Is it OK to extend the Absorb stage of charging?

Rngr275
Rngr275 Solar Expert Posts: 127 ✭✭
in Off Grid Solar & Battery Systems #1
I posted this on the Midnight site but there are opinions on the site that I really appreciate.

Sorry to those who frequent both sites.

Turns out you don't get a lot of charging in the winter... even on a pretty much sunny day! :cry:

My specific gravity has been running a little on the low side. (1.250-1.265) Do you think it would be OK for the next month or so during the depths of winter to set up my classics in the following manner:
ABS Voltage/Trojan=59.2
Set max ABS time to say 5hrs (no way I can get that much during December and January)
Set EA to around 10 amps (~1.5% of my 740AH battery bank)
No Varimax
Follow me on.

Trying to drive/keep my SG up. I will be keeping a close eye on the water level. Temperature has not been an issue... in my 50degree cellar.

I notice the other day: The batteries were not discharged very much, had Varimax on and follow me on, EA=14A, Min ABS=30min, Max ABS=4hr. The absorb only lasted an hour or so before they went to Float. A quick check of the SG showed that the batteries could have taken a much longer ABS (SG~1.26... Full charge SG=1.277).

What do you think?
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Comments

  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #2
    Re: Is it OK to extend the Absorb stage of charging?

    Hi Rngr..

    Well what is often called Opportunity Charging is what you propose, and just for the situation that you note. We usually do run short on charge power in the short days of Fall/Winter. As to the voltage, experimentation and daily SG measurements will tell all.

    See by your Signature that you have a genset, and would also suggest that you increase the inverter's Charger Abs V as well, for those occasions where you run the genset long enough to spend time in Absorb. Thank goodness the the MN Classics include Remote Temp Sensors, but also make ceratin that all chargers also have RTSes, on the same battery as those for the Classic(S), IMHO.

    And still, there will probably be a number of days when your chargers will not get out of Bulk, but a higher Abs V will help the bank get more charge on those days when you do get into Absorb. And, YES do keep a careful eye on water levels.

    My opinions, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
    Re: Is it OK to extend the Absorb stage of charging?
    Rngr275 wrote: »
    My specific gravity has been running a little on the low side. (1.250-1.265) Do you think it would be OK for the next month or so during the depths of winter to set up my classics in the following manner:
    ABS Voltage/Trojan=59.2
    Set max ABS time to say 5hrs (no way I can get that much during December and January)
    Set EA to around 10 amps (~1.5% of my 740AH battery bank)

    How do you know your end amps is 10?

    Set your absorb time to 'forever' and turn off the end amps function. Check your battery charging amps every 30 minutes during absorb. When the charging amperage stops decreasing, that number is your end amps. It may be lower than the 10 amps you are using.

    Another way is to stay in absorb and check SG periodically. When you get where you want to be check and see what the charging amperage is. That is your end amps.

    Hopefully the two methods will yield the same results.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Is it OK to extend the Absorb stage of charging?

    Remember that an End Amps setting is based on the current going out of the charger, which is not the same as what is going in to the battery if loads are being supplied at the same time. For instance if there is an inverter running and drawing one Amp that has to be included, as well as any constant/consistent loads it is powering. Otherwise you may never achieve the End Amps setting. Follow vtMaps' advice to make sure any such loads are included as part of the setting.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #5
    Re: Is it OK to extend the Absorb stage of charging?

    Well, at least Rngr has the FNDC Bat Mon, so he can see what current is charging the batts.

    The one thing that have been considering mentioning, is in the context of raising Absorption V to get more charging into less time, the Ending Current for full charge will be increased with a higher Vabs, and therefore might need to be changed in the CC. BUT, we are speaking of the CC's EA, and there may not be many days in which this would apply, due to short days and weather. There is also a temperature factor that should also change this EA value, as well.

    As noted previously, none of these settings are set and forget. Measured SG is the true measure of the SOC. CC EA, for me has been the very best method of ending Absorb, but is based on measured SG. EA needs does need to be changed a bit from time to time based on SG readings.

    Another factor, especailly with larger battery banks, is that the way that the bank charges on a given day depnends on how it was recharged in the previous couple days, even if the charger completes a full Absorption in each of these days. One can chase one's tail if large changes are made to charger parameters in a single day. It is often good to make small changes and observe over a few days. Of course if a bank is on its knees, a large change is often needed. YMMV, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #6
    Re: Is it OK to extend the Absorb stage of charging?
    Vic wrote: »
    Another factor, especailly with larger battery banks, is that the way that the bank charges on a given day depnends on how it was recharged in the previous couple days, even if the charger completes a full Absorption in each of these days. One can chase one's tail if large changes are made to charger parameters in a single day. It is often good to make small changes and observe over a few days. Of course if a bank is on its knees, a large change is often needed. YMMV, Vic

    Words of great wisdom! "Make haste slowly", as the Romans said.
    SMA SB 3000, old BP panels.
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