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Author Topic: Approaching monitoring and automation nirvana  (Read 3424 times)
stephendv
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« Reply #15 on: February 07, 2013, 07:33:55 PM »

Ah counter built into the sunny island, it's usually reasonably accurate although sometimes it can make big and sudden self-corrections, e.g. today at 11am it went from 92% to 97% in a sudden jump.





* Screen Shot 2013-02-07 at 20.32.59.png (28.03 KB, 1171x355 - viewed 203 times.)
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nowty
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« Reply #16 on: March 14, 2013, 09:43:41 PM »

The Sunny Island is quite intelligent.
If it just based its SOC based upon Ah counting alone then if the batteries go through several partial discharge / charge cycles the error on the SOC gets worse and worse until its meaningless.
So whilst the battery is discharging or charging, if the voltage it measures is significantly different to what it expects it will make a self correction to the SOC. It also makes another self correction at the end of a really good absorption charge.
It also measures the ageing of the battery by giving a SOH (state of health) which is a percentage of the original battery capacity which the battery can now be charged to.
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« Reply #17 on: March 14, 2013, 11:05:10 PM »

Having spent some time watching what the Victron Battery Monitor does there are still a few unanswered questions. It clearly doesn't just equate Ah used with %SOC - the 1050Ah bank can be say 100Ah down but the monitor will say it's 98% charged. I've always assumed that it was making the correction by doing a running calculation using the Peukert Coefficient ie recalculating the capacity based on the rate of discharge. I think this is where the difference is with the SmartGauge as you don't have to tell it the capacity (I don't know about the SI?). The Victron BM is reasonably accurate if the battery is charged as it expects and it sees a good regular absorption phase with the amps dropping off. It's not so good on days where the PV is a bit intermittent and it sees a similar effect and resets itself thinking the batteries have been charged. I don't think it has anything built in to account for battery ageing so the SI may be more sophisticated. There are probably tweakings I could perform to improve it but as a general guide it's OK. The SI seems like it may have some of the SmartGauge type algorithms built in  Huh
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