[Nut-upsuser] APC Smartups protocol - Hidden Programming Mode

[Arjen de Korte]

> Hope nut-upsuser is an appropriate place to post additional info about
> the smartups protocol, please tell me if not.

We would prefer nut-devel I think, since that's more about the development
of drivers and such.

[...]

> Using car batteries
> ===================

[...]

> I'm a bit concerned about the different capacity of the batteries: Since
> the batteries are connected in series, the weakest one will be
> discharged the most, which in turn hurts its capacity. I'm thinking
> about connecting a resistor (e.g. 220 Ohm, 1W) in parallel to each
> battery, so that they at least get the same tension when being charged.

What do you think a car battery actually is? Six individual 2V cells
connected in series. What you're essentially doing with connecting four
car batteries in series, is just adding more cells in the battery string.
As long as you use the same make/type/age of batteries, there is no need
for equalizing with a resistor, the capacity will be practically the same.

Besides wasting energy, you might prevent the charging circuit from
detecting full battery state (since the charge current will never go to
virtually zero). Only in *very* large installations it is worthwhile (and
cost effective) to charge and monitor each cell separately to make the
most out of the lifetime of them. But you'd be looking at the scale of
batteries used in submarines, rather than at a home/small office UPS.

Best regards, Arjen
-- 
Eindhoven - The Netherlands
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