Will I need a "ghost load" for TwinSpin gobo rotators?

[JLNorthGA]

I don't want to damage the GAM TwinSpins. From what I've seen on GAM's website, I can plug the transformer into a dimmer circuit and it should vary the speed. I have seen some threads on this website which indicate that I might possibly damage the transformer by plugging it into a dimmer circuit.

So - do I need a ghost load or what? I have D20 dimmer modules in a Sensor rack. I'm looking to control two GAM TwinSpin gobo rotators.

 

[Les]

You should be fine without a ghost load. I used a GAM Film/FX once and didn't need a ghost load. I never could get the thing slow enough, but I don't think a ghost load would have helped. There just seemed to be a gap between full stop and "too fast for clouds", but it could've been the trim settings on the analog ADJ dimmer I was using.

I'm not sure how, but GAM has found a way around the dimming transformer issues on these units (a lot like how Altman [and similar] Micro Ellipses are).

 

[JD]

Oddly, transformers feeding an inductive device (like a motor) don't flake out as bad as transformers feeding an electronic device when run on a dimmer. In fact, a lot of simple motor speed controls (like for a ceiling fan) are simply modified wall dimmers. This is in part because the windings clip the edge of the waveform in much the same way as the choke does One would also think GAM may have taken some design steps figuring on this. Electronics running off of a magnetic transformer on a dimmer is a real problem due to the "flyback" effect of the magnetic spike in the transformer on the leading edge of the sawtooth waveform. This can cause an over-voltage in the rectifier / capacitor on the secondary. (Switch-mode supplies are actually a bit more tolerant because the conversion to DC takes place at the front end, although operation on a dimmer is highly NOT recommended, unless the manufacturer has approved it.)

Still, a ghost load may clean up the low end problems. Dimmers get flaky on very light loads (below 50 watts) so light inductive loads are a double whammy.