Battery monitor fine-tuning

AceNZAceNZ Solar Expert Posts: 104 ✭✭✭✭
As discussed in another recent thread, I understand that battery monitors only provide approximate readings. However, they are still useful, and I would like to do what I can to improve the quality of the readings mine are producing.

I actually have two. One is integrated into my Victron Quattro inverter/charger; the other is standalone. The inverter/charger uses some degree of temperature compensation, via a probe on the batteries; the other one doesn't. My batteries are eight Trojan IND17-6V.

There are the only three settings on the Quattro:

Capacity (897 AH)
SOC at the end of bulk (90%)
Charge efficiency (95%)

The external meter is a Victron BMV-600S. Available settings and their current values:

Capacity (897 AH)

When voltage is above Charged voltage and current is below Tail current for more than Charged detection time, SOC is set to 100%:
Charged voltage (52.4V) -- vs. 52.8V float
Tail current (4A)
Charged detection time (3 min)

Charge efficiency (95%)
Peukert exponent (1.25)
Current threshold (0.1A) -- current below this level is considered to be zero amps

I've just computed Peukert's for my batteries. Using C/5 and C/20 from the spec sheets, it comes to 1.21.

Any suggestions about how to further tune these settings would be appreciated.

Comments

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Battery monitor fine-tuning

    What sets the SOC to 100% on the Quattro?

    On the Victron and the Quattro, how did you determine the charge efficiency? Is 95% the default value?

    I have a trimetric which resets to 100% when the voltage meets or exceeds Vabs and the current is below 'tail current' (= end amps) for a minute. I think that is the same approach that Victron takes to reset. Trimetric does not have temp compensation, and apparently neither does the Victron.

    I find that in the winter, when my batteries are cooler, the trimetric often resets itself to 100% prematurely. What happens is that my absorb voltage has risen from 29.4 to 30.0 because of temp compensation. My end amps is set to 6. If I am near the end of absorb (30.0 volts, 8 amps), a cloud or a load can drop the controller back into bulk (29.7 volts, 5 amps) which triggers the trimetric to reset. (The trimetric still thinks Vabs = 29.4).

    Another issue with cold batteries is that the battery capacity is reduced, and the SOC is overestimated. Cool batteries have higher internal resistance and therefore higher Peukert factor.

    I don't know if any of this temperature stuff is relevant to your situation... but for those of us with wide seasonal temperature swings, I can definitely see the advantage of temp compensation in a monitor.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • AceNZAceNZ Solar Expert Posts: 104 ✭✭✭✭
    Re: Battery monitor fine-tuning
    vtmaps wrote: »
    What sets the SOC to 100% on the Quattro?

    Their documentation doesn't say, but after watching the charge cycle, I think SOC is reset to 100% when the charger goes into float.
    vtmaps wrote: »
    On the Victron and the Quattro, how did you determine the charge efficiency? Is 95% the default value?

    95% is the default for the external unit. For the internal one, the default depends on battery type. The type of batteries I have aren't on their list of options, but the closest they get has a default of 90%.

    I went through my log books and found times where the Quattro went from charging to discharging within, say 20 minutes, while not in float, and divided the lower discharge voltage by the higher charge voltage. The range was from about 92% to 98% -- that seemed to match-up better with the external meter's default, so I went with that on both meters. However, I'm sure my technique there could be improved.
    vtmaps wrote: »
    I don't know if any of this temperature stuff is relevant to your situation... but for those of us with wide seasonal temperature swings, I can definitely see the advantage of temp compensation in a monitor.

    We don't have huge temperature swings -- winter lows might hit 1C for a few days, and summer highs might hit 29C for a few days. No frost, freezing, snow in the winter. Temp compensation would still be nice, though.
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