Charge controller power loss

beth
beth Solar Expert Posts: 32 ✭
in Off Grid Solar & Battery Systems #1
If an outback fm 80 is being used with an array that puts out 40 amps at 60v.

and you are charging a 24v battery, then if the panels were putting out this max, that would be 100 amps at 24v comming out of the controller correct?

so since the max out put of this controller is 80 amps, are you losing the 20 amps in this example

Thanks all
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #2
    Re: Charge controller power loss

    Controller will limit output to 80A max regardless of what your panels are capable of. You will not capture all available power for PV array in that situation. You need to get another controller and offload excess panels to it, or split array in two. Is 60V 40A measured values or what's on the sticker? Because panels rarely perform at STC rating.
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  • beth
    beth Solar Expert Posts: 32 ✭
    #3
    Re: Charge controller power loss

    Yes that is whats on the sticker, the controller says its good up to 2500w for a 24 v system. and my total array is 2350w.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Charge controller power loss

    From a real-world perspective (instead of theoretical):

    60 Volts @ 40 Amps = 2400 Watts. Your array is 2350 Watts, so that's pretty close.
    Now the thing is the array probably won't put out that much except on rare occasions. More likely it will average 80% (or less) than that: 1880 Watts. Divide that by the charging Voltage of a 24 Volt system: 28.2 Volts. Net result: 66 Amps.

    So whereas the controller will "choke off" the output @ 80 Amps (80 Amps * 28.4 Volts = 2272 Watts, btw - they allow for 30 Volts equalization) most of the time you're not going to see that much current available anyway. But you are about at the "saturation point".

    The old MX60's preferred to run at 75% capacity. I'm not sure if the FM's have this same "feature". :roll:
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #5
    Re: Charge controller power loss
    beth wrote: »
    Yes that is whats on the sticker, the controller says its good up to 2500w for a 24 v system. and my total array is 2350w.

    2500 Watts / 80 amps = 31.25 Volts

    Maybe they mean 2500 Watts when equalizing ??

    Where does the 2500 Watt figure appear ??
    On the unit itself ? If so, that may be it.

    boB
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #6
    Re: Charge controller power loss
    beth wrote: »
    Yes that is whats on the sticker, the controller says its good up to 2500w for a 24 v system. and my total array is 2350w.


    Technically FM80 can do 2500W with 24V system. No lie here. But only during battery equalization mode. During normal charging, your battery will be around 25 - 26V and so would be FM80 output. 25V * 80A = 2000W maximum output power from FM-80 at that battery voltage. Input > Output efficiency will be 95%, so maximum usable PV input power = 2000W/.95 = 2105W. You say you have 2350W PV array. Is it factory rating written on the back of solar panel? If so, then in real world your array will output between 1998 - 2233 Watts due to ambient temperature caused efficiency loss of solar cells and less than perfect solar angle and air clarity. Add wiring loss to that, and PV output will be even less. So you have your FM80 maxed out, and on very cold and clear days you may run into FM80 hard limit. This will cause your system to harvest slightly less solar energy than available. A well designed system will not max out charge controller like that.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,891 ✭✭✭✭✭✭
    #7
    Re: Charge controller power loss
    AntronX wrote: »
    Technically FM80 can do 2500W with 24V system. No lie here. But only during battery equalization mode. During normal charging, your battery will be around 25 - 26V and so would be FM80 output. 25V * 80A = 2000W maximum output power from FM-80 at that battery voltage. Input > Output efficiency will be 95%, so maximum usable PV input power = 2000W/.95 = 2105W. You say you have 2350W PV array. Is it factory rating written on the back of solar panel? If so, then in real world your array will output between 1998 - 2233 Watts due to ambient temperature caused efficiency loss of solar cells and less than perfect solar angle and air clarity. Add wiring loss to that, and PV output will be even less. So you have your FM80 maxed out, and on very cold and clear days you may run into FM80 hard limit. This will cause your system to harvest slightly less solar energy than available. A well designed system will not max out charge controller like that.

    Well designed for what Antron? Most all design is balancing parrameters to the customers need. Most panels never put out their nameplate power levels after 6 months for significant hours. The FM -80 will current limit either way. I doubt Beth needs to be concerned here.

    Other than code, a good case could be made for her having more solar for the summer if this parrameter was important to her.
    "we go where power lines don't" Sierra Nevada mountain area
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #8
    Re: Charge controller power loss

    Well designed for ability to handle all power that panels can generate.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Charge controller power loss
    AntronX wrote: »
    Well designed for ability to handle all power that panels can generate.

    I seriously doubt it is worth spending the extra money for a second charge controller to handle those rare occasions when the panels actually peak production and the batteries need all that current.
    It is the batteries which determine how much panel and what controller is needed, and you base that on an averaged expected panel output; not the rare peak production. This isn't grid-tie where you grab every Watt you possibly can because the utility can take it.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #10
    Re: Charge controller power loss
    AntronX wrote: »
    Controller will limit output to 80A max regardless of what your panels are capable of. You will not capture all available power for PV array in that situation. ......


    If my fixed array has been charging my batteries all morning, and the charge rate starts to taper off, come solar noon, I won't be able to force all those amps into the batteries unless I start an EQ cycle at 11:30 am daily. and that's not good !

    It's always a trade off, I think at max power I can just saturate my controller, but generally, it's only running 30-40A , not it's 60A sticker. Should I have gotten the 45A controller ?

    come on, we're never going to capture "all available power" - i'll settle for most.
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #11
    Re: Charge controller power loss

    OK, she does not "need" another controller. One will work just fine. I did not word my first post clearly enough. BUT in certain conditions the system may run into controller's current limit. How often? I don't know, since I do not know enough data about the system, like: geographical location, panel mounting orientation, battery bank type and capacity, wire size from PV to CC, solar panel type.
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  • beth
    beth Solar Expert Posts: 32 ✭
    #12
    Re: Charge controller power loss

    Thanks for the replies, I did want to max out the controller, I am adding an array to my 24V system and wanted to make it as big as one controller can handle. We do have a lot of partly cloudy days so I want to catch as much sun in those conditions.
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