Equalizing Charge Question

I have modest stand-alone PV system with four PV panels of mixed makes (about 180 watt total) and four 6 volt 220 amp Exide golf cart batteries wired in pairs for a 12 volt system. Also a 12 volt backup generator. PV system has a Solar Boost 2000 controller with an equalizing charge button.

Lately I've thought it time to equalize the batteries and pushed in the equalizing charge button. The batteries freely gas (bubble) because we have been getting sun the past week or more and the voltage rises to about 15.16 volts, but doesn't want to go higher it seems.

Don't I have to get the batteries up to about 16 volts to really equalize them?

Question: should I leave the equalizing charge button on day after day until the voltage rises to 16 volts or will I get enough benefit at 15.xx volts? It makes me nervious that they gas like that and I don't want to damage them by over-charging. Normally the regulator cuts the charge at 14.1 volts.

I got 10 years of use out of my old set of golf cart batteries (Batteries Plus brand) and the current set was bought in 2003 and still going strong. My loads are light but I don't pay attention to the system too much because it is so darn reliable and just works so well most of the year.

Now, however, we are getting into the shortest months plus considerable cloudy weather so of course I am paying more attention of late. Better check the water again soon...

Thanks
PV user since 1988

Comments

  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Equalizing Charge Question

    Paul,

    Trojan recommends a 15.5 V EQ voltage @ 80 F for their flooded-cell batteries, including their T-105 (GC2 "golf cart") model. This is a pretty standard value for flooded cell types. See: http://www.trojanbattery.com/Tech-Support/BatteryMaintenance.aspx I don't know the Exide specs.... their documention doesn't seem to be as good.

    Your 180 W array is fairly small relative to your 440 Ah battery bank. It may be having trouble supplying enough current to cause your batteries to reach their target EQ voltage. You might try completing the bulk and absorb cycles by ~11 AM local solar time, and then see if you can get in an EQ charge cycle between the peak Sun hours of 11 AM and 1 PM local solar time.

    Also note that the 2000E's temperature compensation feature affects the EQ voltage as well as the absorb voltage. If you're using temp comp and the batteries get warm (>77 F / 25 C), the controller will automatically reduce the charge voltage. For example, if your target voltage is 15.5 V and the battery temperature is 86 F / 30 C, the controller will reduce the charge voltage to 15.35 V.

    HTH,
    Jim / crewzer
  • paulstamserpaulstamser Solar Expert Posts: 86 ✭✭✭
    Re: Equalizing Charge Question
    crewzer wrote: »
    Paul,

    Trojan recommends a 15.5 V EQ voltage @ 80 F for their flooded-cell batteries, including their T-105 (GC2 "golf cart") model. This is a pretty standard value for flooded cell types. See: http://www.trojanbattery.com/Tech-Support/BatteryMaintenance.aspx I don't know the Exide specs.... their documention doesn't seem to be as good.

    Your 180 W array is fairly small relative to your 440 Ah battery bank. It may be having trouble supplying enough current to cause your batteries to reach their target EQ voltage. You might try completing the bulk and absorb cycles by ~11 AM local solar time, and then see if you can get in an EQ charge cycle between the peak Sun hours of 11 AM and 1 PM local solar time.

    Also note that the 2000E's temperature compensation feature affects the EQ voltage as well as the absorb voltage. If you're using temp comp and the batteries get warm (>77 F / 25 C), the controller will automatically reduce the charge voltage. For example, if your target voltage is 15.5 V and the battery temperature is 86 F / 30 C, the controller will reduce the charge voltage to 15.35 V.

    HTH,
    Jim / crewzer

    Thanks for the reply!

    Makes sense. I'm glad it's not 16 volts like I thought from early Home Power mag days.

    Yes, my system might be too small and I have room on the rack for another module and I probably should invest in one. That would also help me on cloudy days.

    I dug around and found the user guide for the SB 2000 and it says pretty much what you did. I'm going to try and equalize on a monthly basis and try to do it right. I must admit that I've been very sloppy and neglectful with it over the years.
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