Hi all,

I need a variable speed mains AC motor for a project I'm working on.
Ideally, I'd like to be able to vary the speed using a variac. It needs
to go up to ~4000 RPM, which is beyond most mains drills. Any ideas on
where I can get one, or what bits of equipment I can cannibalise?

TIA


--
Grunff

Grunff wrote:

I need a variable speed mains AC motor for a project I'm working on.
Ideally, I'd like to be able to vary the speed using a variac. It needs
to go up to ~4000 RPM, which is beyond most mains drills. Any ideas on
where I can get one, or what bits of equipment I can cannibalise?


Thinking about it, can anyone think of a reason why I can't use a motor
from say a circular saw? I'm thinking:

http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=26213&id=23107


--
Grunff

In message , Grunff
writes
Grunff wrote:

I need a variable speed mains AC motor for a project I'm working on.
Ideally, I'd like to be able to vary the speed using a variac. It
needs to go up to ~4000 RPM, which is beyond most mains drills. Any
ideas on where I can get one, or what bits of equipment I can cannibalise?


Thinking about it, can anyone think of a reason why I can't use a motor
from say a circular saw? I'm thinking:

http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=26213&id=23107

The circular saw's in use at the moment

wait until the blood's washed off first

--
geoff

In message , Grunff
writes
Hi all,

I need a variable speed mains AC motor for a project I'm working on.
Ideally, I'd like to be able to vary the speed using a variac. It needs
to go up to ~4000 RPM, which is beyond most mains drills. Any ideas on
where I can get one, or what bits of equipment I can cannibalise?

You should know that someone's going to ask what sort of power you're
after

What sort of power are you after ?

--
geoff

raden wrote:

You should know that someone's going to ask what sort of power you're after

I knew someone would ask that...


What sort of power are you after ?

Anything more than ~300W will be fine.


--
Grunff

On Thu, 31 Mar 2005 00:57:29 +0100, Grunff wrote:

raden wrote:

You should know that someone's going to ask what sort of power you're after

I knew someone would ask that...


What sort of power are you after ?

Anything more than ~300W will be fine.



.... and somebody else is going to ask what the project is.....



--

..andy

To email, substitute .nospam with .gl

Andy Hall wrote:

... and somebody else is going to ask what the project is.....

Well...

Since finishing the house, I've had time to get back to some unfinished
projects. One of those is my Tesla coil. The motor is for driving a
rotary spark gap, to replace the static multi-gap I have on there at the
moment.


--
Grunff

On Thu, 31 Mar 2005 09:18:52 +0100, Grunff wrote:

Andy Hall wrote:

... and somebody else is going to ask what the project is.....

Well...

Since finishing the house, I've had time to get back to some unfinished
projects. One of those is my Tesla coil. The motor is for driving a
rotary spark gap, to replace the static multi-gap I have on there at the
moment.

This is getting concerning....

I'm starting to build an impression of all of this.....

- The isolated location
- Motor driven high voltage generation
- Variacs controlling it all
- Large meters on the wall
- The mad professor outfit recently ordered from the lab suppliers
- Strange goings on being heard of in the vicinity
- The howling of dogs in the distance
- The dark night with the thunderstorm and lightning bolts over the
prison quarry

You're making a monster, aren't you??


BTW. B&Q have a good range of coach bolts.






--

..andy

To email, substitute .nospam with .gl

In article , "Grunff"
says...
Andy Hall wrote:

... and somebody else is going to ask what the project is.....

Well...

Since finishing the house, I've had time to get back to some unfinished
projects. One of those is my Tesla coil. The motor is for driving a
rotary spark gap, to replace the static multi-gap I have on there at the
moment.

115mm angle grinders run at about 3000RPM - is that too slow?
I guess if you took off the bevel gear the actual motor speed would
be twice that or more, so you could regulate it down to 4000RPM and
it would be somewhat quieter too.

"Grunff" wrote in message
...
Andy Hall wrote:

... and somebody else is going to ask what the project is.....

Well...

Since finishing the house, I've had time to get back to some unfinished
projects. One of those is my Tesla coil. The motor is for driving a rotary
spark gap, to replace the static multi-gap I have on there at the moment.


