Midnite showing 30-40V input voltage with PV breakers off?? (strings are 140-170V)

treed678
treed678 Solar Expert Posts: 30 ✭
in Advanced Solar Electric Technical Forum #1
Just commissioned my system today. Everything appeared to be working well, but I thought this situation was very odd and don't remember seeing anything about it in the manual. I've seen the two strings range from 120-180V so far.

Just turned on the controller a few minutes ago (it's pitch dark) and still shows 33V. What in the world is going on?? My bank is 52V. All readings look normal otherwise. No beeps, etc.

One other odd thing while the controller was pumping out 33+ amps (and fairly warm) was the very top line or two of text cut off and appeared at the bottom of the screen. It did not return when I just turned the controller back on.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #2
    Re: Midnite showing 30-40V input voltage with PV breakers off?? (strings are 140-170V)

    Hi treed ..

    First, it is normal for the Classic and many other MPPT CCs to show about 2/3rds of battery voltage on the input when the PVs are in darkness, or the input breaker is opened.

    I hope that you have at least a Classic 200, or 250, given the range of input voltages you note.

    Regarding the cut-off lines, cannot guess. Perhaps you should shut off the PV input breaker, and also shut off the battery breaker for one minute and then turn on the battery breaker, and then the PV breaker.

    What Classic model are you using? Is the cut-off display on the MNGP, if so, is the MNGP attached to the Classic when you see cutting off?

    Thanks, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • treed678
    treed678 Solar Expert Posts: 30 ✭
    #3
    Re: Midnite showing 30-40V input voltage with PV breakers off?? (strings are 140-170V)

    It's a 250 (not lite). Whew... glad to hear that about the battery voltage relationship being the reason. Why does this occur?

    The cut off lines on the MNGP cleared up after I cycled the power. I'll monitor this to see if it happens again. I thought it might be pinching or interference with the display cable.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #4
    Re: Midnite showing 30-40V input voltage with PV breakers off?? (strings are 140-170V)

    Mines show 0.2V and 0.3V, and it is very dark.

    I guess Classic may have a capacitor over there which is not completely discharged.

    I don't think it's something to worry about.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #5
    Re: Midnite showing 30-40V input voltage with PV breakers off?? (strings are 140-170V)
    treed678 wrote: »
    It's a 250 (not lite). Whew... glad to hear that about the battery voltage relationship being the reason. Why does this occur?

    The cut off lines on the MNGP cleared up after I cycled the power. I'll monitor this to see if it happens again. I thought it might be pinching or interference with the display cable.

    Hi treed ..,

    Glad that the display issue has resolved. Thanks for the info on the Classic 250, nice box!

    There is a fairly large capacitor set on the PV input to the Classic, as I recall. Believe that there is a fairly high-value resistor across the contacts of the Input Relay, that "precharges" this capacitor. This may reduce the inrush current into those caps when the relay closes upon wake-up Probably a bit too much guessing on my part ... boB from MidNite may chime in.

    Have fun with the new system, and congratulations on commissioning the new system! Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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