I bought a magnetic chuck off ebay. It was a good deal but it came
with the wrong rectifier. And it's not worth the hassle trying to
return it. So, I was wondering if a lamp dimmer, with enough wattage
capacity, could be used with a rectifier to power the chuck. Also, for
the demagnetization of the chuck isn't the best way to achieve this is
to apply ac and slowly decrease the power? I know that to use the
demagnetizer I have the part must be slowly drawn away from the unit.
Thanks,
Eric R Snow

I don't know what DC voltage a mag chuck needs. So you might need a
transformer in addition to the lamp dimmer and rectifier.
Dan

On 16 Jun 2005 13:33:14 -0700, "
wrote:

I don't know what DC voltage a mag chuck needs. So you might need a
transformer in addition to the lamp dimmer and rectifier.
Dan
Oh. The mag chuck needs 100 vdc. Part of the reason for the dimmer is
to limit the voltage to the chuck. But I suppose a transformer would
be OK. I just want to know if a rectifier connected to something that
expects a resistive load will ruin the device.
Eric

Eric R Snow wrote:

On 16 Jun 2005 13:33:14 -0700, "
wrote:

I don't know what DC voltage a mag chuck needs. So you might need a
transformer in addition to the lamp dimmer and rectifier.
Dan
Oh. The mag chuck needs 100 vdc. Part of the reason for the dimmer is
to limit the voltage to the chuck. But I suppose a transformer would
be OK. I just want to know if a rectifier connected to something that
expects a resistive load will ruin the device.

The lamp dimmers use phase control dimming with triacs. They turn on the
triac part way into the half cycle of the AC, so they do not in any way
limit the peak voltage.

They actually eliminate the first part of the waveform rising (or
falling) from the zero crossing point, generating quite a switching
transient which is what causes filament buzz.

Try a variac (variable autotransformer), they will actually reduce the
voltage supplied to your rectifier.

Pete C.

Pete C. wrote:
Eric R Snow wrote:

On 16 Jun 2005 13:33:14 -0700, "
wrote:


I don't know what DC voltage a mag chuck needs. So you might need a
transformer in addition to the lamp dimmer and rectifier.
Dan

Oh. The mag chuck needs 100 vdc. Part of the reason for the dimmer is
to limit the voltage to the chuck. But I suppose a transformer would
be OK. I just want to know if a rectifier connected to something that
expects a resistive load will ruin the device.


The lamp dimmers use phase control dimming with triacs. They turn on the
triac part way into the half cycle of the AC, so they do not in any way
limit the peak voltage.

They actually eliminate the first part of the waveform rising (or
falling) from the zero crossing point, generating quite a switching
transient which is what causes filament buzz.

I don't see any inherent reason why a full wave bridge rectifier after
the dimmer won't work. Try it.

You could also use just a full wave bridge rectifier with an appropriate
sized light bulb in series with the chuck coil to reduce the applied
voltage.

A filter capacitor across the chuck coil might be needed if it acts a
little buzzy running on just the rectified AC waveform.


Try a variac (variable autotransformer), they will actually reduce the
voltage supplied to your rectifier.

Too expensive, unless you've already got a spare one. A 120 to 18 or 24
volt transformer wired up as an autotransformer to subtract its
secondary voltage from the 120 line will reduce the AC voltage to around
100 volts pretty cheaply.

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."

Jeff Wisnia wrote:

Pete C. wrote:
Eric R Snow wrote:

On 16 Jun 2005 13:33:14 -0700, "
wrote:


I don't know what DC voltage a mag chuck needs. So you might need a
transformer in addition to the lamp dimmer and rectifier.
Dan

Oh. The mag chuck needs 100 vdc. Part of the reason for the dimmer is
to limit the voltage to the chuck. But I suppose a transformer would
be OK. I just want to know if a rectifier connected to something that
expects a resistive load will ruin the device.


The lamp dimmers use phase control dimming with triacs. They turn on the
triac part way into the half cycle of the AC, so they do not in any way
limit the peak voltage.

They actually eliminate the first part of the waveform rising (or
falling) from the zero crossing point, generating quite a switching
transient which is what causes filament buzz.

I don't see any inherent reason why a full wave bridge rectifier after
the dimmer won't work. Try it.

I didn't say it wouldn't work, just that it did not reduce the voltage.
If you want to try this approach, don't use a light dimmer, use a fan
speed control. Only a couple $ more and they are at least designed to
deal with an inductive load.


You could also use just a full wave bridge rectifier with an appropriate
sized light bulb in series with the chuck coil to reduce the applied
voltage.

A filter capacitor across the chuck coil might be needed if it acts a
little buzzy running on just the rectified AC waveform.


