# universal motors ?



## clintster7 (Jun 29, 2010)

I ran across an article that mentioned ac, dc, and universal motors .. 
it said that many household including vacuum cleaner motors (most) are universal 
Does that include treadmill motors in general ?

are their larger motors that are both ac and dc compatible ?


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## few2many (Jun 23, 2009)

Vacuums and most electric lawnmower motors are universal because the ARE dc. They have rectifiers and resistors in them.
I have a leaf blower that will plug into a regular wall outlet. Or, I can connect the leads to my 24v forklift batt and it spins, although alot slower due to reduced voltage.
(I've actually connected it to prove this theory, I thought the ac appliance had a brushed motor and a rectifier for this reason and it did)
Also, ac can power a DC motor with just a rectifier. For dc to power an ac motor, need an inverter.


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## JRoque (Mar 9, 2010)

> Vacuums and most electric lawnmower motors are universal because the ARE dc


..._also
_
Universal motors are called so because they operate on both AC and DC. Wood routers (power tool) are mostly universal. Appliances use universal motors precisely because they can run off AC with a simple thrystor circuit to control their speed and this makes it the cheapest solution. Some go even further and tap the windings of the universal motor to change speeds - like in blenders. 

BTW, it used to be difficult to tell if your appliance had an universal motor (instead of an AC one). But now it's easy: you can smell the brush dust coming off all of those cheap Chinese universal motors. And they put those suckers on everything, even the high-end appliances. Carbon dust with your shake anyone?

JR


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## few2many (Jun 23, 2009)

Yup, burned up enough cheap blenders to know that smell very well. Also, the noticeable bit of carbon dust that will fill the unit around the motor.


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## clintster7 (Jun 29, 2010)

just cuirious .. Can a universal motor be turned into generator ? Not that I'm lookin into that.. But may be cool on a mini bike ..lol


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## few2many (Jun 23, 2009)

Only if its permanent magnet, or has seperately excited field and or stator


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## samborambo (Aug 27, 2008)

I think you've all missed the point of a universal motor....

Universal motors are technically series DC motors - the same as most of the forklift type motors used here by forum members. Since the same current flows through the armature as well as the field, reversing the polarity of the motor reverses BOTH currents and therefore the motor keeps turning in the same direction. An AC circuit alternates the polarity of the current 100 or 120 times per second. The motor motor responds with torque in the same direction, regardless of the current direction.

This is the reason why a reversing contactor is needed to reverse most EV motors. The reversing contactor changes the polarity of the armature OR the field, but not both.

So no diodes or thyristors necessary.


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## JRoque (Mar 9, 2010)

> I think you've all missed the point of a universal motor....


Hey Sam, it's true that thyristors are not necessary; I didn't say they were. My point was that appliance makers use universal motors because they're cheap and can have their speed controlled easily (and cheaply) with something like thyristors/TRIAC. And if you want to run your universal motor off DC (and there's value in this), you might need a set of diodes to convert your AC input.

Regards,
JR


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