Universal Motors Principle and Applications in Appliances

You appear to want to get folks here to visit your web site to generate advertisement revenue.

Did you correct the errors pointed out from last attempt at this?

Reported as SPAM.

Beat you to it but its still here.

Very badly formatted, not proof read, misspellings in there and questionable content.

One does not have to be in electrical engineering to dismiss this blog as not worth reading.

Even so or just because English is not your first language you need to have someone proof read this.

Whats it with all the HTML tags in the text?

I give it a 3 out of 10!

Modern washing machines don't use such motors anymore, probably at least 15 years....

The wear on universal motors is simply too high.....

Electric drills and such still use universal motors. Brushes are not going away.

I'm not so sure about that! I just checked my ≈2-year-old handheld drill, saw, etc. Since there is no way to replace brushes, I suspect that there are none. Also, universal motors normally have poor torque at low speeds; these have excellent torque at low speeds.

I have not taken any apart, but based on the sound they produce, and the low-speed torque, I suspect that they are multiphase AC motors with a permanent magnet armature, driven by a variable frequency inverter (essentially stepper motors). The sound leads me to suspect that it is a square-wave inverter system.

only takes ten batteries in series to check it out...

Please elucidate!

Usually (in the drills I have bought and used for mains voltage, not the battery types, though the motors are similar in some ways...) the motor is inside a strong case/housing, that you cannot see into.

But running them unloaded at full speed in a darkened room, you may see some sparking via the air cooling slits. This means that either you have a Universal motor with brushes, or that your drill is shortly going to be defective (in the case of some induction types!! If they truly exist!)

But all the mains drills I have ever had personally were Universal motor types....not that I have had every type of course.

Furthermore, universal motors are used mainly because they have a really high starting and running torque.

Look here on Wiki:-

Universal Motors

....and concentrate on the first sentence of the second paragraph. It says the following:-

Universal motors have high starting torque, run at high speed and are lightweight and are commonly used in portable and domestic equipment.

I read quickly through the article and found no glaring or otherwise big errors....maybe you can point some out?

I would not be surprised to see a Universal motor that used Hall effect sensors instead of a commutator....more like the three phase AC/DC motors available for many years already. VFD types for example.

Have a great day anyway.

I didn't say "starting torque". "I said low speed torque".

If you apply full voltage to a stopped universal motor, it will indeed have good starting torque, but it will quickly then get up to full speed, which is commonly quite high. To make it run slowly, you normally just apply less voltage. At very low speeds, like 60 rpm, you must apply very low voltage (or have very narrow pulse width if it is PWModulated), which of course means low average current and therefore low torque.

At 1/100 of its full speed, this kind of motor tends to run quite erratically if at all, and have considerable cogging.

I just checked my units. The drill is a Milwaukee 12V Cat. 2410-20. It is somewhat difficult to check for sparks, as whenever you pull the trigger, and LED comes on to illuminate the target area, but I covered the LED and held the unit in all sorts of positions, and could see no indication of a spark.

I paid closer attention to the sound in a quiet surrounding. As soon as the trigger is pulled far enough to start the motor, there is a high pitched (perhaps 1kHz) whine. This whine keeps the same frequency as the motor speed increases, indicating a chopper or inverter. As soon as the motor begins to rotate appreciably, another sound of vastly lower frequency becomes audible, and this sound has a frequency proportionate to the speed of the motor. This is the sound that gives me the impression of a square wave at the frequency of poles passing an electromagnet.

The drill is part of a set that also includes a reciprocating saw and a screwdriver, which I got at Christmas time 2 ¹/₂ or perhaps 3 ¹/₂ years ago. I have been really happy with them!

All the motors I've seen that use Hall Effect sensors (like the spin motors in floppies and hard drives), are Brushless DC motors. No sparks...

You misunderstood what I wrote completely, I thought it was easy to understand for anyone, wrong!!! Sorry about that!!!

