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4hv.org :: Forums :: Tesla Coils
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How To Turn A Vacuum Cleaner Motor Into A Synchronous Motor

Author Post
Clive Penfold
Mon Dec 06 2010, 02:17PM Print View
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
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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
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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
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Coronafix
Mon Dec 06 2010, 08:36PM
Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 935
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.
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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
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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
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Steve Conner
Tue Dec 07 2010, 09:51AM
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?
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Clive Penfold
Tue Dec 07 2010, 02:10PM
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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.







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Finn Hammer
Tue Dec 07 2010, 03:04PM
Registered Member #205
Joined: Sat Feb 18 2006, 11:59AM
Location: Hou, Denmark
Posts: 715
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
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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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Clive Penfold
Tue Dec 07 2010, 05:41PM
Registered Member #2015
Joined: Mon Mar 09 2009, 09:39AM
Location: West London
Posts: 8
I just tried it on dc and whilst it runs, it takes about 4 times as much current. So I think that the answer is probably no.

Clive
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Arcstarter
Wed Dec 08 2010, 01:12AM
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Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2252
I just tried this, and i am pretty impressed! I have not yet checked how well it syncs, but the RPM is very stable. The torque is massive compared to an induction motor, even before the mod. This was at 80v.

One thing is, the commutators get hot. At least 300 degrees F, and that is for a 2 minute run. The diodes get pretty hot, but they keep truckin'. Could be partially due to the decrease in rotational velocity, so less wind to cool them. The rotor coils get hot, and the field (or stator, whatever you want to refer to them as) aren't as hot, but still pretty hot. The motor starts to stink a bot (the brushes, not the wire).

Another thing i noticed, is sometimes when i first start the motor, it runs at a higher RPM and stays at that RPM until turned off and back on. Also, when you first turn it on, it takes a second or so to sync up, or at least stabilize, in which period it shakes. I blame the torque, somehow .


This motor was from an electric weed trimmer, just a standard universal motor.

*Great* job, Clive.

edit: Crap, i killed my neon bulb. It was in parallel with the motor, i was going to use it for the 60hz light source to check RPM stability, and when i turned the motor off i saw a big blue light, which melted the internal electrodes together. Next time i turned it on, the glass cracked from the heat of the electrodes.
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Clive Penfold
Wed Dec 08 2010, 01:45AM
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Joined: Mon Mar 09 2009, 09:39AM
Location: West London
Posts: 8
I suspect that you may be putting too many volts on it. My vc motor drew 5 amps at 240 volts before modification. After modding it draws 5 amps at 80 volts. Assuming your weed trimmer motor is rated at 110 volts, I would guess that 40 volts is about right. If you go over the original full load current, the iron will saturate and strange things may start to happen apart from it getting hot.

Regards,

Clive
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Arcstarter
Wed Dec 08 2010, 02:24AM
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2252
Clive Penfold wrote ...

I suspect that you may be putting too many volts on it. My vc motor drew 5 amps at 240 volts before modification. After modding it draws 5 amps at 80 volts. Assuming your weed trimmer motor is rated at 110 volts, I would guess that 40 volts is about right. If you go over the original full load current, the iron will saturate and strange things may start to happen apart from it getting hot.

Regards,

Clive

Another odd thing, my motor would not run right on 40v :P. It spun about 500rpm or so. And, it was very unstable, too. I am using a 200w transformer, and it stays cool, which it normally runs really hot O_O. I am beginning to think this thing is about to start spawning black holes and shooting rabies vaccines at me.
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Steve Conner
Wed Dec 08 2010, 09:32AM
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Arcstarter wrote ...

I am beginning to think this thing is about to start spawning black holes and shooting rabies vaccines at me.

Excellent, try to get some footage for Youtube before it absorbs you into a parallel universe.

I agree that there's probably a delicate band of voltages where the thing will run as a synchronous motor. Too much voltage, and the torque generated by the universal motor mode of operation will overcome the synchronizing torque and boot it to a higher speed, where it'll shoot sparks from its brushes, catch fire etc.

Powering the field and armature windings separately might help stabilise it. Maybe you can even turn off the armature supply once it's up to synchronous speed, and that would make it run better.

Or, you could try powering the field windings alone with the brushes shorted together, and open them once it gets up to speed.
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Clive Penfold
Wed Dec 08 2010, 12:05PM
Registered Member #2015
Joined: Mon Mar 09 2009, 09:39AM
Location: West London
Posts: 8
I wonder if the instability is due to the motor being smaller and the rotating mass being significantly less. My motor has a period of instability for a second or so then it settles down.
The next thing I am going to try is a weighty disc on it to see how it reacts. I'll then be able to look at phase change versus load with a strobe
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radiotech
Wed Dec 08 2010, 05:38PM
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1459
Very interesting project. One thing to further develop is
a means to adjust the magnetization current of the rotor
and to expand the addition of diodes to force several poles
in the rotor which will divide the rotation speed and will
increase the torque. These will be syncronous speeds.

