Too many panels on one MPPT - what happens?





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  1. #1
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    Default Too many panels on one MPPT - what happens?

    Still trying to figure out how it fits together.

    Usecase:
    D250S 25A MPPT controller, like the D250S.
    Several solar panels e.g. Flexopower Baja series.

    How do you determine the maximum number of panels that can be used for the controller in full sun?
    What happens if you add extra panels for low-sun times, and you leave them in at full sun? Do you damage your setup? Or just waste the extra power coming in?
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    Default Re: Too many panels on one MPPT - what happens?

    For my own interest did some research.

    From the CTEK website and manual...

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    &

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    Then from Flexopower website for the Baja panels.

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    So panel's max is running @ 19.8V which is close enough to the CTEK max.

    I would go to 3 panels in parallel.

    I am sure the CTEK would have overload protection (would be surprised if it doesn't) Can't find any direct or definitive answer on this. The Victron MPPT has just that and has a flashing sequence that tells you that.

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    Default Re: Too many panels on one MPPT - what happens?

    Thanks - also found similar info, with lack in the details I had hoped to see.
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    Default Re: Too many panels on one MPPT - what happens?

    Having blown a fuse in my Ctek I would not rely too much on overload protection (it was not during solar). My gut feel is that hi-tech Ctek is fairly sensitive and not robust.

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    Default Re: Too many panels on one MPPT - what happens?

    I use this to monitor incoming solar power but it is not auto.  I would have to put a towel over part of the panel. R360.00 odd from 4x4 direct. 
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    Default Re: Too many panels on one MPPT - what happens?

    My 2c would be based on what I have found.

    Some solar controllers would cut off and stay off even 0.5A before the max current of voltage. This could cause you to think it is charging and not good when unattended.

    The voltage level should NEVER be exceeded as immediate damage might occur. Always use the open circuit voltage.

    Victron MPPT are super sensitive for bat voltage dip if you use the load output. I could not detect it with a multimeter even taking a video yet on a scope one could see the dip.

    Some controllers would just limit the current to the max indicated but keep on charging.

    I have no experience of the D250S.

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    Default Re: Too many panels on one MPPT - what happens?

    Is this not as simple as:

    160 watts generated from panels equals 13.4A. (according to google)If the controller is a 20 amp controller, there should be no problem caused to controller or anything charging from controller? On occasions I get a reading of 19.4V from panels to controller. This is 8 amp? (Again, google) Please excuse if this is all wrong, but most of us use google in determining these calcs.

    If someone who has this experience can explain in terms I can understand, or is it really as simple as above?

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    Default Re: Too many panels on one MPPT - what happens?

    As long as your batteries are taking charge, your voltages will be in control. The use pulls down the PV.

    The problem starts when the batteries are full, and the power has no-where to go.

    This will cause the PV to rise to open circuit voltage, meaning your charge controller must be able to handle THAT voltage.

    Also, in extreme such cases, the charge controller have an inability to absorb/limit the wattage coming in, sending out more voltage than what the batteries will absorb.

    My charge controller detects this and cuts out for a couple of seconds and then starts up again.
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    Default Re: Too many panels on one MPPT - what happens?

    Quote Originally Posted by Sakkie View Post

    This will cause the PV to rise to open circuit voltage, meaning your charge controller must be able to handle THAT voltage.
    No charge controller should ever have a max volts rating lower than the open circuit volts of panels. Even a Victron would become defective in seconds.
    Last edited by ekkekan; 2019/04/20 at 10:56 AM.

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    Default Re: Too many panels on one MPPT - what happens?

    Quote Originally Posted by ekkekan View Post
    No charge controller should ever have a max volts rating lower than the open circuit volts. Even a Victron would become defective in seconds.
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    We have established that the solar panel open circuit voltage needs to be lower than the max controller voltage, 23V in this case.

    Fluffy mentioned that irrespective of what solar power is available, the controller will only supply it's maximum rating. The cheaper ones might blow though if they do not have current limiting.

    A quick look at the specs above: The max output current is 20A. They recommend 50-300W panels. If your batteries are discharged to 12.0V, 300W will give you 25A at 100% efficiency. So it seems that they, like Fluffy, are not concerned about having too much available power at hand, current wise.

    Therefore, if space and funds are available, add more panels than 300W to ensure higher charging rates mornings and afternoons. Try and sell your excess power during full sun times.

    But 300W is more than sufficient for 2 x 40l fridges, from my experience, in sunny conditions. I have 600W, and that gives me enough, even on fully overcast days, and in partial shade


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  12. #11
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    Default Re: Too many panels on one MPPT - what happens?

    The problem is not the max current as the controller will just switch off but the too high voltage will cause damage

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