I've read quite a bit of Tesla's stuff, a lot of it on the web. It would be
interesting to investigate to what extent the mechanical switches might be
replaced by semiconductors, working in low voltage circuits obviously.

j

In message , Andy Hall
writes
On Thu, 31 Mar 2005 00:57:29 +0100, Grunff wrote:

raden wrote:

You should know that someone's going to ask what sort of power you're after

I knew someone would ask that...


What sort of power are you after ?

Anything more than ~300W will be fine.



... and somebody else is going to ask what the project is.....

What's the project ?

--
geoff

On Thu, 31 Mar 2005 18:56:31 GMT, raden wrote:

In message , Andy Hall
writes
On Thu, 31 Mar 2005 00:57:29 +0100, Grunff wrote:

raden wrote:

You should know that someone's going to ask what sort of power you're after

I knew someone would ask that...


What sort of power are you after ?

Anything more than ~300W will be fine.



... and somebody else is going to ask what the project is.....

What's the project ?

He's already said, Geoff.

He's making a monster....





--

..andy

To email, substitute .nospam with .gl

What's the STARTING torque ? And as a secondary question, what's the
total power ?

If you don't have to start against a load, then you can use most sorts
of motor. If it must start "in gear", then you probably need a
"universal" motor, i.e. with brushes, rather than an induction motor.
These are easiest to find anyway.

I don't think an electric drill or saw is a good idea for starters, but
a cheap router will do 4,000 rpm easily and comes with built-in speed
control. Some saws will get you to almost 4,000 and you can add the
speed control.

And forget using a variac for speed control - save it for the "electric
gherkin" demonstration (Google for "electric pickle"). The way to do
it is by phase control (light dimmer, with a few extra bells and
whistles on). Light dimmers are prety rubbish (400W max, most are only
250W and they don't take kindly to motor loads either). However someone
like RS sell a wide range of ready-made phase control modules (just add
a variable resistor) and some of them are cheap (even from RS). If
you have a big induction motor you can't do this, but if you need
something that big then find a cheap 3 S/H phase motor and buy a
cheap(ish) VFD (variable frequency drive) from eBay.

wrote:
What's the STARTING torque ?

Pretty low.

And as a secondary question, what's the
total power ?

I can only really guess at this. It will be spinning a tungsten rod in a
rotary spark gap, so I reckon anything more than 300W will be more than
enough.



I don't think an electric drill or saw is a good idea for starters, but
a cheap router will do 4,000 rpm easily and comes with built-in speed
control.

Yes, I thought of a router after posting about the saw - I'd forgotten
how cheap they've become. My only question is will it go slow enough? I
need quite a wide range of speeds, from a few tens RPM to ~4000 RPM.


And forget using a variac for speed control - save it for the "electric
gherkin" demonstration (Google for "electric pickle").

But I love variacs! And I have several of them...


The way to do
it is by phase control (light dimmer, with a few extra bells and
whistles on). Light dimmers are prety rubbish (400W max, most are only
250W and they don't take kindly to motor loads either). However someone
like RS sell a wide range of ready-made phase control modules (just add
a variable resistor) and some of them are cheap (even from RS).

Found some on RS - surprisingly cheap.


Thanks.


--
Grunff

Grunff wrote:


Yes, I thought of a router after posting about the saw - I'd forgotten
how cheap they've become. My only question is will it go slow enough? I
need quite a wide range of speeds, from a few tens RPM to ~4000 RPM.

c. 8k rpm at the low end - so you would have to gear it a fair bit.

Found some on RS - surprisingly cheap.

CPC have some as well - I posted a link a few days back - 3 models upto
1.5kW


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:

CPC have some as well - I posted a link a few days back - 3 models upto
1.5kW

Found it - great, thanks.


--
Grunff

John Rumm wrote:

CPC have some as well - I posted a link a few days back - 3 models upto
1.5kW

Any idea what would happen if I used the output from one of these to
feed a device which already has its own speed controller (like a
router)? Would it work?


