Community Forums

Rvlegaleagle · 10-19-2017, 09:41 AM

Looking at putting up 5 or 6 solar panels (160w) all on the drivers side of the rig with the ability to tilt them. Will try and park so the drivers' side is facing south which should permit me to maximize the sun for the panels and at the same time minimize the sun on the sides of the rig, especially the ref side for my rig.

All I really know about the solar panels is the wattage. It is the volt stuff (max-min) that is confusing me and especially if there may be shading involved and the affect it may have on the panel array's out put and on the solar controller itself.

Right now I am stuck on whether or not to wire six (6) 160w panels in series in three (3) sets of 2 to a roof top combiner box (or perhaps put the combiner box in a compartment?) and then go from there parallel with 6 gauge wire to the solar controller itself. Seems that this is better for partial shading if there are not too many trees? Without any shading this seems to be better?

OR

Just wire five (5) 160v panels in series to the combiner box on the roof and use 4 gauge wire to the solar controller? Partial shading becomes an issue but I think that would resolve any adverse affects on the charge controller? Not sure what the partial shading would have on the panel array's out put to the solar charge controller

The solar controller I am thinking about is the PT-100 for purposes of continuity. (100amp full battery charging ability is nice). Not concerned with its size or the vertical requirements to hang it. It will be in the same pass through compartment as the rest of the system, and of course separate from the battery compartment which is next store

The issue for me with the PT-100 is still this Po4 fault stuff. Can this be resolved by wiring the panels as described above one way or the other?

As for the rest of the system, 440 or 600 6v AGM amp hour battery bank, the Magnum 3000 hybrid (MSH3012) with the ME-ARC display, BMK and AGS is pretty much what I have decided to go with. Would like to stay with the same company for all devices. Any further explanations, suggestions or further comments would be greatly appreciated. Thanks in advance.

Sparksvonrou · 10-19-2017, 10:13 AM

What is the voltage output of each solar panel? Brand and model number would help. Can't imagine being in series. Mine are around 17-18 volts out (open circuit not connected to anything except the volt meter) from each panel. In parallel the voltage stays the same. The current supplied adds which is what you want. Your charging 12v batteries? You have the solar controller already? 17-18 is perfect to feed the controller which then regulates the charge going to your batteries. Also If you do the math, the length of runs of wire you need do not need 6 gauge wire. The losses are small at the current your going to get. By the way, we use 100w Windy Nation solar panels. Currently selling at $109 including free shipping.

Rvlegaleagle · 10-19-2017, 10:34 AM

"What is the voltage output of each solar panel? Brand and model number would help.".

What are the options, that is part of what I am trying to figure out

How does the "volts" on a panel factor into things and what affect does that have on the solar charge controller?

I think I know that if the panels are all wired in series the voltage stays the same and so you need higher gauge wire to the solar controller. How does that affect the amps though? I believe that amps are what charges the batteries.

I am not sure if you wire 2 panels in series and then have 3 sets of them that means each set is actually wired in parallel? While I believe the voltage stays the same, you can get away with smaller gauge wire but what does that do regarding amps?

Thanks in advance

Sparksvonrou · 10-19-2017, 11:10 AM

No if wired in series the voltage adds, current staying the same. You want them in parallel.

Sparksvonrou · 10-19-2017, 11:12 AM

But... What batteries? 12v? 24v? Need to start with the basics first. Do you have the panels specifications that you're looking at.

vsheetz · 10-19-2017, 11:30 AM

My recommendation based on your initial ask

Six panels. Two strings of three panels using two #10 wire pairs to combiner box (midnight solar, with circuit breakers/disconnect) located near the controller (which is near the batteries). #4 wire from combiner box to controller and controller to batteries. Include a 150a inline breaker/disconnect in the positive wire to the batteries - thus breaker located in the battery bay.

Above is similar to my 1500w system. Wired in three strings. I have a Midnight classic 150 controller, midnight solar six slot combiner box with 15a breakers, and 15 Renogy panels.

The above provides: high voltage for the mppt controller to work it's best, smaller gauge wiring from the roof, some shading mitigation, ability to compare string outputs to ensure panels outputting correctly, ability to have easy maintenance disconnects, etc.

Rvlegaleagle · 10-19-2017, 11:31 AM

Batteries will be 6v AGM, probably lifeline, 4 or 6 of them depending on room. So that is either 440 or 600 amp hours.

I messed up on the series wiring keeping the voltage the same, it adds the voltage all together.

As to the exact panels, that is what I am trying to figure out

along with the charge controller. Still learning.

harryn · 10-20-2017, 02:38 PM

Vsheetz has an excellent model there to follow.

Another thread on here is an excellent place to start and mimic for general information on solar installs.

http://www.irv2.com/forums/f56/pv-sy...os-332341.html

It has nearly everything you need listed, yours is just a bit up sized.

The magnum PT-100 has some great specs and I really like the larger wire size capability on the output side of the controller.

Assuming that you are working with the RV size panels (roughly 58 x 27 inches), then most of these have 3 important numbers:
- Vmp - typically around 18 volts. This is the approximate typical voltage that will come out. This varies more than you might think though winter to summer.
- Voc - this is the highest voltage that the panel will create under most circumstances. The ones I have in the garage are listed at 23 volts.
- Imp and short circuited - this is the highest current it will create - probably around 10 amps for most of them on the market

harryn · 10-20-2017, 02:46 PM

Technically, the correct way to design a setup is to use a "string calculator" to take into account the voltage variation due to temperature effects. IMHO, morningstar has one of the best on-line calculators, but I am not a big fan of their controllers.

A simpler and probably close enough method is to just use the Voc number and use this as the maximum voltage from each panel that has to be dealt with under most circumstances.

The midnight classic 150 and I think the PT - 100 can accept in around 150 volts max and still operate. This is also roughly the same as the DC breaker ratings that you will almost for sure want on the wire coming from the panels to the controller in order to do any maintenance.

Assuming you have (5 panels x 25 volt Voc = 125 volts ) that is about as many panels as you should put into a series string.

harryn · 10-20-2017, 02:52 PM

Since you are using a 12 volt battery system, and the output current maximum from the PT-100 is 100 amps, then:

12 volts x 100 amps = 1200 watts max that the controller can effectively deal with.

5 x 180 watt panels = 900 watts

In theory, you could add some more panels either in a parallel string or possibly 1 more in series.

Interestingly, if you instead used a 24 volt battery bank rather than a 12 volt battery bank, then it would be:

24 volts x 100 amps = 2400 watts - so the same exact solar controller could handle double the number of panels.

24 volt inverters are also more efficient than 12 volt inverters, especially at the higher power draw levels.

This is why I tend to use 48 volt battery packs just like the off grid homes do.

harryn · 10-20-2017, 02:57 PM

If you wire the panels all in series, then I think (not 100% sure) that you don't need a combiner box at all on the roof, just a way to pass the power down to the charge controller.

Obviously shade is a good reason to break up the string into a couple of strings.

Several suppliers make pre-made solar grade wire with MC-4 connectors in 10 awg. That is more than enough for 10 amps at 100 + VDC with negligible losses from the panels down to the controller.