Battery SQ values dfferent

Wilis
Wilis Solar Expert Posts: 84 ✭✭✭✭
in General Solar Power Topics #1
I have had my solar system working 2 months. I have 12 Trojan T105 batteries. Because of a small PV amount and winter sun, I have only run a freezer and LCD TV. On sunny days I reach 29 + volts and absorb charge and a few days go to float. If I don’t full charge for two days I grid charge to make sure the batteries are full. My batteries are 24v and I have three series strings in parallel. The temp in my box has been holding at 75F degrees. To connect the series string I am using 12 inch 2/0 cable. Each series string is connected to a buss bar and then I have two 6 foot 2/0 cable to my E-Panel. I should have the same resistance in the wires. I used a torque wrench to tighten the battery and cables screws. I have never had to add water to my batteries.
Sunday night I removed all loads from the system. Monday morning, before any charging, I checked my battery voltage and each battery was 6.4 volts. When I checked the SQ all were above 1.65 but some were up to 1.285. Yesterday I did a grid equalization for 4 hours. The Magnum MS-AE meter showed 31v and the amp started at 20 and went down to 12. I hoped the SQ values would be closer together. This is what I found this morning after letting the batteries set about 15 hours with no load. My hydrometer is a glass float type purchased at the local gulf cart shop. It is the same as they use with their batteries and seems to work ok.

(First battery) Cells 1,2, 3-1.275
(Second battery) Cells 4,5, 6-1.275
(Third battery) 7-1.285, 8-1.290, 9-1.290
(Forth battery) 10-1.290, 11-1.290, 12-1.290

End of first series string.


(Fifth battery) 13-1.270, 14-1.280, 15-1.275
(Sixth battery) 16, 17, 18-1.275
(Seventh battery) 19-1.275, 20-1.275, 21-1.290
(Eight battery 22-1.290, 23-1.280, 24-1.275

End of second series string.


(Ninth battery) 25-1.275, 26-1.275, 27-1.280
(Tenth battery) 28, 29, 30-1.275
(Eleventh battery) 31, 32, 33-1.275
(Twelfth battery) 34, 35, 36-1.275

End of third series string.
Do I have a problem? Why is the SQ values not closer, even though they are all above 1.277 which a chart shows is full charge? What can I do to make the SQ values closer in each battery?
· Share on Twitter

Comments

  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
    #2
    Re: Battery SQ values dfferent

    Are you concerned about them being a bit high, or just that they vary by .015 points between the high and low cells? The Specific Gravity values do typically vary somewhat, particularly with that many cells... and given that Hydrometer readings are at best only accurate to within .005 points, I'd say that doesn't seem to be so bad at all.
    · Share on Twitter
  • Wilis
    Wilis Solar Expert Posts: 84 ✭✭✭✭
    #3
    Re: Battery EQ values dfferent

    Thanks,

    Yes, I would like to see the values be almost the same, but being new I am not sure just how close is correct. When I installed the batteries from the store, on Sept 29th the values I read then were 1.270 to 1.280 all cells. Now 1.270 to 1.290 is a greater value. Just trying to learn what is correct for my system. Many here have had years of EQ readings. Because I dont have enough PV's yet I am trying to be careful not to do anything bad to my batteries until I save the money to order more panels. Thanks
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Re: Battery SQ values dfferent

    Trojan says to equalize when difference in SG is >0.030
    Equalizing (flooded/wet batteries ONLY) 3.4.2.

    Equalizing is an overcharge performed on flooded/wet batteries after they have been fully charged. Trojan recommends equalizing only when batteries have low specific gravity, below 1.250 or wide ranging specific gravity, 0.030, after fully charging a battery. Gel or AGM batteries should never be equalized.
    • Confirm that the batteries are flooded/wet
    • Check electrolyte level to make sure plates are covered with water before charging
    • Check that all vent caps are secured properly on the battery before charging
    • Set charger to equalizing mode
    • The batteries will gas (bubble) during the equalization process
    • Measure the specific gravity every hour. Discontinue the equalization charge when the gravity no longer rises
    WARNING: Do not equalize gel or AGM batteries.

    From Trojan's battery manual (PDF):

    Yours seem fine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #5
    Re: Battery SQ values dfferent

    The 1.290 is a little high but not that high.

    The only way I know of to get high mix is either from original manufacture mix being high or someone that adds mixed electrolyte, instead of water, when electrolyte level is low in their battery.

    SG of 1.290 is equal to 34.5% sulfuric acid to water mix.
    SG of 1.270 is equal to 32.1% sulfuric acid to water mix.

    Nominal lead-acid at full charge is SG of 1.277 or 33% at 25 deg C.

    Higher then 33% makes battery a little more energetic on discharge and a little sluggish on recharge.

    Again, you are within manufacture tolerance range.
    · Share on Twitter
  • blackswan555
    blackswan555 Solar Expert Posts: 246 ✭✭
    #6
    Re: Battery SQ values dfferent

    They do not seem bad, you will get higher SG`s if the water level is lower (more dense electrolyte)
    I like to fill to as close to identical as I can get before commissioning and recording initial SG`s on install, can always get back there to compare then, but is not the number it-self that is that important, it is what each is doing in relation to the rest on EQ

    Have a good one
    Tim
    · Share on Twitter

Categories