Absorption time only 5 minutes after a relay setting change

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Elimac asked Feb 27, '22

Absorption time only 5 minutes after a relay setting change

Possible bug in MPPT 250/100. Lead Acid/ GEL battery. Settings as follows:

Absorption voltage: 57V

Float: 54V

Minimum Absorption time: 7h

The 250/100 relay is connected to a LVD circuit. Today I changed the "minimum" closed time of the relay to be 5 minutes, to prevent oscillation. Funny is that the Absortion time became to be today precisely only 5 minutes. Ho can this be? Which situation can trigger such a short Absorption time?

Normally this site has between 3h to 6h. So, luckily I spotted this and am doing manual absorption, since batteries have hit LVD in the last days and the need a LONG absortion time today, not Short!

Any advice is welcome.

MPPT Controllers battery

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Elimac answered · Feb 28, 2022 at 12:03 PM

Yes, today it is ok. So beware, if we change values during the day, the MPPT might restart its algo on that day, and complete behavior change must be observed only on following day.

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snoobler commented · Feb 28, 2022 at 08:01 PM

To avoid repeats in the future, would it have been sensible to disable the MPPT until the voltage dropped to the re-bulk level, enable the MPPT, and then trigger a whole new B-A-F cycle?

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Answer 1 · 2022-02-27T17:42:05Z

snoobler answered · Feb 27, 2022 at 05:42 PM

The adaptive algorithm can shorten absorption time.

Hitting the tail current will terminate charge before the absorption period elapses.

Charging at a very low C rate close to the tail current can shorten absorption time as well.

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Answer 2 · 2022-02-27T23:36:40Z

Elimac answered · Feb 27, 2022 at 11:36 PM

Thanks snoobler, but I don't think that's the case. I'm comparing with other days, same algo, and never had this issue.

I will observe tommorrow, I suspect the reason is other: I changed the seetings today, in middle of BULK phase. Possibly, the MPPT read the voltage at the moment after they were changed and restarted the cycle, as if it was morning. Since the voltage was already very high, the adative algo rsulted in such a short ABS time.

If I am right, tommorrow all will be ok.

To avoid this and other problems, I always try to avoid messing with production sites during the day, but today it wasn't possible.

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