ECN Forum Forums Technical Discussion Electrical Theory and Applications Rewiring a capacitor start & run 4 speed fan

Hi all,

My name is Dominic and I'm looking for some help and advice with rewiring an old 4 speed floor fan.

The story is that years ago I inherited an antique fan grom my grandmother after she passed away. I cleaned it up and it looks and runs great- and both myself and my girlfriend love it.

So a few weeks back when I saw a much larger (but similar vintage) floor standing fan I bought it in a heartbeat and was keen for another weekend project to keep me busy.

However the wiring on this one is a fair bit more complicated than the last- and the capacitor and transformer that it used were so rusted and corroded that none of the values were readable. However I'm pleased to say that the windings of the coil are in great condition.

So here are the specifics from what I understand:
1. It runs on 240 VAC at 50HZ and is rated at 2.2A.
2. It has two windings- one of which seems to be the capacitor start winding which appeared to be always energised.
3. It has 4 speeds (plus off) and used a transformer (or maybe a choke?) to achieve this, as well as a 4 speed rotary selector switch.

The only absolutes I know are:
1. The supply voltage of 240 VAC / 50Hz / 2.2A
2. The resitance of the start winding is 68 ohms and the run winding is 31 ohms,
3. That the warn out components are the capacitor, transformer and rotary selector switch.

I've drawn a diagram of how I imaging the circuit would function using a two pole, 5 position rotary switch but I was wondering if someone might have the smarts to tell me whether this diagram is correct- and if so what the values of the capacitor and transformer would need to be?

Or of course if there's a better way to do it using a more modern fan speed controller.

Many thanks,

Dom

The fan before (top part):
[img]http://postimg.org/image/g1odh5icp/[/img]

The fan before (bottom part):

I ran out of editing time so here are some more photos:

The fan before (top part):


The fan before (bottom part):


More fan detail:


The rusted remains of the capacitor and transformer:


The rotary selector switch (2 pole, 5 position):


The name plate and switch backing plate:


The start and run windings:


My understanding of the circuit diagram:

And here's my grandma's fan I restored (just for reference):

Based on your diagram, it wouldn't start on speed 1 (you'd have to turn it to speed 2 to start, then back down). It looks to be what is known as a "bucking" transformer configuration (this article shows the general arrangement, in that case as used to slightly reduce the mains voltage) but while I've known of inductor-based controllers for (older) ceiling fans, this set-up is new to me.

The old cord definitely has to go but observing the level of rust, I'm not even sure if an acceptable earth connection can still be made. The capacitor value might be able to be worked out by trial-and-error (but watch out for dangerous series resonant effects).

One thing you've also missed out in your diagram is the centrifugal switch shown in the picture of the stator coils, this opens the start winding when the motor reaches 75-80% of full load speed, ie: the start winding is never permanently energised.
As far as sizing a suitable start capacitor goes, generally 50uF is a suitable starting point.
As a note of caution, be VERY careful with energising really old gear like this, that switch looks like it's come to the end of it's life, and I would suspect that the transformer would require a megger test before it was livened again.
Be Careful!

That's in motors for applications that require high starting torque (refrigeration compressors, stationary power tools, etc.). Motors used in small-to-mid-sized fans are instead designed with the capacitor permanently in-circuit. (https://en.wikipedia.org/wiki/AC_motor#Permanent-split_capacitor_motor)

It would also become very complicated (to say the least) to set a starting switch for 3 different speeds (ignoring the lowest speed on this fan, as noted before). And a 50uF capacitor rated for 400VAC or more across it continuously would become very bulky and expensive, I would imagine...

Fan Capacitors are usually only a few uF
2.2 uF and rated for 400 V dc or 250 V rms ac.
A cooling fan has low torque. Often the Capacitor remains switched on as the currents are low.
The transformer / inductor is in series, often all the time and causes a bigger phase shift and reduced voltage on the motor windings, hence more slip and different speeds.