Can't adequately charge batteries.

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #32
    Re: Can't adequately charge batteries.
    RobertR wrote: »
    When I was doing the volt / amp checks today, I hooked the two motor home panels together, + to + and - to -. Then did short circuit amp test which was still 10 amps. Volts were of coarse still ~ 20v. I'm not an electrical engineer, I was a physics major, but should that not have doubled the amps to 20?

    If one panel is putting out 10 Amps and the other panel puts out 10 Amps the two together should put out 20 Amps. (Never mind the Volts.) But you have to check each panel individually and then together.

    WARNING: Most DMM's will not read greater than 10 Amps. You can pop the internal fuse or even burn up the meter if the maximum current is exceeded.
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #33
    Re: Can't adequately charge batteries.

    To cut down on all the variables, are you testing somewhat in this manner:

    * Place a large towel over the panel you want to test.
    * Disconnect panel wiring from charge controller.
    * With multimeter set to voltage, place multimeter leads across the two leads coming from the panel. Don't skip previous step.
    * Remove towel matador-style. Just normally, no need to whip it off.

    * Place towel over panel again, because now we are going to check amperage.
    * Change the multimeter switch settings / and test-lead positions for current measurement.
    * Use a multimeter rated to handle the rated current from the panel, otherwise you'll blow the fuse. These leads go across the two wires coming from the panel, just like you did for voltage, only this time with the multimeter set for current, it is basically measuring the short-circuit amperage.
    * Remove towel normally and take amperage reading.

    When reconnecting to charge controller, the temporary towel covering is recommended.

    Remember that when connecting a system together, the controller wants to see a battery connection FIRST, and then the panel(s) LAST in order to get it's logic together and not force it into a safety-shutdown (panel first and no battery makes controller think you are trying to charge an undervoltage battery and will try and keep you safe by either going completely dumb, or defaulting to only float). You are switching the battery in and out of circuit, so getting the connection sequence wrong is a common mistake - I've done it many a time.

    This test will cut out all the variables you have downstream such as possible controller miswiring, switch settings, reversed monitoring and other weirdness. With the panel setup qualified you can now concentrate on other stuff like the batteries may just be in absorb mode, or perhaps you do have a malfunctioning monitoring system.
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  • RobertR
    RobertR Registered Users Posts: 17 ✭
    #34
    Re: Can't adequately charge batteries.

    Two panels in parallel should not read same amps as one. Didn't seem right so I tested other stuff and everything is using 10 amps. Thus the meter must be bad. Scratch all the amp readings and I will have to get another meter.
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  • ILFE
    ILFE Solar Expert Posts: 364 ✭✭
    #35
    Re: Can't adequately charge batteries.

    Not to hijack this thread, but I really need to ask a question here.

    To make sure there is nothing in my Coke Light - other than Coke Light, I need to confirm something I have read - several times, in this very thread.

    Again, to confirm: It is perfectly okay to connect the positive and negative leads together, those wires coming FROM the rear of a solar panel, and then clamp a meter on to that circuit in order to test (Isc)? I mean, that is the proper way to test (Isc) of a panel?
    Paul
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #36
    Re: Can't adequately charge batteries.
    ILFE wrote: »
    Again, to confirm: It is perfectly okay to connect the positive and negative leads together, those wires coming FROM the rear of a solar panel, and then clamp a meter on to that circuit in order to test (Isc)? I mean, that is the proper way to test (Isc) of a panel?

    Yes. the "sc" in Isc stands for Short Circuit.

    You should cover the panel with a blanket (or do it at night) when you make or break any connections to the panel.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • ILFE
    ILFE Solar Expert Posts: 364 ✭✭
    #37
    Re: Can't adequately charge batteries.
    vtmaps wrote: »
    Yes. the "sc" in Isc stands for Short Circuit.

    You should cover the panel with a blanket (or do it at night) when you make or break any connections to the panel.

    And, when light is then introduced to the panel, it will not damage the panel in any way, as it would a battery, say?
    Paul
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #38
    Re: Can't adequately charge batteries.

    According to the sales folks--You are correct, there would be no damage.

