The variable speed controller on my Chester mini lathe has died, it's a 2A,
220 V DC brush motor and looks like a pulse width modulation controller.
Anyone know of either a circuit or a supplier of a board? I've found a
simple12/24 v circuit but I don't want to waste time redesigning if there's
a design out there, or a controller for £110 but could do with something
cheaper.

In article ,
"Newshound" writes:
The variable speed controller on my Chester mini lathe has died, it's a 2A,
220 V DC brush motor and looks like a pulse width modulation controller.
Anyone know of either a circuit or a supplier of a board? I've found a
simple12/24 v circuit but I don't want to waste time redesigning if there's
a design out there, or a controller for £110 but could do with something
cheaper.

You can probably use a bog standard motor speed controller (of the
same type used for drills, etc) followed by a full wave rectifier.
Maplin probably do a suitable motor controller module (and rectifier).
If it's a universal motor (i.e. field windings rather than permanent
magnet), then it will run from AC too and you won't need the full
wave rectifier.

--
Andrew Gabriel

Andrew Gabriel wrote:
In article ,
"Newshound" writes:
The variable speed controller on my Chester mini lathe has died, it's a 2A,
220 V DC brush motor and looks like a pulse width modulation controller.
Anyone know of either a circuit or a supplier of a board? I've found a
simple12/24 v circuit but I don't want to waste time redesigning if there's
a design out there, or a controller for £110 but could do with something
cheaper.

You can probably use a bog standard motor speed controller (of the
same type used for drills, etc) followed by a full wave rectifier.
Maplin probably do a suitable motor controller module (and rectifier).
If it's a universal motor (i.e. field windings rather than permanent
magnet), then it will run from AC too and you won't need the full
wave rectifier.


Would a normal power drill be a suitable starting point, since lots of
them already have speed control in them. Not sure on long term life but
something like one of the green Bosch drill series, or if your really
flush go for the blue industrial.


Joules

Newshound wrote:
The variable speed controller on my Chester mini lathe has died, it's a 2A,

I once bought a lathe with a DC motor speed controller which had died.
The original (''50s?) arrangement had DC generated by an AC motor
driving an AC generator. Speed control was by varying the DC voltage.
Howvever this arrangement had expired.

I found an electronic DC motor speed controller on Farnell/ CPC.
They're used on conveyor belts, apparently. I'm not sure about the
voltage, I've a vague idea it was 110V DC max, but can't recall the
details. Try there.

Newshound wrote:

The variable speed controller on my Chester mini lathe has died, it's a 2A,
220 V DC brush motor and looks like a pulse width modulation controller.

And how about repairing the controller? Shouldn't be to complicated and
-even with pure guessing- the chances to get it working again are high.

I would replace everything that is big, has a cooling fin and three
legs. :-)


Nick
--
The modular DRO
Available now in USA / Canada
http://www.yadro.de
...|....|....|....|....|....|....|..

Newshound wrote:
The variable speed controller on my Chester mini lathe has died, it's a 2A,
220 V DC brush motor and looks like a pulse width modulation controller.
Anyone know of either a circuit or a supplier of a board? I've found a
simple12/24 v circuit but I don't want to waste time redesigning if there's
a design out there, or a controller for £110 but could do with something
cheaper.


Take a look at the site of littlemachineshop.com. IIRC they sell
replacements for these speed controllers for these lathes and the
mini-mills, but I think they also have some info on circuit diagrams as
well. Look under the resources button on their site. They also sell the
mosfets (get the part number from there) and the troubleshooting info
may track the fault back to other than the parts you suspect.


Do a google search for "Mini-mill speed controller repair" or
"mini-lathe circuit diagram". I know that I have seen the diagrams for
these boards floating about the web.

Cheers
Trevor Jones

Take a look at the site of littlemachineshop.com. IIRC they sell
replacements for these speed controllers for these lathes and the
mini-mills, but I think they also have some info on circuit diagrams as
well. Look under the resources button on their site. They also sell the
mosfets (get the part number from there) and the troubleshooting info may
track the fault back to other than the parts you suspect.


Do a google search for "Mini-mill speed controller repair" or "mini-lathe
circuit diagram". I know that I have seen the diagrams for these boards
floating about the web.

Cheers
Trevor Jones

Excellent link, Trevor, looks like they have the beast for $120 and there is
someone in the States who repairs them for £25 plus bits.

I might try repairing, but apart from a pair of power transistors there are
a couple of ICs. One reason I am slightly cautious about poking round with a
DVM or scope is that the board is fairly tight and with 240 V on it rather
than the more normal 12 or 15 it could be easy to fry something by accident.
Will also try the other links, thanks all for the suggestions.

