What could cause 24 volt system panels to only deliver 31 volts?

softdownsoftdown Solar Expert Posts: 3,346 ✭✭✭✭
I suspect this was much of the problem with the 24 volt forklift battery system. I don't know how long that system has only yielded approx. 31 volts. As I recall one wants closer to 40 volts to convert to approx. 29 volts via the charge controller.

Identical panels are currently delivering 75 volts to the 48 volt system. They are wired in serial instead  of parallel. That is the difference. I should be realizing about 38 volts, instead of 31 volts, for the 24 volt system.
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries

Comments

  • softdownsoftdown Solar Expert Posts: 3,346 ✭✭✭✭
    Confession - About 600 watts are coursing through 10AWG wires on the 24 volt system. I did not fix that issue yet - for a few reasons.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • softdownsoftdown Solar Expert Posts: 3,346 ✭✭✭✭
    Thinking that replacing the 10AWG main run wires to the charge controller with 4AWG cables should get the job done handily. Am I right?

    This is an area where 48 volt offers a major advantage to 24 volt. Smaller wires can get the job done with lower losses.

    I have a LOT of 4AWG wiring. It is overkill size wise - but kind of free if one has an abundance.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • BB.BB. Super Moderators, Administrators Posts: 30,740 admin
    What type of solar charge controller are you using?

    A PWM type controller in bulk charge mode will pull the Array Voltage down to near Battery Bus Voltage plus a volt or two (absorb and float will have higher average Vpanel voltage as the PWM cycles between 100% on and near 0% when fully charged in full sun).

    A MPPT controller--Should be at Vmp-array (less a few volts for "hot panels" in full sun). And as the battery goes through bulk to absorb to float, the average Voltage-array will be higher.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • softdownsoftdown Solar Expert Posts: 3,346 ✭✭✭✭
    MPPT controller - and the source of my confusion regarding the low voltage feed. It is not a "long" run from the panels to the charge controller either - maybe 20'ish. Reading the panel voltage at the point they join the charge controller - 32 volts once again. Should be closer to 40. I am very surprised the under size wires lost that much voltage but fail to see another source of this large issue.

    Found a roll of black 6AWG that will look more appropriate than the neon green 4AWG.

    This "system" was, more or less, a toy until I started running three freezers. The commercial freezer has proven to be an energy hog and eventually had to be powered by the much larger 48 volt system.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • softdownsoftdown Solar Expert Posts: 3,346 ✭✭✭✭
    I sit stymied by what should not be happening. Power measures 40 volts when disconnected from MPPT controller. When hooked back up it read 38 volts for a second - then dropped to 33 volts. Thinking my Renogy MPPT controller 40 amp controller is somehow working as a PWM controller.

    Four 180 panels are only delivering 10 amps at 31-33 volts. I believe that number should be 20 amps, or more, at 31-33 volts.

    Already did some of the required work to install a fused combiner box (nice touch) and replace the 10AWG with 6AWG. But:
    1) Fair amount of work remains to be done. Things can always go sideways with unforeseen reasons. "Worst enemy of good is better?"
    2) Not at all convinced that  gains will be significant at all. 10AWG is large enough to comfortably handle 10 amps at 32 volts as I recall.

    I can live with the MPPT controller functioning as a PWM controller. What good choice do I have?

    I am not satisfied with 10 amps at 31 volts from four 180 watt panels. I have a mind to disconnect two panels and see if I still get 10 amps. Seems a decent idea at this point.

    Hardest thing of all? Wait for an expert opinion? Could be hours or days or never. Or press forward and see what transpires. The wires have to be fed through 12" of very tight spaces - something could go wrong.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • softdownsoftdown Solar Expert Posts: 3,346 ✭✭✭✭
    Just got more confusing. Semi cloudy day is keeping the panels and wiring cooler. But I did not expect CC voltage to climb from 31 to 35 volts - battery is 100% charged now - that likely helps.

    The real confusion is that amps climbed from 10 to the 16-18 amp range.

    It is 77 instead of 87 due to the clouds. But I would not have expected that impact on volts and, especially, on amps.

    Electricity behaves weirdly for me.

    I hope somebody may know what is going on.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • Raj174Raj174 Solar Expert Posts: 762 ✭✭✭✭
    edited July 25 #8
    Maybe wiring the 4 panels in series would give better results if it's within VOC limits. It should also work better for equalizing LA batteries.
    3600W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 54.4V 195AH LiFePO4, Kohler Pro 5.2E.
  • softdownsoftdown Solar Expert Posts: 3,346 ✭✭✭✭
    I cleaned the exposed copper wire going into the charge controller connection with gasoline. Then received 20.9 amps of charging power - exactly what it should be. Is it possible that skin oil prevented a good connection prior to solvent cleaning? I've never heard of that but stranger things have happened. The connection was very tight and the wires are clean and shiny copper - new looking with no corrosion. Kept indoors. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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