I'm replacing the motor in an elderly micro lathe with a 24VDC one from an
electric scooter. The power route will be mains switched-mode PSU
switch speed controller motor.

What switch is appropriate here? Is it sufficient to insert a basic switch
into the positive output from the PSU and take the negative output straight
to the speed controller?

Many thanks.

On 05/08/2020 13:25, Bert Coules wrote:
I'm replacing the motor in an elderly micro lathe with a 24VDC one from
an electric scooter.Â* The power route will be mains switched-mode PSU
switch speed controller motor.

What switch is appropriate here?Â* Is it sufficient to insert a basic
switch into the positive output from the PSU and take the negative
output straight to the speed controller?

Many thanks.


Yes.
Id probably put one on the mains side though

--
Its easier to fool people than to convince them that they have been fooled.
Mark Twain

The Natural Philosopher wrote:

Yes.

Thanks.

I'd probably put one on the mains side though.

The PSU will be plugged into (and be close to) a standard switched wall
socket, so I was assuming that this would be enough.

On 05/08/2020 13:25, Bert Coules wrote:
I'm replacing the motor in an elderly micro lathe with a 24VDC one from
an electric scooter.Â* The power route will be mains switched-mode PSU
switch speed controller motor.

What switch is appropriate here?Â* Is it sufficient to insert a basic
switch into the positive output from the PSU and take the negative
output straight to the speed controller?

You want one rated for the appropriate worst case DC current if it is to
last. That is unlikely to be a problem with most mains rated switches.

DC arc currents tend to be persistent if they occur. AC usually quench.

You may well want the sort of switch you can hit as an emergency stop.

--
Regards,
Martin Brown

On 05/08/2020 13:51, The Natural Philosopher wrote:
On 05/08/2020 13:25, Bert Coules wrote:
I'm replacing the motor in an elderly micro lathe with a 24VDC one
from an electric scooter.Â* The power route will be mains
switched-mode PSU Â* switch speed controller motor.

What switch is appropriate here?Â* Is it sufficient to insert a basic
switch into the positive output from the PSU and take the negative
output straight to the speed controller?

Many thanks.


Yes.
Id probably put one on the mains side though

What he says.

But if you really do need to switch DC with serious amps, you want a
proper DC switch, not an AC one.

I recently had to put a manual switch on the 40 amp preheaters for a
small diesel ATV (couldn't get the correct replacement timed relay) and
I used one of these

https://www.ebay.co.uk/itm/New-60Amp...sAAOSwzj1fA-ZF

In article ,
Bert Coules wrote:
I'm replacing the motor in an elderly micro lathe with a 24VDC one from
an electric scooter. The power route will be mains switched-mode PSU
switch speed controller motor.

What switch is appropriate here? Is it sufficient to insert a basic
switch into the positive output from the PSU and take the negative
output straight to the speed controller?

Many thanks.

If you're switching the DC side, make sure you use a switch designed for
that. Luckily things like car electrics switches are plentiful.

--
*I didn't fight my way to the top of the food chain to be a vegetarian.

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

Bert Coules wrote:

I'm replacing the motor in an elderly micro lathe with a 24VDC one from an
electric scooter. The power route will be mains switched-mode PSU
switch speed controller motor.

What switch is appropriate here? Is it sufficient to insert a basic switch
into the positive output from the PSU and take the negative output straight
to the speed controller?

Many thanks.

It will be quite sufficient tor electrical safety to use a single pole
switch. But this will be an expensive and probably short-lived switch
for hiigh DC current into an inductive load. The PSU may not be too
happy if it arcs a little on switch off. You are better getting a
mains one in the right (physical) place. And, as someone else said, you
can get one of those red and green button ones that locks out if the
mains is interrupted so the motor does not come on unexpectedly if power
is restored, and with a big red 'off' button.
--

Roger Hayter

Roger Hayter wrote:

You are better getting a mains [switch] in the right (physical) place.

You mean the right place for conveniently switching the lathe on and off?

So I would route the incoming mains supply through a switch near the lathe,
then away again to the PSU and back as a direct DC 24V supply to the speed
controller (also conveniently near the lathe) and then the motor?

And, as someone else said, you can get one
of those red and green button ones that locks
out if the mains is interrupted so the motor
does not come on unexpectedly if power is restored,
and with a big red 'off' button.

