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Simple Motor Question

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MRSSPOCK

MRSSPOCK

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Aug 29, 2010
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Please forgive my ignorance.

I know this is a Mickey Mouse question.

Am I right to assume ALL brushed motors are DC?

It's not a trick question.

It is just a motor I have taken from a vacuum cleaner.

I was told the control board can be by passed, but the motor I have has got brushes.

(I'm presuming the board is a rectifier / speed control as it has 2 diodes, a triac and a AS25B01 IC and a few other passive components.

Surely there is no way this motor can be connected directly to AC without the above mentioned board?

So, getting back to the question, is it true that an AC motor NEVER has brushes?

Thanks
 
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Vacuum cleaners and many high powered hand-tools use universal motors, which have brushes and are designed to run on AC. These motors will also operate on DC, hence the term universal. These motors run at high speeds and can generate a lot of power in a compact and light motor.
 
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Thanks Compositepro.

So is it possible to attach such a motor to AC directly, or does it need some circuit to do some rectification etc first?

Thanks
 
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Since armature and field are connected in series, the "rectification" takes place in the motor (plus*plus=plus and minus*minus=plus). But you can expect heavy arcing. They all arc a lot and they don't live very long.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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That's great.

Thanks for clarifying that.

Does that mean the board is a speed controller?

The vacuum cleaner started puffing out black carbon dust and making strange noises.

I'm just unsure if the motor is faulty, or is the controller doing something strange, or not doing what is meant to be doing.

I just tried it directly on the AC and the behaviour is just like with the controller attached.

I've had the motor totally disassembled and couldn't see any obvious faults.

Each of the field windings measured 0.3 ohms but I've no idea if that is normal or not.

The armature windings didn't show any resistance at all, with probes attached to various commutator pads.

I will be buying a new motor but would like to have some confidence that it is the culprit.

Thanks
 
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If you looked at the brushes and they look fine then it probably wasn't carbon you were seeing.
The circuit board is a bit of a puzzle. I've never seen or heard of a vacuum that had a variable speed motor. We can tell you exactly what it does if we had a picture of it.

Before spending on a new motor consider a "Hoover Air Steerable". We're pleased with its performance, use it about 3 times a week (freakin dog) and it probably costs about what your motor will.

Keith Cress
kcress -
 
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Here it is.

Ignore the capacitor desoldering.

I removed it to test it but it is fine.

Image1309_dopqaa.jpg


Image1310_npdfww.jpg
 
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Looks like a triac. That's often used for universal motors and DC motors for speed control. I'm guessing a variable resistor somewhere is attached to the board via two of the quick disconnects.
 
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Wild thought here: What is the voltage rating on the appliance data plate? I wonder if this is a sneaky way of making a cleaner that auto-adjusts to a wider supply range than a universal motor would usually tolerate.

A.
 
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@zeusfaber That was going to be my next question.

I began to wonder is it to make it UK / usa compatible.

The label on the cover is 220V - 240V 50Hz 1400W

I don't suppose they would label it in that way if it could cater for multiple input types.

The motor is buried inside again, so I need to remove it again to see there are details on it, but I don't think it has a label directly on the motor.

I suppose a datasheet for the AS25B01 IC might give a clue but haven't found one yet.
 
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Almost each vacuum cleaner has a speed controller that is an ordinary voltage regulator with triac.
The minimum and the maximum value of output voltage, usually are preset with serial resistor and proper resistance of potentiometer.
 
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That is just a fixed speed controller, so it's a speed controller but not in the usual sense of allowing user adjustment. It probably keeps the vacuum from over-speeding on no airflow, provides minimum arcing of the brushes, and probably keeps the current draw below some design or appliance limit.

All the parts on there have private part numbers for the vacuum company so you can't look them up.

Keith Cress
kcress -
 
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Thanks Tmoose.

I couldn't find a fault and the carpet was growing a beard, so I just bit the bullet and bought a new one.

Thanks everyone for your replies.
 
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If the carpet is growing that fast, try dog or cat lacquer. One coat and your carpet will be hair free for weeks. Reapply as required. For more permanent results - Plasti-dip. Be careful as the both the coating and the animal tend to run. So you'll want to prepare to prevent that.

The one chip looks like AS25B01. I found just a picture on a German website with similar connections. It's not proprietary to the vacuum cleaner maker; but it looks like it predates the conversion to the internet of specs, so there's no telling what the specs are without access to an old and large library.

The big one is an ST BTB12-600B; the discoloration suggests it fried. It's under $2 not including shipping/handling.

See the G(ate) and A2 solder pads. It matches the pinout in this document:


If the motor doesn't run when the two connectors that were attached to the board are shorted, then it's possible the motor went first, taking out the Triac. Since the rest of the circuit isn't in the current path to the motor it should be OK; replacing the Triac will let the circuit work. Of course you need a motor.

I don't see any short circuit protection but I suppose if the motor fails, the rest will be discarded. If it's really bad the breaker/fuse to the outlet will stop the fire.
 
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