Explain finish amps

Chuck46
Chuck46 Solar Expert Posts: 95 ✭
in General Solar Power Topics #1
Read everything I can find and nothing is clear. When in the absorbtion state of charging the amps are refered to end, or finish amps.

:confused:So is it the amps I should set my charger to for the absorbtion period or is it the amps the chager ends absorbtio at?:confused: It would be nice if it was cleared up for me but the lititure and answes I have found are not clear on what it means.
Chuck
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Explain finish amps

    It's a choice.
    You can have the Absorb period either run for a period of time (up to 4 hours) or you can have it end when the current rate drops to the "finish Amps" (also programmable).

    In the time mode, the FM counts up from when Bulk charging starts to when Absorb level is reached. It uses this as the timing for the length of the Absorb cycle, up to the limit set (1 hour up to 4 hours).

    In the "end Amps" mode, it remains in Absorb until the current drops below the set value (usually 1-3% of the batteries' total Amp hours).

    Which is better is a matter of choice, somewhat dependent on how your system is used. I prefer the time method myself, but in some cases the end Amps may work better. Judge one against the other: if after full Absorb time is completed the current is still above 3% then pick the time mode. If the Amps drop below 3% before the Absorb time is up, pick the end Amps.

    Others may have their own preferences/opinions.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: Explain finish amps

    To a degree, as I understand, it also depends on your load profile...

    If you do not use much electricity during the day, then the charge controller is "seeing" the actual battery bank usage and when the charge current falls to ~2% of bank Amp*Hour Rating, then the controller can "know" the bank is fully charged.

    If, however, you use >2% current/energy during the afternoon, the controller will never enter float mode because it cannot tell if it is charging a battery or supplying power to your computer system (for example).

    In that case, a ~2-4 hour timer would give the battery enough time to get fully charged, then the controller can fall back to float voltage and still continue to supply your other loads at the time.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Explain finish amps

    Right you are, Bill!

    In fact a scenario where end Amps doesn't work is with a steady load:

    225 Amp hour bank, so end Amps is set to 2 (1%). But that is current from the controller to the batteries, and doesn't take into account the draw from the batteries to the inverter. 2 Amps of current going out means end Amps isn't reached. Batteries stay at higher Absorb Voltage too long; lose more water, shorten battery life.

    Conversely if you have poor insolation the charge controller may be in Bulk mode at a small current for some time before the sun gets full on the panels and charges them properly. This means the Absorb time clock will have run up high for no reason. It may try to Absorb for 3 hours when only 2 is really necessary. So some observation and experimentation is needed to get the settings right for any given system.
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,022 ✭✭✭✭
    #5
    Re: Explain finish amps

    I find that using the finishing amps control doesn't work well when the wind is blowing and the sun is shining.

    Towards the finishing setpoint on the MX, the wind controller is also charging the batteries, the Mx will drop down it's input and presto you're at the finishing amps setpoint when the charge is not complete.

    I go for the time setpoint and check the sg to determine SOC. 2 days of good sun and full SOC is reached well before the absorb time is reached...kick it down to float at that time. But then I'm here and the batteries are FLA's, a SOC check takes 10 seconds.

    Ralph
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  • Chuck46
    Chuck46 Solar Expert Posts: 95 ✭
    #6
    Re: Explain finish amps

    Lets see if I have it close to right.

    My battery setup is Crown CR395 2 rows of 4 series/parallel for 24 volts@790 amp hrs. So my finish amps should be around 7.9 amps. I have my time set to 5 hours on my FM 80 so should I leave the time or what. If they are selectable on the FM 80 what am I missing, been through the manual and cant find where they can be selected? This may be why I burned up a set of batteries. Any help?

    And thanks for things it seems to be clearing up in my gray induced brain.:D
    Chuck

    Well re read manual and I think I understand, it does it on its own. Automatic which ever condition is met first thhats the one it uses, is this right?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Explain finish amps

    It's under the Advanced menu. Absorb Time Limit comes first, pressing <NEXT> should get the Absorb End Amps (page 50 of the manual). Remember this is either/or; if the Absorb End Amps is set above zero, that takes precedence and will switch the charger to Float mode regardless if the Time Limit has been reached. If the End Amps is not reached the timer will continue counting down until it hits zero.
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