testing solar panels

[BruceS]

I have 3 X 24v (nom) solar panels that are 'fixed' in position on top of my motorhome and was wondering if someone might know how to test each individual panel for .......
1. performance.
2. If there is a blown diode. (allowing backfeed at night)

The fully qualified auto electrician originally connected one panel with wrong polarity & after an hour or so I noticed lack of performance & corrected it myself.
Ever since then I've wondered if any damage has been done.
I'm confident they are charging OK ........... more worried about back feed at night.
I can easily disconnect one by one as the connectors are accessable.
Not easy to access the black box under the panels.
Any ideas?

[Newcastle George]

Throw blankets over two and read the output of the third. Repeat, Repeat.

George

[oldtrack123]

HI Bruce
You can check the output of each , as George has indicated
You should not have to worry about the internal diodes preventing back feed at night
THE solar reg SHOULD have that built in


PeterQ

[BruceS]

Thankyou for the feedback.
I was under the impression that if you assume the diodes are 'blown' then if one panel is in the shade then all panels will suffer more than if all diodes are 'good'?
Would there be a test I can perform to check diodes by disconnecting panel by panel?
I'll wait till bright sunshine & check output of each individually. (45.3V approx.)

[oldtrack123]

Thankyou for the feedback.
I was under the impression that if you assume the diodes are 'blown' then if one panel is in the shade then all panels will suffer more than if all diodes are 'good'?
Would there be a test I can perform to check diodes by disconnecting panel by panel?
I'll wait till bright sunshine & check output of each individually. (45.3V approx.)

Hi Bruce
It would be very unlikelythat the bypass diodes would have blown to a short circuit & allowing reverse current to flow
The usual thing with diodes is to blow open circui.
If you have access to the diodes & a multimeter with a diode test function they are very easy to test
when disconnected !!
with one polality of the meter probes you should get a short beep & the opossite plolarity of the probes no beep
Alternatively with the meter set to resistance you should get near zero resistance with one polarity of the probes & very high resistance with the opposite probe polarityl
PeterQ

[T1 Terry]

Hi Bruce,
First check to make, if you have a junction box on the roof, take the lid of after the panels have been in the sun for an hr or so and put your finger on each connection, quickest way to find a bad joint, it will be real hot. If the junction box uses neutral link type bus bars, see if you can get your hands on some boot lace terminals http://www.ebay.com.au/itm/131009606709 ... 963wt_1006 and fit these to the clean stripped wires before putting the cable into the bus bar. Might pay to actually take the busbar brass block out, remove all the screws and run a just a fraction bigger drill through the hole where the wires go in, just to clean the joint up before refitting all the cables. The work loose and oxidise the contact between the brass block and cable creating a very high resistance joint and this wastes a lot of the solar output.
You mentioned a panel once being reverse connected, if the other panels tried to back feed into that panel and the current was high enough the diodes could have actually burst, splitting the plastic case in half. Disconnect the panel cables and put a volt meter across, should be around 36v. Next you need an amp meter that will handle the panel max short circuit output of each panel. As it is a 24v panel the max amps would most likely be less than 10 amps, most multimeters that can handle 10 amps when the red lead is pugged into the high amp socket.
First read the panel short circuit amps output, probably between 7 & 8 amps, now with a towel folded in half, cover part of the panel top to bottom starting from one side. If you look into the panel face you can see the silver ribbons, one connected at the far left to the string that goes down the panel and one at the top of the next string that comes back up from the bottom, just cover these 2 strings, now read the amps again, it should be roughly 75% of the max output figure, cover the next pr and retest, each should have the same effect. If you have a big difference between 2 sections, the bypass diode for that section has blown.
After you have tested the output like this for all 3 panels and it came up ok, the next possible problem is failed blocking diodes, this one is rare, generally they blow to bit or work as expected. Measure the output from all 3 panels from the reading on the solar regulator, cover one panel, the output should still be 60% of the full amount, do the same for each panel, if a bypass diode has failed, the panel you cover that has a major effect on the output when covered is the one with the failed blocking diode, the other 2 panels are back feeding into it trying to turn it into a heater.

[BruceS]

Thankyou Terry for those details!
I might just leave it for you to diagnose when I see you next!!!
I'm very happy with the output/performance but just have this nagging thought about what MAY have happened when one was connected up wrong.
I now realise that one of the batteries has been on it's way to heaven even before I bought the MH.
I can now watch TV & have the Engel going all night (freezer/fridge) and still have a green light by morning.
No more waking up to 22V.