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My PV array series strings are 6 panels long, there are 5 strings. Each panel in the string is 100watt 20volt, 6.25 amp.
The voltage of each string before connecting to the combiner box is 108 volts in full sun 80% (great) but after connecting any of two strings together the voltage drops to 90 volts.
Being new to solar thought I should ask if this is normal or do I have a problem?
the current of each string is the same?
yes, 107.5 volts on every string of 6 panel
I assume that this is when there is no current flow from the string, so this is the open circuit voltage Voc.
When you combine a string to the combiner box, is the solar controller working at this point or are the panels still not supplying current.
I ask because once the panels start delivering power the voltage will drop close to the maximum power voltage Vmp which is lower than the open circuit. Check your panel specs for Voc and Vmp.
If when connected to the combiner box they are providing power then the voltage drop is expected, but if they are not delivering power then I can not explain it.
VMP is 102volts total on each string of 6 panels.
Each string tested 107.5 volts before attaching to the midnight solar only, not on to the charger controller because the breakers are in the off position.
Apart each string tested 107.5 volt and as soon as I attach then in parallel with each other the voltage drops to 90 volts
Amps are the expected double with 2 strings and the expected triple with 3 strings combined.
@WayneC ….May I suggest one of the strings is polarity reversed. Check that each of the three strings has the positives joined and the negatives joined. One of them is reversed.
If the combiner box is dumb, just connectors, then there should be no current anywhere when the strings are connected up but isolated from the charge controller. If you se current on w or more strings then you have circulating currents... BAD
You may have a string reversed or you may have a shaded string that is not being protected from reverse current by a diode.
Many modern panels contain bypass diodes to allow current from fully lit panels to bypass shaded panels, and even parts of them. However 'most' do not contain reverse feed protection, which used to be a common.
Get yourself a DC clamp meter, you dont want to be messing with physically connected current measurments at 100V.
Then check for currents in all connected strings, one at a time as you hook them up.
Also note that MC connectors are NOT rated to be connected and especially disconnected, whils under load, IE when a current is flowing, the prescence of voltage is not an issue.
18V Voc, the open circuit voltage, seems low. Typically 12V 'nominal' would have an open circuit voltage between 21 and 23 with a Vmpp, maximum power point, in the region of 17-18V.
Of course there are many brands and configurations of panels so I may be way off base but you should check you are seeing the voltages you expect based on the spec.
I bought a new voltmeter just in case and rechecked the polarity and its correct., checked the amps and the voltage. The voltage on each string today is 108 volts, amps around 4.
I have 5 stings with (6x 100watt panels on each string). 3 strings going to a Midnight solar combiner box and 2 strings going through a homemade PV combiner box.
As soon as any string is connected to another in either combiner box the voltage drops to 90 volts.
With the old voltmeter.
Update; ......All strings combined or not now read the same voltage before entering the charger controller. Nothing to change but the voltmeter. For some reason the extra Amps was pulling the voltage reading down. Can't explain it but I now have a new but much nicer Voltmeter.
The charger controllers is (now) connected and working. I'm getting the correct watts to match the volts x Amps.
Thank you all
Make it a great day!