I'm not familiar with them; I'll investigate.

Thanks.

"newshound" wrote:

But if you really do need to switch DC with serious amps, you want a
proper DC switch, not an AC one.

I hadn't realised that there's a distinction. Thanks.

"Martin Brown" wrote:

You want one rated for the appropriate worst case DC current if it is to
last. That is unlikely to be a problem with most mains rated switches.

You may well want the sort of switch you can hit as an emergency stop.

Right, thanks.

Roger Hayter wrote:

And, as someone else said, you can get one
of those red and green button ones that
locks out if the mains is interrupted...

Is the locking-out feature also known as a no-volt release? If so,
something like this?

https://tinyurl.com/y2xj6xnu

Long URL:

https://www.amazon.co.uk/KEDU-KJD18-...BBJJCQNCSR9JX1

On 05/08/2020 16:53, Bert Coules wrote:
"newshound" wrote:

But if you really do need to switch DC with serious amps, you want a
proper DC switch, not an AC one.

I hadn't realised that there's a distinction.Â* Thanks.

depending on current, a semiconductor soft switch or even variable speed
controller such as used for RC cars etc might be useful

You can buy a cheap 'servo controller;' to generated the RC signal for them

--
I would rather have questions that cannot be answered...
....than to have answers that cannot be questioned

Richard Feynman

The Natural Philosopher wrote:

depending on current, a semiconductor soft switch or even variable speed
controller such as used for RC cars etc might be useful

Thanks. It's been suggested elsewhere (if I've understood correctly) that
it would be better to put an on/off switch (ideally with emergency stop) in
the main supply to the PSU and use that to control the lathe.

I had a vague recollection that it's ultimately damaging to a switched-mode
power supply to subject it to frequent turnings on and off, but perhaps I
was mistaken.

On 05/08/2020 17:59, Bert Coules wrote:
The Natural Philosopher wrote:

depending on current, a semiconductor soft switch or even variable
speed controller such as used for RC cars etc might be useful

Thanks.Â* It's been suggested elsewhere (if I've understood correctly)
that it would be better to put an on/off switch (ideally with emergency
stop) in the main supply to the PSU and use that to control the lathe.

I had a vague recollection that it's ultimately damaging to a
switched-mode power supply to subject it to frequent turnings on and
off, but perhaps I was mistaken.


It's not great on the mains side capacitors and rectifiers...a bit of
inductance in series will help


--
Theres a mighty big difference between good, sound reasons and reasons
that sound good.

Burton Hillis (William Vaughn, American columnist)

The Natural Philosopher wrote:

It's not great on the mains side capacitors and rectifiers...a bit of
inductance in series will help.

Thanks. Or presumably I could go with my original idea and put the
operational switch after the PSU, leaving that switched on for a whole
session.

Well you are drawing a lot more current the lower the voltage. I'd imagine
the wires to such a motor might well be pretty butch as well, and some on
old cars are so big they would not even go into the normal ac switches.
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Bert Coules" wrote in message
o.uk...
"newshound" wrote:

But if you really do need to switch DC with serious amps, you want a
proper DC switch, not an AC one.

I hadn't realised that there's a distinction. Thanks.

On Wed, 5 Aug 2020 18:13:03 +0100, Bert Coules wrote:

It's not great on the mains side capacitors and rectifiers...a bit
of
inductance in series will help.

Thanks. Or presumably I could go with my original idea and put the
operational switch after the PSU, leaving that switched on for a whole
session.

Or dig abput in the SMPSU and see if the control chip has an "enable"
input that turns it on/off without having to switch the DC. Some
SMPSU's have poor regulation when they don't have suffcient load.

--
Cheers
Dave.

Bert Coules wrote:

Roger Hayter wrote:

And, as someone else said, you can get one
of those red and green button ones that
locks out if the mains is interrupted...

