Amps not adding-up with parallel connection


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,



  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    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

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • littleharbor2littleharbor2 Solar Expert Posts: 1,868 ✭✭✭✭✭
    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.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

  • jonrjonr Solar Expert Posts: 1,386 ✭✭✭✭
    You can (carefully) short out solar panels if you want to verify that your load isn't limiting current flow.

    I am available for custom hardware/firmware development

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