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Gobo Rotators

Discussion in 'Lighting and Electrics' started by calkew5, Jul 7, 2009.

  1. calkew5

    calkew5 Member

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    I have a question about gobo rotators, which I have never used in my life up to this point.

    I've just started a job as a resident designer in a theatre that has a couple of them. All I have left from the last guy that worked here is a collection of paperwork, a sort of "bible" they pass down with the inventory, quirks of the space, admonishments, safety warnings, etc.

    Inside, I found this note:

    "Never plug a gobo rotator directly into a dimmer-always plug into a ghost load first. If you don't do this, the gobo rotator may be seriously damaged."

    Is this true? I know, in the lighting world, everyone is a student and these sort of superstitions get passed down for generations without ever actually being tested. I ask because I have never heard this before.

    I know you're not supposed to use certain kinds of motors with dimmers, but that you can use them with others, and that rotators are specifically designed to be run from dimmers. I also know that a ghost load can help dim really small loads completely to zero. But I've never heard of a ghost load preventing damage to a motor. After all, there's a transformer on the thing rated for 120V (It's a TwinSpin II non-indexing).

    I wonder if it might be a quirk of the rig? The setup here is a little strange. They've got an old 48-dimmer road pack hard-wired into the building. Each dimmer is only 1.2k and they use triacs. Also the wiring on the grid is like 35 years old and apparently shoddy from the beginning...would any of this matter?

    Thanks, guys. And hello, by the way. This is my first post but I've been reading for a while and the quality of information here is outstanding.
  2. gafftaper

    gafftaper Senior Team Senior Team

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    First off you have the one Gobo Rotator out there that is actually designed to be run on Dimmed power. All the other brands require you to run them on a truely non-dimmed wall outlet. Any of those rotators could be damaged if run through any sort of dimmed power.

    The basic Gam Twinspin is designed to simply run off a dimmer the higher the setting of the dimmer the faster it turns. If you were to set it up without a ghost load it's possible that it would be impossible to stop the rotator from working. You could pretty easily burn out your rotator if it was left running 24/7.

    See this recent thread for a discussion of ghost loads and a mirror ball rotator motor.
  3. soundlight

    soundlight Well-Known Member

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    Rosco Vortex 360 can also be run off of a dimmer that can handle inductive loads. Just wanted to clarify this.


    Back on topic: In terms of running the Twinspin IIs without a ghost load, I do it all the time. However, it could be a quirk of the system, something about the specific dimmers or something like that. Dunno.
  4. derekleffew

    derekleffew Senior Team Senior Team Premium Member

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    There's a problem with that phraseology, as one can't plug anything into a ghost load--it has no female connector.

    Perhaps the writer was being overly cautious: much as we all preach here to never plug a moving light into a dimmer, there are exceptions and we've all done it.
  5. calkew5

    calkew5 Member

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    I think I get it. Perhaps what the writer meant to say was: "If you use a gobo rotator directly with a dimmer, you have to employ a ghost load or it won't dim to zero, therefore it won't stop, and it will run forever until it breaks."

    Or, he/she used some other rotators on dimmers, broke them all, and then bought some TwinSpins so that wouldn't happen again.

    Thanks guys.
  6. gafftaper

    gafftaper Senior Team Senior Team

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    Thanks, I didn't realize that.

    Have to agree that it's either an overly protective person writing the manual or a unique quirk of your dimmer system.

    I say give it a try and see if it rotates when the dimmer is turned off. If it does use a ghost load. If it doesn't keep an eye on it anyway just in case.
  7. Kelite

    Kelite Apollo Staff Premium Member

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    Now that the issue has been cleared up by our resident experts, I'll step in and make a small comment. :grin: As mentioned in one way or another, a wall-wart transformer steps down 120V AC to 24V DC for use by the small, automotive style motor. The higher quality (read more expen$ive) wall-warts are heavier in weight and duty and are rated for more mA than the cheaper, lighter weight versions. From a manufacturer's perspective, every extra dollar spent for components results in $3-8 by the time MSRP is printed for the finished product. Thus, a variety of wall-wart transformers exist at varying prices.
    A 250mA rotator transformer will work very well when used according to its purpose (non-dimmed), while a 900mA transformer will better handle the extra heat generated by modifying the sine wave (when dimming the power). As our industry tends to be a bit price sensitive even in good economic times, product A @ ___$ may be viewed as a better buy than product B @ ___$ + $20 (with a more robust transformer).

