Induction Motors

[JPEC]

Hi all,
I know how a brush motor works, but can anyone explain roughly how an induction motor works, as they are so quiet why aren't circular saws etc. fitted with them? Is it weight or cost of manufacture?
If it's cost I would gladly pay extra for a soft humming circular!

Cheers (Going deaf from too many years hunched over the skill saw)

Julian

 

[-David-]

Julian

Have a look at this.

http://230nsc1.phy-astr.gsu.edu/hbase/magnetic/indmot.html

David

 

[johnelliott]

as they are so quiet why aren't circular saws etc. fitted with them? Is it weight or cost of manufacture?

Size for size a series (brush) motor is MUCH more powerful than an induction motor and this is the main reason for the cost difference, it takes more matrerials to make an induction motor of the same power. Sometimes the machine would be so much heavier and bulkier that the use of a series motor is mandated, eg portable circular saw, drills etc.

John

 

[Niki]

Hi JPEC

It's weight, cost and others.
You can read (and see) about the induction motor (IM) and universal (or brush) motor (UM) and many other kinds of motors here
http://en.wikipedia.org/wiki/Electric_motor
http://230nsc1.phy-astr.gsu.edu/hbase/m ... ndmot.html

In general:
IM is bigger and heavier (my grinder, 180W is heavier than the skill saw 1000W).
IM has smaller torque on startup.
IM speed is less than 3000 RPM (single phase).
IM requires special start up circuit.

For the above characteristics, the selection of UM is preferred for hand held power tools (they can also run on different voltage and on AC or DC current).

My table saw noise level is 77db (2500W, no load) and I can still talk to my wife, while the skill saw is above 100db and I cannot even here myself.

niki

 

[JPEC]

Thanks everybody,

I guess my humming skillsaw would cost a fortune, run too slowly and weigh about half a ton then!! :shock:
Where did I put those earmuffs

I have seen mitre saws with induction motors, Elektra Bekum I think, so I just wondered. :roll:

Cheers

Julian