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Single Channel Dimmer Bleed


Don Allen

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I have been using Planet One single channel dimmers as dimmers and switch packs for many years, similar to your Botex dimmers, for birdies etc, but got caught out yesterday when I tried to use one as a switch for my new 8 Eyes Gobo light that I got for a 30 second fireworks effect.

 

They have 8 1W led's in them, one for each gobo and with the led's off, do not draw enough power to hold the dimmer off. I ended up with a slow white flash, so had to put a 25W blue lamp on the dimmer as a ghost load. The 25W blue lamp was not noticeable in the rig.

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This happens to most low powered things with a switch mode PSU in when run from a dimmer.

 

Dimmers do have a small current bleed when off through the snubbing components - normally there is not enough to light anything up but in a SMPSU the load is effectively not connected until the input voltage reaches a certain level. So the bleed current charges up the input capacitor until it reaches the lowest valid operating voltage. At that point the SMPSU starts up and delivers a short pulse of operating voltage to the device. But the input capacitor quickly discharges so it goes off again. This repeats continuously giving a flashing or ticking

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