I need a formula!

Tigelowe
Tigelowe Registered Users Posts: 9 ✭✭
in Advanced Solar Electric Technical Forum #1
I'm new to the forum and I need a formula or recommendation!

The goal of which is to determine the best length of time for the absorption stage to avoid excess gassing and prolong battery life.
Absorption is currently set to the default 2hr 30 min for TS-MPPT-60.

Assumptions (true for now):

The batteries will always discharge to the same level overnight.
The system load will remain constant during the absorb stage.

Known variables:

System voltage: 24
Battery C20 amps (Trojan flooded): 370
Battery voltage in morning: 25
Absorb voltage: 28.2
Typical battery draw amps at start of absorb stage: 10


It would be nice to be able to change any of the above known varaibles and get a new absorb time to start with.

Much appreciated, Joe
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: I need a formula!

    Welcome to the forum Joe.

    My advice is: don't guess, measure.
    If your usage is fairly consistent you can watch the current during the Absorb stage and keep track of how long it takes for it to get down to around 2% (about 7 to 8 Amps) with no loads (including inverter). Compensate the 'End Amps' for the consistent loads if you have to. When you have that time figure, set your Absorb time accordingly (as close as you can get with a slight favour towards longer).

    Or go buy an Outback FM60 or MidNite Classic 150 and use their combined Bulk timing & End Amps function. If you get the MidNite you'll be able to add their SOC shunt to it when it becomes available and save all the trouble.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #3
    Re: I need a formula!

    Do an experiment. Run the absorption and measure

    1. Battery amps, which will be decreasing then go flat
    2. Specific gravity, which will go up until it reaches manufactirer spcified values.

    Do the measurement every half hours. When both conditions are met, you are at your best absorption duration. It depends on absorption voltage too.
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  • Tigelowe
    Tigelowe Registered Users Posts: 9 ✭✭
    #4
    Re: I need a formula!

    Thanks Guys! Unfortunately I have not been able to get back to this because my MS-MPPT-60 is miss-behaving. While in custom mode it will periodically go into R+Y+G flashing which means some custom parameter has change even though I have not made and additional changes. I have provided MS with log data showing the issue and they just recommended I turn OFF DIP switch 8 and re-enable logging. I have just done this and we will see how it goes.
    -Joe
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #5
    Re: I need a formula!

    Every time I see the title of this thread it kicks off a Grateful Dead tune in my head.

    Back to your regularly scheduled broadcast...
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  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    #6
    Re: I need a formula!
    ggunn wrote: »
    Every time I see the title of this thread it kicks off a Grateful Dead tune in my head.

    I need a charge current twice my age....8)
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #7
    Re: I need a formula!
    mtdoc wrote: »
    I need a charge current twice my age....8)

    Charge up my battery in a Faraday cage... :D
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