Power Failure Questionaire Help

Ian Johnston wrote:
On Mon, 20 Jun 2005 14:00:20 UTC, T o d d P a t t i s t
wrote:


"Ian Johnston" wrote:


On Fri, 17 Jun 2005 18:44:03 UTC, T o d d P a t t i s t
wrote:


Not directly They recommend an external 22,000 mfd
capacitor.

Are you sure it's not 22,000uF? 22,000mF = 22F is a blinking large
capacitor (not impossible, these days - I've used a 10F one).

Sorry, yes it's micro 10^-6 not milli 10^-3


Mind you, since capacitors in the 10F range are available, not too
expensive, and about the size of an AA battery, it might be worth
using one. Just be careful folks - Very Nasty Things Indeed will
happen if you short one of these suckers. Stick a discharge resistor
across it for a start.

Ian

The 22,000 uF cap recommendation was a very ugly hack recommended by
the manufacturer, trying to respond to the rules change. Doesn't
work very well, since the half second of hold time reported is somewhat
short of the 5 minutes in the rules.

Worse yet, it causes huge surge currents when it's connected to the
battery, which could blow fuses, diodes, or damage switches. Just
adding the cap is a terrible idea. I'd never do that, without additional
circuitry to handle the potential problems. The supercaps would be
a disaster without additional circuitry.