I specifically mentioned that it was to be a MAINS drill....Though universal AC motors have a lot of similarities with some DC motors....those do not usually run on AC or AC mains!!! Not for long anyway.

Technically seen, the pole pieces are different for a true DC motor, whereas a universal will run on either AC or DC.....its pole pieces are laminated. That costs more....

So please remember, "Universal Motor" implies to most people a motor for mains AC voltages......!!!! Not a Milwaukee 12V DC drill for example........

If you remember (please go back and check!) my very first sentence was:-

Usually (in the drills I have bought and used for mains voltage, not the battery types, though the motors are similar in some ways...) the motor is inside a strong case/housing, that you cannot see into.

Could I have written more clearly?

You were comparing apples with Pears!!!! 12VDC with mains AC......

I personally have never seen a power drill with a VFD or brushless motor up to now, but it could happen any day.....Torque should also be good as well as speed control.......

I have never had problems with my mains drills (one is from 1960 odd, another is from 1974 and the latest one with full electronic speed control, fwd & reverse is from about 1999. I also have two powerful big masonry models, really high wattage) regarding low speed torque.

All have a universal mains motor. But maybe I have simply bought good quality units......the speed control on the latest three have always done its job well, though I do not have an opinion as to what style of speed control is in use. It and both of the older ones were made by Black & Decker before they started making crap equipment.....the masonry ones are a cheaper type from Aldi.....one gearbox will only hammer now, so I bought a second one...

If you have had poor speed control with mains units (you have only spoken about a 12v battery drill!), maybe you should try buying units with a better build quality.....they work far better, even at low speed and have great torque.

By the way, the intention is for a universal motor, as load increases, but without a voltage increase, for it to slow own. As that happens, the current ramps up (I can explain why if you do not fully understand that), so does torque and it finds a new stable speed at which it can run.

If you need the original speed again, you need to increase the voltage to the motor, squeeze the pistol grip for example....but with higher wattage motors, the effect is tiny....my latest B&D is 1500 watts....it hardly changes speed under normal circumstances...

That is all intentional and designed so........

OK! We are both guilty of not reading carefully enough!

My post #8 was responding to Yusef1's comment that "brushes are not going away", where he mentioned drills as an example. I of course thought of the hand-held drills I use regularly, which are battery powered. I do have a mains-powered hand drill as well, but like one of yours, I got it in the early '60's. It is clearly a brush-type motor, single speed, and it still works well, I think with the original brushes. The battery operated units have improved so much, both in battery life and in power, and are so convenient, that I rarely dig out the mains one.

Actually, I did consider taking one of the Milwaukees apart, but decided not to. Upon even closer examination, I think I see only two wires leading to the motor; that means that it must be a brush type motor, even though I can't see any sparks. A multiphase motor must have more than two wires.

In my experience, the term 'universal motor' simply means a motor that will run correctly on either AC or DC, with no reference to any particular voltage level. All the motors I can think of that work on both AC and DC do indeed have brushes, as well as wound coils in the field and armature.

The few times I ever tried to use my mains drill with variable speed was by plugging it into a Variac. Again, at low speed, very little torque. I've never owned a variable-speed mains powered drill.

Yes, I do understand back EMF...

Thanks!

You are apparently answering a comment that I did not make, or probably one you misunderstood or misread....

That is a typical on CR4, so I guess I should be used to it.....

But I expected better from you Yusef1........

Please read my comment again, do please note that I was being specific about washing machines...do you disagree on that his does in any way shape or form? Or should have said something like "and all the other machine/motor type are accurate"?

My comment was JUST the following, go back and check for yourself:-

Modern washing machines don't use such motors anymore, probably at least 15 years....

The wear on universal motors is simply too high.....

By wear, I meant brushes and commutators.....simple!

I thought that each one of you would understand that, or ask in a mannerly way just what was meant!!!

DUUUUUUUUHHHHHHHH!!!! Homer is still alive and well on CR4!!! Sadly....