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Old 03-01-2019, 06:03 PM   #1
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Default Solar panel tweak, possible?

OK, try this again a little different and back to an older plan.


We have three GS100 solar panels for a total of 300 watts. They are 12v panels and have to be parallel to prevent overvoltage on the Blue Sky HB2512ixHV controller. When we had two panels wired series for 24v, we tended to get a bit better output per panel, so it might be interesting to try a bit higher voltage to see if is the voltage or the third panel is just weaker.


The panels appear to have two segments, so assuming nominal 6v each, with two bypass diodes. I am thinking of tapping one of the panels at the diodes to split it into two 6v segments that I could then series each 6v segment to each of the 12v complete panels to make two 18v nominal panels that I could then parallel to the controller.


Anybody have any idea of this would work?
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Old 03-01-2019, 09:37 PM   #2
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I could not find the specs on that particular controller.

The potentially similar? controller that they sell is this one:

https://sunforgellc.com/solar-boost-1524ix/

I used the specs from this one for thinking out loud here, so bear with me.

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The typical challenge that people have with using an mppt controller with panels that are nominally 18 Vmp in parallel, especially in the winter time, is voltage differential.

As an example, a cold AGM battery might require 16+ volts to charge in the winter time, plus many mppt controllers need 3 - 5 volts of differential (drop) from the panel voltage to the battery charge voltage.

This really can put the squeeze on winter charging, and explains why you were happier with the 2 panels in series.

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If a solar panel is "split" to make a 1/2 panel, then usually that section will retain the Vmp of a full panel, but the current flow through each side will drop by 50%.

My interpretation is that instead of getting 8 amps through a 2S panel setup, it would drop to 4 amps in that string.

edit

I didn't look at the GS100 panel specifically. If it really is wired so that it retains full current and the Vmp supplied is 1/2 of normal Vmp, that could be interesting - and might work well.
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The 1524 version is designed for 45 volt max operation (so 2S panels) but 3S is too high. I am speculating that this is also too high for the older model, but this is a guess.

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I did a quick re-read of the 1524 manual. If my quick read interpretation is correct, technically 300 watts of panels is pushing the limits pretty hard. It probably doesn't matter though because rarely do panels actually produce nameplate power ratings on a conversion van.
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Old 03-01-2019, 09:52 PM   #3
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It's an interesting idea. You'd get the voltage to 27V instead of 18V if it could be done.

This guy found that he had to cut the trace:

https://www.instructables.com/id/How...2V-Solar-Cell/
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Old 03-01-2019, 09:58 PM   #4
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I remembered the PN incorrectly, it is a 2512ixHV.
Original post edited now.
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Old 03-01-2019, 10:09 PM   #5
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Quote:
Originally Posted by markopolo View Post
It's an interesting idea. You'd get the voltage to 27V instead of 18V if it could be done.

This guy found that he had to cut the trace:

https://www.instructables.com/id/How...2V-Solar-Cell/

I thought I might need to cut a trace also, but then drew it out and think I have something that might work. It currently has two diodes which should be paralleling the two sections of 6V each. If I make this panel the last on of the strings, I think I can just turn one diode around and leave the trace or connection between the two halves in place, as the new strings will be paralled and they will be connected anyway. This would also leave all the zones with bypass diodes on them.
On EDIT, it does appear I would have to cut a trace or I would lose polarity on one half of the panel, bummer.


Since these panels operated mostly between 17.7 and 21v in good sun, they should be running in the 26 to 32v range which would be nice as it would reduce current by 1/3 or so.

Sounds like it may pay to take off a panel and check it out, once I can do it outside in the sun for testing polarities and continuities. 3 panel setups are a pain unless you have really low voltage panels or a controller that will handle 65v input without frying. The Blue Sea isn't rated that high.
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Old 03-02-2019, 01:04 AM   #6
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Do you think that you can get down to a trace, cut, resolder into two output pairs, re-seal, etc reliably?

I personally lack that level of dexterity, so in my case I would almost for sure be purchasing another panel to play with in my spare time, pretty sure that I would mess up the panel.

I am sure that you don't want to spend the money, but a new charge controller would solve the problem and take 30 minutes to swap out.
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Old 03-02-2019, 01:17 AM   #7
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Quote:
Originally Posted by HarryN View Post
Do you think that you can get down to a trace, cut, resolder into two output pairs, re-seal, etc reliably?

I personally lack that level of dexterity, so in my case I would almost for sure be purchasing another panel to play with in my spare time, pretty sure that I would mess up the panel.

I am sure that you don't want to spend the money, but a new charge controller would solve the problem and take 30 minutes to swap out.

Agree with all of that, and that certainly may be an issue depending on how it all is made. I have never seen the guts of a panel so all new to me if I do try.


Yeah, the controller would be possible, but the mounting space is very limited in our system, with the controller out it's metal box and mounted on the frame that carries the other electronics. I also need a setup that uses a shunt and is totally settable for using amps for for the float transition, so I am pretty limited. The controllers are pretty inexpensive, but the remotes that go with them for the shunt and settings run them up pretty quickly in price. I keep hoping that Blue sky kicks up the input max, but they have only done that on the 24v output model so far. Still hoping for that, as it could be in the same case and also use the same Pro Remote and shunt, so would be a drop in.
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Old 03-02-2019, 03:23 AM   #8
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In that case, one possibility is to replace the 3rd panel with 2 smaller panels that have similar current as the existing ones or something else creative.

Solarland makes some non traditional panel sizes, shapes and electrical properties.

For example they make one that is roughly the size of your existing panels but in a 24 volt nominal panel rather than a 12 volt nominal. If you used it instead of the third panel that you have, it could be wired:
- Existing panels wired 2S
- New panel wired 1S
- parallel this down to the controller

It won't be a "perfect" match but maybe good enough.

Don't worry about poly vs mono, the difference isn't significant in conversion van applications. I actually kind of like poly panels for this area because they are rated to operate better in winter overcast conditions better than the monos. At least that is what the claims are.

You won't like the price but they have very strong frames and seem to be fairly durable.
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Old 03-02-2019, 10:41 PM   #9
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Here is an example of an RV size panel with a nominal 24 volt output.

Vmp = 36.6 volt

https://www.wholesalesolar.com/94332...ly-solar-panel

In theory at least you could replace the existing third panel with it and run it in parallel with the original 2 panels.

I am sure it is just what you are hoping for - another project.
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Old 03-07-2019, 05:14 PM   #10
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If the (NEW) combined output is adequate, why are you messing with it? Or do you need the extra energy?
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