Externet
New Member
Heard of blocking and bypassing diodes; but never noticed any mention in any brand panel specifications as manufacturers implementing them-in. What is true ? Is it an strictly owner's option to add them to external wiring ?
Diodes built-in to panels ?
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ricardocello
Watching and Learning
All panels have bypass diodes built into them, typically 3. They do not specify their performance normally.
Blocking diodes are generally not used by folks in this forum.
I’ve built my own blocking diodes because I like my electrons traveling in one direction only.
Search “blocking diodes” and you will see why people don’t normally use them.
In general, the Voc of even dimly lit panels keeps the current from flowing backwards.
If you had a situation where a string of panels was completely covered (dark), then without blocking diodes,
a parallel lit string could conceivably send power through the dark panels, heating them up.
Blocking diodes are generally not used by folks in this forum.
I’ve built my own blocking diodes because I like my electrons traveling in one direction only.
Search “blocking diodes” and you will see why people don’t normally use them.
In general, the Voc of even dimly lit panels keeps the current from flowing backwards.
If you had a situation where a string of panels was completely covered (dark), then without blocking diodes,
a parallel lit string could conceivably send power through the dark panels, heating them up.
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Watch out for heat generated by blocking diodes.
Example: diode part number - 15SQ045 (sometimes used in solar panel blocking diode package)
Assuming panel Imp = 10A. Forward voltage drop of diode is 0.5V, so heat dissipation = 10 x .5 = 5 watts.
Example: diode part number - 15SQ045 (sometimes used in solar panel blocking diode package)
Assuming panel Imp = 10A. Forward voltage drop of diode is 0.5V, so heat dissipation = 10 x .5 = 5 watts.
ricardocello
Watching and Learning
That’s for sure! I made my own.
At max current in 4s3p, I’m losing about 11W to heat per blocking diode.
Used very beefy 1000V/25A full-wave bridge rectifiers (using two diodes per rectifier).
I also made metal boxes with external bolt-on heatsinks, and keep them in the shade.
As in... having a silicon doping machine in your workshop and the wherewithal to stick the P and N bits together
I'm new with solar, but I discovered these bypass diodes while fiddling with a freebie I was given. It had been culled, so I took it for study. This was a 400w bifacial. In the back there were three connection boxes. I popped the lids off. Interior was filled with white silicone material. I noticed one spot in the silicone was discolored.
I excavated the silicone entirely. The component that burned the silicone was practically falling out, so I ripped it out with pliers. Did the same on the other two and the panel was then generating 46vdc. I thought they were fuses. Wrong.
This puzzled me until some internet research and found the term and purpose of bypass diodes. I guess I could use this panel for a small project?
I excavated the silicone entirely. The component that burned the silicone was practically falling out, so I ripped it out with pliers. Did the same on the other two and the panel was then generating 46vdc. I thought they were fuses. Wrong.
This puzzled me until some internet research and found the term and purpose of bypass diodes. I guess I could use this panel for a small project?
ricardocello
Watching and Learning
As in... having a silicon doping machine in your workshop and the wherewithal to stick the P and N bits together
It’s possible to take DIY to extreme levels, but no, I don’t have a fab in the basement.Although, how hard could it be to dope a chunk of silicon to make a diode?
I simply meant that I hand assembled some off-the-shelf bridge rectifiers, thermal paste, aluminum boxes, and extruded heatsinks.
As opposed to using those inline MC4 off-the-shelf diodes that seem to meltdown and combust.
ricardocello
Watching and Learning
You could replace those diodes if you could find suitable ones,
The risk with no diodes is that you will have no shading tolerance at all, and hotspots might develop.
—Post edited to correct wrong info.
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Funny thing is, the panel generated to specs with them removed.
ricardocello
Watching and Learning
You are correct, removing them is what to do, then no bypassing will occur.
Adding all wires would short everything to 0V. Post above has been corrected.
timselectric
If I can do it, you can do it.
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I would assume that they had failed (shorted). So they were permanently bypassing the cells.
Externet
New Member
Thanks, fellows.
Very surprising that presence or not of bypass diodes in a panel junction box are never told on the specifications sheet or label or on the box itself.
The strings of cells internal to the panel connecting to the top of the image [4 terminals ? ] and the output to the bottom... Can the connections be manipulated removing diodes, bridging, removing/adding linkages to either tailoring having groups of strings doubling the voltage or paralleling them to increase current ? Like for converting ~40V panels into ~20V panels ?
My installation has 'halved cells' panels with 3 'junction boxes' in the rear. No mention on its label nor data if diodes are implemented. Cracking the boxes open is the only way to find out what is in the boxes ?
(images borrowed from the web)
Very surprising that presence or not of bypass diodes in a panel junction box are never told on the specifications sheet or label or on the box itself.
The strings of cells internal to the panel connecting to the top of the image [4 terminals ? ] and the output to the bottom... Can the connections be manipulated removing diodes, bridging, removing/adding linkages to either tailoring having groups of strings doubling the voltage or paralleling them to increase current ? Like for converting ~40V panels into ~20V panels ?
My installation has 'halved cells' panels with 3 'junction boxes' in the rear. No mention on its label nor data if diodes are implemented. Cracking the boxes open is the only way to find out what is in the boxes ?
(images borrowed from the web)
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