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diy solar

My solar panels dont have bypass diodes!

pullin_gs

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Apr 14, 2022
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One of my panel strings has a small area on one panel that gets shaded in late afternoon. Entire string output into MPPP charge controller drops down to almost zero.
I do not believe any of my panels (Santan Solar SS-250P-60....recycled solar-farm panels) have bypass diodes!
I suppose I'll have to put one bypass diode on the panel that gets the shade.
That should get me another hour's worth of power from other two panels in string, right?
 
Did you open up the junction box to verify that the bypass diodes are not installed?
I expect it to have 3 bypass diodes in that junction box.
 
Real easy to tell if there are bypass diodes...shade 2 longwise rows....if voltage goes down but current stays same, you do have bypass diodes, if both current and voltage goes down you do not have bypass diodes
 
For what its worth I have 3 old panels that have zero bypass diodes. Just two wires coming out the back with big gob of silicone sealant.
Do you know made those panels, I have a few Arco Solar panels from ‘1965 that do not have bypass diodes
 
I have 24 of the SanTan Solar 250w panels.
They have 3 bypass diodes in the junction box.
It's possible that your diodes have failed.
1 of mine had a bad diode, that I found and replaced.
This would create what you are describing.
 
huh??? Looking at PDF it does have junction box and knowing manufacturer would say odds of no diodes is slim ... are these used-damaged panels??SOL
Wires exit from molded rectangle SOLID rubber grommet glued to back of panel.....is not serviceable.
I suppose diodes could be molded within it?
Panel behaves as if no diodes....will check see if other panels behave same way (partial shade one panel....whole string goes dead).
This "SS" panel is made by Trina I believe?
PS: Panels are great otherwise....very happy with performance considering what I paid for them.
 
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Non-intrusive testing of bypass diodes:

 
Real easy to tell if there are bypass diodes...shade 2 longwise rows....if voltage goes down but current stays same, you do have bypass diodes, if both current and voltage goes down you do not have bypass diodes
When a row get covered, MPPT controller voltage reading drops a little, but current drops down to around 2% of Imax.
 
Non-intrusive testing of bypass diodes:

Thanks.....added it to my list of things to do tommorrow.
 
I wonder how many of these diodes get damaged from connecting/disconnecting panels under load. People forget to shade their panels before messing with the connection.
 
I wonder how many of these diodes get damaged from connecting/disconnecting panels under load. People forget to shade their panels before messing with the connection.
I'm not sure how that would damage the diodes.
 
Connecting/disconnecting unlikely to damage bypass diodes unless maybe if polarity of connections is reverse. Diodes are large die so even a strong ESD hit is unlikely to damage them.

Most likely damage is cheap diodes without any heat sinking that get cooked from the 4-5 watts of heating when bypassing current flow with diode voltage drop. (8.5A x 0.55v diode drop = 4.7 watts of heating)

Sure sign of a cheap panel is when you find bypass diodes made of two diodes soldered together in parallel. Diodes in parallel do not share
current equally.
 
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Open the box, take a picture and post it up
I'll give odds you will find crispy burnt up plastic diode shells. All it takes is one bypass diode open in the whole series string of panels to lose the whole string.
 
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