Is it safe to run moving lights off of a dimmer?
- Thread starterSwade White
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TNasty
Active Member
Thanks for pointing that out. What you said brings up another reason why I'd avoid using a module other than a relay (or a constant on, which I didn't realize existed until now). What I was pointing out was mostly the fact that on a unit such as an ETC Sensor, there's always a chance of losing your vital configuration (not sure if it would keep all the settings during a firmware update, but a replacement control unit would definitely need to be configured to match the old settings)- pretty much that there's just the possibility that you screw a setting up, where as a specific module just needs to be put back into the right space, which can easily be marked with tape or a note.
EdSavoie
Well-Known Member
[Late night rant]
I still don't understand why many electronics are as picky as they are...
Smoothing out the power from a dimmer is not that hard of a task. Is it normal for every day appliances? No, of course not. But for intelligent lighting designed to operate in the theatrical world? I'd kind of expect it to have the circuitry to cope with it.
I ran a cheap chinese RGB "disco" light that was using the most barebones capacitive dropper power supply, and it still works despite being run off of a dimmer for extended periods.
[/Late night rant]
I still don't understand why many electronics are as picky as they are...
Smoothing out the power from a dimmer is not that hard of a task. Is it normal for every day appliances? No, of course not. But for intelligent lighting designed to operate in the theatrical world? I'd kind of expect it to have the circuitry to cope with it.
I ran a cheap chinese RGB "disco" light that was using the most barebones capacitive dropper power supply, and it still works despite being run off of a dimmer for extended periods.
[/Late night rant]
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Please elaborate / explain your use of the term "barebones capacitive dropper power supply" as it's not pulling into focus any of the several types of A.C. power supplies I'm familiar with. Perhaps @steveterry can elaborate?
Toodleoo!
Ron Hebbard.
JD
Well-Known Member
Lets look at different power handling components and how they react to power:
1) Magnetics: (Transformer, Ballast) build and collapse their magnetic field based on a sine wave. When the waveform is chopped, the field spikes or collapses creating a "flyback" effect that will produce a massive over-voltage. (google Flyback Transformer)
2) Switch-mode: (Most solid-state supplies) Only draw their power near the peak of the waveform, so early and late chops are not a problem. Chop during the power draw near center and you will end up with a nasty current spike on the rectifier diodes.
3) Capacitor Dropper: Produces voltage output based on the input frequency and load current, much like an audio crossover network. Since anything other than a sine wave contains massive amounts of harmonics, these harmonic voltages will pass through as if the capacitor was dead shorted. Boom-boom, out go the lights.
I have never seen "Capacitor Droppers" used in commercial equipment. About the only place they are common is in super-cheap LED consumer bulbs sold at Wal-mart. Concept is the capacitor is put in series with the AC line. The result is it acts like a resistor at a given frequency, so if you know your load and the frequency, you can use it instead of a transformer. Of course, there is NO line voltage isolation. As you might expect, it is VERY likely to destroy whatever is connected if there is any line noise or spikes.
Big Clive reverse engineers one here:
1) Magnetics: (Transformer, Ballast) build and collapse their magnetic field based on a sine wave. When the waveform is chopped, the field spikes or collapses creating a "flyback" effect that will produce a massive over-voltage. (google Flyback Transformer)
2) Switch-mode: (Most solid-state supplies) Only draw their power near the peak of the waveform, so early and late chops are not a problem. Chop during the power draw near center and you will end up with a nasty current spike on the rectifier diodes.
3) Capacitor Dropper: Produces voltage output based on the input frequency and load current, much like an audio crossover network. Since anything other than a sine wave contains massive amounts of harmonics, these harmonic voltages will pass through as if the capacitor was dead shorted. Boom-boom, out go the lights.
I have never seen "Capacitor Droppers" used in commercial equipment. About the only place they are common is in super-cheap LED consumer bulbs sold at Wal-mart. Concept is the capacitor is put in series with the AC line. The result is it acts like a resistor at a given frequency, so if you know your load and the frequency, you can use it instead of a transformer. Of course, there is NO line voltage isolation. As you might expect, it is VERY likely to destroy whatever is connected if there is any line noise or spikes.
Big Clive reverse engineers one here:
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EdSavoie
Well-Known Member
I did say the LED light was cheap!
I was going to explain the basis of a capacitive dropper, but JD explained it already...
As far as I'm aware, my dimmer system is forward firing, which if I remember correctly, is even harsher on electronics not expecting to be dimmed.
Forgive my admittedly limited knowledge in the field of electronics, but would a circuit comprising of (among other things), inductors and a TVS diode not work well at suppressing spikes?
I was going to explain the basis of a capacitive dropper, but JD explained it already...
As far as I'm aware, my dimmer system is forward firing, which if I remember correctly, is even harsher on electronics not expecting to be dimmed.
