"Rheostat"

[nobl13]

I suppose it's reasonable to stop lurking in order to ask a question...

A few theatres ago, I worked for a road house. We had a wide variety of lighting equipment and amongst them were what the boss called "Rheostats." I never actually used them, but they basically looked like dimmers (the ones you put in your house, not theatrical dimmers) in metal boxes, with a twist lock female and an edison male poking out of it. A few times these went out on rentals where the customer didn't have any real dimming controls.

Well, now I'm doing a freelance event and I need a way to dim a Source 4. Does anyone know how to hack one of those poor man's dimmers together, or have some other cost effective measure?

[Charc]

Originally Posted by nobl13

I suppose it's reasonable to stop lurking in order to ask a question...
A few theatres ago, I worked for a road house. We had a wide variety of lighting equipment and amongst them were what the boss called "Rheostats." I never actually used them, but they basically looked like dimmers (the ones you put in your house, not theatrical dimmers) in metal boxes, with a twist lock female and an edison male poking out of it. A few times these went out on rentals where the customer didn't have any real dimming controls.
Well, now I'm doing a freelance event and I need a way to dim a Source 4. Does anyone know how to hack one of those poor man's dimmers together, or have some other cost effective measure?

575W S4? Many dimmers designed for overhead lighting, etc., are rated at 600W. Throw a dimmer similar to this in a junction box, attach appropriately rated cable & connectors, plus strain relief.

[Flyboy]

Originally Posted by charcoaldabs

Through a dimmer similar to this in a junction box, attach appropriately rated cable & connectors, plus strain relief.

We actually use a setup just like that when we need to dim a single light, but don't need board control. We actually have 10A (1200W at 120VAC) rated dimmer switches wired with 14 awg type SJO cable, plus appropriate connectors. This is good even if you have a 750W lamp in your fixture. We have 2kW rated "squeezers" as well (20A 120VAC rated switch w/12 awg SJO).

If you want board control, though, you'll have to rent a small dimmer pack from a local company. You can probably get a cheapy 4-channel dimmer for about $20/week (depending on where you are).

If you're not sure how to wire it, the Do It Yourself network has a step-by-step guide. They also have a cool little video tutorial. Just make sure you have the cable, switch, connectors, and a junction box with strain relief.

[Les]

Look in to autotransformer dimmers. Also known generically (I recently learned) as variacs. If you want to buy one they're cheap on ebay. That's probably what the "rheostat" was. I have a 2,000w here at my house and it's beefy.

[ship]

difference between reostat, auto-transformer and an architectural dimmer for term. First is sort of ok for use overall, the other not listed for other than in a wall box and perminant install. (Not that up to the 2000 Watt versions are not in common use in various forms in a portable way by even me specially made of coruse and breakered.)

Try to avoid just some store bought dimmer in a electrical box - against code in many ways and normally only rated for 500w. Beyond NEC violations, they normally have a big jump between "on" and "off" - like 40% at best and are not really accurate. Only times I send out such things on shows in special Bell Boxes fused or breakered or special NEMA 1 boxes the same, is for shows that won't be using them for active during show adjustment. Shoe box dimmer and a small light board rented in the end at least for liability is much cheaper if not overall in the long run going to be assured to work over such an architectural dimmer that under use will often turn into less a dimmer and more just a switch over time - that dimming curve lessens over time.

[derekleffew]

Type "variac" into ebay and you'll get many results, such as this. Just be careful, as the output is up to 140VAC and your HPL575W, 115V lamp won't last long at that voltage. In theory, it will last only 18 hours instead of 300, at "full" intensity. But it will be bright!

[cutlunch]

Originally Posted by charcoaldabs

575W S4? Many dimmers designed for overhead lighting, etc., are rated at 600W. Throw a dimmer similar to this in a junction box, attach appropriately rated cable & connectors, plus strain relief.

As well as Ships general comments on using house hold dimmers in theatre situations there could be another problem using them.

I had borrowed a box that had 4 of these wired in. They would have handled the lighting load I was using. But as soon I started dimming them they introduced a large amount of hum in the sound system.

We weren't able to have seperate power supplies. So I landed up using a rheostat based Junior 8 system instead.

House hold dimmers may have improved but they are normally built with cheaper components then a theatre dimmer. The inductors used to help suppress interference will be smaller etc.

[nobl13]

Thanks for all the replies. I quite randomly found this "rheostat" equivalent at work (different theatre, long story) today.


I'm still not certain what it should be called. This particular one is rated for 1000w, so I should be fine with a 575w S4... right?

[derekleffew]

Originally Posted by nobl13

...This particular one is rated for 1000w, so I should be fine with a 575w S4... right?

As per our TOS, Control Booth members are legally forbidden from approving of or advocating any particular item or practice involving life-safety, specifically topics involving electrical and rigging.

That being said, and since we love to find problems with pictures...
1. What you have, even if rated for 1000W, is still a non-industrial dimmer.
2. I see no strain relief on either side of the box for the cable.
3. The box is not an appropriate enclosure. Note the open knock-out on the near side.
4. No Circuit Breaker, Fuse, or other OCPD.

I'm sure others will chime in here. As to what it's called, call it a "single, stand-alone, manually-operated, 1000W dimmer". Quite the mouthful for a simple little device.

[Van]

Originally Posted by derekleffew

Type "variac" into ebay and you'll get many results, such as this. Just be careful, as the output is up to 140VAC and your HPL575W, 115V lamp won't last long at that voltage. In theory, it will last only 18 hours instead of 300, at "full" intensity. But it will be bright!

Just wanted to underscore what Derek said in this post. An AutoTransformer is a transformer first and foremost. Most AT's that you see will have a graduated label on the knob side and it will read from 0 to, up to 120% this is because they are transformers and are capable of putting out more voltage than is input to them. Running at more than 100% does reduce the amperage capabilities however. But most importantly you must remember that running an auto transformer at "full" < all the way up> will result in premature failure of whatever 120v lamp/ device you have plugged into it.