In article ,
"david lang" writes:
Andy Dingley wrote:

You use induction motors whenever you can - they're quieter (this is a
domestic appliance after all) and they're cheaper.

Odd. The only experience I have is with high pressure cleaners. The el
cheapo DIY jobbys have brush motors which make a terrible screaming noise -
but they use them to reduce costs.

My 4-5 year old el-cheapo "Deltajet" (cheapest I could find
at the time, for hosing mud off the bicycles) is a 1200W
induction motor.

In the case of lawnmowers, I suspect the use of universal
motors is to make mowers into consumables, which people
will thus tend to change every few years. Just about every
characteristic of a universal motor is inappropriate for
a lawn mower. You can find mowers with induction motors,
but they tend to be in the better quality less well known
makes, which you have to buy from specialists rather than
DIY sheds.

The advantage of
the brushed motor is that they have much higher torque at low speeds
or when stalled (why they appear on power tools) and they're also
more easily controllable for variable speeds etc. There's a lot of
things a washing machine does that a tumble drier just doesn't need.

You can also get a more powerful universal motor in a smaller
physical size, but generally they are significantly less efficient.
E.g. you need around 30-50% more powerful universal motor to get
same cutting power out of a lawn mower as you do from an induction
motor, and the universal motor will run too hot to touch even
with forced air cooling, whilst the induction motor only runs
luke warm. I don't know if this is an inherent design issue, or
if it just reflects that the induction motors are found in better
specified/designed products. Also, universal motors generally run
much faster, indeed much too fast for many applications where they
need to be geared down (e.g. mowers, drills, etc).

I can see the logic in that, but I've always assumed (from my HPC
experiences) that induction motors were much more expensive.

I don't see why they should be technically. It may be a question
of supply and demand, what the market will bear, etc.

--
Andrew Gabriel