Effect of temp. on 24 volt wiring?

softdownsoftdown Solar Expert Posts: 3,346 ✭✭✭✭
I have been realizing 10 amps of charging power during sunny summer time conditions. A major disappointment from four 180 watt panels on a 24 volt system.

Today is pleasantly cloudy and temps are about 77 instead of 87. I am getting 16-18 amps of charging power - instead of 10.

Are my 10AWG charge controller charging wires far too small? Or did I somehow have a power loss somewhere?

Can't hardly fathom a 10F temperature difference giving me a 70% increase in amps from the charge controller. Wire run to the charge controller is 25'ish.
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 ✭✭✭✭
    This issue is eating at me. Seems crazy to get a 70% increase in power because of a 10F drop in temperature.

    Aluminum wire is noted for losing significant conductivity in heat. Copper wire should not behave like this. As far as I know.
    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: 30,738 admin
    Copper has around 0.6x the resistance of the same size aluminum wire...

    Temperature wise, the temperature coefficient of Aluminum is either approximatly the same or somewhat worse the copper (depends on the aluminum alloy type?).

    I agree, the 10F difference in panel/wiring temperature should not be an issue. This does get either into a connection issue (loose/dirty/etc.) or a controller issue. Checking the voltage at the array and at the controller (under load, same conditions) would show if the wiring/voltage drop was an issue).

    With the controller, a bad design, a corrupted controller database, or a faulty controller... Or if the controller is getting hot (poor air circulation/sun on controller) could cause reduction of current too.

    Could even have a faulty solar panel (bad internal connection, shorting bypass diode, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • softdownsoftdown Solar Expert Posts: 3,346 ✭✭✭✭
    Measured 40 volts at the panels and at the charge controller - prior to hooking up to charge controller.

    Very cloudy today so the 4.5 amp power feed is satisfactory. Especially compared to 5 amps in sunny conditions.

    Yesterday I wriggled, pushed, and pulled several things - and disconnected the charge controller for awhile. Could be a bad connection. Could be the charge controller - now ~ 5 years of very light use. Could be a panel diode that reacts poorly to solar heat. So where am I? Like BB said.

    I'll keep checking for awhile. May figure something out over time. If not - time to start replacing the easiest and cheapest until the problem is resolved.
    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: 30,738 admin
    Softdown, what is your array configuration (i.e., 2s x 2p or what)?

    If you have parallel connected array, and a DC Current Clamp DMM, measure the current each string and see if they match or not... Generally, the parallel solar panel currents should match pretty closely (within 10% or better). If they differ by 50% or more, one panel/string is bad (connection, panel, etc.).

    If you do not have a Clamp meter, but have a combiner box--Turn off one string at a time and see if the current drops evenly or not (no combiner box, disconnect on string at a time--Careful disconnecting MC4 or similar connectors--Under load the arcing can damage them).

    Another way to test wiring... On a sunny day, connect the array directly to the battery bank and measure the current (again with a Current Clamp meter--make sure to get panel+battery polarity correct... Connecting solar panel "backwards" to battery can instantly ruin the panel/array). Yes, the array voltage will be at ~Vbatt--But you can check the current and see if it is correct/stable or not and bypass the charge controller. Generally, on a sunny mid day array, you should see >~50% of Imp (array/string/panel). While not perfect, it is a good/quick way to do a load test (variable sun orientation, light haze in air, etc. can cause upwards of 50% loss of harvest--Even though it looks bright and sunny to your eyes).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • softdownsoftdown Solar Expert Posts: 3,346 ✭✭✭✭
    edited July 24 #6
    2p for 24 volt - this system
    2s for the 48 volt system - which has been relatively trouble free outside of the initial battery choice. I'm still surprised how good the valley is for solar energy.

    No progress yet on a proper diagnosis. Was getting low amps so I went to get a screwdriver to disconnect then reconnect. Voila - getting 18.5 amps. Intermittent problems are the worse. My dad said that a dozen times - after 40 years of medical maintenance.

    All the panels read the same during my last clamp meter test.
    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
  • mike95490mike95490 Solar Expert Posts: 8,875 ✭✭✭✭✭
    Wires cannot change enough resistance over 50 degrees, to give those sort of results, the  issue lies elsewhere - I'd be looking for a bad connection.  Use a IR thermometer and check each connector, set screw, fuse, breaker, panel J box
    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

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