--
Grunff

Grunff wrote:

John Rumm wrote:

CPC have some as well - I posted a link a few days back - 3 models
upto 1.5kW


Any idea what would happen if I used the output from one of these to
feed a device which already has its own speed controller (like a
router)? Would it work?

You would end up with cascaded PWM controllers... The switching rates
would be unsynchronised so you would get aliasing between them. Net
result sounds like lots of edges (hence broadband noise) and not alot of
power. That is assuming you do not kill one of the controllers.

All in all I think I would avoid that one ;-)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article ,
Grunff wrote:
And forget using a variac for speed control - save it for the "electric
gherkin" demonstration (Google for "electric pickle").

But I love variacs! And I have several of them...

If you're on a tight budget, a decent variac is likely to sell on Ebay for
more than the cost of a phase control module.

--
*60-year-old, one owner - needs parts, make offer

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:

If you're on a tight budget, a decent variac is likely to sell on Ebay for
more than the cost of a phase control module.


It's not so much that - I wouldn't want to sell any of my variacs - but
it's the kind of project where I try to use whatever I have available.

The CPC modules at £12 seem like a very good deal.


--
Grunff

In article ,
Grunff wrote:

I need a variable speed mains AC motor for a project I'm working
on. Ideally, I'd like to be able to vary the speed using a
variac. It needs to go up to ~4000 RPM, which is beyond most
mains drills. Any ideas on where I can get one, or what bits of
equipment I can cannibalise?

The motor in our Hoover w/m looks a serious bit of kit.
1-2 HP, integrated speed sensor, smooth closed-loop
electronic speed control, in either direction.
The pulley ratio suggests that, at 1200rpm on the
drum, the motor shaft must be doing over 6000rpm.

But you need a circuit diagram to see how to wire
one up.

--
Tony Williams.

Tony Williams wrote:

The motor in our Hoover w/m looks a serious bit of kit.
1-2 HP, integrated speed sensor, smooth closed-loop
electronic speed control, in either direction.
The pulley ratio suggests that, at 1200rpm on the
drum, the motor shaft must be doing over 6000rpm.

But you need a circuit diagram to see how to wire
one up.


I think that's probably way bigger than I need. I really should have
specified the power requirement in my original post :-)


--
Grunff

In article ,
Grunff wrote:

Tony Williams wrote:
The motor in our Hoover w/m looks a serious bit of kit.
1-2 HP......

I think that's probably way bigger than I need. I really should
have specified the power requirement in my original post :-)

A Strimmer or Flymo motor then?

Don't run any universal motor on no-load
though, because of runaway.

--
Tony Williams.

In article ,
Tony Williams writes:
The motor in our Hoover w/m looks a serious bit of kit.
1-2 HP, integrated speed sensor, smooth closed-loop
electronic speed control, in either direction.
The pulley ratio suggests that, at 1200rpm on the
drum, the motor shaft must be doing over 6000rpm.

But you need a circuit diagram to see how to wire
one up.

You have to be careful reusing washing machine motors.
Off-load speed with no feedback control is often significantly
faster than the speed at which the motor armature flies into
pieces, rather explosively. I am also aware of cases where the
microprocessor servo control has failed to limit the speed
when there's no load too, so again be careful, even if you
think you have the servo control connected up correctly when
the load isn't the expected washing machine drum. (The case
I came across, the microprocessor crashes if the speed
increase is as fast as it is with no load, and leaves the
motor powered and running much faster than its top speed.)

--
Andrew Gabriel

Washing machine motors need to have chickens sacrificed to them before
you can understand their arcana.

In article ,
Grunff wrote:
I need a variable speed mains AC motor for a project I'm working on.
Ideally, I'd like to be able to vary the speed using a variac. It needs
to go up to ~4000 RPM, which is beyond most mains drills. Any ideas on
where I can get one, or what bits of equipment I can cannibalise?

If it helps, the speed of a drill motor is something like 10,000 rpm
before the gearbox.

--
*Welcome to **** Creek - sorry, we're out of paddles*

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:

If it helps, the speed of a drill motor is something like 10,000 rpm
before the gearbox.


There's a thought - and you get speed control as part of the deal. Maybe
it's time for a PP drill.


--
Grunff