Prostar PS15 malfunction?

texneus
texneus Registered Users Posts: 5 ✭
in Advanced Solar Electric Technical Forum #1
Hi everyone, first post. Not sure if this is the best place for this question so mods feel free to move it if there is a better spot.

I have an off-grid system at my cabin in remote northern MN. Original install date was 2000 with updates in 2008 to include upgraded panels and fresh batteries, professionally installed. That update left me with 2x new 150 watt panels (do not recall the make or model), 8x Trojan T105 batteries (arranged in series/parallel banks to provide 24V). The original charge controller and inverter still remained (a BZ Products CC20 plus and Heart Interface (now Xantrex) Freedom 25 inverter).

Last summer I replaced the charge controller (failing) with a Morningstar Prostar PS15 (the model without the meter). The controller appears to have been working properly since installation, with system voltages falling within expected ranges, until yesterday. That's when the call came from the people who look after my cabin because the inverter will not turn on and indicates a battery fault. We did some back and forths and have determined the following:

The inverter has cut out due to high battery voltage (per the manual, it shuts off when V>31.5 volts and will reset when voltage falls below 30.5V). A reading at the battery terminals confirmed the voltage is ~31.7V. The status lights on the charge controller show it thinks the batteries are full (green battery light) but the green charge light is also on, showing it is still dumping power into the batteries. The charge controller therefore appears to be malfunctioning.

I've asked them to check again in a day or two (thinking perhaps they caught it during an equalization cycle) and to disconnect the panels if the voltage is still too high. I'll know more when I get there around the end of the week and can check the system out in person, but is there anything I need to be checking for? Is it possible to run any diagnostics on the model without the meter? Is it possible to adjust voltages on this model? Is it possible to know if this controller is equalizing vs. malfunctioning if this behavior is observed again in the future?

This cabin is remote with no internet or cell phone connection, hence the request for information in advance. Thanks!
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #2
    Re: Prostar PS15 malfunction?

    Was is "room temperature" for the controller? Very cold temperatures can add around 60 mV per degree C for every degree below ~25C.

    One complaint about many AC inverters is their maximum DC input voltage. For folks that live in cold weather spots, it is not unusual for a normally charging battery to fault the inverter because of excessive DC battery voltage during charging.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • texneus
    texneus Registered Users Posts: 5 ✭
    #3
    Re: Prostar PS15 malfunction?
    BB. wrote: »
    Was is "room temperature" for the controller? Very cold temperatures can add around 60 mV per degree C for every degree below ~25C.

    Good question Bill, but unless I'm doing something wrong that does not explain the observed behavior. I looked in the PS15 manual and it says float voltage is 28.8V (14.4V x 2) @ 25C and temperature compensation is -5mV/Cell/C, or +600mV per 10C drop in temperature. To reach 31.7V float the batteries would have to be ~-10F, assuming my math is right.

    The batteries and controller are located in a well insulated crawl space. I don't know the exact temperature but based on passed experience it is rare to get less than +20F down there, besides which even the outdoor air temperature has not been that cold yet, so I don't think temperature compensation explains what I'm seeing.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Prostar PS15 malfunction?

    31.7 is "cold Absorb" Voltage on a 24 Volt system.

    This will probably sound weird, but it should be checked just in case: what size wires are used and how are the wires run? If the controller's output is connected to the inverter input then wires run from there to the batteries there is the possibility of loose/poor connection allowing the controller to push the Voltage very high at the inverter input without actually bringing the batteries up that high even if the reading is taken at the batteries.

    Another question: are you using the battery sense terminals?
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #5
    Re: Prostar PS15 malfunction?
    texneus wrote: »
    The batteries and controller are located in a well insulated crawl space. I don't know the exact temperature but based on passed experience it is rare to get less than +20F down there, besides which even the outdoor air temperature has not been that cold yet, so I don't think temperature compensation explains what I'm seeing.


    But it could still be if you have a defective temperature sensor or remote temperature sensor attached to the controller. One good reason for having the CC able to display the temperature it is using.
    SMA SB 3000, old BP panels.
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  • texneus
    texneus Registered Users Posts: 5 ✭
    #6
    Re: Prostar PS15 malfunction?

    Understand exactly what you're talking about regarding connections, I believe all connections terminate at the battery posts but will confirm. Wire to/from the controller is 10gage, wire to the inverter is 000 gage, IIRC. I am not using the remote voltage sense as the batteries are right next to the controller.

    Failed temp sensor is an interesting theory, is there a way to check this (I don't have the model with the meter).

    Thanks again!
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #7
    Re: Prostar PS15 malfunction?
    texneus wrote: »
    Understand exactly what you're talking about regarding connections, I believe all connections terminate at the battery posts but will confirm. Wire to/from the controller is 10gage, wire to the inverter is 000 gage, IIRC. I am not using the remote voltage sense as the batteries are right next to the controller.

    Failed temp sensor is an interesting theory, is there a way to check this (I don't have the model with the meter).

    Thanks again!

    Even though the wires are short, using the remote voltage sensor will eliminate the voltage drop in the connections as well as the cables and so is preferred anyway. The wire for the remote V sensing can be as small as you want, since no current will be flowing in it.

    If a remote temp sensor is optional, I would just unplug it and see whether the behavior of the CC changes. If the only temp sensor is inside the CC, I would try raising the temp of the CC with a heater or other means and see whether the voltages drop. If they do not, then you have a problem. Remember though that you need to use a meter, because some CCs will show the programmed voltage at all times and using the temperature corrected voltage.
    SMA SB 3000, old BP panels.
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  • texneus
    texneus Registered Users Posts: 5 ✭
    #8
    Re: Prostar PS15 malfunction?

    Quick update from "up North" while in town (with data service). When we arrived after dark batteries were at 26.4 volts. Batteries are right about 30F. Doing the math i'm pretty certain the batteries weequalizing, as at 30F the voltage applied would indeed have been 31.7v when temp compensation is considered. For now all appears to be working well. Happy new year all!
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