- Joined
- May 27, 2016
- Messages
- 3,469
OK Andy. Using your diagram, I will attempt some explanation. It looks very like your motor is the standard "squirrel cage" induction motor. If you are able to peek into it, you see bound up coils arranged around the casing, as "stator" coils, and a rotor looking like steel laminations, which hide the way they become rotating magnets by induced currents from a sort of transformer action.
You will see that the coils "M" are shown horizontal, and the coil "S" is shown vertical. This is deliberate. While parts of the coils may be physically distributed around the outside of the rotor, with half the windings of a coil on one side, and the remainder on the opposite side, what you have is one set making a field arranged physically 90° to the other.
Next is to notice that the coils "M" are wired either in series for the high voltage option, 230VAC, or in parallel for the low voltage 115V option. This is why T1 joins T3, and T2 joins T4 in the 115V connection. That is a permanent linkup, altogether downstream of any reversing switch arrangement.
The way these work is the mains AC connection is powering across the "M" windings (series or parallel - makes no difference except for the voltage it is connected to). It is making a field that rises and falls as the AC sine wave at rises and falls at 60Hz. If that was all that was connected, the motor would just buzz loudly, and get hot in the coils.
The trick to getting it to rotate is to have a SECOND field also rising and falling in a sine-wave manner, set at 90° to the "M" windings. This is provided by the "S" windings. Then we throw in a new condition. It needs also to have the mains AC power offered at the "S" windings NOT to be simply the AC power as being offered at the "M" windings, but a modified version artificially shifted 90° in phase timing. This is achieved by putting it in series with a large value capacitor, built to take the AC current. The capacitor initially charges up, and from then on, it delivers a voltage that varies 90° out of phase, looking like the cosine rather than the sine.
This is exactly the condition that creates a rotating field that the rotor magnet then follows, but with a continuous "slippage" where it can never quite "keep up", because that is what is necessary for it to suck some of the power (induced) to make itself it's own rotor magnet poles.
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So in the end, you have mains AC applied across the "M" windings, with one end common to the "S" windings, and the mains AC going to the other end of the "S" windings via the capacitor. A common arrangement to reverse is to simply swap the mains live from the "M" to the "S", but in your case, a more refined arrangement is used. To reverse the direction, the connection to the "M" windings is left alone, and the T5 and T8 connections for the "S" windings swapped over instead. You can see this in the tables for CW and CCW rotation.
Notice also that the symbol for the capacitor is shown as two capacitors (sort of) in series. This is real! Capacitors made for making a 90° shifted artificial AC power are of electrolytic nature, normally requiring the correct polarity DC across them, and would degrade rapidly if AC were directly applied. By internally using two capacitors connected "back-to-back, this problem is circumvented, and at the same time, the voltage rating of the series combination is doubled.
The symptom of buzzing with no rotation means there is no rotating field. One of the windings is open circuit, or the capacitor is not effective, or one side of the series capacitor connection is not making it, either to the common connection with the "M" coils, or to the live side.
I have not the means handy to make you a diagram yet, but if you really still need it, I can make up a sketch of what the connections should be for making this motor run. Meantime, check the continuity of the coils. T1 to T2 should read the same resistance as T3 to T4. The T8 to T5 winding should not be open circuit, and it's resistance may well be a little different. These resistances may well be very low ohms. You may need to use a multimeter with a "relative zero" button, to account for the resistance of your probe connections.
The good thing about these is they are made of very fundamental stuff. Copper, and iron and insulation. If it is not burned out, nor has a short-circuit turn (or turns) in the windings, then there is not much to go wrong. With no power applied, the rotor should turn freely. There needs not to be any odd small screws, swarf, chips, bits of rag or other stuff between the coil poles and the rotor. Also, no distinctive smalls when it it "buzzing".
My apologies if any of this is stuff you already know. I would not wish to do that to you.
In that case, consider it as perhaps handy for others who might find it useful.
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