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"Rheostat"

Discussion in 'Lighting and Electrics' started by nobl13, Apr 22, 2008.

  1. nobl13

    nobl13 Member

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    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?
     
  2. Charc

    Charc Well-Known Member

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    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.
     
    Last edited by a moderator: May 30, 2014
  3. Flyboy

    Flyboy Member

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    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.
     
    Last edited by a moderator: May 30, 2014
  4. Les

    Les Well-Known Member Premium Member

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    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.
     
  5. ship

    ship Senior Team Emeritus Premium Member

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    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.
     
    Charc likes this.
  6. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    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!
     
  7. cutlunch

    cutlunch Active Member

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    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.
     
    Last edited by a moderator: May 30, 2014
  8. nobl13

    nobl13 Member

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

    [​IMG][​IMG]
    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?
     
  9. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    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.
     
  10. Van

    Van CBMod CB Mods Premium Member

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    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.
     
  11. David Ashton

    David Ashton Active Member

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    You can buy 1 or 4 channel dimmers off ebay for well under $100 new or even cheaper used, and they have slider faders and protection, worth buying one to go with your s4.
     
  12. Les

    Les Well-Known Member Premium Member

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    What key words would one type in to find such dimmers? All I usually find is DJ and homeowner grade stuff. I'd personally like to find a 4-8 channel dimmer panel (architectural style) without all the chases and stuff. Could be analog or DMX. End Hijack.
     
  13. Van

    Van CBMod CB Mods Premium Member

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    Look at American DJ stuff or , shudder, NSI, I believe makes some of those DJ type packs.
     
  14. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    I recently bought this, and am happy with it for what it is. In fact, what they sent was a Chauvet DMX-4.

    If you're looking for something more self-contained, consider Dove Systems. The SceneMasterI is a staple for rental houses for small shows.

    The little 6ch. Leviton 1000 console, or PocketConsole™ and "shoebox" dimmers would be a good choice also, giving you DMX control. I think it would be difficult to find an analog-only solution these days.
     
  15. ship

    ship Senior Team Emeritus Premium Member

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    Should be fine... looks like a 1Kw dimme from the rear and in a bell box that - what’s that has a knockout hole open from the side?

    Such dimmers are only rated for wall use, but in a bell box within some spirit of the code in knock out holes not being knocked in and shorting etc. Still wire nuts are never acceptable for use on portable equipment and I don’t see a strain relief in use, much less I see some kind of in-line splice within the cable going on within the box - ... interesting work... not normal practice in the box itself not seemingly grounded that’s a bad and against code type of thing amongst stuff like lack of strain relief for the cord observed etc.

    Lots of reasons not to use the box presented, but on the other hand given the dimmer, this even without circuit overload protection over it... been there in using them and they do work. Sort of a grey area - in this case I would not though closer than to being within a wall box type 1900 type wall duplex box.

    Yep, close to but missing lots of details and in part why one typically rejects such a thing. And what does happen to that electrical box if under multitudes of that box bouncing about as carried up a stair case or dragged along a floor when the wire nut comes loose and the box touches an energized circuit?

    Someone had an idea but not the spirit of the code or in general concept of safety in mind in screwing up a good start. Strain relief? Perhaps not so much afterall.

    Reostat, Variac, Auto-Transormer... This 1Kw dimmer is better quality but no so much that it does in this instance not qualify as spare parts to be taken apart and not used.

    I'm also in further noting this spice the lack of a 6" of wire out from the tap on both sides of that tap. This in part no doubt due to the in-line splice of the cord. Hard to do a proper splice if just splitting the jacket of the cable some, removing some wire and adding a wire nut as best possible. Hard to do properly - especially with wire nuts sinking down to the bottom of your workable area on the cable jacket in perhaps it got tight or perhaps it bottomed out on the cable jacket.. .shouldn't be a question - should if properly done be a 6" lead of wire within the box.

    Nothing about how this was done was proper other than perhaps the dimmer and box choice... after that a world of difference between what is properly and professionally done and something that is hack the NEC would attempt to save lives in not using by way of rules against the use of. You will no doubt also note a tag on the dimmer stating something like not other than for in the wall use. Important concept though broken - only broken with care and for special purposes and only than if properly and safely done within the spirit of its use.

     
    Last edited: Apr 29, 2008
  16. ship

    ship Senior Team Emeritus Premium Member

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    Got my variacs and use them frequently for either low voltage or test lighting. Mine range from 0 to 130v. Funny thing is every time I meter their output its not accurate to the scale. The 130v setting is in my case at least not 130v given a supply voltage of 120v, its 120v. Possible but in my case the scale itself is reletave and if I'm using it I meter out what the output voltage is for accuracy if I need accuracy. Mine at least does not add to the voltage supplied but potentially it could in making that 300 hour lamp into a as stated 18 hour lamp.

     
  17. JD

    JD Well-Known Member

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    Yea, I have one of those too. Dirt cheap, and works nice, despite coming through with 14/3 (at least the Optima does)

    One heads up- They rate the unit at 10 amps per channel (2400 max for all), but only use the BTA16 triac (16 amps) so it's really more of a 600 watt per channel unit. If you get board, you can change them to BTA24 triacs (same package, 25 amp rating) for about $1.84 each. All those little 4 packs like the Elation and Chauvet seam to be that way.
     
  18. JD

    JD Well-Known Member

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    Very Premature! (As quartz lamps push the limit to begin with.)

    FYI: Generally, Variacs have 4 terminals or leads. They are Neutral, Variable Tap, Fixed Tap, and End Winding. For bench use, the Neutral and Fixed Tap terminals are used to input line power, and the output will be 0 to 120%. For use as a lighting dimmer, the Neutral and End Winding terminals are used, and the output is 0 to 100%. I have seen a few that have 5 terminals, with the fifth being at about 20% . This is rare and is this way in case the core needs to be reverse rotation.

    Ship, it's possible that your's already has the input moved to the End Winding position.
     
    Last edited: Apr 29, 2008
  19. ship

    ship Senior Team Emeritus Premium Member

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    Hmm, very interesting note that I'll check on. Just got in a 30KVA transformer that had five taps and instructions on how to do so, this could be the possibility in while dial said 130V+ it could only max out to line voltage. Never opened them up(dual dimmer) and that would be a very valid point to check into. Thanks.
     

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