Charge Profile - New Batteries

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Rybren
Rybren Solar Expert Posts: 351 ✭✭
in Solar Beginners Corner #1
I picked up four 6V US Battery US 2200 XC2 232 Ah batteries for my new off-grid system at my camp. They are wired in a 24V configuration.

When I received the batteries, two measured a SG of 1.255 across all cells and two were at 1.265 across all cells (Temp compensated readings). US Battery states that 100% SOC is 1.270 or greater.

I hooked up the batteries to the Classic 150 and set the charge voltages to Absorb 29.4, EQ 30.6, Float 26.0 per the US Battery Charge Specs for a 2-stage charger (Float is not a Stage according to them). Absorb time was set to the default of 2hrs and end-Amps were not set. After about an hour of Bulk and two hours of Absorb, the Classic went into Float. A check of the SG showed that the lower batts were up to 1.265 and the others were at 1.275. I decided to do an EQ for an hour to bring up the lower batts. Once the EQ had completed, the lower SG had moved to 1.270 and the others remained at 1.275. I had to return home, so didn't try to do another hour's worth of EQ.

I went back to the camp the next day (Saturday) and it was fairly overcast, so I didn't bother with trying to do an EQ. We used the new system to power the lights for the evening and I played around with testing various loads on the Samlex Inverter. (it ran my circular saw without a hitch) On Sunday, I ran another EQ for an hour and the SG was the same as the day before (1.270 and 1.275). I had to leave and didn't have a chance to try to bring up the SG again.

Before leaving the camp, I set the Absorb time to 2.5 hrs and set the End Amps to 6.9 (3% of C/20). However, on re-reading the Charge specs this morning, it says to run absorb at 29.4V until reaching 3% of C/20 Ah and then hold for 2-3 hrs before terminating. I think that by setting the Classic's End Amps to 6.9, I may be cutting the Absorb off too soon. Luckily, there will be no loads on the system until next weekend (inverter breaker is off) so it will be sitting at Float until next weekend.

The Battery Charge spec says that Absorb Termination can be by Maximum Time of 2-4hrs or by dV/dt (4mv/cell per hour) I have no idea what this means, but I'm pretty sure that the Classic can't be configured this way :D

Just thought I'd share...
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #2
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    Re: Charge Profile - New Batteries

    I am just curious. Why do you equlize that often while 1.270-1.275 SG seems to be good with no variations between cells?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
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    Re: Charge Profile - New Batteries

    Charge specs given for batteries are rarely designed to match the abilities of solar. For one thing their first stage is "constant current" which is (as yet) unobtainable from a solar charge controller. As such you have to fiddle 'til you find what works best on your system. If at the end of charging you find the SG is high enough and the water loss over time minimal then that's the best you can hope for.

    I would not worry about an SG difference of 0.005 per cell at all.
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  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    #4
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    Re: Charge Profile - New Batteries
    NorthGuy wrote: »
    I am just curious. Why do you equlize that often while 1.270-1.275 SG seems to be good with no variations between cells?

    'Cause I'm a noob and I wanted all cells across all batts to be the same.
    I would not worry about an SG difference of 0.005 per cell at all.

    Okay, Okay, I get it. :D

    What aboot ending absorb? End amps or Time?

    I wish I could figure out the Classic Varimax settings for absorb time. There's nothing in the manual and in the Video, Ryan says "I know what works for me..." but there's nothing about what to look for to select the settings.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
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    Re: Charge Profile - New Batteries
    Rybren wrote: »
    What aboot ending absorb? End amps or Time?

    I wish I could figure out the Classic Varimax settings for absorb time. There's nothing in the manual and in the Video, Ryan says "I know what works for me..." but there's nothing about what to look for to select the settings.

    Both. To start with set your Absorb End time to its maximum. Then watch the current (this is tedious) through the Absorb stage during a typical use/recharge cycle. You will see a point where the current 'plateaus'. Check the SG; it will most likely be right up at 'fully charged'. Holding it in Absorb beyond that point is not going to help anything; longer time at high Voltage loses more water.

    From this little experiment you should have two important numbers: an End Amps figure that will include the draw of 'typical' concurrent loads and a maximum Absorb time (how long it took to get to that End Amps rounded up to the next hour). Even so this is only a starting point. As you use the system you may see a need to boost/reduce the numbers somewhat.

    Keep in mind that having these numbers off by a little bit either way will not produce catastrophic results, only a shortening of what would be the maximum life of the batteries. After you used it for a while and find you get to the proper SG reading on any day when full charge should have been achieved you're doing all right.
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  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    #6
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    Re: Charge Profile - New Batteries

    Thanks 'Coot. Will give your methodology a try.

    Jerry
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