Wire Size

kipkohl · 02-12-2023, 01:43 PM

Not sure if this post should be here or under electrical, but it's a Geo Pro trailer.
I'm wondering if anyone knows what gauge wire Rockwood uses between the solar controller and batteries on the new trailers with the 190w panel and Go Power 30a PWM controller?
I want to upgrade by adding a 2nd 190w panel, 30a MPPT charger, and two 100w LiFePO4 batteries. If I keep the controller in the same spot, the length of the run would require 4g wire. I'm kind of assuming Rockwood didn't run 4g, but if someone knows for sure that would be great.
Thanks for any info you might have.

2WheelJon · 02-13-2023, 10:12 AM

Quote:

Originally Posted by kipkohl

I want to upgrade by adding a 2nd 190w panel, 30a MPPT charger, and two 100w LiFePO4 batteries. If I keep the controller in the same spot, the length of the run would require 4g wire. I'm kind of assuming Rockwood didn't run 4g, but if someone knows for sure that would be great.

At maximum output two 190 watt panels would deliver 31 amps at 12 volts. Using the amp capacity of the wire needed, and staying within the NEC code of not going over 80% of that capacity, 8 gauge wire would work for your setup. It’s easer to run, and cheaper, than 4 gauge.

Maximum output of the panels would push the upper limits of your controller. However, unless you’re in southern AZ and your panels are pointed at the sun it’s unlikely that you will see the panels’s maximum. You should be fine.

kipkohl · 02-13-2023, 10:47 AM

Thanks 2WheelJohn, good info. on the charge controller. I'm still wondering about the wiring between the charge controller and the batteries. I'm assuming that it would need to be larger than 8g: 4g is what I determined looking a wiring size chart. I don't know what gauge the stock wire is.
I think I've mentioned in another thread that my wife and I are new to TT's and are trying to get it all figured out before we the plug on one. The advice and information I've received here has been very helpful.

TitanMike · 02-13-2023, 10:48 AM

Quote:

Originally Posted by kipkohl

Not sure if this post should be here or under electrical, but it's a Geo Pro trailer.
I'm wondering if anyone knows what gauge wire Rockwood uses between the solar controller and batteries on the new trailers with the 190w panel and Go Power 30a PWM controller?
I want to upgrade by adding a 2nd 190w panel, 30a MPPT charger, and two 100w LiFePO4 batteries. If I keep the controller in the same spot, the length of the run would require 4g wire. I'm kind of assuming Rockwood didn't run 4g, but if someone knows for sure that would be great.
Thanks for any info you might have.

To answer your first question re: wire size I would answer "Too Small".

Usually there is a lot of #8awg wire used from chargers/controllers to batteries which is OK if the controller is close to the batteries.

For a 30 amp Solar controller like yours, which will deliver no more than 30 amps, however the distance between controller and batteries becomes a big factor.

Using this calculator https://www.wirebarn.com/Wire-Calculator-_ep_41.html you can see that 30 amps on a #8 wire will yield a 2% voltage drop (or less) as long as the TOTAL length of wire (both directions) is no greater than 14 feet. That would translate to 7 feet one way.

Of course if you can tolerate 5% voltage drop (which means wasting a scarce resource) then #8 awg wire is OK for up to 36 feet or 18 feet one-way. Unfortunately a 5% voltage drop on a 12v system means that 13.8 volts (avg charging voltage) will now drop to 13.1 volts which is barely a trickle charge.

One solution is of course to move the Solar Controller to a point as close as practical to the batteries. The higher voltage coming from the PV panels overcomes the resistance of the wires supplying power to the controller and the shorter wires carrying the output to the batteries will have less total resistance resulting in less voltage drop.

One thing often overlooked when just using "tables" is the fact that 12 v wiring is for Direct Current and unlike 120vac wiring wire length is BOTH DIRECTIONS. If your controller is 15' from the batteries then for wire size calculations it's really 30' for calculation purposes. Your statement that #4 wire would be required was correct for most trailers based on where FR mounts controllers (and converters) in relation to the batteries. With #4 awg wire however there is a problem. Most Controllers won't accept wire sizes greater than #6awg.

In summary, if you want to maximize the charging capabilities of your solar panels/controller, moving the controller closer to the batteries is highly recommended. Roof mounted panels already give up output due to the inefficiency of flat mounting and even more is given up with voltage drop issues.

kipkohl · 02-13-2023, 11:47 AM

"To answer your first question re: wire size I would answer "Too Small"."

LOL...that's what I figured. I thought about moving the controller, but I thought it would be easier to re-wire between the controller and the batteries than between the panels and the controller. If I can still use #8 wiring between the panels and the new controller location, I'm assuming I could splice the new wiring in at the stock controller location.

That's interesting about the wire run lengths, and is counter-intuitive to my small brain. I would of thought that doubling the distance would apply to AC current since it travels back and forth as opposed to the one way direction of DC. Just when I think I'm getting a handle on this whole electricity thing something like this pops up.

Thanks for your input...very helpful.

TitanMike · 02-13-2023, 12:02 PM

Quote:

Originally Posted by kipkohl

"To answer your first question re: wire size I would answer "Too Small"."

LOL...that's what I figured. I thought about moving the controller, but I thought it would be easier to re-wire between the controller and the batteries than between the panels and the controller. If I can still use #8 wiring between the panels and the new controller location, I'm assuming I could splice the new wiring in at the stock controller location.

No reason to not use the existing wires from panels and batteries. Wires from panels are most likely #10 awg and from controller #8awg.

Just make sure to "splice" them solidly. Since there are most likely two different wire sizes, rather than crimp connectors consider one like this:

https://www.amazon.com/MECCANIXITY-T...l%2C145&sr=1-4

kipkohl · 02-13-2023, 12:11 PM

Great!, thank you. One more question, if you don't mind; If I add another 190w panel for a total of three, would that stock wiring still work or would I need to think about upgrading the wiring? I've been internet searching this stuff, but my Google-fu is not great. So again, I really appreciate the info I get here.

TitanMike · 02-13-2023, 12:15 PM

Quote:

Originally Posted by kipkohl

That's interesting about the wire run lengths, and is counter-intuitive to my small brain. I would of thought that doubling the distance would apply to AC current since it travels back and forth as opposed to the one way direction of DC. Just when I think I'm getting a handle on this whole electricity thing something like this pops up.

Thanks for your input...very helpful.

With AC current the electrons move back and forth as you stated. It's just a "push/pull" action and as such there is less loss than in a DC circuit where the electrons have to make the full trip through the circuit.

kipkohl · 02-13-2023, 12:41 PM

Quote:

Originally Posted by TitanMike

With AC current the electrons move back and forth as you stated. It's just a "push/pull" action and as such there is less loss than in a DC circuit where the electrons have to make the full trip through the circuit.

Gotcha

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