Solar panel diode confusion - Page 1
Forum section: electronics / beginners

author: andrewlapham
author_rank: Contributor
timestamp: September 15, 2019, 07:24:26 am
content: Hey guys can someone explain the purpose of this diode? Im guessing its not to block the flow of current from the battery to the panel otherwise it would be the other way around. Is it some sort of rectifier?

author: fourfathom
author_rank: Super Contributor
timestamp: September 15, 2019, 07:34:32 am
content: This is most likely a "bypass diode", used to let a series string of panels continue to operate (at a lower voltage) when one of the panels is shaded. Without this diode, the shaded panel would present a high impedance and prevent current from flowing in the string. Here's a link to an explanation:https://www.electronics-tutorials.ws/diode/bypass-diodes.html

author: andrewlapham
author_rank: Contributor
timestamp: September 15, 2019, 08:48:49 am
content: Ahh ok. I have two of these panels in parallel but need to add a blocking diode would it make sense to just flip the exsisting diodes?

author: andrewlapham
author_rank: Contributor
timestamp: September 15, 2019, 09:00:26 am
content: Just had a look and its a schotty 1n5819

author: oPossum
author_rank: Super Contributor
timestamp: September 15, 2019, 09:06:16 am
content: It is wired in series so it is a blocking diode. A bypass diode would connect to both leads from the cell array.

author: andrewlapham
author_rank: Contributor
timestamp: September 15, 2019, 09:46:04 am
content: but if its s blocking diode isn't it facing the wrong way?the picture i posted has the configuration i assumed it should be in but the fact that the diode is flipped is still a mystery to me.

author: fourfathom
author_rank: Super Contributor
timestamp: September 15, 2019, 03:41:56 pm
content: Quote from: oPossum on September 15, 2019, 09:06:16 amIs it wired in series? Looks parallel to me, although it's not completely obvious. You could repurpose this diode as a series blocking diode but this may not be necessary, especially with such a low-power panel. It will depend on your charge controller.

author: thedoc298
author_rank: Contributor
timestamp: September 15, 2019, 11:56:40 pm
content: I don't know what that box is or it's usage, but the diode would function as a reverse polarity diode.

author: boB
author_rank: Frequent Contributor
timestamp: September 16, 2019, 12:02:02 am
content: The diode is what fourfathom said it was for. Shading of the panel when it is in series with other modules.A small diode works here because the PV module is very small (5 watts ?)boB

author: oPossum
author_rank: Super Contributor
timestamp: September 16, 2019, 01:14:59 am
content: Looks like series to me.

author: boB
author_rank: Frequent Contributor
timestamp: September 16, 2019, 01:26:56 am
content: If it is series, then it would most likely so be that the battery is not discharged as much by the panel over night.PV modules are very leaky that way so the diode can help that.

author: oPossum
author_rank: Super Contributor
timestamp: September 16, 2019, 01:35:42 am
content: Is this panel sold for some specific use like battery charging?Small panels intended for direct connection to a lead acid battery will typically have a series diode to prevent discharge of the battery. Panels intended for use with a charge controller or inverter will typically have a parallel diode or no diode.

author: fourfathom
author_rank: Super Contributor
timestamp: September 16, 2019, 03:11:57 am
content: Quote from: oPossum on September 16, 2019, 01:14:59 amYes, looking at your annotations you appear to be right (and I was wrong). It is a series diode, and is there to prevent a dark panel from draining the battery. A good controller won't let this happen anyway, but with a cheap controller or a direct battery connection the diode is probably a good idea.I tested some of my 100W panels and they actually didn't leak significantly until the reverse voltage exceeded the panel Voc (open-circuit voltage). Other panels may be more leaky than mine were.

author: andrewlapham
author_rank: Contributor
timestamp: September 16, 2019, 10:38:16 am
content: Quote from: oPossum on September 16, 2019, 01:14:59 amjesus that picture really cleared everything up for me, i thought the diode was facing the wrong way and it was wreaking my head. haha, thanks