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Understanding SOC

7223 Views 13 Replies 6 Participants Last post by  supchrgamx
I've been digging into the CAN bus trying to read battery state. Here's what I have so far

SOC is available as percent ModePID: 22005B. Standard vehicle PID for SOC does not return data.

max SOC 84.313728. For the rest of the post, I will instead refer to these as decimals ie. 0.84313728
min SOC unknown. Determined one of two ways: (MAX_PCT - 65%) or (16.5*MAX_PCT-10.2). I use the latter.

Polling for SOC every 3 seconds gets the best results. It sometimes gets updates while the car is off, the updates are more frequent when the car is on.

Based on 100% SOC = 16.5kwh, each 1% of SOC should represent 0.165kwh. However, when I try to compare percentages to kwh usage based on knowing the current charging rate, the numbers are insane.

| SOC | Duration (min:sec) | Charge(kwh)/% |
| 0.77254906 | - | |
| 0.77647057 | 5:11 | 0.29152 |
| 0.78431374 | 12:27 | 0.241217 |
| 0.79215683 | 15:03 | 0.20099 |
| 0.84313728 | 0:46:40 | 0.13915

Charging Rate 0.912kw (114v * 8a)

So based on this table, except for the last one, I'm getting 2x the kwh per pct that I should be. Which makes me think SOC is highly inaccurate. I've thought about switching to looking at HV volts/amps directly, but haven't done as much research on it. Has anybody else tried to determine battery status by looking at CAN data?
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I do a comparison between both of my 2013 Volts every six months or so. I am overdue now but here is a capture of my last comparisons of my grey and blue volt from 12/2015 and 8/2016.

My blue Volt runs consistently about 83.5% at Full SOC and 19.5% at fully depleted.

My grey Volt runs at about 85% at Full SOC and 19.5% at fully depleted.


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