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How To Turn A Vacuum Cleaner Motor Into A Synchronous Motor

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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

Arcstarter

Wed Dec 08 2010, 01:12AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

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.

Clive Penfold

Wed Dec 08 2010, 01:45AM

Registered Member #2015 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

Arcstarter

Wed Dec 08 2010, 02:24AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

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.

Steve Conner

Wed Dec 08 2010, 09:32AM

Registered Member #30 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.

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

radiotech

Wed Dec 08 2010, 05:38PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

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.

Arcstarter

Thu Dec 09 2010, 03:36AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

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:

Coronafix

Thu Dec 09 2010, 08:54AM

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

So how does it work under load? Inquiring minds want to know. :)

Steve Conner

Thu Dec 09 2010, 10:37AM

Registered Member #30 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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