Solar, 4 awg, 28ft, -- ok??

[apollumi]

I've been racking my brain trying to find the best way to put the 4 solar panels I bought onto my camper and think I have found my answer. The camper is a toy hauler and what I plan on doing is have the panels hang down over the ramp for the toy hauler. The panels will swing out and up btw, letting the ramp come down.

The only problem to what I think is my solution is the distance of the wire run.

My panels: panels - 4 x 145 Watt @ 18 volts x 7 amps each. (DMSOLAR on Amazon)

My plan: 2 sets of 2 panels in series run to a combiner box at the panels. Then from the combiner box 28ft to the charge controller. So, 36 volts @ 14 amps running 28' on 4 awg wire to the charge controller.

I've run it through a voltage drop calculator and wanted to verify the numbers. It didn't look bad at all but I'm still very much green at this stuff.

The below is what I get running copper 4 awg 28ft @ 14 amps and 36 volts. If this is right I'm pretty happy.

Votage drop: 0.19
Votage drop percentage: 0.53%
Votage at the end: 35.81

[RPAspey]

that's real good number drop wise.

make darn sure the Vopen of the combined panels isn't going over what the controller is rated, Vmax. (I think those are the right acronyms)

[apollumi]

It does look like a pretty good number. I was looking at the back of the camper this morning and realized I'll probably have to add another 4-5 feet to that.

Actually I was thinking those numbers looked too good. Thought I had done something wrong. Could somebody verify what I was looking at was correct?

[TURBS]

Originally Posted by apollumi

I've been racking my brain trying to find the best way to put the 4 solar panels I bought onto my camper and think I have found my answer. The camper is a toy hauler and what I plan on doing is have the panels hang down over the ramp for the toy hauler. The panels will swing out and up btw, letting the ramp come down.

The only problem to what I think is my solution is the distance of the wire run.

My panels: panels - 4 x 145 Watt @ 18 volts x 7 amps each. (DMSOLAR on Amazon)

My plan: 2 sets of 2 panels in series run to a combiner box at the panels. Then from the combiner box 28ft to the charge controller. So, 36 volts @ 14 amps running 28' on 4 awg wire to the charge controller.

I've run it through a voltage drop calculator and wanted to verify the numbers. It didn't look bad at all but I'm still very much green at this stuff.

The below is what I get running copper 4 awg 28ft @ 14 amps and 36 volts. If this is right I'm pretty happy.

Votage drop: 0.19
Votage drop percentage: 0.53%
Votage at the end: 35.81

In the "files" section there's a chart for what your seeking.
Files section right next to "user cp"

Turbs

[TURBS]

[RPAspey]

just ran your #'s, 36v, 15a and 10 meters. about .75 %. you could go a size smaller and save some $. #6 wire will get you about 1.1% drop. still great.

[apollumi]

Originally Posted by RPAspey

just ran your #'s, 36v, 15a and 10 meters. about .75 %. you could go a size smaller and save some $. #6 wire will get you about 1.1% drop. still great.

Yeah, might do that. I just called a company locally and # 4 awg is $2.00 a foot. So I'd be looking at $120.00 or close to it.

I noticed my battery cables only has the "+" side going to the convertor (current setup) and the "-" goes to the frame. Is this the norm? Can I just connect the negative wire to the frame? I was thinking I'd have to bring all of the wires to a common post for positive and negative connections as well as the inverter. I was also thinking I would need a ground wire coming off of the solar panel frame to the frame. Everything with fuses, etc.

[RPAspey]

both wires must run from panels to controller and NOT be connected to anything else. they should be fused.

I know using the chasis for negative is commonplace for 12v systems. Doing so will add additional impedance in the negative leg of the controller causing problems. remember that thing you just calculated, voltage loss? Steel doesn't conduct electricity nearly as good as copper. In autos, I don't think there's a 30' run anywhere, so loss will be minimal.

If you run your copper wire to the battery, you are setting yourself up to install a shunt for a battery monitoring system. On those systems, positive current is not measured. Only the negative side passes thru a shunt. All negative current must be measured.

here's a basic schematic of my system. Take it as a guide, as there have been some corrections/changes made since I drew it up.


dang it, it posted upside down, sorry.

[apollumi]

Cool. I just didn't know if using the frame was best or not. Or, if it might be necessary due to how the convertor was wired, etc..

[RPAspey]

yes, there must be a wire from negative to frame, just don't use the frame as a primary current conductor. The frame needs to be tied to negative for things like running lights to work...at least on my aluminum skin trailer.

[RPAspey]

here's a link to my website showing pix of my camper mods. Some pix show the conduit I used to get the #4 wire, battery temp signal, and the shunt wires back to the controller.

http://www.pbase.com/rpaspey/2012apr27

[apollumi]

I took a tape measure and measured out the entire run adding in a few feet extra to be safe. It came out to 42'. So much for eyeballing it. I think I'll be going with the 4 awg anyway because of this. I found an electrical company close that will charge me 96 cents a foot (19 strand) for 4 awg. Does that sound right? Pricing it via online companies it was looking like $1.50 to $2.00 per foot. The $2.00 price was tinned marine grade though.

I also got surprised by how long the battery to inverter was going to be. When I looked at it I thought it would be 3' tops. When I measured out how long it would need to be with a little added in for safety I came up with 10' . Should I go with welding cable or will 2 awg be ok? It's a two battery (in parallel) setup that will run a laptop and a 32" LCD (5 amp 12v after conversion) and blueray player as the heavy draws.

[RPAspey]

The 19 strand is building wire, think STIFF! But not impossibly so. Of you have any bends that are tight, say less than 2" radius, you might be stressing that #4. It will work, but you might have an issue where the extra flexibility will be desired. I bought my #4 fine stranded pure copper power cable at a local megatronix store. It's a auto stereo type place. I think 100 feet was $150.

now the inverter cable should be sized for the DC draw at max output to keep losses at less than 3%. You'll probably only need a 400-500 watt inverter for those items. size the wire according to that.

[RPAspey]

one thing to think about is future desires. If you think you might ever go bigger, panels or inverter, run even bigger wire now. Yes it will cost more now, but will be cheaper on the long run. Nothing like pulling out $200 worth of wire to be replaced with $300 worth of wire.

here is a link to some high flex pure copper wire ...note that if the link works that it is only an example. no endorsement intended. http://www.amazon.com/gp/aw/d/B0050X...sr=8-5&pi=SL75

[apollumi]

I think the only place "stiff" will be a problem is in the combiner box. The rest of the wire will run down beside the ramp (toy hauler) and then along the frame I-beam and lastly will come up through the floor to the distribution panel. I plan on putting the wire in conduit from the roof to the bottom of the TT.

I was also looking at a 1000 watt pure sine wave inverter with remote for the camper. See below.

Sunforce 11240 1000 Watt Pure Sine Wave Inverter with Remote Control : Amazon.com : Automotive

[RPAspey]

We had a few of the Sunforce inverters in the vans at work. they worked good for a while. The guys were rough on them though....occasionally wet from rain/snow, dusty/dirty, banging into them with equipment, constant overloading, etc. we use a commercial inverter now, built for abuse, about 7x the cost.

anyway, if you do the math, you'll need a larger cable, #2 @ 3meters & 90Amps, to keep power losses down. That's for the 1000w inverter nearly maxed out. If you keep your loads at 500 watts max, you'll be ok with #4 wire with a loss of >2%.

[RPAspey]

oops.. that's <2%