What gauge wire?

Keith Haw wrote:

pianotuna wrote:
Hi,

#10 will be just fine with a pwm controller. I would add a temperature sensor.

Hate to sound stupid but, where would I find a temp sensor and where would I connect it?

Thanks
Keith

Some controllers have a connector for the temp probe and it may be an additional item to purchase. The probe end is attached to a battery post or glued to the case.

Some controllers have a temperature sensor build in and if they are in the general area of the battery that's good enough. Note that batteries should be isolated from electronics due to their vapors.

Some controllers don't have a temperature sensor.

Knowing the temperature allows the controller to better adjust the amount of charge.

pianotuna wrote:
Hi,

#10 will be just fine with a pwm controller. I would add a temperature sensor.

Hate to sound stupid but, where would I find a temp sensor and where would I connect it?

Thanks
Keith

You don't understand all the ramifications of lower voltage in a pwm system. We've had this discussion before. I had shown voltage is also important for pwm charging.

pianotuna wrote:
Hi Salvo,

You know that pwm doesn't control voltage so the top 2.6 volts on a 17 volt panel don't matter a hoot, assuming a 14.4 charging voltage. #10 wire is good for 30 amps. 280 watts/12.8 volts =~22 amps max.

The $102 Eco-Worthy 20amp MPPT is the lowest cost "real" MPPT but it can only do about 42-45 Voc input limit, so it can do one big panel (250w max?) but not two 12v panels in series. (22 +22=44)

So that forces you to pay kazillions of dollars for MPPT just to run a couple of 12v panels and BTW you don't get any more amps with the MPPT unless you are at the North Pole. The MPPT method requires voltage and the panel loses voltage as soon as the sun gets on it, costing you amps. (you can't get anything with no sun and you lose when the sun is out!)

So the money does not work out for going MPPT in this case just to be able to use some skinnier wire.

Go parallel and PWM. You can wire it all sorts of ways, even use two PWM controllers (eBay $20 each) one for each panel and parallel them to the battery, or several other ways, doesn't matter, you will get your "expected amps" (two times the Isc of one panel)

My 130w panel got its expected amps (its Isc of 8.2a) even on hot days (which badly degraded the MPPT set but had no effect on the PWM set)), on 45 ft one way of #8 as an example.

IMO first try it on the existing wiring and if not satisfied, then get into improving the wiring.

Hi Salvo,

You know that pwm doesn't control voltage so the top 2.6 volts on a 17 volt panel don't matter a hoot, assuming a 14.4 charging voltage. #10 wire is good for 30 amps. 280 watts/12.8 volts =~22 amps max.

If it were an MPPT controller then wire size matters big time. My personal choice was and would be MPPT with a series connection for the panels.

What's your rational for that conclusion? Where's the analysis? My hunch, it's not pretty.

Hell, let's do it right now.

10 awg wire resistance = 1.0 mohm/ft
We got 70 ft of wire.

Total wire resistance = 70 ft * 1.0 mohm/ft = 70 mohm

2 x 140W panels outputs about 2 * 8.7A = 17.4A.

Wire loss:
V = I * R = 17.4A * 70 mohm = 1.2V
P = I^2 * R = 17.4A^2 * 70 mohm = 21.2W

The cable causes a 1.2V drop and consumes 21.2W, or about 7.6% of 280W.

pianotuna wrote:
Hi,

#10 will be just fine with a pwm controller.

Keith Haw wrote:
I've thought about welding cable and wou?ld like to use that but the controller is setup for 8ga max best I remember. So how do I get around that?

I bought gold plated connectors like these. They are cheap and effective.

Hi,

#10 will be just fine with a pwm controller. I would add a temperature sensor.

That's not a bad option either but don't know what the controller would cost, have to check that.

What's the difference in the way they charge? Or the charge rate?

An alternative is to leave the 35 ft, 10 awg cable in place and go serial. You now need a mppt charge controller. You may find a controller cheaper than new cable. If you go serial then the two panels have to match. 140W each.