Try a variac (variable autotransformer), they will actually reduce the
voltage supplied to your rectifier.

Too expensive, unless you've already got a spare one. A 120 to 18 or 24
volt transformer wired up as an autotransformer to subtract its
secondary voltage from the 120 line will reduce the AC voltage to around
100 volts pretty cheaply.

I've got an entire milk crate full of 1 kw variacs. A few 2 kw kicking
around as well.

Pete C.

"Eric R Snow" wroteclip)Also, for the demagnetization of the chuck isn't
the best way to achieve this is to apply ac and slowly decrease the power?
(clip)
^^^^^^^^^^^^^^^^^^
If you're talking about demagnetizing the chuck, meaning allowing it to let
go of its load, you may not have to be that elaborate. The technique of a
"tapering" AC field is needed when you need to get rid of ALL the residual
magnetization. And it is usually applied to the type of steel that holds a
field with the power off. Your chuck was probably designed not to hold a
residual field. Try just interrupting the power and see what happens.

On Thu, 16 Jun 2005 14:52:25 -0700, Eric R Snow
wrote:

On 16 Jun 2005 13:33:14 -0700, "
wrote:

I don't know what DC voltage a mag chuck needs. So you might need a
transformer in addition to the lamp dimmer and rectifier.
Dan
Oh. The mag chuck needs 100 vdc. Part of the reason for the dimmer is
to limit the voltage to the chuck. But I suppose a transformer would
be OK. I just want to know if a rectifier connected to something that
expects a resistive load will ruin the device.
Eric


The fullwave rectified voltage delivered to an inductive +
resistive load is the mean value of the RMS input i.e 0.9 x RMS volts.
so rectified 110/120v AC supply will be fine.

Although the rectified voltage applied to chuck is half sine
waves, the inductance is so high that the current flow is close to
pure DC. No capacitor should be fitted as it is not needed and its
presence would upset the 0.9 Vin relation.

To avoid inductive arcing, switching should be on the AC side
of the rectifier. If you want to play with a lamp dimmer - it depends
on detail design. Some will accept an inductive load some will refuse
to dim and just deliver full output. Damage to the dimmer is
unlikely.

Demagnetising by applying 60HZ Ac to the chuck is a
non-starter. Because the chuck inductance is so high more than a
thousand volts would be needed. Using the dimmer and successsive
polarity reversals is a miserable business because it needs lots of
graded reversals.

The following kludges work pretty well:-

Remove the rotor from a fractional horsepower motor and remove the
piece slowly from on or near the stator teeth.

Restack the laminations of a power transformer so that a stack of"E"
laminations remain. Remove workpiece slowly from on or near the
exposed ends of the"E".

Raid the dump for a defunct colour TV and remove the demagnetising
coil that is located on the bulbous flare of the tube. Twist it back
on itself so that it forms a triple loop instead of the original
single loop (this the same twist as the one used for tidily storing
spare bandsaw blades). Pass the workpiece slowly through the triple
loop.

These are all short term rated demagnetisers - if power is applied
for more than 30 sec they'll get pretty hot.


Jim

On Fri, 17 Jun 2005 13:52:37 +0100, wrote:

lots of sensible comments

You stole the words out of my keyboard G


Mark Rand
RTFM

On Thu, 16 Jun 2005 19:10:04 -0400, Jeff Wisnia
wrote:

Pete C. wrote:
Eric R Snow wrote:

On 16 Jun 2005 13:33:14 -0700, "
wrote:


I don't know what DC voltage a mag chuck needs. So you might need a
transformer in addition to the lamp dimmer and rectifier.
Dan

Oh. The mag chuck needs 100 vdc. Part of the reason for the dimmer is
to limit the voltage to the chuck. But I suppose a transformer would
be OK. I just want to know if a rectifier connected to something that
expects a resistive load will ruin the device.


The lamp dimmers use phase control dimming with triacs. They turn on the
triac part way into the half cycle of the AC, so they do not in any way
limit the peak voltage.

They actually eliminate the first part of the waveform rising (or
falling) from the zero crossing point, generating quite a switching
transient which is what causes filament buzz.

I don't see any inherent reason why a full wave bridge rectifier after
the dimmer won't work. Try it.

You could also use just a full wave bridge rectifier with an appropriate
sized light bulb in series with the chuck coil to reduce the applied
voltage.

A filter capacitor across the chuck coil might be needed if it acts a
little buzzy running on just the rectified AC waveform.


Try a variac (variable autotransformer), they will actually reduce the
voltage supplied to your rectifier.

Too expensive, unless you've already got a spare one. A 120 to 18 or 24
volt transformer wired up as an autotransformer to subtract its
secondary voltage from the 120 line will reduce the AC voltage to around
100 volts pretty cheaply.