    HOWEVER. A decade or more ago as I recall, one of the founders of Midnite Solar (posts here as "boB"), attempted to design a solar power protective device shorted the output of the panel to reduce the chance of electrical shock and fires (arc faults). At that time, the panel mfg. said they were not comfortable with shorting the output of the panels.

    So--while it is OK for testing (seconds to minutes), I would avoid leaving a panel "cooking" in full sun with the output shorted for days-years.

    The current for a shorted panel is, very roughly, 1.25x the Imp current... Power=I^2R=1.25^2=1.56... So you get 56% more heating (from current flow through panel) and you do not move ~15-18% of the energy from the sun (as electricity) from the panel--So you are looking at something like ~71%+ more heat heat retained on the panel during a short circuit test--And heat is never good for electronics.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #39
    Re: Can't adequately charge batteries.

    And blocking light from the panel while connecting the MC4 connectors together (shorting) is just to protect the contacts themselves.

    These contacts are not made for "interrupting current" and you will probably "pit"/spot weld the contacts as you make/break the connections--Damaging the contacts themselves.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #40
    Re: Can't adequately charge batteries.
    BB. wrote: »
    The current for a shorted panel is, very roughly, 1.25x the Imp current... Power=I^2R=1.25^2=1.56... So you get 56% more heating (from current flow through panel) and you do not move ~15-18% of the energy from the sun (as electricity) from the panel--So you are looking at something like ~71%+ more heat heat retained on the panel during a short circuit test--And heat is never good for electronics.

    I think you counted the same heat twice. The light that hits the panel is either reflected by, transmitted through, or absorbed by the panel.

    The absorbed light is converted to heat and electric energy. All of the electric energy is either dissipated in the panel or exported to the load. A loaded panel therefore runs cooler than an unloaded panel. To the extent that a short circuit has any resistance at all, it is a load, and therefore a shorted panel runs cooler than an open circuit panel.

    I think an open circuited panel and a short circuited panel will heat up the same amount... with one difference: the difference is where in the panel the electric energy is dissipated. In the open circuit panel no current flows, so all of the light that hits the photocell is converted into heat in the photocell. In the short circuited panel, there is current flow and some of that current flow heats up the inter-cell wiring in the panel rather than the photocell.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • ILFE
    ILFE Solar Expert Posts: 364 ✭✭
    #41
    Re: Can't adequately charge batteries.
    RobertR wrote: »
    Two panels in parallel should not read same amps as one. Didn't seem right so I tested other stuff and everything is using 10 amps. Thus the meter must be bad. Scratch all the amp readings and I will have to get another meter.

    My apologies, Robert. I was just shocked to learn what I did about checking the short circuit current (Isc). I hope you've found a new multimeter by now.
    Paul
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #42
    Re: Can't adequately charge batteries.

    Shorting the leads - with multimeter in between - is the way I do it. It blew my mind the first time I measured amperage that way, but knew that some old-time controllers with relays that merely ping-ponged between and upper and lower voltage limit did exactly that by internally shorting the leads inside the controller.

    Reminder to take your time so you don't blow the fuse in the multimeter. In my haste to make measurements on a panel, I successfully took the voltage reading, covered the panel, moved the multimeter switch to read amperage, BUT FORGOT to move the negative lead on the multimeter itself to the current-measuring jacks! POOF. Instant blown fuse. More advanced Fluke multimeters will beep if you forget to do this.

    Also note that you are not just measuring the panel current output itself, but are also checking for bad / blown bypass diodes that may exist inside the junction box on the back of the panel.

    Another bad day - in my haste to hookup a temporary system to my Sharp 80w panel, I accidentally attached the panel leads to the battery directly, BUT in reverse polarity! POOF. One of the finely-tuned bypass diodes that were a factory-matched set went up in smoke. I had to replace it with some 10A generic solar schottky diodes.

    Thing was, with the blown diode, the voltage measurement was just fine. However the panel was only putting out half it's rated power. Those bypass diodes inside the junction box serve to cut the panel in half electrically so if some shade falls across one or more cells in the panel, they don't bear the full brunt of the panel now that they are reverse-biased by the shade. These diodes are something that many homebrewers leave out.

