Solar panels wire to controller: Length of wire?

In addition to a battery temp sensor cable, My MS TS-45 PWM controller has a separate cable that measures the Volts at the battery's terminals. These two cables allow the controller to adjust Volts at the controller's terminals so the correct Volts arrive at the battery terminals. This works no matter what the Amps and through all charging stages.

If you are using AGMs, you might as well shoot for the lowest maintenance setup. I leave my solar connected 365/24/7 and promise to inspect the AGMs once a year. :)

HTH;
John

I agree if it is no real trouble, fatter wire is better. I also like that kind that has the zillion fine silky strands instead of a fewer number of thick strands. The former is very flexible for curving in tight spaces like in a RV battery compartment.

--controller location--It is easier with 5ers. The TT battery box could have a second box beside/under it for the controller I suppose.

To have a controller "1.5 maybe 2 feet to the batteries" AND to ensure that on-board temp-comp doesn't work against you, you have to keep both controller and the batts in the same space, more-less.

Which means, you either have to put the controller on the trailer tongue out in the open - not recommended, or to put controller and batts in a big tongue box - OK for AGM but not so for flooded, or to put controller and batts into reasonably big storage nook - again, OK for AGM but with flooded there is an issue of venting, plus acid fumes affecting the controller.

BFL13 wrote:

EsoxLucius wrote:

OregonTRX4 wrote:
I have 50 feet of 10 gauge wire on the way. So my understanding is that I can wire the panels about 40ft from panels to controller and then my controller will be 1.5 maybe 2 feet to the batteries. Should this be okay with minimal voltage loss?

Yes, but the panels would have to be wired in series and the controller would have to be MPPT. The wire between the controller and batteries should be 2 gauge.

That seems way over the top to me.

My 130w panel placed up on the roof has approx. 40ft one way (so 80 ft for both ways of #8 wire (pre-wired for solar) to the front battery compartment where the PWM controller is. Then there is another 2 feet approx. of #8 from controller to battery.

That is no different from having it sitting out from the trailer the same distance away from the front of the trailer.

I get full 8.2 amps (Isc of the panel) showing on the Trimetric from solar until battery voltage reaches mid -13s. Forum member Salvo commented that if I had less voltage drop, my amps would not taper from IV curve until battery voltage went a little higher than that.
I am still getting say 7.9 amps at 14v and from then it only takes a brief time to reach 14.6 (voltage shoots up fast after passing 14)

I am fine with the results I am getting as is. YMMV.

I changed my position well before 8:48 AM and your point, and those following, are well taken. I still like perhaps larger than necessary wire controller to batteries.

Get thicker cables to batteries. I would try and keep the V drop under 0.1V.

Yes, you can raise the setpoints on the controller to compensate for V drop at high current, but then at low current there will be no V drop and your voltages on battery will be higher than needed.

Having the controller inside the rig where you can see the read-outs and push the buttons can mean the controller-battery distance is too great for what you want. Or it might be ok, "depending"

If you move the controller to be near the batteries, you can't see it. To beat that some have remote readout/control panels you can keep inside, but they often seem to cost as much as the controller.

I find the Trimetric I have anyway tells me pretty much how the solar is doing. I just have to interpret the numbers for what else is going on in the rig, so I don't care about not seeing the controller up by the batteries.

My controllers also have their temp comps built into the main unit, not on a remote wire, so being inside the rig where I could see them would screw up the voltages anyway if the temp inside is different from out where the batts are.

You can save money and trouble by just putting the controller out by the batts and foregoing having a remote panel and also any remote temp comp. You can go out and peek at the controller when you are out anyway seeing if the propane thing has turned red yet :)

BFL13 wrote:
The fear of controller-battery voltage drop is that it will not let the batteries reach the controller's high set point, so the batteries will be undercharged.

If amps have tapered by then, the voltage drop will be less anyway, as Almot mentioned. Regardless of that, you can just raise the high set point to allow for the drop so as to get the batteries up where you want for Vabs. . . . . . . .

That is exactly my problem. 25 feet or more of #6 from the controller output to the 4 GCs causes a full volt drop at 20A. This means that the controller "sees" 14.8 Volts at the battery while the true battery voltage is only 13.8V. The controller then reduces the charge. As the charge current decreases the voltage drop also decreases, and if the sunlight lasts long enough the battery will eventually reach 14.6V, sometimes all the way to 14.8V but not for long.

The fear of controller-battery voltage drop is that it will not let the batteries reach the controller's high set point, so the batteries will be undercharged.

If amps have tapered by then, the voltage drop will be less anyway, as Almot mentioned. Regardless of that, you can just raise the high set point to allow for the drop so as to get the batteries up where you want for Vabs.

But that all depends on where the batteries ought to get to. Nobody mentions this. AGMs and Wets not the same and AGMs vary among them. Maybe your set-point is already high enough even with the drop.

And even if not, who cares about that if your bank is so large compared with the size of your solar array that you will not get it full by dark anyway? Solar then is just a help to reduce your gen time. Nothing wrong with that either, but it means you don't care about the finer points of reaching "full" or being "undercharged" from the solar.

That is another of the many possible individual situations where only you know what you really need. All we can do is say how ours is working and you can decide if that has any application to your own situation.

For less than 2 feet, you'll be fine with the 10 gauge from the controller to the batteries. If you had bigger wires there, the charging might go a little faster but probably not much. Either way, you'll get up to full voltage at low amps, when there is not enough loss to matter. Or, "what BFL said". :)

EsoxLucius wrote:

OregonTRX4 wrote:
I have 50 feet of 10 gauge wire on the way. So my understanding is that I can wire the panels about 40ft from panels to controller and then my controller will be 1.5 maybe 2 feet to the batteries. Should this be okay with minimal voltage loss?

Yes, but the panels would have to be wired in series and the controller would have to be MPPT. The wire between the controller and batteries should be 2 gauge.

That seems way over the top to me.

My 130w panel placed up on the roof has approx. 40ft one way (so 80 ft for both ways of #8 wire (pre-wired for solar) to the front battery compartment where the PWM controller is. Then there is another 2 feet approx. of #8 from controller to battery.

That is no different from having it sitting out from the trailer the same distance away from the front of the trailer.

I get full 8.2 amps (Isc of the panel) showing on the Trimetric from solar until battery voltage reaches mid -13s. Forum member Salvo commented that if I had less voltage drop, my amps would not taper from IV curve until battery voltage went a little higher than that.
I am still getting say 7.9 amps at 14v and from then it only takes a brief time to reach 14.6 (voltage shoots up fast after passing 14)

I am fine with the results I am getting as is. YMMV.