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.

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.

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

Dave

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

James Sweet wrote:
Why do they have to be able to reverse the drum? I've never seen a
dryer that did that, obviously they must exist but I'm not sure of
the benefits.

To stop the clothes getting tangled, also the stopping then going the
other way will help stop areas of stagnation (and hence slow drying)
occuring. Mine a "Tricity Bendix TM 220 W" certainly has this drum
reversing indeed it is sold as a feature of this model and is called
"reverse action".
--
This post contains no hidden meanings, no implications and certainly no
hidden agendas so it should be taken at face value. The wrong words
may be used this is due to my limitations with the English language .

In article ,
raden writes:
In message .com,
writes
Or how about this :-

http://www.electricstuff.co.uk/marxthree.html


STOP IT STOP IT STOP IT

You're giving me ideas

I've got this terrible urge to dig out some perspex
sheet I've got left over in the garage...

I built a Van de graff generator when I was at school,
but that was rather disappointing. (On later reflection,
I'm not sure the belt material I used was a good enough
insulator.)

Then I built a high voltage generator using a car ignition
coil, EHT valve rectifier, and a capacitor made from
kitchen foil and a large roll of cellulose acetate
overhead projector film. I got really 'cracking' 4"-5"
sparks from it for a day, until the cellulose acetate
broke down.

--
Andrew Gabriel

On Thu, 22 Dec 2005 12:13:57 GMT, "david lang"
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.

Induction is cheaper for a specific power, or for almost all large
motors. Brushed is cheaper for small low powered motors that still need
high torque. If you can go to a direct-drive design, then using a
brushed motor and no gearbox is usually cheaper, but you need a motor
that can provide the required torque on its own shaft.

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.




I suspect the main reason there is power to weight/cost ratio. You can
get a tremendous amount of power out of a compact universal motor but an
induction motor suitable for that would be a lot heavier and more
expensive. A universal will burn up at the drop of a hat though, a
friend of mine retrofitted his electric mower with a surplus pool pump
motor when that happened, he said it worked really well but those motors
are expensive new.

soup wrote:
James Sweet wrote:

Why do they have to be able to reverse the drum? I've never seen a
dryer that did that, obviously they must exist but I'm not sure of
the benefits.


To stop the clothes getting tangled, also the stopping then going the
other way will help stop areas of stagnation (and hence slow drying)
occuring. Mine a "Tricity Bendix TM 220 W" certainly has this drum
reversing indeed it is sold as a feature of this model and is called
"reverse action".

Well damn, I cleaned up and tested out the Creda dryer which is the mate
for the washer I've been refurbishing and it does in fact reverse the
drum periodically. Nifty little machine, not like anything I've used
before. If the washer was a bit larger capacity and I didn't have a big
Neptune front loader already I'd definitely keep this pair but a friend
of mine has more of a need for them than I do.

Andrew Gabriel wrote:

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.

Ditto cheap high pressure cleaners. The £30 B&Q jobbies have a motor life
of 10-12 hours. Even a cheap Chinese induction motor will run for 50-60
hours. Qua;ity industrial machine will have an induction motor rated at
800-1000 hours.

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.

Ditto cheap high pressure cleaners.

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).

Indeed. High pressure pump wants to run at 1400 rpm, or 2800 at a pinch.
The cheapo HPCs use a ring gear to slow the motor down.

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.

Maybe mass production. Many el cheapo HPC's use domestic vacuum cleaner
motors.

Dave

Ditto cheap high pressure cleaners. The £30 B&Q jobbies have a motor life
of 10-12 hours. Even a cheap Chinese induction motor will run for 50-60
hours. Qua;ity industrial machine will have an induction motor rated at
800-1000 hours.




1000 hours sounds awfully low for a good induction motor. The 3HP main
pump in my spa runs 4 hours a day for the filtration cycles and it's 10
years old. Isn't used year round but it must have at least 5000 hours on
it and the bearings felt like new when I replaced the shaft seal. Theres
well used equipment at a friend's machine shop with motors dating back
to the 1940s that are still running strong.

James Sweet wrote:

1000 hours sounds awfully low for a good induction motor.

Depends on what you pay for them. On a cold water HPC the motor will be
about 65% of the total build cost, so they don't use the top grade -
besides, the pump etc won't last much more than 1,000 hours anyway.

Dave

Sam Goldwasser wrote:
http://search.ebay.co.uk/search/1-fa...QQfclZ4QQfnuZ1

A capacitor with a digital readout? Now they've gone over the top!


I think that you need to understand the market they are trying to sell
into. When you see the claim "A CAPACITOR stores current." you see what
level they are aiming at!