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How To Turn A Vacuum Cleaner Motor Into A Synchronous Motor

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Clive Penfold

Mon Dec 06 2010, 02:17PM

Registered Member #2015 Joined: Mon Mar 09 2009, 09:39AM
Location: West London
Posts: 8

Allow me to reveal my latest discovery or possibly invention if no one has
thought of it before!

A vacuum cleaner motor can be made to run at synchronous speed with the
addition of a diode; actually 2 in parallel for mechanical balance

Mains vacuum cleaner motors are usually series wound AC brush motors. The one I
removed from a 1100 watt Miele cleaner ran at 18,000 rpm and drew 5 amps at 240 volts.
Having dismantled it, I soldered two 3 amp 1000 volt diodes across 2 opposite
commutator segments (180 deg apart), tucked down behind the commutator. One would have done
but to maintain physical balance, I used a pair opposite each other and applied
a liberal amount of epoxy resin to stop them flapping about.

The motor is still series connected as before and runs at 3000 rpm (at 50 Hz) quite happily
from 30 volts AC where it draws 0.8 amp to 80 volts AC where it draws 5 amps at no load.

One thing that I haven't looked at yet is the phase change of the rotor as the
load varies but it is probably no worse than an induction motor with flats
machined on it. Also, I don't see why it shouldn't work with John Freau's phase controller circuit.

I will be interested to hear of other peoples experiences who try it.

I have also posted to the Pupman list and there is a discussion running on this subject on the tcbouklist, where I originally posted.

Regards,

Clive

Herr Zapp

Mon Dec 06 2010, 07:29PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Clive -

How are you determining that the motor's rotor speed "locks-up" at EXACTLY 3,000 RPM throughout the 30-80 VAC input voltage range?

Herr Zapp

Clive Penfold

Mon Dec 06 2010, 07:44PM

Registered Member #2015 Joined: Mon Mar 09 2009, 09:39AM
Location: West London
Posts: 8

With a laser tachometer. The motor starts spinning at about 20 volts till at 30 it settles at 3000 rpm. Increasing the volts up to 80 the speed stays the same even if I apply a load with a piece of wood on the shaft

Coronafix

Mon Dec 06 2010, 08:36PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Got any photos of it? It is a bit hard to visualise, maybe it's still too early in the morning for me.
Sounds like an easy fix to an old problem, well done.

Clive Penfold

Mon Dec 06 2010, 11:07PM

Registered Member #2015 Joined: Mon Mar 09 2009, 09:39AM
Location: West London
Posts: 8

Have just checked with a scope using a pickup coil looking at a magnet on one channel, and the mains on the other and it is synchronous

Clive

Herr Zapp

Tue Dec 07 2010, 02:24AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

"Have just checked with a scope using a pickup coil looking at a magnet on one channel, and the mains on the other and it is synchronous."

Clive -

Please clarify - you stated that this is this a series-wound motor; I'm not sure I understand what you mean by "using a pickup coil looking at a magnet".

Herr Zapp

Steve Conner

Tue Dec 07 2010, 09:51AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I guess he means that he put a disc on the shaft with a magnet etc, and used a pickup coil to sense the magnet?

I saw this on the TCBOUK list, and from what I know of motor theory, I can't see why it wouldn't work. It probably won't be the world's best synchronous motor, but it's free and easy to make, so who cares?

Clive Penfold

Tue Dec 07 2010, 02:10PM

Registered Member #2015 Joined: Mon Mar 09 2009, 09:39AM
Location: West London
Posts: 8

Here are some pictures, which should make things clear. As you can see, the 2 field coils and the brushes are all in series. This type of motor is sometimes referred to as a universal motor. When I checked for synchronous operation, I set my scope to "line" which locks the timebase to the mains. On one channel I displayed a mains waveform to prove it was locked to mains. On the other I connected a small coil which I could offer up to a small Neodymium magnet that I had taped to the shaft. When the motor was running from 30 to 80 volts the 2 waveforms stayed synchronised.

Steve, thanks for clarifying a couple of points.

Finn Hammer

Tue Dec 07 2010, 03:04PM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

Clive,

Offering you the benefit of doubt, untill this thing has been thoroughly investigated and documented:
A "hats off" from me, for a truly remarkable discovery.

Cheers, Finn Hammer

Dave Leddon

Tue Dec 07 2010, 05:27PM

Registered Member #3486 Joined: Tue Dec 07 2010, 05:22PM
Location: Pleasanton, CA
Posts: 1

Interesting. Does this imply that one could use a single motor for both sync and asynchronous by using DC power for the async case?

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