DIYbanter - View Single Post - A wall-wart alternative

wrote:

My smoke detector draws 7 uA = 60x370C, which makes C = 315 puffs, eg 2
0.001 uF 400 V caps in series, Digikey's P1058-ND, $11.43/100. They also
sell 12 V zeners suitable for 9 V batteries, 1N5242BDICT-ND, $13.65/100.

Nick

You have to supply bleeping power, relying on the battery would be
unsatisfactory. In which case it'll draw bleeping power al the time,
but since its almost entirely capacitive, and a house's total load is
normally lagging, this will in fact reduce overall current consumption.
A tiny tiny bit.

NT