solar problems/need guidance

[sensij]

yeah I have a rms clamp meter. so I didn't know you could short the panel. that's the way ill go then. thanks

Ok. It may be obvious, but just to make sure it is said... the clamp meter needs to have DC current measurement capability. Some are just AC current only.

[bcroe]

bcroe you are correct with your advice and I thank you for it. i as far as thr gfi fault i followed it, that's how i found the 3 problems so far.have worked on dc power plants from -48v, +24v, up to 10,000 amps for last 37 years. I might not know the system but I do know caution. i found 3 faults so far, one bad connector and looks like some animal ate the insulation off the other 2. and that's only after going through 20% I'm thinking about a cage around all the panels to stop the critters

OK, thanks for confirming you did track down wiring problems; from your description above, it
would be advised to check 100% of your wiring for damage. Again keep in mind, these voltages
are far more dangerous than the sort of potential we in the phone and related bus encountered.

Critters can be a problem, I have been lucky to suffer no damage with a ground mount; raccoons,
turkeys, ground squirrels, and many others inhabiting the area. It will not be a surprise the day I
find a cooked deer in my array.

Once your wiring is fully repaired and still isolated from inverters, you should not be able to draw
any kind of voltage from any array lead to ground. My low impedance tester is several 75 bulbs in
series, which draws off any static charges. And draws a nice (controlled) arc when current flows.

Your MC4s are low quality, non precious metal connectors which will not tolerate much abuse.
Don't leave them exposed to the elements, they quickly oxidize. Don't interrupt current with
them, not even for a single low voltage panel. Instead make a test circuit with your meter and
a switch. Plug this into the panel AND THEN close the switch to make a current reading. Open
the switch and move on. This will allow you to grind off the latches on your MC4 test connectors
to save a lot of test time.

Don't try this for multiple panels in series, as it will arc the switch to destruction. Only a large
high voltage DC disconnect can handle this, and doing it very many times will soon wear
it out; I consider it for emergency or nighttime use only.

As for measuring current, inserting a meter in a high current DC circuit is a lot more difficult
than it appears on the blackboard. My advice is get a nice DC clamp on ammeter, a very
useful tool around PV. Otherwise put a shunt resistor in the circuit (could be permanent)
and use your sensitive DVM to measure the voltage across the shunt. You can measure
the current of an entire string as well as one panel, but you will only be able to make one
measurement a day, moving the test connection at night. Bruce Roe

[max2k]

yeah I have a rms clamp meter. so I didn't know you could short the panel. that's the way ill go then. thanks

panel normally is source of current so it tolerates being shorted very well. bcroe even recommends to do this on outside installations to keep connectors protected from weather. If you think about it panel doesn't 'produce' the energy it can only 'shorten' less than 20% of what already fell on it anyway.

Something is up with your meter- can you connect it to 1.5V AA battery for a second? It should give you 1-3 A current.

[tim a]

that worked thanks

[Mike90250]

yeah I did that to one panel, 40 vdc but 0 amps, these are 12 year old panels. its suppose to be 40v and 5.25 amp per panel

Please be careful about connecting your series ampmeter, even to a single panel. 40V is a really stout arc welding voltage and will easily damage the MC connectors

[tim a]

I will mike, thanks

[tim a]

OK, thanks for confirming you did track down wiring problems; from your description above, it
would be advised to check 100% of your wiring for damage. Again keep in mind, these voltages
are far more dangerous than the sort of potential we in the phone and related bus encountered.

Critters can be a problem, I have been lucky to suffer no damage with a ground mount; raccoons,
turkeys, ground squirrels, and many others inhabiting the area. It will not be a surprise the day I
find a cooked deer in my array.

Once your wiring is fully repaired and still isolated from inverters, you should not be able to draw
any kind of voltage from any array lead to ground. My low impedance tester is several 75 bulbs in
series, which draws off any static charges. And draws a nice (controlled) arc when current flows.

