1.5w battery trickle charge panel question

machineman
machineman Solar Expert Posts: 129 ✭✭✭
in General Solar Power Topics #1
I got one of those cigarette lighter plug 1.5watt battery charger solar panels from harbor frieght ($15). I 'm using for my propane generator to keep the starter lead acid battery charged. When I connect it to my battery the total voltage reads 19v. Seperately they read 12V battery and 7v panel(not full sun). Is this OK to have 19v+ on the battery?

Thanks.

Off Grid Cabin, 24V 440ah 6V GC battery bank, Xantrex MPPT60-150 CC, Magnum MS4024 inverter-charger, >1200w Solar bank

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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #2
    Re: 1.5w battery trickle charge panel question

    Nope, should read max of about 14V. At 1.5W, I do not thing it is large enough to raise the voltage that high.

    Just to cove all bases, explain how you hook the panel and how you measured voltage.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #3
    Re: 1.5w battery trickle charge panel question

    Your panel is so small, it really doesn't matter what the panel voltage is,,, your are not going to hurt the battery. As a matter of fact, 1.2 watts probably isn't even enough power to keep the battery at float voltage.

    Your open circuit voltage of ~19 vdc is fine for a 12 volt battery. Most panels are even higher.

    (Rereading your post suggests, as Ken points out, there is something screwy in the results you are getting. The battery should show ~12.6vdc off charge, off load, fully charged. The panel should show somewhere north of 19vdc off the battery, off load. Please explain how you are measuring the voltage and with what meter.)

    Icarus
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  • machineman
    machineman Solar Expert Posts: 129 ✭✭✭
    #4
    Re: 1.5w battery trickle charge panel question

    I put a 12v cigarette ligher outlet inside the generator houseing so I could use the existing plug the panel came with since it had a fuse in it. The positive wire from the panel is attached diretly to the positive battery cable where it hooks on to the starter selonoid. The panel negative wire is hooked to the chassis ground. The battery negative cable is also tied to the chassis ground.

    Measurement:
    ~19v when using DVM attached to positvie battery cable and chasis ground. With solar panel pluggd in.

    ~12v when using DVM attached to positvie battery cable and chasis ground. Without solar panel pluggd in.

    ~7v when using DVM attached to positvie solar wire and solar panel ground wire. Panel is not connected to battery. This voltage will vary with the amount of sunlight.


    Here's the panel I have: http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=44768

    Off Grid Cabin, 24V 440ah 6V GC battery bank, Xantrex MPPT60-150 CC, Magnum MS4024 inverter-charger, >1200w Solar bank

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: 1.5w battery trickle charge panel question

    Does not sound correct... You may have a floating/broken ground wire somewhere between the lighter ground and the true battery/chassis ground. That is the only way (assuming your meter is accurate) you would see 19 volts (which happens to equal 7v+12v=19v). Are you 100% sure the shell of the cigarette lighter socket is properly grounded? Not mounted in a plastic/painted housing, and/or shock mounted by rubber bushings?

    First, the solar panel, not connected to anything, in reasonably full sun, should read ~17-21 volts. The output voltage is only weakly related to sunlight on a solar panel... Basically, once you have any sunlight, or strong light from a cloudy sky, the voltage should go up to ~17-21 volts. In full sun, it should still read ~17-21 volts. If it reads less than 14 volts or so--it will not trickle charge your battery and is of no use.

    With your meter set to 200 milliAmp (or higher) scale, just placing the meter across the panel output should read ~100 milliAmps or 0.1 amps in full noontime sun. The output current (short circuit current in this case), is very proportional to the amount of sunlight. You will see a difference bettween noon sun and 4pm sun in short circuit current.

    Lastly, when you connect the solar panel to your battery--your battery should still read around 12.6-12.8 volts or so--This small solar panel will not make any difference in your battery's voltage at all between being connected or not (or, at most, a few 0.010's of volts of difference). Over time, it may jack the battery voltage up to 13.1-13.8 volts or so during a sunny day. After the sun goes down, your battery will drop down to 12.8 volts or so.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • machineman
    machineman Solar Expert Posts: 129 ✭✭✭
    #6
    Re: 1.5w battery trickle charge panel question

    I will check the ground wire next cabin trip.

    Off Grid Cabin, 24V 440ah 6V GC battery bank, Xantrex MPPT60-150 CC, Magnum MS4024 inverter-charger, >1200w Solar bank

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