Solar output exceeding charge controller rating?

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OneSock
OneSock Registered Users Posts: 3 ✭
in Off Grid Solar & Battery Systems #1
I have a Xantrex PWM charge controller rated at 30 amps. It's hooked up to an array of 6 solar panels that can put out about 32 amps in full sun if all 6 panels are switched on (each has an independent on/off switch). I've confirmed that if the solar output exceeds 30 amps, the controller will limit it to precisely 30.

I don't really need the extra 2 amps. My only concern is whether exceeding the controller's rating by this small amount might cause damage over the long term. If so, I can just leave one panel switched off except on overcast days.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,044 ✭✭✭✭✭
    edited October 2022 #2
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    Is it a, C-30? I've seen their other controllers, C-40 and C-60 put out more than rated current. Pushing it like that all the time will be hard on it but they  are really tough, well built controllers. The C-30 doesn't have cooling fins so may have different characteristics. 

    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.

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  • OneSock
    OneSock Registered Users Posts: 3 ✭
    #3
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    It doesn't give the batteries more than 30 amps, and I suppose the excess gets dissipated as heat.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #4
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    Looking at the specifications, the maximum solar array current is Isc=30 amps (short circuit current).

    PWM type controllers are a simple "on/off switch" (I would assume some sort of transistor(s)). The controller has no ability to regulate excessive current flow---I.e., controller "on", the current is whatever the solar array outputs (and "off" is off--No current flow). If there is an array with Ioc-array > 30 amps, the controller runs the risk of burning out the switching transistors.

    A MPPT type controller has a large inductor in the power circuit. So the current rises from zero amps to maximum safe current (sort of "charging" the inductor), then the switch turns off and the current starts to drop again ("discharging" inductor).

    By changing the on/off "duty cycle" to the switching transistor, the controller can safely (and efficiently) limit its output current to max rated.

    Both types of controllers typically have a heat sink and thermal sensor so they can reduce current/power flow to keep from overheating and damaging the components.

    A quick buck mode converter Wiki page (most MPPT controllers are "buck mode" type):

    https://en.wikipedia.org/wiki/Buck_converter

    I could be wrong (I don't work for Xantrex, have never seen this new model)--Things do change.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,044 ✭✭✭✭✭
    #5
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    OneSock said:

    It doesn't give the batteries more than 30 amps, and I suppose the excess gets dissipated as heat.
    Not the controller series I was thinking..

    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.

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  • NANOcontrol
    NANOcontrol Registered Users Posts: 261 ✭✭✭
    #6
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    PWM controllers use the Isc of the panel to limit the current to a safe level. The chances you will see the panels full rated Isc in practice are small usually. 2A over the max calculated with a good name controller is probably safe.
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  • checkthisout
    checkthisout Registered Users Posts: 31 ✭✭
    #7
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    OneSock said:
    I have a Xantrex PWM charge controller rated at 30 amps. It's hooked up to an array of 6 solar panels that can put out about 32 amps in full sun if all 6 panels are switched on (each has an independent on/off switch). I've confirmed that if the solar output exceeds 30 amps, the controller will limit it to precisely 30.

    I don't really need the extra 2 amps. My only concern is whether exceeding the controller's rating by this small amount might cause damage over the long term. If so, I can just leave one panel switched off except on overcast days.

    What does the manual say about overpanelling?

    Most manufacturers say 150% of wattage rating.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #8
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    Over paneling usually only applies to MPPT type charge controllers.
    PWM controller should never be over paneled as they do but have the ability to limit output current.
    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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