Re: bleeder resistors

Hi Peter,

P = I * E, so P = 9v * .1A = .9W, use 2W resistor for safety (or two 1W
resistors of proper value).

Couldn't tell any difference between using the resistor and the
regulator IC?

Should be safe enough after the fan stops turning (using resistor) to
work on. Might be something left, but not enough to matter. DO unplug
it (240V MAINS) before working on it!

Alan KM6VV


cadcamcenter wrote:

>
> Alan Marconett KM6VV <KM6VV@a...> wrote:
>
> > One might also consider getting one or two 24V fans (or 12V,
> whatever),
> > and connecting them in series with a dropping resistor across the
> > supply. Many of these fans take around 250 mA, just calculate the
> value
> > of the series resistor.
>
> I have a 24V fan (no data on I or W) but measured 0.1A when connected
> to 24VDC which makes its "resistance" 240? I have a 33VDC power
> supply so
>
> 33V = (R + 240)0.1 and R = 90 ohm?
> watt = 0.1x90 = 9 watt?
> (values from hopefully not too faulty memory)
>
> With an arrangement like that, the voltage falls off to a reasonably
> low value after less than 1 minute, but am I asking/expecting too
> much for the voltage to fall off to ZERO after a reasonable time so
> that I can fiddle with the box without fear of discharge in the wrong
> place? I can still measure volts after hours and mV the next day?
>
> I used a 3-legged 24V transistor voltage regulator earlier and
> thought that changing to resistor in series should discharge the
> capacitor much more efficiently, but it seem there is no difference.
>
> Peter