Amps not adding-up with parallel connection

junglesolar

Hello,

I am experiencing what I imagine to be a very basic wiring problem but which is causing me some considerable frustration...

I have a system comprised of 26 panels (325, 340 & 370w) split into 3 separate strings (for each type of panel exclusively), each with their own combiner box and charge controller. But I have been unable to utilize more than 2 panels on any given string, as I have simply not been able to complete a "successful" parallel connection…

My design configuration is to have 2 panels wired in series, and then each series-pair combined in parallel to supply the controller.

My series connections I make by wiring the + of one panel with the - of the second panel. Using my multimeter I see a doubling of voltage, as expected.

I then try to make a parallel connection by wiring the + of one series-pair (as above) to the + of the second series-pair, and the - of the first to the - of the second. My understanding is that I should see a summing of the amperages of the two series-pairs. But I do not. Instead my multimeter reads not only the same voltage (as expected) but also the same amperage of only one of the series-pairs.

For example, with 2 40v panels, I have one series pair reading 80V and 10.4A, and another series-pair reading 80V and 10.2A. I wire the + to + and the - to - from one pair to the other, and I still read 80V and 10.4A.

Should I not be getting 80V and 20.6A?

I have tried making this parallel connection directly between pairs using 2AWG wire (which I since learned is a bad idea!), and using a combiner box with independent relays and switches, but the result is the same in either case. And with any of the 3 types of panels. Even with a full 6-string combiner box where I read 6 inputs all at say 80V and 10-10.5A each, I can never get an output of more than 80V and 10.5A.

I just can not figure out what is going on, what I have missed or done wrong, and am desperately in need of help.

I don't know if it is related, but I have been experiencing something I don't understand on the battery side of things too. I have 8 12V 100Ah sealed batteries, all connected in parallel at the moment as I am using a 12V inverter (this will change to a 48v setup to suit or new inverter later). For a while, I had two 100A MPPT charge controllers connected in parallel to this battery bank, and without a fuse (also a very bad idea I now to know). I did not seem to be having any problems with the battery bank though until I installed a 100A fuse between the battery bank and charge controllers - now this fuse keeps getting blown! Does anyone know what could be causing this, and/or whether it could be linked to the wiring problem I am having on the panel side of the charge controllers?

Any help or direction would be so incredibly appreciated.

Feeling lost in the jungle with solar panels,

Ahki

mike95490

Perhaps the charge controller you are using is maxed out and cannot extract anymore from the panels.
 MPPT controllers are rated for output amps
Four 340W panels =1360watts at 13V is 104 amps

If your batteries are not demanding much power, they won't take power from the controller.    Switch a couple heavy loads on, turn off all the other controllers & panels, and just try 1 group, with a hefty load on the inverter

littleharbor2

Most multimeters are rated for 10 amps. Do you have access to a DC rated clamp meter? Some clamp meters are AC and DC for voltage and only AC for current. Be sure you use a DC rated clamp meter and have it set right and zero'd out if needed.

jonr

You can (carefully) short out solar panels if you want to verify that your load isn't limiting current flow.