Schneider MPPT60 input and output power not matching

fasterskifasterski Registered Users Posts: 10 ✭✭

I have noticed some issues with my solar charger. I have noticed a problem when I added a 3rd 250 watt panel in series. It seems the input and output numbers where pretty close before that.

So now I have the system showing bulk charge the input power is 160 W with 98.9V and 1.7 AMPs for a total of 171 Watts. On the output side it shows 23.7 V and 1.8 Amps. The SCP does not show Wattage for output less than 100. Those readings are with no AC power coming in (breaker off) Load was about 400 W. Battery SOC 80 %.

Can anyone comment on this. System is using 24 volts (200 Ahrs) All equipment is Schneider (SCP, Batt Monitor, SW4024)

Comments

  • BB.BB. Super Moderators Posts: 26,769 admin
    Sounds like there may be a problem with one of the panels or array wiring issue? Assuming Vmp~36 volts per panel, the 99 volts Vmp-array sounds OK.

    The Schneider charge controller is different than many others. The Vpanel ground on the input is not the same as the Vbatt ground on the output. For many charge controllers, you can tie the two grounds together or even just make all connections to one of the grounds.

    With the MPPT60 from Schneider (as I recall), you must attach Vpanel ground to your array, and the Vbatt ground to to the output of the charge controller. If you "bypass" or "short" the two grounds, it bypasses an internal current shunt that the controller needs for proper operation.

    Do you have a DC Current Clamp meter you can measure the input and output currents with? And do a short circuit on your array so you can measure Isc (short circuit current) of the array in full sun?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 3,258 ✭✭✭✭
    Hey Bill! Thanks for the rain last night! :)
     A comment from me is a 60 amp controller running 1.8 amps is in the noise of calibration. Same with no output below 100 watts.
    When you measure again the input and output should be really close once you get the charge up, 23.7v is not good. There will be some conversion loss also added in this application. When you "grow" the array these errors will fade. 
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail offgridsolar@sti.net

  • HorseflyHorsefly Registered Users Posts: 251 ✭✭✭
    I was just about to post much of what @Dave Angelini said. I don't think you can expect much accuracy on the SCP with readings that low. You should be able to scroll through the input and output readings on the MPPT60 itself, but it won't be much different than on the SCP. I think I have seen some difference on the lower end of input/output power.

    Bill is right that the Schneider MPPT does require a different negative PV lead from the negative battery.  I caught that just before I finished my wiring plans.

    I can't see how adding a third panel in series would make the input and output numbers to be further apart, except that there is a sweet spot for the MPPT where it has maximum efficiency. I don't know what that is for the MPPT60 from Schneider, but on mine it seems to always be north of 90% efficiency.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 4 x Vmax XTR12-155 12V, 155AH batteries in a 2x2 24V 310AH bank.
  • fasterskifasterski Registered Users Posts: 10 ✭✭
    Hey guys,
    Thanks for your feedback and sharing your knowledge and experience on this. There is definitely something weird happening since a an additional panel has been added. I could see a peak of over 670 Watts coming out of the total of 750 Watts for the three panels. So the panel is working. I check my grounds and there are not common as far as MPPT is concerned. I have to double check but it seems that the there is something happening with shading or amount of sun hitting the panels and how MPPT is calculating the juice coming out of them. Not sure if this makes sense but the additional panel has thrown off the charge controller.
    Perhaps I can reset the charge controller and see how it goes tomorrow.

    Also is it possible to have the panel malfunction on the low light condition? Shading etc.?

  • BB.BB. Super Moderators Posts: 26,769 admin
    Any shading is bad for solar electric psnels. Just a few cells partially shaded can kill the string output by 1/3rd to 1/2.

    If your new panel  is partially shaded, it can kill the string output current and/or voltage.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • fasterskifasterski Registered Users Posts: 10 ✭✭


    Hi folks , thanks for your inputs again.

    Here is an upload of the screen shot showing the anomaly. Notice the output current is mere 50W, yet 188 W coming in.
  • fasterskifasterski Registered Users Posts: 10 ✭✭


    Here is the array. Like I said temp setup. :) You can see a lot of shading. So question is . Is the charge controller correct showing 200 W of power coming in, and the output is incorrect. Perhaps it is the other way around. Will see what happens when they are in full sun light .
  • fasterskifasterski Registered Users Posts: 10 ✭✭

    Here is another update once the panels are out of shade. It seems that there is about 120 to 150 Watts loss between in and out on the charge controller. Is this to be expected? Seems adding an extra panel is not realizing full potential. Has anyone seen anything like this?
  • Dave AngeliniDave Angelini Solar Expert Posts: 3,258 ✭✭✭✭
    Good Idea! ;)
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail offgridsolar@sti.net

  • EstragonEstragon Registered Users Posts: 1,435 ✭✭✭✭
    FWIW, I have 4500w STC array going into 2xMnClassic150s. Checking one of the CCs, input (in bulk with sun not hitting well yet) is 4.4a@84.3v, output is 6.5a@53.7a, so in=371w, out=349w, loss is 22w or ~6%.

    12v array is in float with little overnight load. In 0.8a@66v=53w, out=3.3a@13.4v=44w, loss is 9w or ~17%

    Your Vin vs Vout is fairly high, which would affect efficiency some, but your losses seem high to me.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Super Moderators Posts: 26,769 admin
    You are lucky to get much of any electrical power from a 1/2 shaded panel in the string... When solar cells "go dark"--They actually stop current flow (cells go "high resistance") and impede current flow from the rest of the panels. Shade=Very poor energy production for solar electric panels.

    Adding a third shaded panel will (generally) reduce the output of the other 2x series connected panels.

    Put the panels in full sun (no shading not even from grass on the bottom of the panels), and see what you get.

    Note, charge controllers regulate voltage (and current for MPPT controllers) to the battery bank. If the battery bank is >~80% full and no other DC loads (AC inverter, etc.), the battery bank may not accept all available current/power from the charge controller...(i.e., you may have 20 amps available from solar array+contorller, but battery bank is near full and only accepting 10 amps durign Absorb or float stage.

    So do not panic if you get less than expected power from the solar array until you understand what the batteries and charge controller think should be flowing. In general:
    • Bulk Mode (less than ~80% state of charge): Charge controller is outputting 100% available power into battery bank
    • Absorb Mode (roughly 80-90% state of charge): Charge controller is holding 14.75 volts (or whatever) to battery bank, and batteries are accepting/limiting charging current (plus any DC loads)
    • Float Mode (~90-100% state of charge): Charge controller is holding ~13.6 volts and the batteries are taking very little current (1% to 0.1% of their capacity) plus any DC loads
    Hope that makes sense.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 3,258 ✭✭✭✭
    Show the main "system performance" combox screen which will show the AC loads from the inverter. The CC screen is not the best for the overall input/output. I would say you are pretty close at this low of a power with a conversion loss of 100vdc down to 24V nominal. The loss goes up at low power BTW.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail offgridsolar@sti.net

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