perplexing charge controller readings

lazza
lazza Solar Expert Posts: 336 ✭✭✭
in Off Grid Solar & Battery Systems #1
HI Forum

I've come across a perplexing issue. We have just added 2 120W kyocera panels with a STECA PR1515 charge controller. The system already had a few panels with another STECA PR3030 (hence why we chose the same make of charge controller)

I suspected that there was a problem with the 1st charge controller as it was giving voltages lower than the measurement of the inverter and the measurement i took at the connectors. EG Battery reading 12,7V but charge controller reading 12,2V. I reset it a few times but it kept reverting to "erronous" readings. I thought that one possibility is that the STECA has some kind of algorithmically adjusted measurement to measure the real battery voltage.

So we installed the 2nd charge controller. Once installed, the 2nd charge controller gave the same reading as my voltimeter at the battery terminals, whilst the first was still giving "erronous" readings of a about 0,7V less than the new charge controller.

My logical conclusion is that the 1st charge controller is faulty, but maybe you guys have loads more experience, and could have other explanations?:confused:

thanks for any pointers

Larry
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Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: perplexing charge controller readings

    that makes me question if your meter may be faulty. got another voltmeter to try? maybe borrow one?
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #3
    Re: perplexing charge controller readings

    definitely not the volitmeter, has been giving perfect readings last few days- and it gave the same reading as the new solar charge controller-
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  • TheBackRoads
    TheBackRoads Solar Expert Posts: 274 ✭✭
    #4
    Re: perplexing charge controller readings

    Bad wiring to/from original CC?
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  • snuffy
    snuffy Solar Expert Posts: 72 ✭✭✭✭
    #5
    Re: perplexing charge controller readings

    I'd think it was a wiring issue also. The outputs of both CC's should be hardwired to the batteries and read what the batteries read. I'd be checking connections.
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #6
    Re: perplexing charge controller readings

    I couldnt identify any problems with the wiring. The only thing that they've done is lift the charge controller with spacers and threaded the four leads (+ve, -ve of batteries and PV) behind the charge controller. I've seen this done before for neatness.

    I dont suppose this could interfere with the charge controller internal measurements?

    ps I've attached a photo of the installation- the new controller that we installed is in the top left, the "faulty" one is to the right of it with the blue and brown leads.
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  • snuffy
    snuffy Solar Expert Posts: 72 ✭✭✭✭
    #7
    Re: perplexing charge controller readings

    Is there a breaker or fuse between the CC and the batteries that could be causing the problem? That should be the only thing between the batteries and output of the CC.
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #8
    Re: perplexing charge controller readings

    Only in our part of the installation- you can see the 20A fuse there.

    In the original installation they havent put any breakers/protections (unfortunately it is a common bad practice here).. so the blue and brown wires go directly to the batteries, the connections of which I checked and they are sound.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #9
    Re: perplexing charge controller readings

    Are the cables between charge controller and battery thick enough? When you took the manual readings with the voltmeter did you take them at the charge controller side of the cables, or at the battery side - and was there a difference?
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #10
    Re: perplexing charge controller readings

    HI Stephen

    The answer is no, they are not thick enough- they are only 6mm2 when they should be 16mm2. Thus there is a 0.2V difference between the battery readings and the CC connector readings.

    However, this doesnt account for the "erronous" readings from the existing CC. For example, at one instant the batteries were reading 13.6V, the CC connectors were reading 13.8V (accounted for by the voltage drop due to insufficiently sized cables), but the CC display was showing 13.0V!