Is the locking-out feature also known as a no-volt release? If so,
something like this?

https://tinyurl.com/y2xj6xnu

Long URL:

https://www.amazon.co.uk/KEDU-KJD18-...XTF83DY/ref=pd
_lpo_201_t_1/262-3640514-5452456?_encoding=UTF8&pd_rd_i=B07XTF83DY&pd_rd_r
=156d6152-5e83-438d-ba26-ffee6ad3852d&pd_rd_w=GsiGZ&pd_rd_wg=iQUVH&pf_rd_p
=7b8e3b03-1439-4489-abd4-4a138cf4eca6&pf_rd_r=SK9SGYBBJJCQNCSR9JX1&psc=1&r
efRID=SK9SGYBBJJCQNCSR9JX1

Yes, that's the sort of thing I was thinking off. You can get them with
just the red and green button and not the added rather gross red one!

--

Roger Hayter

Roger Hayter wrote:

Yes, that's the sort of thing I was thinking off. You can get them with
just the red and green button and not the added rather gross red one!

Thanks for that. Yes, the massive panic switch is perhaps a tad over the
top for my little Unimat lathe.

On the subject of whether to place a switch in the mains line or the 24V
feed, I've been advised that a switched-mode PSU doesn't like being
frequently switched on and off (as would happen if the operations switch for
the lathe was before the power supply). Would a switch like the ones we're
talking about be equally effective in the 24V supply to the machine?

Bert Coules wrote:

Roger Hayter wrote:

Yes, that's the sort of thing I was thinking off. You can get them with
just the red and green button and not the added rather gross red one!

Thanks for that. Yes, the massive panic switch is perhaps a tad over the
top for my little Unimat lathe.

On the subject of whether to place a switch in the mains line or the 24V
feed, I've been advised that a switched-mode PSU doesn't like being
frequently switched on and off (as would happen if the operations switch for
the lathe was before the power supply). Would a switch like the ones we're
talking about be equally effective in the 24V supply to the machine?

It wouldn't work at all unless it was a specific 24V one. And the
contacts on a mains one wouldn't be suitable anyway.

As a matter of interest, do power supplies like their output switched on
and off any better?


--

Roger Hayter

Roger Hayter asked:

As a matter of interest, do power supplies like
their output switched on and off any better?

An excellent question! I've no idea: my information about frequently
switching the input on and off came secondhand from someone on a Unimat
group who has done the same motor-replacement as I'm preparing for: he found
the advice in the instructions which came with his PSU. Mine has no such
warning.

Bert

On Thu, 6 Aug 2020 09:13:50 +0100, Bert Coules wrote:

Thanks for that. Yes, the massive panic switch is perhaps a tad over
the top for my little Unimat lathe.

I know you'll have your long hair tied back, won't wear a scarf, roll
up your sleeves, take off your tie, etc but... Having a stop(*)
button that you can reach for any bit of machinery can be a life
saver. Also the "no volt release" feature can prevent nasty
surprises. Not sure I'd like to be turning something and have the
local supply auto-reclosure do it's few seconds
off-on-off-on-off-on-lockout thing, machine starting and stopping,
lights going on/off. The machine latching off straight away, is one
less thing to worry about.

Also will the SMPSU object to the inrush current of a motor? Either
by deciding there is an overload and shutting down (with/without
restart attempts) or letting the magic smoke out? ISTR that you
mentioned a speed controller, can that be "got at" to provide soft
start on/off control as well as speed? Might just a switch across the
terminals of the speed potentiometer with an RC ciruit to make the
control voltage ramp up.

(*) Bear in mind that this "stop" button only removes power it
doesn't apply a brake so the machine will still needs to run down or
otherwise dissipate it's kinetic energy.

--
Cheers
Dave.

Dave Liquorice wrote:

Having a stop(*) button that you can reach
for any bit of machinery can be a life
saver.

I do take the point that a small lathe potentially can inflict as much
damage as a large one.

ISTR that you mentioned a speed controller,
can that be "got at" to provide soft
start on/off control as well as speed?

As it happens, the speed controller's (small) potentiometer does have a
click-off position at its closing point, but the general experience of
people who have also done this motor replacement (which is not an uncommon
procedure) is that the lathe can be reluctant to start at the lowest speed
setting: the usual recommendation is to leave the control partly open and
not use it as an on-off switch. I don't know if switching on and
immediately rotating the control to say quarter-full would overcome that.

My original idea of a simple on-off switch between the PSU and the speed
controller, plus an overall on/off/safety cutout switch before the PSU might
perhaps provide an ideal all-round solution?