    The ControlBooth is definitely the place to get great advice from those within our industry that have been there, done that, and spilled ketchup on the T-shirt.
    Last edited: Jul 8, 2009
  8. JChenault

    JChenault Active Member Premium Member

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    This thread is especially interesting to me as I had an issue with a smartmove. What my dealer told me that Apollo said is not what I understood you to say, - so let me restate what I think I heard you say and see if I have it right.

    If I plug the wall-wart into a dimmer, I am at risk for the wall-wart overheating and dying. I will not, however, do any damage to the motor in the unit.

    If I choose to run the unit on a dimmer, the wall wart is unlikely to die if I run it at or close to 100% and/or for a short period of time.

    According to my dealer, his contact at Apollo said the motor would burn out if it was run through a dimmer.

    Can you clarify please?
  9. Kelite

    Kelite Apollo Staff Premium Member

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    Great question(s), and thanks for asking. Let me see if this helps clear things up-

    The Apollo SmartMove gobo rotator incorporates a stepper motor that receives the stepped down voltage through the wall wart transformer. This transformer is intended to operate with pure 120V power, NOT dimmed power. Even locked at 100%, some dimmers modify the sine wave enough to build up heat within the wall wart. The higher the mA rating of the wall wart, the more heat and abuse the wall wart can take. (Before eventual failure, of course.)

    The stepper motor is protected from the modified sine wave by the circuit board, which stands between the wall wart and the actual stepper motor. In a dimmed power environment the wall wart heats up, due to the modified sine wave, and will fail over time. In the event the wall wart (though compromised due to high heat/resistance) continues to pass the modified 12VDC power to the stepper motor, the circuit board will cause the unit to shut down- preventing damage to the SmartMove stepper motor.

    In defense of the dealer's warnings of damaging the stepper motor- not all gobo rotators (or other 12 VDC accessories) are configured in such a way to place a protective barrier between the modified wall power and the actual stepper motor. Some other manufacturers' products (steppers in particular) may become damaged due to modified sine wave power, whereas the Apollo SmartMove stepper will be protected by 1) the wall wart, and 2) the printed circuit board.

    <According to my dealer, his contact at Apollo said the motor would burn out if it was run through a dimmer.> In defense of any sales reps at Apollo who have all been through detailed product training, dimmed power is a no-no. Whether a rep stated 'motor failure' or 'wall wart failure' to the dealer, I cannot answer. If the confusion began with us here at Apollo, I offer my sincerest apologies-



    I hope this helps clear up the matter,
    Last edited: Aug 5, 2009
    JChenault and (deleted member) like this.
  10. calkew5

    calkew5 Member

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    Kelite, what you say makes a lot of sense, since the two rotators I have in my posession have had their transformers replaced at some point in the past. I wondered why. Now I get it: the transformers died but the rotator itself is fine.

    Thanks.
  11. Kelite

    Kelite Apollo Staff Premium Member

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    Thank you calkew5, I appreciate your added comments. Yes, the transformers were more than likely damaged by dimming, but the rotators should be in fine shape. (Slap a new set of tires and brakes on her, and she'll move right out!)

    My guess is the newer wall wart transformers are rated higher than 300mA. Is that accurate?

    Thanks again,
  12. philhaney

    philhaney CBMod CB Mods

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    You realize of course, now I have to get that put on a T-shirt, right :lol:
  13. calkew5

    calkew5 Member

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    I'm not sure because all of mine are in the air right now (working fine, I might add) but I think they're 900mA.

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