Constant power in dimmer circuits?

[Sayen]

Just a quick question - maybe a 'duh' moment, but...

I'm helping a local school troubleshoot their theater. They have a Strand CD80 dimmer rack, and a number of circuits which do not seem to work. Sending signal from a 1-1 patched console turns on about half of the circuits. However, plugging a plain old fashioned Home Depot circuit tester on a 2P&G adapter shows constant power on every circuit - just enough to light up the tester. Is that normal? I've used the tester in other theaters and have never noticed it lighting up even when the circuit isn't switched on by the board.

There is not enough power to turn on a light without the console.

The company that did the install was somewhat less than reputable, so I'm not sure where to begin the investigations.

[icewolf08]

Yes, it is normal, there is usually a little bit of voltage leakage even when the dimmer is at zero. As you said, not enough to light a lamp, but enough to trigger some electronics. It is usually no more than around 3 volts, but on older dimmers or dimmers where the trims are off you could get a little more.

[xander]

How old are the racks? When dimmers get old the pots can leak. The leak might be enough to power a very small lamp.

-Tim

[Sayen]

Thanks!

Couldn't be that old...maybe 10 years or so? There aren't any records for the theater that we could find.

[Footer]

Most dimmers always have power on the line until there is resistance on the line. This is why you have to put "dummy" loads on flicker lamps. This is also the reason why you should not use off the shelf circuit testers on dimmers. Either use it in conjunction with a 100w light bulb and a two-fer or buy a tester made for theatrical use. These testers, such as the Gam-Check or generic tester such as the one below have a resistor in line with the tester circuit.

[jerekb]

So for the longest time every one said that our SL floor pocket containing channels 18 & 19 didn't work. I decide to test this one day and found that they were just labeled or wired wrong cause if I brought up 18 then 19 came up and vise versa. now i just make sure and patch them switched to avoid confusion. so when you test them try testing them all at once or something like that.

[willbb123]

Originally Posted by jerekb

So for the longest time every one said that our SL floor pocket containing channels 18 & 19 didn't work. I decide to test this one day and found that they were just labeled or wired wrong cause if I brought up 18 then 19 came up and vise versa. now i just make sure and patch them switched to avoid confusion. so when you test them try testing them all at once or something like that.

I know our ETC Sensor dimmers can be patched at the dimmers. I would assume you can do it with most dimmers. That way you dont have to worry about when you make a patch sheet and patch the board.

[willbb123]

Originally Posted by icewolf08

Yes, it is normal, there is usually a little bit of voltage leakage even when the dimmer is at zero. As you said, not enough to light a lamp, but enough to trigger some electronics. It is usually no more than around 3 volts, but on older dimmers or dimmers where the trims are off you could get a little more.

I am designing for a Community Theater right now and we are renting some 6 channel Leprecon dimmers. They have the extension cables that have the little LED that lights up when powered. When have the dimmers powered, but not on (from the board) there is enough current to power the LEDs in the cables. As soon as I plug in a light, the LEDs go out. So I'm thinking the same thing is happening to you with the tester.

I have read (no idea the source) that most dimmers "leak" by design. It is not enough current to make the lamp glow, but it heats it. That way it lessons the chance of heat shock and the lamp blowing when you bring it up to full.

As to why your dimmers are not working.... I have no idea...

[Sony]

Which half of the circuits light up? Is the rack addressed properly? What model rack is it? What board is it connected to? Have you tried it with a different board?

I have a Strand CD80 Supervisor rack at work, we may be able to help you out more if you give more information.

[seanandkate]

Yea, the dimmers aren't leaking. That's what's called their "trim" level -- and it's settable (I remember setting them on old CD80 portable packs). It's one of the many reasons you unplug an instrument before relamping regardless of whether or not the fader is at "0".