This would work if it's a shunt motor
http://cgi.ebay.co.uk/Eurotherm-Driv...0-NR_W0QQitemZ
110005248523QQihZ001QQcategoryZ42899QQrdZ1QQcmdZVi ewItem

I've no experience of using one with a series motor, but I don't see why
not.


In message , Newshound
writes
The variable speed controller on my Chester mini lathe has died, it's a 2A,
220 V DC brush motor and looks like a pulse width modulation controller.
Anyone know of either a circuit or a supplier of a board? I've found a
simple12/24 v circuit but I don't want to waste time redesigning if there's
a design out there, or a controller for £110 but could do with something
cheaper.



--
Neil J. Harris

Newshound wrote:

I might try repairing, but apart from a pair of power transistors there are
a couple of ICs.

I would ignore the ICs and focus on the power transistors. They don't
cost that much (I guess) and even if that blind shot fails, you didn't
waste too much money.


One reason I am slightly cautious about poking round with a
DVM or scope is that the board is fairly tight and with 240 V on it rather
than the more normal 12 or 15 it could be easy to fry something by accident.

Yes, absolutely right. Unsolder the transistors, check them outside. Did
you remove power while unsoldering? ;-)


Nick
--
The modular DRO
Available now in USA / Canada
http://www.yadro.de
...|....|....|....|....|....|....|..

One reason I am slightly cautious about poking round with a
DVM or scope is that the board is fairly tight and with 240 V on it
rather
than the more normal 12 or 15 it could be easy to fry something by
accident.

Yes, absolutely right. Unsolder the transistors, check them outside. Did
you remove power while unsoldering? ;-)


Nick

LOL!

I was thinking about looking with a scope to check that the oscillator and
pulse width modulation circuitry was working. One trouble is that the FETs
are labelled K790 and Maplins / RS don't recognise them. Although I guess
the type isn't critical as long as they'll take 240 V.

Newshound wrote:

I was thinking about looking with a scope to check that the oscillator and
pulse width modulation circuitry was working.

I hope that you only do that, when you know what you are doing.


One trouble is that the FETs are labelled K790 and Maplins / RS don't
recognise them. Although I guess the type isn't critical as long as
they'll take 240 V.

Just googled for K790 and found this:
http://groups.google.com/group/uk.re...browse_thread/
thread/dac2a8ba7e5d9a85/6c41a666cf602009?lnk=raot


HTH,
Nick
--
The modular DRO
Available now in USA / Canada
http://www.yadro.de
...|....|....|....|....|....|....|..

Have you tried chester, for a new PCB - when i was at there open days -
they seemed to have motors and PCBs for sale for the little lathes and
mills.

like the guy ^^^ if u want to play have a look at the 'FETS' i seem to
remember a post on here saying that if you upgrade them to 500v each,
its much better than the standard 240v fitted ones

One trouble is that the FETs are labelled K790 and Maplins / RS don't
recognise them. Although I guess the type isn't critical as long as they'll
take 240 V.


Add "2S" to the front, to give 2SK790, and google again.

eg:
http://www.digitroncorp.com/part/2SK790

(This is common in the part-numbers of semiconductors.)

As a substitute, try 2SK2698
500V 15A 150W

--
Ron

""Nick Müller"" wrote in message
...
Newshound wrote:

I was thinking about looking with a scope to check that the oscillator
and
pulse width modulation circuitry was working.

I hope that you only do that, when you know what you are doing.

Well, I was working at CERN designing digital circuits for the Soviet
particle accelerator at Serpukov in 1970.....

Newshound wrote:
wrote in message
oups.com...
Have you tried chester, for a new PCB - when i was at there open days -
they seemed to have motors and PCBs for sale for the little lathes and
mills.

£95 including vat and delivery. Or $119 from the link in the States. A bit
expensive for a machine that hasn't turned out to be all that useful,
particularly as I think I can do the same thing with some Maplin bits for
less than a tenner. But thanks for the thought.


That's the DIY spirit!

"Newshound" wrote in message
...
I might try repairing, but apart from a pair of power transistors there
are a couple of ICs. One reason I am slightly cautious about poking round
with a DVM or scope is that the board is fairly tight and with 240 V on it
rather than the more normal 12 or 15 it could be easy to fry something by
accident. Will also try the other links, thanks all for the suggestions.

The only difference between frying something at 15volts and 240volts is the
sparks!

Steve