Outback FM-80 trouble

LOTW
LOTW Solar Expert Posts: 25 ✭
in Off Grid Solar & Battery Systems #1
I have an fm60, fm80, fndc, and vfx3648. At rest the battery voltage of all devices is calibrated to the fndc battery voltage. Under load, same story. When the fm80 starts charging, it's indicated battery voltage rises faster than the actual battery voltage, to the point where when absorb is reached, it's off by about a full volt. Fm60 and vfx still read correct vs. the Flexnet.

Anyone encounter anything like this? Has been this way since I bought and installed fm80 a month ago.

Thanks for any help.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Outback FM-80 trouble

    This sounds as though the wire size between the FM80 and the batteries is too small, allowing too much V-drop under load. The result is the Voltage at and from the controller will be higher than what it is by the time it reaches the battery (which is a load under these circumstances). The other devices reading Voltage at the battery will show the actual Voltage as they are not having the current-affected Voltage drop.
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  • LOTW
    LOTW Solar Expert Posts: 25 ✭
    #3
    Re: Outback FM-80 trouble
    Cariboocoot wrote: »
    This sounds as though the wire size between the FM80 and the batteries is too small, allowing too much V-drop under load. The result is the Voltage at and from the controller will be higher than what it is by the time it reaches the battery (which is a load under these circumstances). The other devices reading Voltage at the battery will show the actual Voltage as they are not having the current-affected Voltage drop.

    Some voltage drop of some sort would make sense, but I don't believe it's the cabling. They are 2awg, and only about 4feet long to the battery bus including the breaker. Maybe a defective breaker...? Also, I had my FM-60 in that exact position before, and it did work fine. Same array, same cabling, just moved it over on the bracket and hooked the old cables up to the FM-80.
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #4
    Re: Outback FM-80 trouble

    Have you actually measure the batt voltage and compared that to the fm80 terminal voltage. Whip out a meter and take the cover off the fm80.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • LOTW
    LOTW Solar Expert Posts: 25 ✭
    #5
    Re: Outback FM-80 trouble
    zoneblue wrote: »
    Have you actually measure the batt voltage and compared that to the fm80 terminal voltage. Whip out a meter and take the cover off the fm80.

    Not sure what that will tell me that I don't already know. The Flexnet DC cannot be calibrated voltage-wise, so it is effectively a full time volt-meter, connected directly to the positive bus. All other devices have to be calibrated in the menus to match the flexnet measured voltage. They all are and do, except when the FM-80 is charging, it reads sometimes as much as a volt higher than the actual flexnet DC battery voltage, therefore rendering the charge terminating capability of the FN-DC inoperable.
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #6
    Re: Outback FM-80 trouble

    No i meant get a DVM and measure it. That will tell you if its a real problem or a monitering problem.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: Outback FM-80 trouble

    adding do the measurement on both ends when it is outputting high from the cc with the same meter. even a few tenths of a volt drop to the batteries can serve to improperly charge the batteries. if you are seeing a 1v difference then your batteries are not charging properly and you must take steps to rectify where the problems lie be it insufficient wire gauge, bad connections, even some bad fuses or circuit breakers can unduly drop the voltage.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #8
    Re: Outback FM-80 trouble

    Agree with both zoneblue and Niel, the highest probability is a higher than normal resistance somewhere between the actual terminals of the CC and the actual terminals of the batteries. With low or no current flow, it would be far less, or not noticeable, but at high charge rates, it's going to show up.
    First thing I'd do is wait till the charge controller is charging heavily, then check the voltage right on the battery terminals and compare it with the voltage reading on the actual terminals on the controller. I suspect you'll see a voltage difference, the cause of which should them be easily tracked down.
    Good luck.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    Re: Outback FM-80 trouble

    There is another possibility... Do you have a remote battery temperature sensor? Or are you relying on the Charge Controller's internal temperature sensor.

    At -5mV per cell--A 1.0 volt difference based on temperature correction would be:

    1 volts * 1/0.005 volts per C per cell * 1/12 cells (24 volt battery bank) = ~17 degree C (controller ~31F warmer than battery bank).