The reason for adjusting the magnetization current is to
allow adjustment of primary reactive current which will swing
from leading to lagging with a sweet spot in the middle
where power factor is unity.

The use of a syncronous motor in this way is called a
syncronous condenser and are used like this on machines
even today.

The brushless syncronous motors, (slip rings for DC)
use essentially the same principle as your universal motor,
i.e. get the power for the magnet by induction.

You are probably getting close to another type of motor
by shorting segments of a wound rotor with a diode, that is
a repulsion induction motor.

Next steps for you could involve using SCR's for the diodes,
and finding a way to remotely (while rotating) to adjust firing
angle.This will change the DC in the rotor which will allow adjustment
of the reactance angle of the machine (power factor)

What we did here, in a motor class, is used an auto alternator
to provive 3 phase power to power another alternator which ran
as a motor, the field of which was adjusted to vary power factor
at syncronous speed. table top system at 14 volts at 85 Hz
allowed every manner in experiments with transformers,motors and capacitors in the 3 phase system.

Try and spend some time looking at the patents. A hundred
years or so should do it, and let us know what you find. One
intersting one would be the "Stat-X-Ator" machine.
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Arcstarter
Thu Dec 09 2010, 03:36AM
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2252
I will take a youtube video as soon as i can find my cam and batteries .

Something i noticed is that the more load i put on the motor while running, the less current it pulls! Wicked!

My motor is not smaller than yours, Clive. Maybe a little bit smaller, but not significantly. It is the same size as my 2hp vacuum cleaner motor just about. I think yours acts the same as mine, just a bit unstable at first, but quickly stabilizes.

EDIT:
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Coronafix
Thu Dec 09 2010, 08:54AM
Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 935
So how does it work under load? Inquiring minds want to know. :)
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Steve Conner
Thu Dec 09 2010, 10:37AM
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
radiotech wrote ...

the addition of diodes to force several poles
in the rotor which will divide the rotation speed and will
increase the torque. These will be syncronous speeds.


That won't work, because the stator is only 2-pole.
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radiotech
Thu Dec 09 2010, 07:34PM
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1459
Arcstarter wrote;

"something i noticed is that the more load i put on the motor while running, the less current it pulls! Wicked!"


This can make sense if you consider that the load is correcting the
powerfactor. Your ameter cant indicate phase angle, but if while
running, you add capacitors after the ammeter, and the current
drops, then the motor has a lagging power factor.
You can start with about 20 ufd per amp of motor current at 60 Hz.
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Clive Penfold
Thu Dec 09 2010, 08:09PM
Registered Member #2015
Joined: Mon Mar 09 2009, 09:39AM
Location: West London
Posts: 8
I've just made a flywheel out of a bit of 3/8 inch by 5 inch diameter aluminium plate. The motor takes significantly longer to spin up. However, when it reaches synchronous speed, there is a lot of phase instability; about + -20 degrees at 1 Hz which eventually dies away after about 10 seconds (viewed with a stroboscope). In an attempt to investigate this more thoroughly ie turning the volts up and down and applying braking to the disc, I appear to have blown the diodes! Ho hum
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radiotech
Thu Dec 09 2010, 08:18PM
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1459
Your comment about milling the flats in the rotor, will
turn the machine into a reluctance syncronous motor and it should run if you short all the segments of the
rotor out, But it wont start. It will have to be spun to start.
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klugesmith
Fri Dec 10 2010, 03:39AM
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1478
More applause for Clive! I've long thought about how to synchronize a universal motor without active feedback, but never dreamed of such an elegant solution.

On a tangent...
Just stumbled upon a video about another kind of synchronous motor (permanent magnet type).
This guy is playing with a microwave oven turntable motor, cranking it by hand,
and gets an unexpected shock. Happens soon after 4:10 and he talks about it for the next couple minutes.


Then, most respectably, he takes the motor apart to understand the offense. See 2:00 to 3:00 here.


Reminds me of when I found a hoard of ancient telephone ringer magnetos at an estate sale.
As recounted by my wife to a friend: "He turned the crank and said Ow, I just got a shock.
Then turned it again and said Yes, there it goes again!"
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OiD
Sun Jan 30 2011, 07:37AM
Registered Member #2150
Joined: Tue Jun 02 2009, 08:33PM
Location:
Posts: 29
Well I must say it's a very nice solucion. Unfortunately I can't solder the diode to my motors for some reason and the diode flies of at medium speed...
I will try with some other motors, for this looks promissing!
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