Here's a picture of the junction box on the back of a Victron SPP041751200 175W panel:
Notice the three diodes - yet only two panel sections (three tabs). The panel physically is an arrangement of 4 x 9; electrically connected in two banks of 18 cells each.
I'm wondering why there are two diodes rather than just one across the more positive panel half? (right-hand side in this view)
(Aside: the soldering job is not fantastic on these...)
Hi BenL,
here is a link with a good explanation about the 3 diodes setup :
https://gold-coast-solar-power-solutions.com.au/posts/solar-panel-diodes/
Michel
@MichelG - indeed that article shows 3 diodes; though on a panel that has three sections (four terminations). In other words, that's showing the "expected" situation - as many bypass diodes as there are distinct series strings within the panel.
This Victron panel has two series strings (three terminations), so ought to have two bypass diodes. For some reason Victron have installed an extra bypass diode on one side.
The only reason I can think of is basically laziness: this junction box is obviously designed for up to three strings and probably come with diodes preinstalled for three strings (three diodes), and Victron just slapped it on and wired it in for the two strings. It'll "work", but will have a higher voltage drop and a few watts of wasted power when that half of the panel needs to be bypassed.
I'll probably replace that superfluous diode with a link.
Hi BenL, my panels have 2 series of strings and 3 diodes... As written in the information, it is also a way to protect the panel itself, in case of issues in any string, and just "losing" half of the panel's production.
In my installation, i just fixed the non-working diode, that was the easiest thing to do, personnally, I won't remove it. My 2 cents.
Have a nice day.