    The new CC we installed showed the correct battery voltage of 13.6V

    Hence the quandary:confused:
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  • snuffy
    snuffy Solar Expert Posts: 72 ✭✭✭✭
    #11
    Re: perplexing charge controller readings

    So it's your charge controller meter that's giving incorrect readings then? I was thinking you were getting those readings on a separate DVTM you were using.
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #12
    Re: perplexing charge controller readings

    Yes it's the old charge controller, well i say old, the existing one. So, for example, I get a 13.6V reading from my voltimeter at the battery, a 13.6V reading from the new CC we have just installed, BUT a 13.0V reading from the existing one.
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  • snuffy
    snuffy Solar Expert Posts: 72 ✭✭✭✭
    #13
    Re: perplexing charge controller readings

    Let's see if I got this correct then. With your separate voltmeter you read 13 volts at the output terminals of one controller and 13.6 volts at the output terminals of the other controller and both controllers are hooked to the same battery bank? If a separate meter measures them both at 13.6 volts then indeed the problem is with the old charge control. If a separate meter measures one at 13 and one at 13.6 then the problem is external to the CC.
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #14
    Re: perplexing charge controller readings

    No, with my voltmeter i read 13,6V at the output of the new controller, 13,6V at the batteries, 13,8V at the output of the old controller (accounted for by the voltage drop due to insufficient cabling).

    The readings on the new controller correspond with my voltmeter ie 13,6V, whereas the old controller gives a reading of 13,0V.
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  • snuffy
    snuffy Solar Expert Posts: 72 ✭✭✭✭
    #15
    Re: perplexing charge controller readings

    OK then the problem is with the old CC. I'm not familiar with your CC but on my Outback there is a function in the software called V Batt calibration which will change the readings on the meter. Don't know if yours has a similar function. But if it's drifting around I suspect hardware/component issues.
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #16
    Re: perplexing charge controller readings

    That sounds like the most likely explanation to me too- it's a very simple system and there's no recalibration option or similar.

    I was wondering if having the cables wired underneath it at the back of the old CC, could be interfering with the internal components... is this possible or a daft suggestion?

    thanks
    Larry
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #17
    Re: perplexing charge controller readings

    Probably not... Obviously, using the much heavier wire will work much better for proper battery charging. But it will not fix the meter calibration error (and, if the meter is in error, are the charging set points also in error?).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #18
    Re: perplexing charge controller readings

    Well this is what worries me- that by registering a lower voltage, the CC may be overcharging the GEL :roll: batteries (there's no way to change set points on these simple controllers)... not a good state of affairs, but I couldnt convince the owner to call the electrician that put it in to replace it as it's within warranty.. because he's embarassed.. cant win sometimes
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  • snuffy
    snuffy Solar Expert Posts: 72 ✭✭✭✭
    #19
    Re: perplexing charge controller readings
    lazza wrote: »
    That sounds like the most likely explanation to me too- it's a very simple system and there's no recalibration option or similar.

    I was wondering if having the cables wired underneath it at the back of the old CC, could be interfering with the internal components... is this possible or a daft suggestion?

    thanks
    Larry

    Heavy current flow in the charger leads if it's PWM could possibly interfere with meter readings under the right conditions. Re-arranging the leads should show a change. Are both CC's wired the same way? I wonder if it's just a meter problem or if effects the charge voltages also. It appears to be close to proper charge voltages from what I've gathered.
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #20
    Re: perplexing charge controller readings

    Yes, both CC are wired in exactly the same way, except the new one has a fuse in the positive cable between the CC output and the battery. It could be that it's just the meter, but i fear that it could be affecting the battery charging- ie giving a bulk charge for too long...
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #21
    Re: perplexing charge controller readings

    I think he also swapped the two meters with each other and found the problem followed the meter.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • snuffy
    snuffy Solar Expert Posts: 72 ✭✭✭✭
    #22
    Re: perplexing charge controller readings

    I didn't see where he did that but it would be a useful test if he could. I wonder if these CC's have remote voltage sensing leads or if they read the voltage at the output terminals?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #23
    Re: perplexing charge controller readings
    lazza wrote: »
    I suspected that there was a problem with the 1st charge controller as it was giving voltages lower than the measurement of the inverter and the measurement i took at the connectors. EG Battery reading 12,7V but charge controller reading 12,2V. I reset it a few times but it kept reverting to "erronous" readings. I thought that one possibility is that the STECA has some kind of algorithmically adjusted measurement to measure the real battery voltage.