Forgive my admittedly limited knowledge in the field of electronics, but would a circuit comprising of (among other things), inductors and a TVS diode not work well at suppressing spikes?
TVSS devices - aka MOVs, have a limited life. They degrade as they absorb hits, and typically are deployed with a clamping voltage a fair bit higher than nominal, so they don't die immediately - they only handle the large, infrequent spikes. They also don't filter harmonics. Inductors can do more filtering, but they are not a panacea, and for that matter, your dimmer probably already has a current-limiting inductor on it.
Short of rectifying your cruddy dimmer power to DC and then inverting it, whatever band-aids you put on are going to be a distant not-first-choice.
JD
Well-Known Member
Many don't know that. We use a lot of APC battery backups at work, one on each computer. After about 4 years, the batteries are due. At that point, we change the whole unit since the MOV's are surly degraded as well. (That, and the battery is often over 50% of the cost of a new unit.)
As for Capacitor Droppers, I have always felt they are pure insanity. Although we knew it would work in theory, the first time I ran into one was 10 years back in a 40 watt florescent work-light I purchased at home depot. Took it apart to mount it and inside there were only two parts. A capacitor and a starter. Thing went right back to home depot for a refund!
BillConnerFASTC
Well-Known Member
Ford
Sr Product Manager, Chauvet Professional
Hi Bill,
You absolutely could use whatever power source you desire, and dim the LED via DMX... to a limit.
Firstly, the power supplies in the units cannot be auto sensing, because the light would have no way of knowing if when it is receiving 120v, that voltage is nominally half of a 240v circuit, or all of a 120v (+/- 10%) circuit. So our units require you to set the voltage supplied via a switch.
Then (via the menu), you can select the type of control you are planning to use: DMX control, Dimmer Control, or to Auto Sense (which senses whether the unit is on a dimmer, or plugged into a constant power source).
If you set the unit to DMX control, the PSU will believe that it is being given line voltage... even if it is not. So, as long as your voltage is within about 10-15% of normal, your fixture will behave properly via DMX, even if the power is being supplied by a dimmer (Parked on, or in "switch mode").
That's why our ED190 is equally suited to be used in both legacy dimmer systems, and in a newer installation which has DMX distribution.
You absolutely could use whatever power source you desire, and dim the LED via DMX... to a limit.
Firstly, the power supplies in the units cannot be auto sensing, because the light would have no way of knowing if when it is receiving 120v, that voltage is nominally half of a 240v circuit, or all of a 120v (+/- 10%) circuit. So our units require you to set the voltage supplied via a switch.
Then (via the menu), you can select the type of control you are planning to use: DMX control, Dimmer Control, or to Auto Sense (which senses whether the unit is on a dimmer, or plugged into a constant power source).
If you set the unit to DMX control, the PSU will believe that it is being given line voltage... even if it is not. So, as long as your voltage is within about 10-15% of normal, your fixture will behave properly via DMX, even if the power is being supplied by a dimmer (Parked on, or in "switch mode").
That's why our ED190 is equally suited to be used in both legacy dimmer systems, and in a newer installation which has DMX distribution.
BillConnerFASTC
Well-Known Member
JD
Well-Known Member
Power supplies can be designed to work off of dimmers and not be damaged. Best example of this are the Cree lamps designed to work off of household dimmers. Like a switch-mode supply, the circuit starts with a bridge rectifier with enough capacity so it won't cook a diode if chopping is happening mid-waveform. The lamp has a small dedicated 8 bit processor which monitors the phase angle of the incoming waveform and proportionately adjusts the PWM drive that powers the LEDs. All for under $10 ! The only drawback is that if the voltage is too low, the processor can't run and the lamp shuts off at about 5%
The thing is that movers (especially discharge type) were never designed to deal with a chopped waveform. They contain many supplies and often a ballast circuit. To make the compromises needed to assure the unit would not be damaged on a dimmer would require a lot of changes which would affect not only price, but size and complexity of the internal electronics. Most movers can tolerate some distortion of the waveform, but generally they expect clean AC for an input. Could you run them off a dimmer? Well, I guess you could plow a cornfield using a Corvette instead of a tractor, but why?
The thing is that movers (especially discharge type) were never designed to deal with a chopped waveform. They contain many supplies and often a ballast circuit. To make the compromises needed to assure the unit would not be damaged on a dimmer would require a lot of changes which would affect not only price, but size and complexity of the internal electronics. Most movers can tolerate some distortion of the waveform, but generally they expect clean AC for an input. Could you run them off a dimmer? Well, I guess you could plow a cornfield using a Corvette instead of a tractor, but why?
Dionysus
Well-Known Member
Its not just the fact that it has to smooth, its also that there is a choke (inductor) and capacitance in the circuit. Current and Voltage literally become out of sync (Power Factor), not good. But of course the bad waveform is not good either.
I also see people not realizing the difference between SCR, PWM and other dimmer types all the time.
