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Strange battery setup?


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So to the best of my poking around knowledge, my auxillary battery charging system looks like this :

image.png.31359d3dfe09031ccdb1224d0e7ed9e4.png

Warning: I'm very new to thinking about electricity.  So, my understanding is that when the switch (which is in the cab by the steering wheel) is down, the truck battery activates the solenoid (12v) through that wire. Then power flows through the other wire from the truck battery through the solenoid to the coach battery (or is it possible for it to flow both ways?). The truck will not start if the switch is down.

This is pretty different from other RV systems, right? Doesn't the alternator usually charge the coach battery through the isolator, rather than via the truck battery? Can you charge batteries in series like this?

I've been having trouble with the truck dying on me, both while driving and when it's sat for bit, and especially when I have the lights etc on, and so I'm wondering if maybe this is the culprit (or it could be I just haven't fully figured out how to work the ststem). It's also worth noting that the solenoid terminal connected to the truck battery (+) looks all rusty. I'm tempted to just disconnect the whole isolator system from the truck battery and see if that solves things, or at least helps me narrow down the issue to the alternator or the wiring between the alternator and the battery (I bought a new battery yesterday, so that's shouldn't be the problem from this point forward). Does that seem like a terrible idea? Then at least I can charge the aux battery with my generator and not have to worry about draining power from the truck battery.

If all the parts are working, is this even a good system for charging the back battery?

Thank you all for your help! It's all such a puzzle :)

Edited by zaddylonglegs
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Ain't fixing the POs "fixes" fun.  here is a correct diagram...https://www.etrailer.com/question-24154.html

Some people will wire a switch between the coach battery and the control post, this gives them a boost function if the truck battery is weak.

A cheap digital volt meter from Harbor Freight will become your new BFF, when fixing old RV wiring.

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Seriously ?. Ah well, in 20-30 years I'll be an RV genius so WATCH OUT world.

Since I'm working against the impending freezingness of Vermont winters, I'd love to get things sufficiently road ready for now and then work on projects while I'm somewhere warmer. Does it make sense to you to just unhook the three wires from the solenoid, wrap them in electrical wire, and then let the batteries do their own thing until I get a chance to fancy the charging system up? (I have a generator for the aux battery.) If I disconnect those three wires, will I be losing power anywhere? I'm not exactly sure how the Truck Battery-Solenoid-Aux battery circuit is completed ... I suppose I'd need to follow the wire back to the aux battery and disconnect there as well.

Thanks so much for your help, much appreciated

Edited by zaddylonglegs
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Emergency bypass, just bolt the two battery wires to one terminal of the isolator. Make sure that the alternator output is connected to the truck battery.

The normal source of the 12v switched to trigger the solenoid is the wiper motor hot lead.

Edited by WME
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After you get a volt meter and verify that the truck battery is getting a charge (14v+) then you can just disconnect the big wire going from the truck battery to the isolator.

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Some setups use a system such as that the ideal is to combine both batteries in case you have a weak truck battery to give it a kick but generally the switch is momentary meaning you have to hold it on. Usually the isolator relay is keyed so the system is automatic. The automatic ideal is to keep both batteries charged while you are running the engine.

Edited by Maineah
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  • 2 weeks later...
On 11/12/2018 at 12:30 PM, zaddylonglegs said:

Can you go into more detail? I was suggesting isolating the batteries from each other altogether, rather than bypassing the solenoid (if that's what you meant)

the reason for the isolater is so when the engine (alternator) is running - you get good voltage in the back.

usually the isolater is between the engine battery & the cabin battery and controlled by a 12v circuit that is hot when the ignition is "on".  My rig has it wired to the hot side of the windshield wiper circuit.put 2 jumper cables end to end and reach from + terminal /coach to + terminal /start for a jump if needed.

Looks like per your diagram, a manually operated switch was used. 

Note that the amount of voltage flowing is no where near enough to jump the engine started if one is trying to back flow.

 

 

 

 

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