[Nut-upsuser] Ablerex MARS

[Arjen de Korte]

Carlos Rodrigues schreef:

> Right now megatec just calculates a linear approximation. It doesn't
> give accurate values, but it is enough to have a fuzzy idea of the
> charge left (like saying "it's almost noon" instead of "it's 12:45"),
> and I'm not seeing how to plot a more accurate charge that fits all
> the models that megatec is supposed to support (especially given I'm
> no electrical engineer).

I'm an electrical engineer and have worked with lead acid batteries
(telecom power supplies) for more than a decade. The only reliable way
to determine the charge level for a battery is monitoring the current
going in- and out of the battery (coulomb counting). And even then
you'll have to compensate for a lot of variables (change of charge
efficiency- and retention over temperature and lifetime for instance).

All methods relying on measuring terminal voltage are unreliable at
best. There are far too many variables involved (temperature, age of the
battery, exact type of chemistry, history of (ab)use, etc) that make it
impossible to give an estimate based on voltage alone.

Arjen