    So we installed the 2nd charge controller. Once installed, the 2nd charge controller gave the same reading as my voltmeter at the battery terminals, whilst the first was still giving "erroneous" readings of a about 0,7V less than the new charge controller.

    My logical conclusion is that the 1st charge controller is faulty, but maybe you guys have loads more experience, and could have other explanations?:confused:
    That is what I pulled from here... I may be wrong though...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #24
    Re: perplexing charge controller readings

    No I havent swapped the CC cables between the two, and dont want to go messing with someone else's cabling.

    The 2nd CC was installed in parallel with the other panels and CC with two 2 more panels to give more power to the system.

    Nothing as complex as remote voltage sensoring on these CC.

    I'm pretty sure it's got component issues the older CC- maybe i'm "buscando 3 pies al gato" as the spanish say "trying to see if the cat has 3 legs"
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  • snuffy
    snuffy Solar Expert Posts: 72 ✭✭✭✭
    #25
    Re: perplexing charge controller readings

    He swapped the CC's, not the meters. Yes I think there's a problem in the old CC. Not good at all if it thinks the battery voltage is lower than it really is.
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  • snuffy
    snuffy Solar Expert Posts: 72 ✭✭✭✭
    #26
    Re: perplexing charge controller readings

    It's interesting that the low readings are as stated previously .7 of a volt lower. It's as if the unit is now referencing ground through a diode junction. Which would lower the readings by .7 of a volt. I wonder if there's a pico fuse in the sense circuit that blew due to a reverse polarity hookup of the battery leads when they were rerouted?
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  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    #27
    Re: perplexing charge controller readings

    I had a bp unit like these, I think a re badged Steca.
    When you set them up you select gel or flooded . Are both the same ?
    Just a thought.
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #28
    Re: perplexing charge controller readings

    "The 2nd CC was installed in parallel with the other panels and CC with two 2 more panels to give more power to the system."

    does this mean all pvs are paralleled and in common to both ccs as well as a common battery bank? this could be a problem as no pv should see more than 1 controller. try splitting up the pvs to individual controllers so that half go to 1 cc and the other half of the pvs go to the 2nd cc.
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #29
    Re: perplexing charge controller readings
    snuffy wrote: »
    It's interesting that the low readings are as stated previously .7 of a volt lower. It's as if the unit is now referencing ground through a diode junction. Which would lower the readings by .7 of a volt. I wonder if there's a pico fuse in the sense circuit that blew due to a reverse polarity hookup of the battery leads when they were rerouted?

    Aha, now that would make sense-- although not sure what a "pico" fuse is.. and highly likely that the monkey that installed it reversed the polarity at first try (although these gadgets are supposed to have sufficient protection against it).. thanks for the input snuffy
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #30
    Re: perplexing charge controller readings
    niel wrote: »
    "The 2nd CC was installed in parallel with the other panels and CC with two 2 more panels to give more power to the system."

    does this mean all pvs are paralleled and in common to both ccs as well as a common battery bank? this could be a problem as no pv should see more than 1 controller. try splitting up the pvs to individual controllers so that half go to 1 cc and the other half of the pvs go to the 2nd cc.

    nope, i guess i havent explained myself correctly:

    Existing installation: STECA PR3030, about 500W of panels in parallel at 12V
    Our addition: STECA PR1515, 2 KC120 panels in parallel at 12V

    They share a battery bank, but are separated. The problem reading comes from the STECA PR3030- showing 0.7V less than both my meter and the display on the new CC.

    I havent swapped or changed anything on the original installation. Hope this is a bit clearer

    Cheers
    Larry
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #31
    Re: perplexing charge controller readings

    when all else fails try to ask the makers of the controllers to see what they say.
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