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Old 11-13-2018, 12:08 AM   #21
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Solar panel

Even with part of panel in shade it will still produce some power and you have to check the amps it is putting out not volts
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Old 11-13-2018, 12:46 AM   #22
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Originally Posted by johnlochbuie View Post
Even with part of panel in shade it will still produce some power and you have to check the amps it is putting out not volts
You do have to check volts. For example, with a PWM controller, if the volts isn't higher than 13V, there will be zero charge(amps)
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Old 11-13-2018, 01:23 AM   #23
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Originally Posted by lamokadave View Post
Here's a shot that is only producing .4 Amos
https://photos.app.goo.gl/xALYUHyYxtENJ6BW9
With 12 of 36 cell in the shade, the voltage would drop to below the charging voltage of a 12v battery.
Each cell is .5-.625 volts times the number of cells.
36 cells: VMP=18.9v (18.9/36 = .525v) VOC=22.5v (22.5/36 = .625v)
Specs from Renogy 100w solar panels.
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I guess its's possible they could have them in the junction box. If the panel had 6 rows with a pair of rows tied at the bottom, there would only be 2 diodes needed at a minimum and they could probably do that in the junction box. 4 rows would only need one diode at a minimum.

So basically, if you are only shading the first 2 rows(when I say rows, that's the length of the panel)the remaining rows should output if the panel has individual bypass diodes. However, if you only have one panel, shading is going to essentially kill your output since the voltage will be too low to do anything. That is why you want to run series if possible. There is no good reason to run in parallel with an MPPT controller.
The bypass diodes are for parallel panels not series. They keep higher voltage from flowing backward into a shaded lower voltage panel. If you look at a solar panels, you will see the silver wires connecting one cell to the next. There is no room for a bypass diode between the cells. If the a bypass is on each row, the shadow is on two of four rows or half the 22.5v panel. 11.25v is not high enough to charge a 12v battery.
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Old 11-13-2018, 01:49 AM   #24
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The bypass diodes are for parallel panels not series. They keep higher voltage flowing backward into a shaded lower voltage panel. If you look at a solar panels, you will see the silver wires connecting one cell to the next. There is no room for a bypass diode between the cells.
You are mistaken. You are referring to blocking diodes.

Do a search on solar panel bypass diodes.
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Old 11-13-2018, 03:15 AM   #25
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You are mistaken. You are referring to blocking diodes.

Do a search on solar panel bypass diodes.
Bypass Diodes in Photovoltaic Arrays
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I stand corrected a bypass-diodes is per panel or cell. Still you need a voltage high enough to charge a 12v battery.

Victron mppt manual, Page 7:
"PV voltage must exceed Vbat + 5V for the controller to start.
Thereafter minimum PV voltage is Vbat + 1V."
Victron MPPT Manual-SmartSolar-charge-controller-MPPT-100-30-&--100-50-ENglish .pdf
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Old 11-13-2018, 10:21 AM   #26
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There are some knowledgeable people responding here.
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Old 11-13-2018, 10:52 AM   #27
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I stand corrected a bypass-diodes is per panel or cell. Still you need a voltage high enough to charge a 12v battery.
And that is why you put panels in series!

I put together a very small system for my brother..2 125W panels. Works much better when in series with partial shading.
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Old 11-13-2018, 12:25 PM   #28
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In addition to that panel on my roof, I also have a front mounted solar port. Can I plug in a secondary panel to that port and have it work with the panel and controller already installed? Would that secondary panel also need it's own controller? My concern is I'm not sure if my roof top panel making its .4 amps is enough to maintain the batteries through the winter considering the common parasitic loads in the trailer
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Old 11-13-2018, 12:45 PM   #29
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In addition to that panel on my roof, I also have a front mounted solar port. Can I plug in a secondary panel to that port and have it work with the panel and controller already installed? Would that secondary panel also need it's own controller? My concern is I'm not sure if my roof top panel making its .4 amps is enough to maintain the batteries through the winter considering the common parasitic loads in the trailer
yes you can. I would be troubleshooting why the panel on your roof doesn't work though. If you want as a test, disconnect the roof panel and plug in your portable panel.
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Old 11-13-2018, 01:04 PM   #30
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yes you can. I would be troubleshooting why the panel on your roof doesn't work though. If you want as a test, disconnect the roof panel and plug in your portable panel.
I believe we determined that the shading on my panel is the issue
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Old 11-13-2018, 01:12 PM   #31
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I believe we determined that the shading on my panel is the issue
Is it always in shade?
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Old 11-13-2018, 02:11 PM   #32
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Hi Dave,

Killing the parasitic loads will also help. If you don't have a master cutoff, that's something to consider adding.

Hope this helps.

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Old 11-13-2018, 02:38 PM   #33
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I do have a battery disconnect but my understanding that will also disconnect my solar.
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Old 11-13-2018, 02:42 PM   #34
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Hi Dave,

It shouldn't if the controller is wired in the usual manner.

Easy enough to test, though. Kill the master switch in daylight and watch what happens with your charging activity.

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Old 11-13-2018, 02:43 PM   #35
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I do have a battery disconnect but my understanding that will also disconnect my solar.
Depends on how it's wired up. I have my solar connected to the battery side of the disconnect. I don't want the solar to power anything in the trailer if the switch is turned to off.
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Old 11-13-2018, 02:45 PM   #36
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Is it always in shade?
The way my parking spot is oriented at my paid storage spot, yes, the a/c unit will always cast some shadow on the panel. It's never been a problem between May and recently in North central AZ, but between now and March/ April, I'm not sure what to expect.
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Old 11-13-2018, 04:11 PM   #37
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I used the battery disconnect and indeed the solar controller is still showing the display screen with the 3 parameters. I assume that eliminates all the parasitic loads.
With no load, should the 0.4 amps I'm getting likely 6 hrs per day keep the batteries good. Controller shows them at 90% now at 12.9v
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Old 11-13-2018, 04:15 PM   #38
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12.9v means it's not even at float voltage.

What controller do you have?
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Old 11-13-2018, 05:08 PM   #39
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12.9v means it's not even at float voltage.

What controller do you have?
It a Go Power GP-PWM-30. I can tell you that under normal good charging conditions it typically reads 13.6 or a bit higher. When the sun goes down however so do the volts into the high 12s.
Years ago I picked up a solar battery maintainer to use with a trolling motor.
I think it's like 2w, measures 11.5 x 3.5.
I tested it today in the sun and it puts out over 23 volts.
Any value or potential harm in plugging this into my current system to augment my panel?Click image for larger version

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Old 11-13-2018, 05:16 PM   #40
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Originally Posted by lamokadave View Post
It a Go Power GP-PWM-30. I can tell you that under normal good charging conditions it typically reads 13.6 or a bit higher. When the sun goes down however so do the volts into the high 12s.
Years ago I picked up a solar battery maintainer to use with a trolling motor.
I think it's like 2w, measures 11.5 x 3.5.
I tested it today in the sun and it puts out over 23 volts.
Any value or potential harm in plugging this into my current system to augment my panel?Attachment 191375
You can connect it direct to your battery. It has a built-in controller.

The Go Power GP-PWM-30 has a maximum solar panel input of 28V voltage. You can only add more solar panels in parallel and parallel solar panels have to be identical. Same watts, VMP, VOC, IMP, ISC.
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