    If I had a serious system that incorporated bypass diodes inside the rear junction boxes, I'd definitely check them once a year or so to make sure that the diodes are physically snug and not loose from thermal expansion creating a high-resistance connection or burnout. Certainly inspect and snug them down upon receipt. The multimeter test will help you spot stuff like this, even if the mono/polycrystalline cells are sound.
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  • ILFE
    ILFE Solar Expert Posts: 364 ✭✭
    #43
    Re: Can't adequately charge batteries.
    PNjunction wrote: »
    Shorting the leads - with multimeter in between - is the way I do it. It blew my mind the first time I measured amperage that way,

    I have to ask. Could you simply connect the two ends together, from the panel, and read the amperes with a clamp on ammeter? Or, does it need some resistance from the meter in between the positive and negative sides?
    Paul
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  • Brianellul
    Brianellul Solar Expert Posts: 95 ✭✭
    #44
    Re: Can't adequately charge batteries.
    ILFE wrote: »
    I have to ask. Could you simply connect the two ends together, from the panel, and read the amperes with a clamp on ammeter? Or, does it need some resistance from the meter in between the positive and negative sides?

    Yes you can connect the two ends together and read the current with a clamp meter. Amp meters connected in series have a very low resistance and therefore (for most calculations) can be considered as a wire, i.e. zero resistance.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #45
    Re: Can't adequately charge batteries.

    i would not leave it shorted for long though as the wires will heat.
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  • ILFE
    ILFE Solar Expert Posts: 364 ✭✭
    #46
    Re: Can't adequately charge batteries.
    niel wrote: »
    i would not leave it shorted for long though as the wires will heat.

    I would certainly hope so. If they didn't, I don't think I would be installing that particular panel. :D
    Paul
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  • RobertR
    RobertR Registered Users Posts: 17 ✭
    #47
    Re: Can't adequately charge batteries.

    It's working. I am getting a 10 amp or better charge with decent sun. All I can figure is all the connecting and disconnecting to measure the panel out puts reset something in the controller.
    Thanks for everyone's help.

    PS: bought a clamp amp meter at a local pawn shop. Seems to work fine. Clamp it around one of the wires, and when short them just long enough to read amps. A second or two is enough. The day I checked them one was putting out ~ 6 amps, and the other ~ 5.
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  • ILFE
    ILFE Solar Expert Posts: 364 ✭✭
    #48
    Re: Can't adequately charge batteries.
    RobertR wrote: »
    It's working. I am getting a 10 amp or better charge with decent sun. All I can figure is all the connecting and disconnecting to measure the panel out puts reset something in the controller.
    Thanks for everyone's help.

    PS: bought a clamp amp meter at a local pawn shop. Seems to work fine. Clamp it around one of the wires, and when short them just long enough to read amps. A second or two is enough. The day I checked them one was putting out ~ 6 amps, and the other ~ 5.

    For DC circuits, do make sure the ammeter is a DC ammeter. You cannot use an AC ammeter for DC circuits. Please don't ask me how I know this. :D

    I already had an AC ammeter, but had a DC ammeter shipped from a shop in Bangkok, Thailand, because I couldn't find one anywhere here in Cambodia.
    Paul
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  • upa123
    upa123 Registered Users Posts: 17 ✭
    #49
    Re: Can't adequately charge batteries.
    RobertR wrote: »
    To answer previous questions, the panels are approx 4 foot long, 2.5 foot wide each approx 2 years old. Volt reading on each panel was 19.5 but that was not on a full sun day. It was partly cloudy.

    Ok I have done the following. I have a total of 6 solar panels available to test. 2 in motor home, 2 on office roof, 2 on warehouse roof. I tested them all for volts and amps, and angled toward the sun at approx same angle as the ones on the motor home they all read the same. ~ 20v and 10amps.

    As questioned by a previous poster, are you sure these are 350 watt rated panels? My 72 cell 280-300 watt GT panels are 6.5 ft by 3.25 ft. It really sounds like you have nominal 12 volt panels of much lower wattage rating, they seem like roughly 100-125 watt panels based on your approximate size and amperage and VOC readings. You might have to crawl on the roof and verify your spec labels.
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  • RobertR
    RobertR Registered Users Posts: 17 ✭
    #50
    Re: Can't adequately charge batteries.

    The meter has both AC and DC settings. Thanks
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