Dimming Motors
- Thread starterbrozeph20
- Start date
Most "Real" mirror ball motors are Shaded Pole and are usually rated 1/125th-1/5th HP. Capacitor start motors are usually reserved for something 1.5HP and above, that would be a REALLY big mirror ball.
It was a 4' mirror ball. "oh ive got big balls, oh ive got big balls....." (AC/DC). So if putting a motor on a dimmer is safe than why am i paying so much for ABB inverters to speed up and down motors?
David Ashton
Well-Known Member
if it is a synchronous motor you need a variable frequency drive, which is expensive.
Yep, and they dont make 3 phase dimmers, yet i believe if you couple the control of 3 SSR's together, and then wire each of them up on the 3 legs, the SSR's will be a 3ph dimmer, but i perfer staying with the inverters or variable freq drives (VFD's). They work off of changing the voltage in to DC and then rechanging it back to AC. When you change the motor speed it actually changes the AC retification on the output side, so you are changing the frequency of the sine wave rather than the voltage, pretty cool eh?
David Ashton
Well-Known Member
A 3 phase wave chopping motor control/dimmer cannot work because below 60 degrees of switching angle you have phase 1 on then 2 on then 3 on, so until you are over 1/3 output a motor does not see all three pases at the same time, this is the same phenomena which causes high neutral currents in dimmer systems.
David Ashton
Well-Known Member
dafunkmonster
Member
Yes that is what's refered to as a "non-Dim" setting. Most Consoles will allow you to set a dimmer to be at 100% at a given dmx value, eg you can set dimmer 12 to go to @full @ 10%. Meaning that anytime you set a value of 10% or more for dimmer 12 it will go to full or 100%. If You read all the previous posts you will discover there are issues with even this form of control when dealing with motors and SCRs However the original question was about the efficacy of "dimming" a motor which implies using a dimmer as a speed controller for a motor, which is a horse of a different color.
"Non-dim" mode puts the dimmer in a full or off state. However the electricity is still being messed with on the way through the dimmer. The result is much different than electricity that hasn't been through a dimmer at all. Generally speaking, electronic devices do not like the results of what a dimmer does to the wave of electricity. Prolonged, and in some cases even short, use will damage an electronic device. There are some exceptions so read the manual for both the dimmer and the device. If you aren't sure call the manufacturer before plugging anything into a dimmer.
Summary:
-If the device has any sort of electronics in it do not plug it into a dimmer. You will probably damage it, maybe not right away, but eventually.
-Devices without any electronic controls (such as fans and motors) may or may not work on a dimmed circuit. However, I don't think you will harm them by trying them. (Am I wrong here? Can you hurt a motor by trying it?)
-Some devices (like the gobo rotator the original poster didn't buy) are designed to be used on dimmed circuits.
-Always read and follow the manufacturer's instructions when it comes to selecting a power source for a theatrical device.
Sayen
Active Member
For those of us who are a little slow, what's the risk to the dimmer when running a small motor? I've seen conflicting posts around here. I have a few devices purchased before we had a workable DMX situation, and honestly wouldn't mind running them to the point of failure so they can finally be replaced, but not at the risk of my dimmers.
David Ashton
Well-Known Member
David Ashton
Well-Known Member
Rubbish, read the thread, a dimmer is built to survive the arcing of a theatre lamp, which is just about the most vicious act that is possible, as has been stated a dimmer will burn out a synchronous motor but any motor with brushes,[universal motor] will work fine.You need to understand that the average fan speed controller or drill controller is simply a dumbed down dimmer, but works on EXACTLY THE SAME PRINCIPLE.
It is not dangerous.
It is not dangerous.
I thought it would be good to ask an engineer about this before sticking my foot in my mouth. Lary Cotten wrote all the software for the LCD controllers from High End and ran the Software section of HES's R&D dept for several years. here's what Lary said:
"wow, there's are so many variations in both dimmers and motors that it's hard to give a flat answer.
An incandescent lamp is just a big resistor, and you don't connect arc / discharge lamps to dimmers, so the bit about "survive the arcing of a theatre lamp" seems a bit odd. The closest reality to that would be the inrush current into a cold filament.
If you're controlling a motor which itself has control circuitry, as in a brushless DC motor, then it's a very fair bet that it's internal controller won't care much for "dimmed" power.
For "raw" motors, i.e. no control circuitry, motors are very much inductive, which require special attention from the dimmer. This is why not all dimmers are good for low voltage halogen/tungsten lighting that uses transformers.
Dimming of nearly all types is handles using pulse width modulation, i.e. PWM, but the types of PWM range from old fashioned 120Hz zero-crossing phase control dimming, to modern "sine wave" dimmers which PWM at 50kHz plus and are filtered such that the output is basically clean AC all over again at some voltage proportional to the dim level.
Inductive loads care a whole lot about frequency of the incoming AC power, so there's a good chance the motor and dimmer won't get along.
Also, drill motors are DC motors, and nothing here specified what sort of rectification was going on between the AC dimmer and the DC motor.
I can imagine that some brushed motors would work OK with some dimmers, since those motors run at a speed proportional to average incoming voltage, but that's about it.
Keep in mind that as recently as two months ago, I've had a tech plugging in the moving lights to my dimmer packs.
They say that "it takes all kinds", but I believe that many kinds are quite optional."
so sayeth an engineer who's been creating lighting products for 20 years.
I don't think anyone would argue that not using dimmers for motors or electronics is a good idea. it's accepted standard practice, at least in the US.
peace, Tim O
I have controlled all types of motors, fans, ect from conventional dimmers, but you have to put a "ghost" load of incandescent lamps on the dimmer at the same time. Usually this load goes offstage so it isn't seen by the audience. THIS DOES NOT WORK FOR DC MOTORS AND SYNCHRONUS MOTORS LIKE CLOCKS. If you have ever taken apart a pinspot, you will find the lamp is usually a 6 or 12 volt lamp and a transformer that drops the 120 line down. This is an inductive load just like a motor. Usualy a 100 watt load works fine to fire up a box fan, which we needed to do in Peter Pan when we had to adjust the wind levels in the sails.
David Ashton
Well-Known Member
The arcing I'm talking about is the arcing when a lamp blows and the protection which is built in to protect the output devices because 90+% of output device failure occurs due to arcing of blown lamps and the resultant extremely high current.
Universal motors are ac/dc that is why they are called universal.
The question was, can you hurt the dimmer?
The answer is still no,
I know nothing about software development, but have a lot of experience in power control, I did my training in that area.
Of course a motor with a control system built in would have problems.
I answer the questions asked.
I do not write a thesis on all the other possibilities.
Simple question-simple and correct answer.
Universal motors are ac/dc that is why they are called universal.
The question was, can you hurt the dimmer?
The answer is still no,
I know nothing about software development, but have a lot of experience in power control, I did my training in that area.
Of course a motor with a control system built in would have problems.
I answer the questions asked.
I do not write a thesis on all the other possibilities.
Simple question-simple and correct answer.
Last edited:
bigwhiskey
Member
LOL if you don't think an engineer involved with moving light design is a qualified source, there's no rebuttal. the thing that makes a moving light move is ..a motor! don't you suppose the software folks are intimately familiar with what makes them work, and capable of suggesting best practices?
It seem to me you're really focused on being right about this motor/dimmer thing.
peace, Tim O
It seem to me you're really focused on being right about this motor/dimmer thing.
peace, Tim O
