Solar Charge Controllers- how they work

lazza
lazza Solar Expert Posts: 336 ✭✭✭
in Off Grid Solar & Battery Systems #1
HI

I was testing two charge controllers, one a victron blue solar 20A, the other a cheapo import from China.

What interested me is they seem to reduce current to the batteries as battery voltage increases, in 2 different ways:

1. The Victron has the panels at the same voltage as the batteries and reduces the charge in pulses.. dropping every now and again... i guess this is pwm.

2. The China import seems to slowly open the circuit of the panels so that when the battery voltage approaches the maximum charge voltage, the 12V panel is approaching 20V.. so it's almost in open circuit and very little current is flowing.

Can anyone enlighten me as to why they work in a different way, and which of the two methods is best?

Cheers
Larry
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Comments

  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #2
    Re: Solar Charge Controllers- how they work

    How weird... this is the 1st time ever I have had no reply to a thread... have I offended someone? :D
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  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    #3
    Re: Solar Charge Controllers- how they work

    I don't know much about the inner workings of the charge controllers you mention, however, I would be cautious about el cheapo units from China. I once had a small PWM charge controller from China that went up in smoke, literally.;):blush: The controller was connected properly and should have been able to handle the power from the panels.

    Attachment not found.

    Saving a few $ isn't worth the risk of having your house go up in flames IMO. Quality MPPT controllers are generally worth the money spent on all but the smallest systems.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Solar Charge Controllers- how they work
    lazza wrote: »
    How weird... this is the 1st time ever I have had no reply to a thread... have I offended someone? :D

    No, I'm just mired in a word swamp. :p

    PWM controller like the Victron has the ability to switch the current on/off vary rapidly to accurately maintain Voltage on the output side. This is the way the better charge controllers work (including MPPT types once fixed Voltage stages are reached).

    The Chinese unit you describe sounds like it is functioning either as a shunt controller, "bleeding off" excess current to ground (not good; limits current handling capacity as the excess power turns to heat inside the controller) or internally raising in-line resistance to reduce current (again not good as the excess power has to be dissipated inside the controller). This will not be as accurate for regulating output Voltage either.

    There is also a relay-type controller which has "on" and "off" Voltage set points which can be quite far apart (like the old mechanical regulators on vehicles).
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #5
    Re: Solar Charge Controllers- how they work
    northerner wrote: »
    I don't know much about the inner workings of the charge controllers you mention, however, I would be cautious about el cheapo units from China. I once had a small PWM charge controller from China that went up in smoke, literally.;):blush: The controller was connected properly and should have been able to handle the power from the panels.

    You probably can repair it by re-soldering back these 2 mosfets, which you can buy for $7.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: Solar Charge Controllers- how they work

    I am guessing that the China controller is not "slowly" reducing current flow--Because as Marc said, that would take the controller out of the digital "on/off" operating mode into the analog mode (transistor with "variable resistance" modifying current flow).

    Operating a transistor in the linear mode would generate lots of heat (voltage drop * current = power)....

    My guess is that the charge controller is operating as a PWM, but in the higher frequency range (100's to 1,000's of Hz / cycles per second). And you cannot see that with a standard meter.

    If the battery voltage is being held to the proper charging voltage (i.e., ~14.5 to 14.8 volts) while the current is slowly dropping (and the "average" voltage at the array is slowly rising)--Then all should be fine as the battery is in the Absorb charging range and wants to slowly see the charging current drop as it finishes that last 10-15% or so charging to full.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    #7
    Re: Solar Charge Controllers- how they work
    NorthGuy wrote: »
    You probably can repair it by re-soldering back these 2 mosfets, which you can buy for $7.

    I actually returned the failed controller to the dealer and they sent me a new one. It was a new controller that failed right out of the box! I have since sold the replacement controller.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
    Re: Solar Charge Controllers- how they work
    northerner wrote: »
    I actually returned the failed controller to the dealer and they sent me a new one. It was a new controller that failed right out of the box! I have since sold the replacement controller.

    you sold a failed controller? i suspect the mosfets needed a tad of heatsinking if the voltage max wasn't exceeded.

    lazza,
    it is not our purpose to compare one cc to another especially when it concerns cheap controllers. now many of us have noted some aspects of some controllers in many threads, but don't expect us to know every cc out there as we don't. in general the old adage of buyer beware holds true for if you buy cheap, you get cheap. pretty simple concept.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #9
    Re: Solar Charge Controllers- how they work
    lazza wrote: »
    2. The China import seems to slowly open the circuit of the panels so that when the battery voltage approaches the maximum charge voltage, the 12V panel is approaching 20V.. so it's almost in open circuit and very little current is flowing.

    I'm speculating here, but I think the midnite classic does the same thing. It doesn't seem to use PWM, instead it hunts up the MPPT curve away from Vmp till it finds a point that produces the right amount of current needed by the batts. I just checked it now and it's in absorb so needs to reduce the current; the Vmp of my array is 89V, yet the classic is reporting input voltage as 101V. Perhaps since it has MPPT functionality, the engineers decided to capitalise on that and not bother with PWM too, since you could just use the MPPT to find the right amount of current somewhere on the curve.

    As I said, speculation :)
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #10
    Re: Solar Charge Controllers- how they work

    lazza, I think, sold the replacement.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    #11
    Re: Solar Charge Controllers- how they work
    niel wrote: »
    you sold a failed controller? i suspect the mosfets needed a tad of heatsinking if the voltage max wasn't exceeded.

    I returned the failed controller to the dealer I bought if from and they sent me a new one. I didn't even bother testing the replacement unit, and just sold it still in the box.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #12
    Re: Solar Charge Controllers- how they work

    ok now i understand.
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #13
    Re: Solar Charge Controllers- how they work

    Great, thanks for all your replies, that burnt one looks suspiciously like the cheapo one I have. Err :blush: will take it apart and check!
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #14
    Re: Solar Charge Controllers- how they work
    northerner wrote: »
    ...I once had a small PWM charge controller from China that went up in smoke, literally.;):blush: The controller was connected properly and should have been able to handle the power from the panels.
    Saving a few $ isn't worth the risk of having your house go up in flames IMO. Quality MPPT controllers are generally worth the money spent on all but the smallest systems.

    Is that an actual hole I see in the power device (FET?) on the far left?
    SMA SB 3000, old BP panels.
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #15
    Re: Solar Charge Controllers- how they work

    Here's mine, it doesnt look the same:

    Attachment not found.
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  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    #16
    Re: Solar Charge Controllers- how they work
    inetdog wrote: »
    Is that an actual hole I see in the power device (FET?) on the far left?

    Not a hole. Looks like soot from the burnt FET next to it.
    Here's mine, it doesnt look the same:

    It is a different one, yes.
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