Fluctuating Voltage from a Large Hi-Voltage Panel-(315 watts)

[Solar trucker]

Does anyone have any suggestions as to where I should be looking at to troubleshoot this problem?
The input voltage to the controller (The Kid) keeps varying anywhere from 21V to 61V...
This fluctuation happens also when the conditions are completely clear outside and the level of sunlight
is constant....I tried switching PV cables to the combiner...Also tried feeding the kid controller with a different panel and it worked fine!

It seems like to me that either the Panel Junction box may be at fault or the short 3ft cables (mc4 connectors attached) may be faulty! Is there an easy test for the junction box and connections?
Guess I could open up the box and just throw a meter on the ribbons coming out of the panel??
Does anyone know a place one can acquire a new Amphenol Junction box easily in Arizona?

[Robin]

Does this panel have a warranty? If so, use it. If not, try to locate where the voltage is being lost. Can you unscrew the back end of the MC4 connectors to inspect them? The junction box is going to be a problem.

[Solar trucker]

Hi Robin, no the panel doesn't have a warranty...bought it used from a garage sale about 2 weeks ago..
I put a volt meter on it at time of purchase, and got a solid 61V with good light on the panel...
It didn't fluctuate at all then.  Although I only tested it for a few seconds to make sure it was up to the
rated spec!  The Junction box is a TYCO Electronics with 3ft cabling terminated by MC4 connectors!

All the components...The Panel (Sunpower-SPR315 watt)...junction box and cables almost look mint condition, so I don't think there was any physical abuse...The back end of the MC4 cables screw into
the junction box, guess I could try doing that first and try to narrow it down to either the cable (s)
or the box...The box of course is siliconed very nicely to the back of the panel and that will take considerably more work to troubleshoot!

[CDN-VT]

U own it now SOooooooooo

I would use a DVM in mega amp scale 10A &  short both mc4's to the DVM & watch if it flakes out . Any tone colour on the front  face surface & from behind with the sun on it ? Isc test is what this is & make sure the panel output is less than 10 amps so the internal fuse in the DVM is not blown.Load testing is the best way to figure weak spots
Like Robin posted , open up the mc4's & inspect or bypass .then replace if there arced in the terminals .

VT

[zoneblue]

So you dont have to worry about warranty, then teh junction bix usually opens with care. AS CD said to rule out controller issues, do the Isc test.

[Solar trucker]

Ok guys, I've done some more testing in the last couple of days!  I swapped out the 315 watt panel and
put a 327 watt panel on the kid controller with THE SAME PV INPUT CABLING AND CONNECTORS..
THE only variable in this test would have been the solar panel, junction box and short cables...that
connect to my input cables!

The 327w panel and 315w panel have specs that are almost identical...ie: Voc is 64.7...When I installed
the 327w panel yesterday the kid was showing an input voltage of 61.6 and there was no fluctuation of
voltage on the kid LCD or my Fluke meter, which was identical to the kid reading!
So in the light of this...am I to assume that my 315w panel has some issue in the junction box and/or
short leads coming from the box?  After I went back to the 315w panel today, the input voltage went back to 39V to 41V...

[CDN-VT]

You read my post & from ZB where he said try CD's thoughts ?
RE read mine & see if YOU can diagnose it . Swapping is not diagnosing . If you had a terminal that had arcing damage ,that could & would transfer arcs into a good terminal . There is a poor connection to be found .

If I found a Bad MC4 connection on a joint  , I would need to replace both terminals , plastic also if it was heat damaged .(I have the tools for this ) if not just cut & inspect wire core & install a new MC4 end.
Above is assuming it was a bad end. As ZB posted , the junction box is tricky & some are glue sealed plus.

RE-read ISC test

VT

[Solar trucker]

Ok will try this test...As you say there is a bad connector or joint in the junction box...

[CDN-VT]

Like Robin said , it could be just a bad terminal end.
Way back in 90s , I got a bunch of MC4 M & F ends that were good together , but on a quality Canada Solar panel the I found the male was over size & spread the female so the next normal male would have a loose fit causing a poor connection .

On those after I found out & could ID them , i changed them out & resized the female on the correct ends with the tool .

Yours could just be a terminal end or a bad crimp , box could be next , but I would look at the panel from behind loaded & look for a hotter spot  & see if pushing it from underneath makes a difference on the meter. Same inside the J box.  I use a small infrared temperature gun also to find the hot spots.

I Know , but it is what it is , I know Tall Gurl understands .

VT