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BA working great, unusual problem though...

Posted: Sun Aug 29, 2010 7:00 pm
by timoski
which is when turning OFF the power dosent drop out straight away as you would expect. Its quite a slow drain down to 0V, as seen on the ole multi meter. What could cause this?

Also, I need to know how to wire the power LED. Searched high and low on the site and the forum ,but came up empty handed. Any help , especially the LED , would be greatly appreciated. Thanks!

Re: BA working great, unusual problem though...

Posted: Mon Aug 30, 2010 11:08 am
by chrisp
That's normal, Timoski The caps on the power supply store energy (as well as even out the spikes), so when you switch off that energy is slowly drained (the LED, is the major current drain on the cap's power after switch off, so when you get the LED in place it will improve the power down significantly). I once did a project with a stupid amount of capacitance on the line, and it took over a minute to power down after the power was switch off. In fact, that was dangerous because it meant there was still a lot of voltage left in the box even after the power had been disconnected.

Power LEDS are pretty straightforward to wire - run a wire from your BA 48V to one leg of a 4K7 resistor, the other leg to LED A (the longer leg), and LED K (the shorter leg) to 0V on your BA.

Everyday LEDS should run at about 10-15mA - any more and you shorten their life and increase power demands, any less and they get a bit dim (or don't light at all). Now V=IR so R=V/I, in this case 48/0.01 (for 10mA) = 4K8 ohms. For 15mA its 48/0.015 = 3K2 ohms. Any resistor between those two values should be fine.