Solar Charger & Truck Power Question

adamis wrote:
I realized that my batteries had not been properly topped off while charging from the truck while driving like I assumed they would possibly because they were getting too many AMPS when they needed a trickle for top off.

Never too many amps as long as the voltage is regulated. You need to verify the truck is actually charging the TC battery. It may take a very long drive to fully 100% charge the battery. Just like leaving that charger on at home for 12+ hours you would need to drive 12+ hours to do the same thing.

^^ that is my take on it. In addition, a solar charger may not work well using the truck alternator as a source. Solar panels have V-I characteristics very different from an alternator. There are controllers made to do this (I have one installed in my camper), but without large enough wire from the truck nothing will not work well.

Wiring the truck battery to be charged by the second circuit on the solar charge should work though.

Agree with work2much in that I would focus on getting the solar charging instead of hybridizing the system. To drop back a bit, your truck should be able to put a peak charge into your camper batteries. The primary reason this often doesn't work is there is a load in the camper drawing current that is taking away from the current charging the battery. IF you have a heavy enough charge wire going from the truck to the camper this isn't a problem. But wire acts like a resistor. As current flows through a resistor a voltage is "dropped" across the resistor thus limiting the voltage making it to the load. Suppose the charge path between the truck alternator and camper batteries is 0.5 ohm. The truck alternator will put 14.7 volts onto the wire, but if there is a load in the camper taking 4 amps you'll lose 2 volts due to that resistance so the most the battery in your camper will see is 12.7 volts, even as the alternator is supplying 14.7.

The solution for the truck charge is to run heavy wire between the alternator and camper batteries to reduce this resistance, or to eliminate the stray current draw in the camper while on the road. Drop that 0.5 ohm to 0.05 ohm with heavier gauge wire and you'll now see 14.5 volts at the batteries with the camper still drawing the same current. Or, eliminate all loads in the camper and even with the light wire you'll now get the full 14.7 volts on the camper battery. A 3-way fridge set to DC can draw a lot of current and is the primary suspect in what's preventing your camper battery from getting a good charge on the road.

All that said, since you have solar and solar charges the battery with the engine running or not, I'd try to focus on that charging source. The fact it isn't already topping off the battery while on the road tells me either something isn't wired properly or the camper is drawing more current than the solar is supplying so the battery is never able to get topped off.

See if you can find what's drawing current in the camper (do you drive with the fridge on DC?) and get an idea how much current you need just to operate the camper. Adding a second solar panel may solve your problems and could be an easy solution since you've already installed a charge controller that'll handle much more than the single panel you have now can supply.

adamis wrote:

Is there a reason I'm not thinking about for why I wouldn't want to do this?

Yes. The reason IS that you have not analyzed the situation properly.

If a battery is not coming up to a full charge, it is not getting ENOUGH power, not too much.

Do you own a multi-meter ?

I'm gonna have to read your post again; the first time through some parts of it did not make any sense to me.

Edit: It seems like you have two situations to deal with here.

First is the one set of batteries not being charged while going down the road; or that set being worn out so they don't hold a charge.

Then there is keeping both sets topped off while in storage. IF your controller has outputs for two sets AND your panels have sufficient capacity, maybe 100 watts, then that shouldn't be a problem.

These two situations should not be combined into one ......as they have entirely different solutions.

Getting the inputs and outputs straight would help the discussion too.

Yes, a bit confusing. I would leave the solar panel and charge controller per manufacturer design.

If you have solar panels and a charge controller I would try and improve that system to your needs rather than mixing/relying on truck charging and solar charging through one controller. The trickle charge from the truck will just confuse the charge controller.

As far as storage, if it is long term I would just pack the batteries home and maintain them there. If it is short term disconnect the neg lead on both truck and camper. If the storage is outside you could use your solar system to maintain the batteries. Personally I don't like leaving hot DC electrical systems out of my sight for more than a day or two.