SW4024 Absorb/Bulk Timer?

stmar
stmar Solar Expert Posts: 373 ✭✭✭
in Grid Tie and Grid Interactive Systems #1
I still can't seem to understand the Absorption/Bulk Timer on my Trace/Xantrex SW4024. It is Menu 10 Set Absorption Time h:m. I have it set for 2 hours and when the grid goes down and then comes back on it should start that time. Since I put in the new battery bank it does not take the full 2 hours and instead goes to Float in a shorter time, sometimes less than an hour. I can't seem to find any definitive documentation so can anyone with an older SW4024 chime in and tell me if they have the same experience. When I had my older battery bank it took the full 2 hour charge, I did back off the charging amps from 30 to 12 amps since I am on the grid and wanted to set it where my generator could handle it without having to change anything and that is the only setting that I have changed with my new bank.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #2
    Re: SW4024 Absorb/Bulk Timer?

    How low does the Voltage drop ?? There is probably a re-bulk voltage trigger that has to me met before it resets and will do a full charge cycle. It might not really be in Absorb, it's just raising the amperage to raise the voltage. Also the battery bank size and the 2 % ending amp rule may over ride the time. New batteries can really surprise you as their charge level can really come up fast ( voltage ) and it can throw things off. your SG level is the Gold Standard.
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  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #3
    Re: SW4024 Absorb/Bulk Timer?

    It drops to about 25.4 under load of about 4 amps and if I take the load off it jumps to 25.7 without charging. These are AGM so SG is not available. I guess everything is working as it should but I wanted to see if anyone else had a similar experience. My bank stays in Float, 26.8, most of the time, if the load is light and the sun is out during the day it goes up to the 27 - 28 range so the bank is being charged.
    P.S. I can't find anything about what would "trigger" a less charge time, it makes sense though.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #4
    Re: SW4024 Absorb/Bulk Timer?

    Just a guess here, but most 12 V systems have a 12.5v trigger, so a 24V system could have a 25v or below trigger for a new cycle. Sorry, I missed your AGM batteries.
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  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #5
    Re: SW4024 Absorb/Bulk Timer?

    Wonder where I could find out about that? I don't recall anything in the documentation/manual. It does seem like what may be happening, the voltage has never dropped below 25 to my knowledge.
    Blackcherry04 wrote: »
    Just a guess here, but most 12 V systems have a 12.5v trigger, so a 24V system could have a 25v or below trigger for a new cycle. Sorry, I missed your AGM batteries.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #6
    Re: SW4024 Absorb/Bulk Timer?
    stmar wrote: »
    Wonder where I could find out about that? I don't recall anything in the documentation/manual. It does seem like what may be happening, the voltage has never dropped below 25 to my knowledge.
    Call customer service. I have a little cousin SW3012, on the SCP I see Bulk, Absorb, Float and Charging. I see it switch to charging status after it's gone to float and voltage drops the amps climb it will switch out of Float to " Charging ". As the amps drop it will then drop back to Float. This is something I have never saw on a Xantrex before.
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  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #7
    Re: SW4024 Absorb/Bulk Timer?

    We had a storm and a few bumps so the inverter went to bulk several times, it then went to float in about an hour. When it was in bulk, charging at 28.8 volts, the AC input was only 4 amps. I have the max charge set at 12 amps so there must be some automatic control that determines length of time for bulk and rate of charge.
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  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #8
    Re: SW4024 Absorb/Bulk Timer?

    Does anyone know why the AC input would show 4 amps while it is in Bulk charging? I thought it would be 12 amps since that is what I have it set for.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: SW4024 Absorb/Bulk Timer?
    stmar wrote: »
    Does anyone know why the AC input would show 4 amps while it is in Bulk charging? I thought it would be 12 amps since that is what I have it set for.

    Probably the difference between the maximum limit (12 Amps) and what it needs at the moment (4 Amps).
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  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #10
    Re: SW4024 Absorb/Bulk Timer?
    Cariboocoot wrote: »
    Probably the difference between the maximum limit (12 Amps) and what it needs at the moment (4 Amps).
    So it is only taking 4 amps of grid power to keep it at Bulk, 28.8? Makes sense, once it gets to Bulk it would just be maintained at that voltage and the amp draw would be less than max so as not to overcharge. Still can't find anything or anyone that knows about why charge time is cut short, has to be because of the state of charge.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: SW4024 Absorb/Bulk Timer?
    stmar wrote: »
    So it is only taking 4 amps of grid power to keep it at Bulk, 28.8? Makes sense, once it gets to Bulk it would just be maintained at that voltage and the amp draw would be less than max so as not to overcharge. Still can't find anything or anyone that knows about why charge time is cut short, has to be because of the state of charge.

    Since the chargers in inverters aren't constant current the current is at its maximum when Voltage is lowest. Once Absorb level is reached the current will definitely go down (while Voltage remains the same) as that stage progresses.

    There are several ways of determining how long charging remains in Absorb. One is the Up/Down timer which counts up during Bulk and then down during Absorb, but this is usually not used in AC chargers. Another is current level (i.e. End Amps) where Absorb stage is terminated based on the amount of current being drawn (this is sometimes expressed as % of the maximum charge rate and sometimes as SOC). Some Magnum inverters actually have a shunt connection and will measure SOC the way a battery monitor does, and use this to control charging. I'm not sure if the old SW's do this or not. And then there is the old standby 'fixed time' Absorb which says "X hours" and that's it. Really not the best way to do it as depending on actual SOC the time may be too long or too short, neither of which is good for batteries.
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  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #12
    Re: SW4024 Absorb/Bulk Timer?

    As you can see from the start of this post, I thought my inverter was fixed time but after observing it over the last few months I think it is more advanced. I found a guy that may know so will see if he has any input.
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