Solar charging an Optima AGM battery

Discussion in 'The Projects Forum' started by privateer2001, Mar 18, 2014.

  1. privateer2001

    Thread Starter New Member

    Mar 16, 2014
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    0
    Hi all!

    I just got a van to store tools in, and also a free Optima Red Top battery N9978RED 1000CA (I think its AGM) to power the door locks (which I don't have a key to) and some LED lighting. The van is disabled (engine shot) and will be sitting in a field far away from power. The battery is down but will take a charge which I will top up with a Gel cell charger before I put it in the field.

    Another friend gave me a solar charging panel about 6" X 12" which comes with battery clips. I think its a "battery maintainer", but its a Chinese jobby, so no identifying markings. On a sunny day, it puts out 22+ volts (open load voltage) and short circuit current of 70ma. I want to use it as a charge maintainer for the battery. Will it work in this capacity as is? Is there any problem with just hooking this device straight up to the battery? Or do I need a "charge controller" in between? The suggested charge rate is C/20 for this battery. http://www.artecindustries.com/Optima-Battery-Group-78-Red-Top_p_27.html

    What I'm concerned about is when this slow trickle charger does bring the battery up to max capacity, will it continue charging? And is there a circuit that I should use for stopping that? Is that what the charge controller does? Or can this unit be used without a charge controller/as is?

    Oh, further: Upon hooking the solar panel up to the battery for a minute today, the voltage output plummeted to 11.5 volts now that it was under load. Putting the ammeter in series, I couldn't really detect much current flow... maybe 10 to 20ma, if that. Any idea if that's normal or should it settle around 13.5V somewhere?

    Any ideas would be welcome as I've never experimented with solar chargers, AGM batteries, or charge controllers. Thanks and all the best!

    Privateer2001
     
    Last edited: Mar 18, 2014
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    As long as there is a diode in series with the outputs then it's fine to just clip this onto the battery. It's not very strong and not going to damage the battery ever.


    The diode is needed at night so the battery doesn't discharge thru the (dark) panel. Lots of panels have this diode built in. This can use just about any diode you find.
     
  3. privateer2001

    Thread Starter New Member

    Mar 16, 2014
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    0
    Ernie, thanks for getting back to me on this. I would imagine this has a diode built in, as well. How can I test that, I wonder, without tearing the thing apart for a visual inspection? maybe hook the panel up, put it in darkness and see if there is any current flow? So I don't need a charge controller unless I had a more powerful solar cell?
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
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    Sounds like your battery is discharged; will need to be charged before a 1 W solar panel can maintain it. See no problem with over charging at less than 70 mA. Your diode check sounds OK, when checking charging current, cover SP & see if current reverses. Start at a meter setting of around 5 A.
     
  5. bwilliams60

    Active Member

    Nov 18, 2012
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    AGM batteries are supposed to be held to a maximum 13.8 - 14.1 VDC. That is why they sell specific chargers for AGM and GEL cell batteries. The fact that it only puts out 70mA may be the saving grace but it would take a while to charge.
     
  6. burger2227

    Member

    Feb 3, 2014
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    Might be a good idea to check the current draw on the van battery when it is just sitting idle. Hopefully it will be using less than 70 ma.
     
  7. #12

    Expert

    Nov 30, 2010
    16,261
    6,768
    This is how I did one for my lawn mower battery.
     
    Last edited: Mar 20, 2014
  8. burger2227

    Member

    Feb 3, 2014
    190
    24
    I did something similar for the one in my car that used a cutoff, but I later found that I really didn't need it.

    [​IMG]

    I adapted it for my hand vacuum charging instead.

    [​IMG]
     
    monaali likes this.
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