Your MC4s are low quality, non precious metal connectors which will not tolerate much abuse.
Don't leave them exposed to the elements, they quickly oxidize. Don't interrupt current with
them, not even for a single low voltage panel. Instead make a test circuit with your meter and
a switch. Plug this into the panel AND THEN close the switch to make a current reading. Open
the switch and move on. This will allow you to grind off the latches on your MC4 test connectors
to save a lot of test time.

Don't try this for multiple panels in series, as it will arc the switch to destruction. Only a large
high voltage DC disconnect can handle this, and doing it very many times will soon wear
it out; I consider it for emergency or nighttime use only.

As for measuring current, inserting a meter in a high current DC circuit is a lot more difficult
than it appears on the blackboard. My advice is get a nice DC clamp on ammeter, a very
useful tool around PV. Otherwise put a shunt resistor in the circuit (could be permanent)
and use your sensitive DVM to measure the voltage across the shunt. You can measure
the current of an entire string as well as one panel, but you will only be able to make one
measurement a day, moving the test connection at night. Bruce Roe

thank you for the information. I will use it. I found another group of bare wires today already. and yes every panel and wire leading to them will be checked. is it worth to put up a squirrel cage around the array?

[max2k]

thank you for the information. I will use it. I found another group of bare wires today already. and yes every panel and wire leading to them will be checked. is it worth to put up a squirrel cage around the array?

you need to get rid of them completely- they tend to populate attics and in order to do that they must make holes in your roof. You can buy special trap cage for them and after they got caught drive them out of town to nearby forest / whatever where they belong. In terms of climbing I saw them hanging comfortably on a vertical brick wall or climbing upper part of the roof under negative angle. I don't think anything less than electric fence will deter them .

[SunEagle]

you need to get rid of them completely- they tend to populate attics and in order to do that they must make holes in your roof. You can buy special trap cage for them and after they got caught drive them out of town to nearby forest / whatever where they belong. In terms of climbing I saw them hanging comfortably on a vertical brick wall or climbing upper part of the roof under negative angle. I don't think anything less than electric fence will deter them .

I don't know but I think cats and hawks are pretty good at eliminating squirrels.

[tim a]

you need to get rid of them completely- they tend to populate attics and in order to do that they must make holes in your roof. You can buy special trap cage for them and after they got caught drive them out of town to nearby forest / whatever where they belong. In terms of climbing I saw them hanging comfortably on a vertical brick wall or climbing upper part of the roof under negative angle. I don't think anything less than electric fence will deter them .

found 1 hole so far. I am starting to dislike squirrels.

[tim a]

I found 1 panel so far with a 27.8v (should be 40v) should I leave or look for a replacement? it is in a string of 7 in series and two 7 strings in parallel

[sensij]

I found 1 panel so far with a 27.8v (should be 40v) should I leave or look for a replacement? it is in a string of 7 in series and two 7 strings in parallel

You are measuring open circuit voltage? With 7 in series, that voltage loss isn't going to hurt the overall performance much, but if there is an internal short, it could be a safety hazard.

[max2k]

I don't know but I think cats and hawks are pretty good at eliminating squirrels.

cats- not much, those critters outrun them easily especially on the verticals . My cat was a hunter but he couldn't catch even single one of those. They actually had a nerve and were teasing him on regular basis. The cat was able to catch a bird in one jump if it was stupid enough to fly over too low over him but not a single squirrel.

[max2k]

You are measuring open circuit voltage? With 7 in series, that voltage loss isn't going to hurt the overall performance much, but if there is an internal short, it could be a safety hazard.

depends of the nature of the loss- if that voltage reading was taken under Vmp / Imp or in the area then yes, not much production loss would result. If it was Voc then panel could develop huge resistance somewhere but since voltmeter has high input resistance on its own it still shown some voltage. When put in string this panel wouldn't let any significant current through. Hopefully bypass diodes would still work.

I'd replace the thing after checking one more time and making sure it was not shaded during measurements.

[tim a]

You are measuring open circuit voltage? With 7 in series, that voltage loss isn't going to hurt the overall performance much, but if there is an internal short, it could be a safety hazard.

thank you