On Thu, 6 Aug 2020 10:55:31 +0100, Bert Coules wrote:

ISTR that you mentioned a speed controller, can that be "got at"
to
provide soft start on/off control as well as speed?

As it happens, the speed controller's (small) potentiometer does have a
click-off position at its closing point, but the general experience of
people who have also done this motor replacement (which is not an
uncommon procedure) is that the lathe can be reluctant to start at the
lowest speed setting: the usual recommendation is to leave the control
partly open and not use it as an on-off switch.

One would really need to see how the pot and the pot switch are
wired. It might be that you could just series connect another switch
with the pot one to give a seperate on/off function.

I don't know if switching on and immediately rotating the control to say
quarter-full would overcome that.

Probably. Is the speed controller a PWM one or variable DC volts? I
wouldn't have thought a variable voltage controller would be any good
for a lathe as the torque would be too low at low speed settings (why
it's reluctant to start at low settings...)

My original idea of a simple on-off switch between the PSU and the speed
controller, plus an overall on/off/safety cutout switch before the PSU
might perhaps provide an ideal all-round solution?

Apart from the difficulty in finding a suitably rated DC switch.
Can't remember if you stated a power for the motor but I should
imagine it's a couple of hundred watts which, at 24 V, is 10(ish) A.
24 V truck switches might be suitable or use a beefy 24 V truck
relay. Just seems a bit "messy" to mechanically switch the DC when
there is already something there doing it electronically.

--
Cheers
Dave.

Dave Liquorice wrote:

I don't know if switching on and immediately rotating the control to say
quarter-full would overcome that.

Probably. Is the speed controller a PWM one or variable DC volts?

It's PWM.

My original idea of a simple on-off switch between the PSU and the speed
controller, plus an overall on/off/safety cutout switch before the PSU
might perhaps provide an ideal all-round solution?

Apart from the difficulty in finding a suitably rated DC switch.
Can't remember if you stated a power for the motor...

It's 150W. It's the standard electric scooter motor recommended for this
project.

A 24 V truck switches might be suitable or use a beefy 24 V truck
relay. Just seems a bit "messy" to mechanically switch the DC when
there is already something there doing it electronically.

If you mean the speed controller, I can wire everything up and try it. I
don't have a mains switch yet, apart, of course, from the switched wall
socket where the PSU is plugged but I can hardly use that as an operational
switch for the lathe, except for testing.

Thanks for the thoughts, Dave.

Bert

On 06/08/2020 12:07, Bert Coules wrote:
Dave Liquorice wrote:

I don't know if switching on and immediately rotating the control to say
quarter-full would overcome that.

Probably. Is the speed controller a PWM one or variable DC volts?

It's PWM.

which effectively IS variable DC volts, especially if run in series with
MUCH better than a potentiometer which wastes power and limits current
at low voltage settings

My original idea of a simple on-off switch between the PSU and the speed
controller, plus an overall on/off/safety cutout switch before the PSU
might perhaps provide an ideal all-round solution?

Apart from the difficulty in finding a suitably rated DC switch.
Can't remember if you stated a power for the motor...

It's 150W.Â* It's the standard electric scooter motor recommended for
this project.

Oh blimey. Its a crappy old speed 600 style motor then.

you can control that ever so easy from a DC source.

Its even easier to switch it with a semiconductor like a 2N3055.


A 24 V truck switches might be suitable or use a beefy 24 V truck
relay. Just seems a bit "messy" to mechanically switch the DC when
there is already something there doing it electronically.

If you mean the speed controller, I can wire everything up and try it.
I don't have a mains switch yet, apart, of course, from the switched
wall socket where the PSU is plugged but I can hardly use that as an
operational switch for the lathe, except for testing.

Thanks for the thoughts, Dave.

Bert



--
"What do you think about Gay Marriage?"
"I don't."
"Don't what?"
"Think about Gay Marriage."

On Thu, 6 Aug 2020 12:07:15 +0100, "Bert Coules"
wrote:

Dave Liquorice wrote:

I don't know if switching on and immediately rotating the control to say
quarter-full would overcome that.

Probably. Is the speed controller a PWM one or variable DC volts?

It's PWM.

My original idea of a simple on-off switch between the PSU and the speed
controller, plus an overall on/off/safety cutout switch before the PSU
might perhaps provide an ideal all-round solution?

