Solar Charging a battery whilst on load

Discussion in 'General Electronics Chat' started by Steven Ksiezak, Nov 30, 2010.

  1. Steven Ksiezak

    Thread Starter New Member

    Nov 30, 2010
    This site has an excellent article giving information on battery Ah ratings and how it affects discharging and charging however I need to know how to rate a solar charger under a given set of circumstances. I have a lead acid battery powering an electric fence energiser. (I know it would be better with a deep cycle battery).

    The problem is this. The battery is a rather large 12V 120 Ah. The energiser takes 160 mA. The solar charger I want to use is a 12W unit delivering a peak O/P of 650 mA. I will use a controller to stop over charging. I am taking the simplistic view that the load is small in comparison with the top up current, Am I right or should I lower the battery Ah or could I get away with a smaller solar panel. What obvious point have I missed.

    Any help gratefully recieved

  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    That may not be enough solar panel to keep the battery charged.

    Peak power is almost never seen, once a panel has been installed for a few months.(Initial readings over the first week or two can be extremely good/high)
    Peak power also only occurs for one or two hours a day(sunny ones).

    Figure 8 hours of useable output with a majority of it being about 1/2 power(say 4-5 hours) SO you would get 300mA charge current for 5 hours(good sun). That's only 1.5 Amp hours of power. Meanwhile the circuit has used almost 4 amphours of power in a 24 hour period.

    You need a much larger panel and a circuit to energize/de-energize it based on battery voltage under load.
  3. retched

    AAC Fanatic!

    Dec 5, 2009
    For more reliable service, a larger panel or an array with a charger would do the trick.

    Will the fence unit run directly off the panel?

    I would calculate the drain from the battery versus the recharge time with available sun.

    Here is good info on charging.

    That will give you the info you need to size a charger for the battery.

    Remember to figure in the hours of sunlight you get a day.
  4. SgtWookie


    Jul 17, 2007
    Keep in mind that charging lead-acid batteries is only about 75% efficient. For every 1A you put in, you only get 750mA back out; the rest of the power is dissipated as heat due to the chemical activity.

    Automotive-type batteries will quickly fail if used in a deep-cycle application.