[Nut-upsdev] Re: Changes to megatec.c

[Arjen de Korte]

> You will notice that I made the following guesses:

[...]

> - Battery manufacturers recommend a minimum of 10.8V for a 12V battery
> as the cutoff discharge voltage (further discharge will cause battery
> damage) but the UPS is likely to shut off before that, so I
> guesstimated 11V for a 12V cell to be a reasonable "empty battery"
> voltage.

The cutoff charge depends heavily on the application of a VRLA battery. If
you're using a 1/20 C (or 20 hour) discharge rate, 10.8V may be a
reasonable cutoff voltage. However, in most UPS systems, discharge
currents will be well in excess of 2 C. It is not unreasonable to use a
lower cutoff voltage in that case, to account for internal losses in the
battery and/or wiring losses. Common cutoff voltages for a 12V battery in
UPS systems will be as low as 9.7 or 9.8V. You'll get practically half the
specified runtime with a cutoff voltage as high as 11V.

Best regards, Arjen
-- 
Eindhoven - The Netherlands
Key fingerprint - 66 4E 03 2C 9D B5 CB 9B  7A FE 7E C1 EE 88 BC 57