Absorb time for U-225 with SW5548plus??

Just wanted to crosscheck a setting on the SW5548plus charging 16 Universal battery U-225s(6vdc T-105 type). Currently I have inverter set at 2 hour absorption stage when charging from the genset. Is that excessive or not enough to finish off properly for that particular brand? Can't seem to find a consensus on here. I haven't found more than 0.1 volt difference between batteries 1 month after equalization. Currently set to equalize once every 3 months by genset(and monthly by the Tristar hooked up to 12 KC85's) for 4 hours. It would seem that just 1 hr monthly with the generator would do the trick though we only have 25amps AC to play with at the moment. Any comments and tips would be much appreciated :D

Comments

  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭✭
    Re: Absorb time for U-225 with SW5548plus??

    Absorb time depends on several factors. First is the absorbtion voltage setting. You can set between 14.2 and 14.8 vdc. Second is charging current set for phase 1 constant current. The higher the charge current rate the less the battery will be charged when hitting the bulk voltage level.

    SW5548 plus has a second setting that is very useful in terminating bulk charge. You can independently set bulk termination based on current (in addition to time). 5-10% of initial phase 1 charge current is usually good to terminate. If timeout is set short it will switch to float before bulk current drops to 5-10% level.

    Final consideration is how you are using generator and if you have an alternate topping charge source like a PV array. Once battery gets above 85% charge, the charging efficiency drops off alot. You may find you consume almost as much generator fuel getting that last 15% of recharge as it took to get to 85% level. You should also set a charge level, or select generator size, to load generator to 50-75% of generator rated power. This get the best fuel efficiency.

    For my system, during a hurricane outage, where fuel is gold, I run the bulk voltage up to 15.2 vdc and terminate generator within about 10 minutes of reaching that voltage. This gets me slightly above 85% recharge. If more then a week, I do a full recharge once and then return to 85% level recharges.
  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭✭
    Re: Absorb time for U-225 with SW5548plus??

    Sorry, I think in 12v battery increments.

    You have two strings of eight 6v. Two times 225 amp-hour, or 450 amp-out 48 vdc battery system.

    You can charge at 90 amps if you have a 7500 watt generator capable of that power at 120vac output.

    The SW series only measures input AC current (they have no dc current measurement capabililty)

    The best way to figure the setting AC charge current is to calculate output power, divide by inverter efficiency (about 90%), then converter back to 120 vac input current.

    For example, 90 amps at initial discharged state of 8 x 6.15 vdc = 49.2 vdc, would be 4.43 KW into batteries. 4.43kW/0.9 efficiency for inverter = 4.92 kW AC input power at 120 vac from generator. 4.92kW/120vac = 41 amps setting for AC charge on AC2 gen input.

    When approaching bulk voltage of 8 x 7.25 vdc, the dc current will have dropped as it is measured as AC input current. 41 amps X 120 vac = 4.92 kW. 4.92 kW x 0.9 efficiency = 4.43 kW. 4.43 kW / 58 vdc = 76 amps into batteries.

    Last tid-bit. Generators without a rewire (parallel winding) switch for producing full rating power at 120 vac will not make rated power from half leg of 240 vac output.
  • rplarryrplarry Posts: 203Solar Expert ✭✭✭✭✭
    Re: Absorb time for U-225 with SW5548plus??

    David
    I don't rely so much on a time for the absorb cycle. I let the absorb cycle go until the batteries reach C/100 charge rate. In your case that would be 4.5 amps going into the batteries. When that rate is reached then you can consider the batteries fully charged and switch to float. My batteries take more than 2 hours to get to c/100 but less than 3 hours, so I let them absorb for 3 hours.
    Hope this helps,
    Larry
  • BB.BB. Posts: 27,579Super Moderators admin
    Re: Absorb time for U-225 with SW5548plus??

    David,

    Are you using a temperature corrected Hydrometer to measure the specific gravity of your cells? The only 100% accurate way to check the charge of your battery (and individual cells).

    2nd, you might wish to look at a battery monitor--pretty close to being a "fuel gauge" for your batteries. If it saves one bank from over/undercharging, it is usually worth the price and effort to install one.

    The Trimetric is a good lower cost device. I like the features on the LinkLite and LinkPro from Xantrex--they have a programmable output you can set for alarm/turn off inverters if the battery falls below 50% State of Charge (or other values/parameters).

    Very useful especially if you are not the only one using the power system (spouse, guests, etc.)--much easier to check charge levels (at any time, under charge, under load) and for non-techie type people to prevent killing your bank with too deep of discharge.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DavidinNicaDavidinNica Posts: 14Registered Users
    Re: Absorb time for U-225 with SW5548plus??

    Thank you all for the replies! I haven't been able to check back lately(for one internet service is not the best in Central America... ).

    BB - I do have a hydrometer but the float broke getting it down to here :cry: Try finding one of those down here! I too like the Trimetric and have one on order.

    In the meantime I think I will try to do bulk charging in the early morning and let the panels finish off the charge. We'll add more panels soon and get a step down transformer so we can use the generator to its fullest. It seems 2 hours isn't enough for the Absorption stage. In the last few weeks the voltage seems to sag more after completing the charge with the generator.

    :D
  • BB.BB. Posts: 27,579Super Moderators admin
    Re: Absorb time for U-225 with SW5548plus??

    Try looking around automotive/truck related places--hydrometers used to be very popular around those shops in the US when I was young (4+ decades ago :cry: ).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • hillbillyhillbilly Posts: 334Solar Expert ✭✭✭✭✭✭
    Re: Absorb time for U-225 with SW5548plus??

    As Bill said, get a hydrometer. All other "tests" can be misleading under certain circumstances. As far as how long you need to have them in absorb stage charging, it's really best to monitor both the charge acceptance rate AND the SG of the electrolyte itself. Try this for a bit, one the charge acceptance rate drops down to say 2% or so of the total capacity start taking measurements with a good hydrometer, then once all cells are full see how long the batteries were in absorb stage. Hopefully you'll see some consistency here, and be better educated on what your batteries need to fully charge.
    One thing I can say, from personal experience: stay away from cheapo hydrometers (no floating balls or dials). As to the breakage of that float, they do tend to be very fragile; I've broken two of them just getting them to my home (a lot less wear and tear than going all the way to Nicaragua). Don't give up...
    Good luck
  • DavidinNicaDavidinNica Posts: 14Registered Users
    Re: Absorb time for U-225 with SW5548plus??

    Thanks BB and hillbilly! I will try and get a float down here intact :-)
    Can't wait for battery technology to leap out of the 19th century!!! :D
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