Amp from PV not able to be kept - cycling to zero regularly

schirmatschirmat Registered Users Posts: 4
I'm new to solar electricity and I bought a small PV 50W
IpMax 2.78a
VpMax 18v
ISC 3.4a
Voc 21.6v

with a MPPT MPPT24Z-20

Unforutnately even at full sun the controller will go up to 1.7a and quickly drop to zero then will grow back to 1.7 and drop again to zero, after a while it stabilizes at 0.2-0.4a

Any idea if the controller or solar pannel are defective? Anything I can do to check it out?

Thanks for your help!
I made a video here of the setup and behavior


  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    I cannot tell from the video what is happening... It looks like your battery voltage is at 12.9 VDC, which could be fully charged (resting voltage), or be deeply discharged and that is the voltage when being charged.

    What is the battery type (flooded cell, AGM, etc.) and battery Amp*Hour capacity (I assume it is a "12 VDC" battery)?

    Anyway, the first step is to disconnect the solar panel, and then the battery bank (in that order).

    Make sure that the wiring from the charge controller to the battery is short and heavy (you really do not want more than ~0.05 to 0.10 volts drop from controller to battery bank for optimum charging).

    Next, connect the battery bank to the charge controller first (this is because most charge controllers get their power for the internal computer from the battery bank, and decide on 12 or 24 volt system based on battery voltage). If you do not connect the battery voltage first, the charge controller can end up in a "confused" state, or damaged (if you had higher voltage array).

    Second, connect the solar panel to the input of the charge controller (you can cover/lay panel face down while connecting the wiring if a bit of sparking bothers you).

    Do you have a separate volt meter handy? If so, measure the Vpanel input for a couple of these "cycles". And measure the Vbatt voltage for another couple of cycles...

    And let us know the results.

    Also, you purchased an MPPT solar charge controller (assuming it is MPPT--There are a lot of fake units out there too). A PWM (less expensive) would work in your present setup too (small wattage, low voltage single solar panel).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Wheelman55Wheelman55 Registered Users Posts: 176 ✭✭✭
    OP...certainly do what BB recommends.  From my experience...the amp output goes down to 0.0 when the battery is at 100% SOC.  After you do what BB lined out, run your battery down to say 80% SOC, and then see what your MPPT says.  During full sun (noonish on a clear day) the MPPT should show nearly full amps.  Once the battery is back to 100% the amps will go back to zero.  

    Building Off-Grid in Terlingua, TX
    14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048, Mini PDP, MPPT 80-600, SCP. 3 - Discover AES 42-48-6650 48 volt 130ah LiFePO4 batteries
  • schirmatschirmat Registered Users Posts: 4
    Thank you so much!

    • Battery is 55ah Sealed lead acid, which voltage dropped now at 11v apparently according to my voltmeter (it was a bit more than 12 yesterday and nothing has been plugged to it apart from the controler / solar pannels) don't know if the controller is draining more than charging..
    • Always kept this order as per manual ( plug: 1st battery to controller - 2nd solar pannels to controller, un plug in reverse order)
    • cable is 12awg brand new 7ft long
    • VPannel oscillate between 16-18v
    • VBattery when plugged oscilate between 11-12v but the controller says 12.9-13
    my voltmeter is analog maybe not super precise
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    It sounds like a charge controller problem... The battery (no loads) should be climbing in voltage over a few hours (at least) to ~14.4 volts, then held there for a few hours (2 hours for lightly discharged, 6+ for deeply cycled).

    If you cannot get your charge controller to work correctly (is there a factory reset?), then you need to get your battery on a charger pretty quickly, or it will sulfate and eventually die.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • schirmatschirmat Registered Users Posts: 4
    Yeah that's my thought - would the solar panel be too small hence the controller not able to keep a stable amp even while voltage seems good? Does that make sense?

    I find it odd that the amp rises then crashes, rises - crashes, rises - crashes until it looks like the controller says ok im keeping the charge at 0.2 

    yes i will stop my tests until i can fully charge this battery 

    Thanks again!
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    It depends on how the MPPT algorithm works on that controller... But they could "scan" the Vmp of the array (from min-max or max-min current, and measure the voltage)... Then run the math for Pmp=Vmp*Imp...

    That it is scanning the array (it seems), and not coming up with an "answer"--Perhaps there are some advanced settings you can try (set Vmp-array to 16 volts, or turn off MPPT and run PWM mode, etc.)?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • schirmatschirmat Registered Users Posts: 4
    It doesnt look like i have too many options there. do you have a reliable controller you'd recommend for a small system? might be 100w max someday. I thought that adding a few more $ to get an mppt would bring me better efficiency from a small pannel but maybe a better pwm is a better option than a cheap mppt (not considering the fake ones ...!)
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    I am not in the solar business... So hopefully, some others here can make some suggestions for a smaller/reliable/probably PWM charge controller.

    I believe you are in Montreal, so folks that can give you Canadian solar suppliers may be better for you (unless you make border crossings often).

    Our host, Northern Arizona Wind & Sun, certainly stands behind their products... So a quick look at there products would be a good start. (I do not work for NAWS--Just a volunteer here like pretty much everyone else).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    What it could be is the controller uses the incoming voltage to set the charging current but as soon as the charging begins the input voltage collapses below the required value, it resets then the cycle repeats itself. Having a higher input voltage would probably solve the problem, 2 panels in series would supply more headroom, I think it's operating on the edge of its limitations.

    PWM would definitely work as the voltage limitations are not an issue and may be more efficient on such a small system, Morningstar have excellent products and support, personal experience, Midnight, Victron, Outback  and other reputable manufacturers may also be good choices.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • joshbeenejoshbeene Registered Users Posts: 1
    Did you ever figure out what’s going on???  I’m having the same issue so I went onto google and found this thread. 
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    JoshBeene, welcome to the forum.

    I would ask that you create a new discussion and describe your system (array, battery bank, charge controller, loads, etc.)... Then we can discuss your system specifically.

    Checking the voltage on the battery bus terminals, the charge controller Vbatt terminals, and the Vpanel input terminals the controller is where I would start.

    There are a lot of variables (array voltage/current, sun, charge controller PWM/MPPT type, battery state of charge, any active loads, etc.)...

    And because the charge controller could be in different "modes" (Bulk, maximum charge current to battery. Absorb, holding battery at ~14.x volts and still charging. Lastly Float: holding battery at 13.7 volts or so to keep charged and supply current to any loads while the sun is still up)... 

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLARCinFLA Solar Expert Posts: 1,460 ✭✭✭✭
    edited May 13 #13
    There has been a lot of reports of similar 'mppt' controllers being fake.  Internal examination shows they are PWM controllers.
    (2) Inside MPPT battery charger CHINA - YouTube

    An actual MPPT controller may drop into PWM mode if the panel voltage is too close to battery voltage.  MPPT controllers need a panel Vmp of 3 to 5 vdc above battery voltage to allow for DC to DC buck converter operation and do their MPPT search.

    Your panel picture looks like 16 PV cells, but it is likely 32 half cells in series.  32 cell panels will not work well in MPPT mode with the charge voltage required for a 12v battery.  You should have, at minimum, a 36 series cell panel to run an MPPT controller on a 12v battery.
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