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| Snub has more Electric Motor Questions: |
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| snub:
I have a surplus motor that I am using for my magnetic tumbler project. It is 120 VAC, 3 speed motor (1575, 1400 and 1250 RPM according to the tag on the motor.) Here is my 'rendition' of the motor tag: I only had a 'single pole- double throw' switch to experiment with, so I just used the high and low speeds. Problem is, the motor only runs at one speed, regardless of the switch position. This is according to my digital non contact tachometer. Even with the switch out of the circuit, it doesn't matter if I hook up the black, blue or red wire to the second line in wire, it still runs at a single speed, which is 1720 RPM. Which doesn't coincide with the rated fastest RPM of this motor. Strange thing is, I have another project with a 3 speed motor, and it does the same thing. Will only run at a single RPM. Also, when you switch between high and low speeds, the 'sound' of the motor changes, but the RPM doesn't. Here is how I wired it: I'm wondering if that brown wire needs to go somewhere else, besides ending at one terminal of the capacitor? |
| Bluechip:
Hi Snub Your 1720 RPM is right for a 60Hz motor with 2 pairs of poles. What you may have is a motor designed to run via an external control circuit. ie under a system known as Pole Amplitude Modulation (PAM) .... and you don't have that! Dunno how much you know about Induction motors but the general rule for rotational speed (sychronous) is : Numbers of cycles per MINUTE / Number of pairs of poles So, for 60 Hz you get 3600/1=3600 3600/2 = 1800 3600/3 = 1200 etc. Less a bit for the slip you get 3450, 1725, 1150, etc. which is what you see on the Rating Plate These are the more common numbers for 60 Hz motors. By way of the switching some of the windings you get wider or narrower pole widths, effecively varying the number of poles. The result of this is the motor speeds do not appear to correspond to the usual equation. Instead of the sychronous speed following the equation each time, you get a set of speeds grouped together, as you seem to have Tried to understand this stuff years ago, it's gruesome .. You get this arrangment on desk fans, spin dryers etc. I think you should get another motor :( Try a search on the motor maker/type. See if any info. Can't really help from here, but I can admire your problem :scratch: Dave BC |
| John Hill:
I do not know anything about this particular motor but by looking at your diagram we can see there are not too many possibilities. We will assume that the white/brown/capacitor network is common to all speeds so what we have left is three wires, you have already tried connecting to these wires individually and the speed does not change, but the sound does. Dave has told us these motors operate by interaction of multiple run windings so it is logical that with just one run winding connected, no matter which one, the speed will be the synchronous speed, which you have shown it is. I think the only options left are to connect black-blue, blue-red, and red-black in turn and see if that gets you the three speeds. John |
| Bluechip:
Hi Troops Assuming that's what the motor IS !! Could be :zap: :zap: What is it off anyway? Could be a clue if known. Still reckon it's a better idea to find a tame one .... Dave BC |
| kwackers:
I don't know an awful lot about motors - but I'd *imagine*... If the motor works by switching in varying amounts of poles - then presumably if you apply 'live' to say the red wire and get 1720rpm, the I'd think if you leave that connected and also apply power to another (say blue) then this would 'create' more poles? So instead of switching the wires you simply connect more of them. Of course it could also be that the wires need connecting to neutral... However, I'd start by measuring resistance between all wires to give myself some idea of how it's wired internally first. |
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