On Thu, 21 Sep 2017 00:49:18 +0100, "Dave W"
wrote:

snip

Again, (and it still leaves me with a headache) it's all down to the
capacity changing with current drawn. I think thinking of 'remaining
time' is *way* advanced for this project and all I would like to do is
to display the current voltage and the predicted voltage that
represents the 50% DOD at the current current. ;-)

Well if 'remaining time' is too advanced, what's wrong with my simple
formula?

No, nothing Dave ... I'm just still trying to be open to all ideas and
options. ;-)

It's better than nothing.

Quite.

It might be better to display the source voltage
Vo
rather than the terminal voltage Vr, and when it gets to 12.19V you have
reached the 50% discharged point. Vo = Vr + (Ir x Rt) is the rearranged
formula.

I was hoping to display both, the actual voltage and the predicted
cutoff voltage (at that instant current reading) just so that *I* can
get a feel of how things are going (as my feeling on how things are
going may be better in ITRW than any AI). ;-)

snip

As I mentioned elsewhere, if you had 10 points taken from a graph that
represented 10 different currents and their resultant voltages (to 50%
DOD) you could simply look for those 10 and display accordingly.

The trick is to not have just 10 but a completely dynamic calculation
that would work with anything from 1A (realistically) and 30A. ;-)

I can't see the need for that as my three calculations of internal
resistance
were all pretty similar, as would be 10 intermediate curves.

Ok

You mentioned
that
for a liquid battery you could measure the specific gravity to find the
50% point, so surely that point will also have my predicted source voltage
of
2.19V?

Well, if all things do tally then yes, it should. However, the
specific gravity of the electrolyte is independent of the charge rate
or terminal voltage, it's just an instantaneous reflection of the
chemical charge state (so not much use ITRW when on the move without
some auto-reading system (and a non gel battery) etc.


Cheers, T i m