My corded 110vac leaf blower suddenly became “super-charged” to the point where the fan blade exploded !
Dis-assembly shows simple 110v brush-type 2wire motor connected to a 3position switch providing Off/High/Low speed control using a 10amp diode in-line.
There are no visual signs of any damage to the motor parts, so I clipped the motor leads (no switch) and hooked up a test cord.
Holy cow! this thing runs faster than my air tools !

Experience tells me something is shorted,,, so why doesn’t it burn up ?
My Guru says because there is no load... no fan blade... no heat... yet.

So, my question is, if the diode cuts the voltage to 55v @60cps giving half-speed, how to I cut that in half ? 30cps??
The forum-posts say maybe a capacitor. But, I fear a 10amp cap inside a plastic box in my hand!
Blowing fire out of a dry-leaf blower is definitely not recommended.

Any advice is appreciated.

 

A diode in series with the Universal motor will give half voltage and a Quarter of Wattage, you can slow it down further using a dimmer circuit or a 1uF to 3.3uF capacitor in series with the motor..

 

Loss of field strength in the field winding can cause high speed operation, including 'run a way'. When you apply a voltage to the rotor, the rotor needs to spin in the motors magnetic field fast enough to produce a counter EMF very close to the applied voltage. If the field is reduced, the rotor needs to spin faster in order to produce that counter EMF.

The field can be reduced due to shorted windings or (for shunt wound motors) an open field.

 

So, one of the FIELD coils is open or shorted. I guess the Guru was right. Thank you.
New leaf-blowers are $50. Not worth the T & M to repair.
Thanks again.

 

you can slow it down further using a dimmer circuit or a 100nF to 330nF capacitor in series with the motor..

Really?

At 60 Hz, a 0.1 uF cap has an impedance of almost 27 K. Seems a bit high for a multi-amp application.

ak

 

I ment 1 to 3.3 uF...

 

No problem, SantaClaus brought me a new one. The old one is in the recycle bin.
Maybe you missed my meaning about "Blowing fire out of a dry-leaf blower".
Speaking from burned experience, I trust a fat-capacitor about as far as I can throw it.
I recommend your cheapo-home-dimmer be installed in a metal outlet box ONLY.
We had a tenet remove a ceiling light to install a cheapo-fan, and the cheapo-dimmer exploded in the plastic outlet box.