I dont know if you know Northguy from NAWs forum, i asked how he does it, here:
http://www.wind-sun.com/ForumVB/showthread.php?21012-Battery-manager-and-generator-start/page4
His theory is that Ah in/Ah out is 100% efficient, with the primary exception of absorb stage hydrolysis (self discharge being the other factor).
He also debates the topic at some length here:
http://www.wind-sun.com/ForumVB/showthread.php?20759-Internal-battery-function-%28from-another-thread%29
Frankly im still having a hard time understanding it, but the basic idea to not to try to compute SOC rather just the negative Ah from a known charged state. Seems to be a very good starting place. Its how to account for the bubbling stage that i need to go back and reread NG's post.
I think I may have seen that thread before, at least the first part. I regard Northguy as a very bright guy.
I don't think I agree with almost anything electrical or electro-chemical being
100% efficient though. Battery amp-hour efficiency may get close to that at
times though. If it were 100% (no exceptions) then SOC would be easy stuff.
I ~think~ that what might be missed there is mainly I^R losses.
And what discharge and charging C rate is that at ? That will make a difference.
And you can measure battery capacity. You do have to get the
battery to almost 0% by measuring its resting voltage. Deep cycle batteries are
made to be discharged all the way but you don't get nearly as many cycles
so you don't want to measure capacity very often because of that.
Just be careful when charging back up to make sure each battery's voltage
is as equal as possible.
But, battery capacity changes over the lifetime of a battery. Some will get
better capacity with the first charge cycles, level off for a while and then
decline with more aging and A-Hour ins and outs.
If you do not know battery capacity, then you can only know when it is
at 100% SOC, but not percentage of its actual capacity below that 100%
You might get lucky though and the batteries might actually have a similar
capacity to what their rating is ?
The Trimetric has pretty much been the standard in the industry and it
starts out at 94% A-Hr efficiency by default. I wonder why ?
Ralph at Bogart (Trimetric) and others have been making SOC meters
successfully for many many years now and I believe they have been
through this all quite a bit.
There appears to be a LOT of great dialog in those threads, 100% efficiency
or not. These guys bring up a lot of good brain exercise !
Thanks.
boB