Need wiring help

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Need wiring help

Postby vitya-velik » Mon Apr 18, 2016 6:51 pm

I have 2 12V 35ah batteries a fan, 3 12 V led lights and a couple 12 v sockets. How would I wire my trailer and what else do I need? What kind of wire. Charge controller. Fuses. Anything else?

I also want to buy a 150 watt solar panel.

It would be nice of someone had a simple wiring diagram and told me all the parts that I need to buy.
Thank you!

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Re: Need wiring help

Postby lfhoward » Mon Apr 18, 2016 7:53 pm

I recommend a Blue Sea fuse panel. Get one with 6 fused circuits and 6 grounds. The big posts on the fuse panel go to the + and - of the battery bank using thick wire, like 8 gauge for your application.

The battery bank should be wired in parallel using battery cables. + to + and - to - to keep the output voltage at 12 volts. The wire to the + on your fuse panel should come from the + terminal of one battery and the - of the fuse panel should be wired to the - of the other battery, to equalize the load between the two.

If you like, put a heavy duty breaker and switch in the + line between the battery and the fuse panel. For the loads you list, a 50 amp breaker should do it.

At the fuse panel, I would suggest running a circuit to each component, using a fuse of the correct amperage for that device. Here's what I would do:
1 - 5 amp fuse - ceiling fan
2 - 15 amp fuse - power outlet
3 - 15 amp fuse - power outlet
4 - 5 amp fuse - LED lighting
5 - empty
6 - 10 amp fuse - input from solar charge controller

The ground for each circuit comes back to its own ground screw on the Blue Sea panel, completing the circuit.

14 or 16 gauge wire should do fine for each of your circuits. Get those crimp connectors that can slide on to the tabs of your fuse panel as well as to each other -- that makes wiring a lot easier.

A 150 watt solar panel is a nice size, and Renogy makes a nice panel. Be sure to get an MPPT charge controller because that is the type that most effectively charges and maintains your batteries and extends their life. Use whatever fuse amperage and wire gauge the instructions recommend for your solar charge controller and the panel.

Hope this helps! I don't have a way to sketch a diagram right now but hopefully you can picture it.
My off-road camper build on an M116A3 military chassis:
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Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
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Re: Need wiring help

Postby MtnDon » Mon Apr 18, 2016 8:28 pm

lfhoward wrote:
At the fuse panel, I would suggest running a circuit to each component, using a fuse of the correct amperage for that device. Here's what I would do:
1 - 5 amp fuse - ceiling fan
2 - 15 amp fuse - power outlet
3 - 15 amp fuse - power outlet
4 - 5 amp fuse - LED lighting
5 - empty
6 - 10 amp fuse - input from solar charge controller

The ground for each circuit comes back to its own ground screw on the Blue Sea panel, completing the circuit.

14 or 16 gauge wire should do fine for each of your circuits.


Not quite.
Fuses protect the wiring between the power source and the device. Size the wire to the maximum load to be allowed on the circuit. A maximum load of 15 amps should be wired with 14 gauge wire as a minimum.

16 gauge wire is rated to a maximum of 7.5 amps. That would be okay for the ceiling fan circuit, but not the general purpose power outlet circuit with a 15 amp fuse.


Before buying any solar equipment check the battery manufacturers maximum amp charge rate for the batteries. For example this battery has a max charge rate of 8.5 amps. That can vary with type of battery chemistry; always check the mfg specs to stay within warranty terms. Two of those batteries in parallel means 17 amps would be the maximum charge rate. That is just an example; check your own battery specs. When you know that you can select the largest panel size that should be used. A 150 watt, 12 volt panel probably puts out a maximum of 8 to 8.5 amps so with the referenced battery up to 2 panels could be used with 2 batteries in parallel.

Whether or not you need an MPPT charge controller on a small system is a topic that will raise lots of differing opinions. MPPT always costs much more. It is not always worth the expense especially when the panel is a so-called 12 volt panel not raised to the optimum sun power angle as many are if roof mounted in a fixed flat position. I'll start the argument with that statement and recommending a PWM controller
Our 6x12 deep vee nose cargo trailer camper conversion... viewtopic.php?f=42&t=58336

We have a small off grid cabin we built ourselves in the NM mountains; small PV solar system; 624 watts PV, Outback CC & inverter/charger ... http://countryplans.com/smf/index.php?topic=2335.0
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Re: Need wiring help

Postby lfhoward » Mon Apr 18, 2016 9:03 pm

MtnDon, thanks for the catch on the wire gauge for the 15 amp power outlets. Glad you read through my post carefully.

I have a 3 battery system with an MPPT charge controller, but I am not one to argue with a PWM controller if a lower price is needed. I think Renogy has a bundle on Amazon with their 150 watt panel and a PWM controller for a reasonable amount of money.
My off-road camper build on an M116A3 military chassis:
http://www.tnttt.com/viewtopic.php?f=50&t=62581
Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
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Re: Need wiring help

Postby noseoil » Tue Apr 19, 2016 7:50 am

150 watts is a bit more than necessary for a (combined) 70AH of battery. The 100 watt panel is smaller, lighter & would be cheaper to install in general. The 150 watt panel would certainly provide more juice during the day, but the system really doesn't need it to work. Most of the drain is at night, so the 100 watt panel would really be plenty to work well. Our 100AH battery comes back in a day with the 100 watt panel & I think I might have gotten by with an 80 watt panel.

Here's the numbers for an 80 watt panel. If the 70AH system draws down over night to 50% (35AH used all night), with an 80 watt panel charging at 4.5 amps during the day, the time needed for a full charge to bring things back to 100% would be 7.7 hours. The 150 watt panel would cut this time in half, with the "extra" capacity being wasted once the battery is fully charged. I know having the extra would be better on a cloudy day, but we typically don't use as much capacity as we have available from a battery, especially with LED lighting. With the 100 watt panel, time would be reduced to a bit more than 4 hours for a full charge, plenty. YMMV!
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