Apart from the difficulty in finding a suitably rated DC switch.
Can't remember if you stated a power for the motor...

It's 150W. It's the standard electric scooter motor recommended for this
project.

A 24 V truck switches might be suitable or use a beefy 24 V truck
relay. Just seems a bit "messy" to mechanically switch the DC when
there is already something there doing it electronically.

If you mean the speed controller, I can wire everything up and try it. I
don't have a mains switch yet, apart, of course, from the switched wall
socket where the PSU is plugged but I can hardly use that as an operational
switch for the lathe, except for testing.

Thanks for the thoughts, Dave.

Bert

You could add a switched extension in the mains lead, with the switch
next to the lathe for emergency cutoff. Perhaps a big red button you
can whack.
--
Dave W

Dave W wrote:

You could add a switched extension in the mains lead, with the switch
next to the lathe for emergency cutoff. Perhaps a big red button you
can whack.

Thanks. this has been discussed higher in the thread, with opinion divided
as to whether or not a big red slammable emergency button is rather over the
top for a Unimat micro lathe.

Bert

Bert Coules wrote:

Dave W wrote:

You could add a switched extension in the mains lead, with the switch
next to the lathe for emergency cutoff. Perhaps a big red button you
can whack.

Thanks. this has been discussed higher in the thread, with opinion divided
as to whether or not a big red slammable emergency button is rather over the
top for a Unimat micro lathe.

Bert

But I think near unanimity that at least a small red cutout button would
be a Good Thing.

--

Roger Hayter

On 05/08/2020 13:25, Bert Coules wrote:
I'm replacing the motor in an elderly micro lathe with a 24VDC one from
an electric scooter.Â* The power route will be mains switched-mode PSU
switch speed controller motor.

What switch is appropriate here?Â* Is it sufficient to insert a basic
switch into the positive output from the PSU and take the negative
output straight to the speed controller?

Many thanks.


What's the maximum current? Scooter motors typically draw 20A under
heavy load.

I'd be inclined to switch the motor with a big-ass relay, controlled by
a push-on push-off button switch. Use a relay with a 24V coil and you
can power it from the existing PSU. I'd use a plug-in relay then if/when
it gets unreliable it will be easy to change it.

Bill

On 06/08/2020 09:46, Bert Coules wrote:
Roger Hayter asked:

As a matter of interest, do power supplies like
their output switched on and off any better?

The 33V DC psus that charge disability stairlift batteries are
permanently powered, but after each operation of the lift they are
abruptly connected to the DC-DC converter in the chair that charges the
battery. Weirdly, although the supplied psus seem to be mostly rated at
1.2A, the initial current draw is usually about 1.85A.

Bill

On 07/08/2020 01:58, Roger Hayter wrote:
Bert Coules wrote:

Dave W wrote:

You could add a switched extension in the mains lead, with the switch
next to the lathe for emergency cutoff. Perhaps a big red button you
can whack.

Thanks. this has been discussed higher in the thread, with opinion divided
as to whether or not a big red slammable emergency button is rather over the
top for a Unimat micro lathe.

Bert

But I think near unanimity that at least a small red cutout button would
be a Good Thing.

Dead man's handle in the form of a foot pedal?

Bill

On Fri, 7 Aug 2020 02:29:07 +0100, williamwright wrote:

Thanks. this has been discussed higher in the thread, with
opinion
divided as to whether or not a big red slammable emergency button
is
rather over the top for a Unimat micro lathe.

But I think near unanimity that at least a small red cutout button

would be a Good Thing.

The NVR feature certainly and if the switch is of "standard"
appearance all the better. TBH neither the table saw or small pillar
drill have nice big bashable "stop" buittons but rather fiddly little
things, I'd rather have something easier to bash.

Dead man's handle in the form of a foot pedal?

Starting to get complicated. In fact thinking about it wasn't the
lathe orginally mains powered? So it surely has a mains NVR
already... google Maybe not Unimat have been around before things
like NVR's or guards on belt drives where thought neccessary. B-)

--
Cheers
Dave.

Many thanks for all the latest replies. A switch across the mains supply,
located near the lathe (which the PSU won't be) is clearly a good thing.
And a panic cut-off does seem to be the majority recommendation.