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Forum Index : Windmills : What kind of motors in vacuum cleaners?
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| adric22 Regular Member  Joined: 06/08/2008 Location: United StatesPosts: 47 |
Just curious if anyone knew if vacuum cleaners, circular saws, etc.. Do they typically use permanent magnet motors, or series wound? |
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| KiwiJohn Guru  Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Unless there has been a change in recent times they were mostly series wound. |
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| Dinges Senior Member  Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
A universal motor: http://en.wikipedia.org/wiki/Electric_motor No permanent magnets inside. Some may be series wound, others shunt wound, some a combination of these two windings, depending on the required motor characteristics. And useless for windturbine applications, in case you are wondering... |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Ummm... right, I was likely in error. |
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oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
KiwiJohn, No you weren't A universal motor is a ac series wound motor. It is just lucky that the field coils being in series with the armature all see the current in the same phase, and so can run on ac or dc. hence universal motor. Their are characterised by: 1. Ac or Dc 2. Lots of electrical noise and carbon dust 3. Low reliability 4. Low efficiency 5. They are frequency sensitive. A change in freq, usually requires a change in design parameters. (inductive reactance to frequency) I have worked with thousands of these rotten things, and they are worse than one may think for a wind turbine. They usually aim for 15-18000 rpm... thats bad, but worse, they are usually wound for only one direction. If you reverse the armature in relation to the field coils they run reverse with much much sparking on the armature. This is because they wind them "advanced" just like advancing ignition timing from TDC to 15 or so degrees advance to get better performance. Usually they are shifted 2 brush segments or so. If you carve the blades the wrong way... watch out. The high voltage ones have high resistance brushes, and the low voltage (36v 700w etc) have only 2 turns per coil on the shaft. I also know an idiot who rewound one just to see how they ticked....( it would be true to say that I had a lot of trouble  )
However, that being said, if you used a high voltage 1500w vac motor (10mm shaft) with low volt brushes, cut out the stator claws and put in 2 big neo's, you should get a respectable little alternator for a 20" blade... maybe 50w@ 30 mph.  Not sure how long the bearings would last with this loading... probably better than I think, and armature cooling may be required if you live in a wind tunnel.
Have never seen a shunt type vac motor, all were universal series wound motors..... except for some Japanese ones that were actually small three phase brushless types, with their own controllers, cute and expensive... but no armature sparks either... but they did have permanent magnets..and they were from vacuum cleaner machines.... does that count? ........oztules Village idiot...or... just another hack out of his depth |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Correct Oz. I should've expressed myself more clearly; it's the wound-rotor DC motor (with commutator and brushes) that's normally wound series, shunt or compound (a combination of series and shunt, to get the desired characteristics). I suppose there's no reason an AC commutator motor for e.g. a drill couldn't be wound shunt or compound, but I figure the series-characteristic is the most desired one for such applications. I haven't seen as many motors as you but I don't recall any being shunt-wound either. Not sure though that the universal motor is *by definition* series wound. I thought it was 'universal' because it ran on both AC and DC (Hey, isn't that an Aussie band?). But the vast majority (if not all?) are series wound indeed. The most common motor in consumer appliances is indeed the (series-wound) 'universal' (runs on AC and DC) motor. Which even runs on very much reduced DC, a 12V battery may be enough to get them to run (of course only at very limited power). One project I have considered in the past, using the (rewound) rotor of such a universal motor, was to build an AWP-type generator: the old rotor of a drill-motor would become the stator of the generator. A custom drum rotor would then have to be turned and magnets glued on the inside. A bit like the CD-ROM motors ('outrunners'), where the stator is inside the rotor. The advantages are that the magnets would be inside the drum, thus pressing outwards (centripetal force) as the windmill is running. Another advantage is that there's more room for magnets this way (compared to a standard motorconversion). Third advantage would be that it'd be relatively easy to enclose the rotor and make the entire genny weatherproof. The downsides are that nearly nothing of the old motor is re-used, just the (rewound) rotor. The geometry of the rotor of a universal motor is designed for high RPM: a long and relatively small diameter rotor. Another disadvantage is that it'd be a lot of work building one and it would yield relatively little power for that effort (those universal motors have pretty small rotors). But I still think it could be an interesting project to try out. Just that I've got so many projects in the works or planned... |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
On drills where the rotating direction can be varied it's sometimes done by varying the position of the brushes. By rotating the brushes a little (20 deg. perhaps) it starts turning in the other direction. Have a look at a drill (not the cordless variety) and see if there's a lever near the brushes that can be rotated by the operator (usually the lever is on both sides of the drill, both left and right). But I also know of at least one drill where turning direction can be varied by means of a switch. Haven't really opened it up to check the wiring but I assume the switch reverses the connections to the field coils. Universal motors... cheap, nasty, but also very powerful and small. Not to wax poetic here, but without them the world would be a very different place. Too bad they're no longer designed to be user-maintained, like replacing brushes. Guess it shows...cheaper to buy a new drill than a set of brushes and replace them. Besides, I get the impression that most of these motors fail from defect windings, long before the brushes wear out... |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Dinges, They do the two segment shift on Vac motors because they never change direction, and so are optomised for just that direction. Drills on the other hand if required to reverse now days, use neutral wind (equal torque ccw and cw. A case in point: I was given an old single direction Bosh drill the other day and decided to convert it to bi-directional, and variable speed (because it had a good two stage gearbox), but they had designed it for optimum cw rotation, and so sparked like hell when I reversed the armature wiring. So I decided to see if I could offset the brush housing by 15 deg or so....and I could.... but... To twist the knife a bit more, they used one way bearings to easily achieve the split box.. so it actually locked up after 1 1/2 turns ccw. So I kept the variable speed I had put in, but had to ditch the reverse. 
I have seen the variable brush format you talk of... but very rarely. .........oztules Village idiot...or... just another hack out of his depth |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Oztules, maybe you're diving the wrong dumpsters, but over here people toss drills (good brands like Bosch too) when the powercord is broken (usually where it exists the drill). I've repaired plenty where all I needed to do was shorten the cord a little. Variable speed (some both electrical and with an adjustable mechanical gear), reversible direction, some with hammer function. I stopped collecting them at the dumpster when I had about a dozen (I started becoming picky too, interested only in 'good' brands with all the nice features; didn't even take the plain ones home anymore ). Given a few away of them over time but still have 5-6 good drills lying about the place.
So, converting one to variable speed would never occur to me (though I have used in the past a triac based quicky & nasty external regulator to vary RPM). And mechanically converting to reverse the rotating direction... wow. Talk about impressive hacks. Guess I got spoiled with the things my fellow countrymen throw away. Stuff that's easily repairable so no need to go out of my way to try to incorporate such niceties as variable speed and rev.direction myself. |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Dammit, Not only can he use Femm properly, but he's even got a better standard of rubbish...
.........oztules Village idiot...or... just another hack out of his depth |
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