Alternator Charging ? Again

mkirsch wrote:
This is not that complicated!!!

First off, the current tapers down as the battery gets closer to full charge. This is NORMAL. You can't force 20A if the battery won't take it, and you don't want to, because it will boil the acid right out of the battery.

At its most basic, a dedicated charging circuit requires a red + cable from the "jump start" lug in the engine compartment to the + on the battery. Next it needs a black - cable from a good ground in the engine compartment to the - on the battery. 6ga, 4ga or even 2ga wires. If you want to go totally boogots, use 0ga.

Now that you have the basic circuit set up, you want a way to disconnect it when you unload the camper. Put a heavy Anderson connector like the one pictured earlier in the thread in the cable somewhere convenient, probably in the bed of the truck.

You probably don't want that live 12V connection in the bed of the truck, and you may want to isolate the camper battery from the truck battery while camping, so you don't run the truck battery dead and strand yourself. Something as simple as this:
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Running an inverter to power the converter is just silly. You can't mount the inverter in the engine compartment because of heat. You can't mount it under the cab because road debris and water will destroy it. You can't mount it in the cab because the fan noise will drive you insane. The only place you can mount it is in the camper, so you're running big heavy wires all the way back there anyway. Why not just hook them straight to the battery, save yourself $1500 on the inverter, save the space and weight, and not make unnecessary conversions back and forth from DC to AC and back?

I already have the inverter (was $169 actually) and the other equipment, so no added cost involved.

My testing with the heavy cables proved that they get better amps (twice the amps) as the 7-pin does. Both taper the amps down a lot soon after the truck is started. Only be recharging this way when the batts are low enough to accept all the amps anyway, so that is not an issue for tapering at high SOC.

But the Vector or PowerMax chargers have the constant amps in Bulk stage at even higher amps than the heavy cables provide, and with that no tapering, you get way more AH restored for the time the truck is running.

Conversion efficiency just does not matter. It is AH restored in the time allowed that you go by for "efficiency", where more AH is better.

My test showed that the inverter ( Xantrex 2000w MSW) will run the charger with the 25 ft long heavy cables (#1 cu-al) as input from the truck battery, which was my first worry. Usually, you need the inverter on short fat wire for its input with heavy 120v loads. The 35 amp Vector showed as 630w on the inverter's readout doing 33 amps (its max on shore power too) and the 55 amper showed 950w doing 50 amps (less than its max of at least 57 on shore power) So the whole set-up will run something more than 630w easily but not quite 950w it seems.

I wanted to try the 40 amp Vector instead of the 35, which might have been "just right" but it won't run on that inverter for some reason (needs PSW maybe?)

You are right about disconnects. The 7-pin is always connected with the truck camper when parked and camping, and with the Chev truck, that means an open path to (and from!)the truck battery. With the 5er, I always unhitch and free the truck (which allows for levelling the 5er too) so the 7-pin gets disconnected anyway. I have to remember to disconnect the 7-pin while camping with the TC--way too easy to forget to reconnect when driving away!!!--always do the brake and signal lights check at the back to make sure the 7-pin is connected, same as with the 5er.

With the big jumper cables with the big 600a parrot clamps, connecting and disconnecting is easy without using a switch, but keeping them from shorting on anything is awkward for sure. Have to use ties to keep the pos clamps out in the open for one thing.

I have a way to put the charger inside the camper so it is easy to get at to operate it, and that leaves the inverter mounting to solve. (the inverter has a remote on /off that can be inside)

If the big cable clamps will pass through the camper's cable hatch, at the left front side, the inverter can be inside the camper. Or I might need to run wires to external clamp-on points as suggested above.

There is a little door at the bottom of the camper that opens to the left front corner of the truck bed, which might come into play. I already carry a pair of 6s in that corner to parallel with the regular camper batts via the cable hatch above there, but there is room above them in the truck bed corner. Or might put a big cable hatch in that door or nearby down there.

Something will work!