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bigcountry
bigcountry Registered Users Posts: 22 ✭
in Solar Beginners Corner #1
I have my first little pv system
http://www.northerntool.com/shop/tools/product_200466740_200466740

The question i have is i have 21 volts coming out of the panels but at the charge controller i have 11.5. Can anyone tell me why this is.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: question
    bigcountry wrote: »
    I have my first little pv system
    http://www.northerntool.com/shop/tools/product_200466740_200466740

    The question i have is i have 21 volts coming out of the panels but at the charge controller i have 11.5. Can anyone tell me why this is.

    Under what conditions?
    21 Volts would be a Voc, which a panel will produce with just about any amount of light on it.
    The output of the controller should be connected a battery, and what you're looking for is not Voltage so much as current flowing from the charge controller to the battery. Without bright, direct sunlight on the panel that won't be much. If the battery is only 11.5 Volts (pretty low) it would probably need a lot of time to realize any Voltage increase. If the load exceeds the battery & panel's power capacity, the Voltage will simply go down no matter what. 60 Watts isn't a lot of power (in reality the panel will produce more like 50 Watts).
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  • bigcountry
    bigcountry Registered Users Posts: 22 ✭
    #3
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    Re: question

    The voltages are both on the PV side of the charge controller not the battery side.
    the wires coming from the 3 panels go into a connector that goes from 3 to 1 it reads 21 volts at each panel and also coming out of the connector the takes the 3 down to 1 but at my 2 wires that go into the charge controller from my panels is 11.5 volts.

    The voltages are not from the battery side of the charge controller.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: question

    Let's make sure we're on the same page.

    Each panel, individually, not connected to anything has a Voc of 21.
    But when you connect them together in parallel the Voc drops to 11.5?

    (If that is the case it is probably due to one of the panels being connected with reverse polarity in respect to the other two.)
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #5
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    Re: question
    bigcountry wrote: »
    the wires coming from the 3 panels go into a connector that goes from 3 to 1 it reads 21 volts at each panel and also coming out of the connector the takes the 3 down to 1 but at my 2 wires that go into the charge controller from my panels is 11.5 volts.

    Sounds like the three panels are each providing 21 volts into a combining connector, which in turn sends out 21 volts on wires going to the charge controller - - but at the other end of those wires, where they enter the charge controller, there is only 11.5 volts.
    Is this correct?
    If true, what is the battery voltage?
    What size are the wires?
    How long are the wires?
    Is everything connected when you are making those voltage measurements?
    Is there a possibility that one (or both) of the wires between the combiner connector and the charge controller have been damaged, broken or cut?
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  • bigcountry
    bigcountry Registered Users Posts: 22 ✭
    #6
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    Re: question

    All the wiring is what comes with the kit it looks to be about a 14 gauge. Battery voltage is 12.3 vdc
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #7
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    Re: question
    bigcountry wrote: »
    All the wiring is what comes with the kit it looks to be about a 14 gauge. Battery voltage is 12.3 vdc

    Is everything connected when you are making those voltage measurements?
    Do you have 21 volts at one end of the wire and only 11.5 at the other end of the wire, or does the original 21 volts at the panel end also drop to 11.5 when you connect the charge controller?
    Need answers to these questions before we can go any further.
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  • bigcountry
    bigcountry Registered Users Posts: 22 ✭
    #8
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    Re: question

    The 21 volts is at the panels and all the way to the end of the splitter.

    Then i have a about 16" piece that goes from the splitter to the charge controller and i am loosing the voltage between the splitter and the charge controller
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
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    Re: question
    bigcountry wrote: »
    The 21 volts is at the panels and all the way to the end of the splitter.

    Then i have a about 16" piece that goes from the splitter to the charge controller and i am loosing the voltage between the splitter and the charge controller

    Splitter = combiner. (Yes it's important to get the terms right so everyone is talking about the same thing.)

    I'd suspect that this is where your Voltage is being lost, as it would not be possible to drop 10 Volts in 16 inches of wire with nothing on the other end. Even if the wire were very small gauge.

    Connect the panels one at a time to the combiner and check the V out at the end of the wire afterward. You should see 21 Volts there, the same as from each individual panel. Be sure the polarity is correct as well. If the first panel puts out 21 Volts after the combiner and the second panel added also has an output of 21 Volts then with the addition of the third panel the V out suddenly drops to 11.5, that one is reversed (assuming all put out 21 at their wires).

    If the one panel puts out 21 Volts but the V out from the combiner is 11 (with only one panel on) then there is a short that's killing the Voltage. If the Voltage drops when the controller is connected then the controller is loading the panels without sufficient sunlight for them to produce enough power to supply Vmp (probably around 17.5) @ current.

    It's a tedious process of checking Voltage at the same point as each component is added in to find out which one is causing the drop.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #10
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    Re: question

    For a simple PWM controller... The Battery sets the solar panel voltage while charging (bulk phase--basically if battery is 12.50 volts, solar panel will be at ~12.5 volts or a bit higher too. Once the battery is >~80-90% state of charge, the PWM controller starts turning "on and off" (maybe every second, or hundreds-thousands of times a second) and the solar array will "bounce" between battery charging voltage (say 14.2 volts) and Voc (~20 volts or so).

    If you are having other behaviour, with the battery discharged (or under load), take your volt meter and measure at the battery, then up the string--sort of like:
    • 12.20 volts Battery Posts
    • 12.30 volts Battery Output of charge controller
    • 12.30-13.xx volts solar array input
    • 12.30-14.xx volts at solar array power connection
    If you see something like above, then everything is probably OK.

    If you see 12.2 at the battery and >13 volts at the charge controller battery output--then you may have a bad connection and/or too small of gauge/too long of wire from battery to charge controller.

    If the charge controller is in Absorb or Float mode, then you will see the Vpanel input and Varray at higher voltages as the controller "cycles" on and off.

    Another way to look for problems--Set your DMM to 2 volts full scale (or even 0.2 volt or 200 millivolt full scale) and measure each length of wire/connection (put black wire on battery post, put red wire on corrisponding charge controller output--you should see a maximum of 0.100v (100 mV) drop. If you see more more drop on one span of wire and/or electrical connection, there is probably your problem.

    Note: Measuring voltage drop on wiring (either across the +/- or on each span of wire), you should have lots of current flowing to generate the voltage drop (V=I*R; if I~0.0 amps, then Voltage drop is near zero volts too).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • bigcountry
    bigcountry Registered Users Posts: 22 ✭
    #11
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    Re: question

    Thank you all for the info when i get home from work i will check it out again and will see what i find today
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