solar charging

System
System Posts: 2,511 admin
in General Solar Power Topics #1
I have a solar panel that has a output of 10 watts.

Do i need a charge controller ?

I am using it keep a trickle charge on 12 volt battery for a small travel trailer.

Thanks.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: solar charging

    Short answer, without more information, we have no idea.

    Need to know the specs. for the solar panel (Voc, Vmp, Imp, does it have a blocking diode). And we need to know the type of battery and voltage/current ratings.

    If the battery is a "car sized" wet cell battery (~80-120 amp*hours), if the solar panel is designed for trickle charging a 12 volt storage battery (has blocking diodes), and the solar panel gets good sun during the day--you probably don't need a charge controller.

    However, you should be checking the water level in the battery every month or two and ensure that you don't "boil the battery dry" during the sunny months.

    If there is some small load on the 12 volt battery (I don't know, say a burglar alarm), a trickle charger is probably not going to work well and you should have a larger panel and a charge controller. A trickle charger will not usually do a good job of recharging (even a small load) a battery in this case.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: solar charging

    Thanks for the reply.

    Here is all the information that i have.

    battery- group 27, marine/rv, deep cycle.

    solar panel-rated max power-10w

    lmp-.58A

    VMP-17.2V

    ISC- .66A

    voc-21.6v

    max.system voltage-715v


    max. series fuse rating1A

    I hope this helps.

    Thanks again.

    Mike Goforth
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  • System2
    System2 Posts: 6,290 admin
    #4
    Re: solar charging

    have you checked the actual output of that solar panel?

    What part of the country do you live in?

    Do you have any other electical devices running at the same time, for instance a Co2 monitor?

    What brand is your solar panel?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: solar charging

    Mike,

    The panel voltage/current looks fine with that battery for a trickle charger (without controller).

    Don't know if the panel has a blocking diode or not. You can purchase a 1-5 Amp Schottky diode and put that in one of the leads to block backwards current flow (do you know how?). And you should put a 1 amp fuse near the positive battery power source in case there is a short somewhere.

    You should monitor the battery voltage at night (after the sun has been down for an hour or two) with an accurate DVM and make sure that you are not discharging the battery below 80%-75% of capacity from lack of charge current (not enough panel, not enough sun, not clear day, panel not pointing at sun, etc.). From the Wind-Sun Battery FAQ, your resting voltage (for a 77F degree battery) should be between 12.42 and 12.70 volts DC.

    If your battery gets below 12.42 volts, then you need to give it a recharge to prevent long term damage to the battery plates (sulfate hardening).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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