Connect with us

Solar charging a small SLA

Discussion in 'General Electronics Discussion' started by scwhiteley, Aug 13, 2011.

Scroll to continue with content
  1. scwhiteley

    scwhiteley

    5
    0
    Aug 13, 2011
    Hello guys and gals,

    I've started figuring and ordering parts for yet another portable stereo project and could use a little input. For this stereo, I'd like to use solar panels to provide charge for the battery pack. It should be mentioned that the solar panels will not be the only source of charge for the battery, and it is unlikely that the panels will ever have to charge the battery in a completely discharged state. That being said, it would be nice if the solar panels could, on occasion, completely recharge the battery if, for some reason, a wall charger were not available (due likely to poor planning and/or the coming apocalypse).

    For starters, I'm thinking of using a 12v 3.2 Ah SLA for the battery, mainly because it is more simple to charge than a NiMH battery pack (I think.)

    The solar panels I'm looking at are rated to provide 15.4v at 100 mA. (although, I could potentially expand the system to provide 200 mA).

    The crux of my question is this: will the solar panels provide enough current to charge the battery in any state (either partially or totally discharged)? And if so, how necessary is a charge controller for such a low current source? In other words, is it even possible for the 100mA panel to overcharge the SLA to the point that it would cause it to gas? Would the appropriate approach just be to connect the panels (via diode) to the battery terminals, no controller necessary?

    Thanks for your consideration,
    Chad.
     
  2. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    A charging rate of 1/32C should be safe enough by itself, and 15.4V is just slightly above the nominal charging voltage for those batteries, with a diode it's within.
    During one full day of sunshine you'll only get 0.8Ah into the battery however, taking 4 full days for a full recharge. Any state is ok, & I say yes to your last question.
     
  3. scwhiteley

    scwhiteley

    5
    0
    Aug 13, 2011
    Excellent, thank you for the reply.

    I'm thinking now that I might expand the solar array to provide 150mA, just to boost it a little.

    I wish i had a good text resource for all of this info. I've never taken any electronics courses, so I'm learning most of this stuff off forums like this.

    Maybe it's time to invest in some reading material.

    Thanks again,
    Chad
     
  4. scwhiteley

    scwhiteley

    5
    0
    Aug 13, 2011
    As a follow up question, would it be okay to charge a 12 or 14.4 v NiMH battery pack using the same, low current, uncontrolled solar setup mentioned above, or is that asking for trouble?

    Thanks again,
    Chad
     
  5. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    What capacity? Nevertheless, even if NiMH is not too keen on overcharging, and even if it's as small as 900mAh it should work just fine.
    Notice that the 14.4V pack will have an end-of-charge voltage of 18V however, and that the panel may run out of steam before it reaches this voltage.
     
  6. scwhiteley

    scwhiteley

    5
    0
    Aug 13, 2011
    I usually use AA NiMH cells which are rated for 2000 - 2600 mAh. I wasn't aware that a 14.4 pack needed 18v at the top end. What's your calculation there? What about for a 12 v pack?

    Thanks again,
    Chad
     
  7. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    100mA / 2000mAh = 1/20C = safe long-term charge.
    It's around 1.45-1.50V per cell, so a 10-cell 12V pack has 14.5-15V end-of-charge.
     
  8. scwhiteley

    scwhiteley

    5
    0
    Aug 13, 2011
    Sounds good.

    Another quick question:

    I think I'd like to expand the solar array beyond the single 100mA panel. I also have some 15.4v 50mA panels. I'm assuming it would be okay to hook up the 100mA panel in parallel with one of the 50mA panels to build a 150mA charger. This seems like a straight forward, no problem assembly, but I've been wrong before. Do you see any problems with this approach?

    Thanks again,
    Chad
     
  9. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    That should be ok, same voltage, only 50% more current. I'd use separate diodes for each panel nevertheless.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-