    Some charge controllers display a "temperature corrected" voltage vs the "measured voltage" (I don't know if Outback reports actual vs corrected temperature on the charge controller's display)... If your charge controller "gets warm" after a few hours of high current charging, it could account for the "reported" voltage depression vs actual correction (using the internal temperature sensor).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #10
    Re: Outback FM-80 trouble

    the temp of the cc would not affect the voltage readings and it has a bts at the batteries which would raise or lower the voltage set points to account for its needs at various temperatures of the batteries. this would not make the voltage different at the cc than at the batteries.
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  • LOTW
    LOTW Solar Expert Posts: 25 ✭
    #11
    Re: Outback FM-80 trouble
    waynefromnscanada wrote: »
    Agree with both zoneblue and Niel, the highest probability is a higher than normal resistance somewhere between the actual terminals of the CC and the actual terminals of the batteries. With low or no current flow, it would be far less, or not noticeable, but at high charge rates, it's going to show up.
    First thing I'd do is wait till the charge controller is charging heavily, then check the voltage right on the battery terminals and compare it with the voltage reading on the actual terminals on the controller. I suspect you'll see a voltage difference, the cause of which should them be easily tracked down.
    Good luck.

    Thanks everyone. Next time I get out there, I will measure for a voltage drop across the cabling and breaker, and go from there. I'm thinking the most likely culprit is the breaker, because I have short runs of 2 awg all into bus bars otherwise, and it was all working perfectly previously with a different CC, so I can't imagine where else the resistance could be coming from. If i'm getting no voltage drop across the cabling, then I guess my next contact is with Outback.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
    Re: Outback FM-80 trouble

    Something else that should be mentioned: Outback controllers have the ability to reprogram their Voltage readout to compensate for differences like this. In other words you can check the built-in meter's accuracy against a Fluke and adjust it to read correctly (at the controller). Normally it is not far enough off to matter, but there's always the possibility that this one has for some reason been run to +1 Volt.

    At any rate, the time when you need the Voltage to agree at battery and controller is when Absorb starts (max. Voltage in the charging cycle and most current at that point). This will ensure the controller actually enters Absorb stage when the battery really is at the right Voltage for it.

    Oh, and when checking the Voltage readout against a meter disconnect the RTS.
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  • LOTW
    LOTW Solar Expert Posts: 25 ✭
    #13
    Re: Outback FM-80 trouble
    Cariboocoot wrote: »
    Something else that should be mentioned: Outback controllers have the ability to reprogram their Voltage readout to compensate for differences like this. In other words you can check the built-in meter's accuracy against a Fluke and adjust it to read correctly (at the controller). Normally it is not far enough off to matter, but there's always the possibility that this one has for some reason been run to +1 Volt.

    At any rate, the time when you need the Voltage to agree at battery and controller is when Absorb starts (max. Voltage in the charging cycle and most current at that point). This will ensure the controller actually enters Absorb stage when the battery really is at the right Voltage for it.

    Oh, and when checking the Voltage readout against a meter disconnect the RTS.

    I assume you are talking about the VBAT Calibarion in the advanced menu? It is only a +/- .6v max adjustment, and is calibrated to match the FNDC Vbat (which is supposed to serve as your true battery voltage), and does as long as there is no sun. The VFX and FM-60 are the same. The issue is when the sun is shining, the discrepancy on the FM-80 shows itself. And you are right, at the worst time. For the FN-DC to terminate charging, the charge current has to be within .4v of the set absorb voltage, and the end amps met for 5 minutes. Obviously I can't meet this if the charge controller locks to absorb .8v early. The voltage drop suggested absolutely makes the most sense, I just need to find out what is causing it.
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  • LOTW
    LOTW Solar Expert Posts: 25 ✭
    #14
    Re: Outback FM-80 trouble

    Solved- loose connection on breaker, corroded over time. Thanks everyone for the help.
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  • gww1
    gww1 Solar Expert Posts: 963 ✭✭
    #15
    Re: Outback FM-80 trouble

    My mx 60 and fm 80 read .1 to .2 volts higher then the battery voltage at the battery and at the charge controller connections. The fm 80 is compensated at the max -.5 the mx is compensated at +.2. The fm 80 starts cutting production when going into absorb at a lot lower voltage then the mx60. lately the mx 60 stays in bulk a lot of the time even while cutting pv production. before I put loads on the battery it seemed to cycle seemlessly. for two days I ran without loads and it is no longer seemless and never stays in absorb and I don't see float but do see battery full at times. I am new enough that I am living with my equipment and watching very closely. I need to get internet connections cause I can't get enough questions ask to adress my knowladge void. I called outback on my inverter funtion and will need to call further.
    Cheers
    gww
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