a separate truck fed circuit just to the ARB in the camper, it only draws a couple amps)I will have enough solar eventually to handle most of my loads, so I'm wondering if I really need a truck charge circuit at all??. I have a small Honda I could bring if I was camping in lousy weather(not likely for an extended time, I would just pack up and leave)

Sorry for the ramble, any thoughts?

Sent from my Passport

 

[DiploStrat]

This comes up from time to time. Seems like a good idea, but consider:

-- Your truck generates 12v. Boosting it to 120v and then dropping it to 12v again with cost you 20% or more.

-- You would need an inverter in the truck and then an inverter/charger at the batteries. Good inverters aren't cheap.

-- Modern Chevrolets have excellent charging systems; a run of 1/0 AWG doesn't cost that much.

-- Remember, your alternator only produces but so much electricity. To a degree, you can trade volts for amps and vice versa, but the total amount available remains the same. So if you lose 20% of it ...

Worth noting. While voltage drop is important; you want as little as possible, voltage drop is dependent on amperage. So even if you have as much as 0.5v drop at the start of the charge cycle, you are still going to get a reasonable charge because the battery voltage will be at its lowest. Once the battery begins to take a charge its voltage will rise. By the time you reach the absorb stage your amp flow is going to be down in the 15-25A range. With a 1/0 or 1 AWG your voltage drop will be minimal. And proper high voltage is most important in the absorb, not the bulk stage.

Run the calculator a few times: http://www.calculator.net/voltage-d...nce=15&distanceunit=feet&amperes=25&x=42&y=15

So while you do want the biggest, baddest cable you can afford, there is a lot of scope for compromise in the real world.

 

[ripperj]

Thanks for the reply, I should have id the truck better , it's a Ram Hemi. I need to measure the output of the alternator, my AGM s need 14.7 volts, I'm not sure if it outputs that high at the alternator, never mind at the end of 18 feet of cable. I have played with the voltage drop calculators a bit, assuming I could get 15v at the alternator , 4/0 would get me the 14.7 at the batteries. The big upside of the inverter feeding the charger is that I could get any voltage I wanted at the camper batteries
Thanks again for the input

 

[pugslyyy]

Thanks for the reply, I should have id the truck better , it's a Ram Hemi. I need to measure the output of the alternator, my AGM s need 14.7 volts, I'm not sure if it outputs that high at the alternator, never mind at the end of 18 feet of cable. I have played with the voltage drop calculators a bit, assuming I could get 15v at the alternator , 4/0 would get me the 14.7 at the batteries. The big upside of the inverter feeding the charger is that I could get any voltage I wanted at the camper batteries
Thanks again for the input

I'm with Diplostrat - don't get too fixated on the Voltage until you understand the current that is going to be required to supply them at 14.7. I have a 3500W generator driving a 3000W inverter/charger to keep my AGMs happy.

 

[pugslyyy]

I think this is a nice (albeit round'about) way to charge.
Your 120vac batterycharger can be 'dialed in' to the specifics on your camper battery, AGM, Lithium, etc.
On the off chance you park where 120vac mains is available, Just plug in to that.
Best of all, you have a truck mounted 120vac source to plug in your electric saltblock polisher.

It does give a certain amount of flexibility - and the ability to charge the house off of shore power is a nice bonus. When my truck sits for a while I just keep it plugged in and don't have to worry about it.

 

[ripperj]

I already have the Magnum Charger Inverter (MM1212) up and running. I have the ARC remote and BMK battery monitor(Magnums version of the Trimetric)
Its pretty neat to monitor what's going on, although I was surprised to see that the lower end gear doesn't monitor AC input amps and volts, but the extra $1000 will be put to good use elsewhere.
I spoke with Full River (battery manufacturer) and they said 50-60 amps is ideal, the 1212 maxes out at 70amps.

 

[pugslyyy]

I already have the Magnum Charger Inverter (MM1212) up and running. I have the ARC remote and BMK battery monitor(Magnums version of the Trimetric)
Its pretty neat to monitor what's going on, although I was surprised to see that the lower end gear doesn't monitor AC input amps and volts, but the extra $1000 will be put to good use elsewhere.
I spoke with Full River (battery manufacturer) and they said 50-60 amps is ideal, the 1212 maxes out at 70amps.

Sounds like you've done your math!