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Old 01-08-2020, 09:04 AM   #1
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2019 28' Flying Cloud
Dripping Springs , Texas
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Installing Bypass Diode across entire solar panel

So I'm considering a 400W system for our 28' AS. My current intent:
- Use the existing Zamp wiring provided with the trailer (yes, yuck)
- Connect two sets of 100W panels in series
- Plug each pair to one of the Zamp inputs on the roof (leave remaining port unused)

We already have members reporting good results with this setup, others will never go there since they are firm believers in a full parallel approach. However the factory Zamp wiring is best suited for a series-parallel installation.

So let's pretend we've settled on series-parallel. Has anyone installed bypass diodes for each panel connected with that topology? This would seem to alleviate concerns about a string getting wiped out by shading.

If I google for "bypass diode for entire panel" I only get results showing the internal bypass diodes already present within the panel junction box. (BTW these already perform the same function at the cell level as I'm proposing at the panel level.) I can't find any examples where someone has actually installed bypass diodes across the panel.

I did find some articles online showing how it _should_ be done.

Like this:


Suitable diodes seem cheap:
https://www.amazon.com/gp/product/B0...GWS04X9MGBC2EH

To make the connection parallel, is it not simply a matter of connecting the diode across the black and red wires just before they exit the junction box?

References:
https://www.electronics-tutorials.ws...ss-diodes.html
https://sinovoltaics.com/learning-ce...-solar-panels/
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Old 01-08-2020, 01:33 PM   #2
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It would seem only one blocking diode would be required if its' current capacity was high enough.
It would be connected between the common series outputs and the battery. Far right where you little black arrow is shown.
Dave
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Old 01-08-2020, 02:09 PM   #3
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Quote:
Originally Posted by Outbackga View Post
It would seem only one blocking diode would be required if its' current capacity was high enough.
It would be connected between the common series outputs and the battery. Far right where you little black arrow is shown.
Dave
Please ignore the blocking diodes for this discussion; they're only present since I copied the diagram from one of the articles instead of drawing my own.
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Old 01-09-2020, 02:54 PM   #4
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Anyone? Am I over-thinking this?
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Old 01-10-2020, 09:12 AM   #5
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Do the math...?

Not much in response to this question, so I'll toss in my thoughts. I've been researching solar as well but I am not an expert. But from what I've learned...
A set of panels in series will add the voltage of each panel but the series will be limited to the smallest current of all the panels.
A set of panels in parallel will add their currents, but the output will be limited to the smallest voltage.
If I got that right, when a bypass diode kicks in, that series will essentially be one panel, 5.5 amps and 18 volts and the other series would be 5.5 amps and 36 volts (assuming full output on all other panels). This parallel join would produce 11 amps at 18 volts or 200 Watts.
Without the bypass, and say moderate shading, the one panel might be reduced to 2 amps at 15 volts (its my understanding that amps drops off faster then volts with shading). Join these up and the shaded side is 15 + 18 volts = 33 but limited to 2 amps. Non-shaded would still be 5.5 amps at 36 volts. These two series parallel combine to 7.5 amps at 33 volts or 247 watts. If shading drops the one panel to 1 amp at 16 volts, then the result would be about 210 watts. More shading and you are below the 200 watts the bypass produces.
So it seems its all about how much shading and if you have bypass diodes, when do they kick in.
So, where am I messing up?
Safe travels!
Fred
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