Jeff
Thanks Jeff for the reply. That autotransformer idea might be best. I
do have a variac but it gets used for all sorts of jobs and I don't
wanna tie it up for just one machine.
Eric

On Thu, 16 Jun 2005 22:23:58 GMT, "Pete C."
wrote:

Eric R Snow wrote:

On 16 Jun 2005 13:33:14 -0700, "
wrote:

I don't know what DC voltage a mag chuck needs. So you might need a
transformer in addition to the lamp dimmer and rectifier.
Dan
Oh. The mag chuck needs 100 vdc. Part of the reason for the dimmer is
to limit the voltage to the chuck. But I suppose a transformer would
be OK. I just want to know if a rectifier connected to something that
expects a resistive load will ruin the device.

The lamp dimmers use phase control dimming with triacs. They turn on the
triac part way into the half cycle of the AC, so they do not in any way
limit the peak voltage.

They actually eliminate the first part of the waveform rising (or
falling) from the zero crossing point, generating quite a switching
transient which is what causes filament buzz.

Try a variac (variable autotransformer), they will actually reduce the
voltage supplied to your rectifier.

Pete C.
So the dimmers keep more and more of the waveform on either side of
the peak as the power is increased? And they always reach peak
voltage? I thought that they started conducting at zero and used more
and more of the voltage until peak voltage is reached. But after
reading your post that doesn't make sense to me.
Eric

On Thu, 16 Jun 2005 23:53:58 GMT, "Pete C."
wrote:

Jeff Wisnia wrote:

Pete C. wrote:
Eric R Snow wrote:

On 16 Jun 2005 13:33:14 -0700, "
wrote:


I don't know what DC voltage a mag chuck needs. So you might need a
transformer in addition to the lamp dimmer and rectifier.
Dan

Oh. The mag chuck needs 100 vdc. Part of the reason for the dimmer is
to limit the voltage to the chuck. But I suppose a transformer would
be OK. I just want to know if a rectifier connected to something that
expects a resistive load will ruin the device.


The lamp dimmers use phase control dimming with triacs. They turn on the
triac part way into the half cycle of the AC, so they do not in any way
limit the peak voltage.

They actually eliminate the first part of the waveform rising (or
falling) from the zero crossing point, generating quite a switching
transient which is what causes filament buzz.

I don't see any inherent reason why a full wave bridge rectifier after
the dimmer won't work. Try it.

I didn't say it wouldn't work, just that it did not reduce the voltage.
If you want to try this approach, don't use a light dimmer, use a fan
speed control. Only a couple $ more and they are at least designed to
deal with an inductive load.


You could also use just a full wave bridge rectifier with an appropriate
sized light bulb in series with the chuck coil to reduce the applied
voltage.

A filter capacitor across the chuck coil might be needed if it acts a
little buzzy running on just the rectified AC waveform.


Try a variac (variable autotransformer), they will actually reduce the
voltage supplied to your rectifier.

Too expensive, unless you've already got a spare one. A 120 to 18 or 24
volt transformer wired up as an autotransformer to subtract its
secondary voltage from the 120 line will reduce the AC voltage to around
100 volts pretty cheaply.

I've got an entire milk crate full of 1 kw variacs. A few 2 kw kicking
around as well.

Pete C.
Pete,
How do the fan speed controls work? And, you wanna get rid of any of
those variacs for cheap?
Eric

On Fri, 17 Jun 2005 13:52:37 +0100, wrote:

On Thu, 16 Jun 2005 14:52:25 -0700, Eric R Snow
wrote:

On 16 Jun 2005 13:33:14 -0700, "
wrote:

I don't know what DC voltage a mag chuck needs. So you might need a
transformer in addition to the lamp dimmer and rectifier.
Dan
Oh. The mag chuck needs 100 vdc. Part of the reason for the dimmer is
to limit the voltage to the chuck. But I suppose a transformer would
be OK. I just want to know if a rectifier connected to something that
expects a resistive load will ruin the device.
Eric


The fullwave rectified voltage delivered to an inductive +
resistive load is the mean value of the RMS input i.e 0.9 x RMS volts.
so rectified 110/120v AC supply will be fine.

Although the rectified voltage applied to chuck is half sine
waves, the inductance is so high that the current flow is close to
pure DC. No capacitor should be fitted as it is not needed and its
presence would upset the 0.9 Vin relation.

To avoid inductive arcing, switching should be on the AC side
of the rectifier. If you want to play with a lamp dimmer - it depends
on detail design. Some will accept an inductive load some will refuse
to dim and just deliver full output. Damage to the dimmer is
unlikely.

Demagnetising by applying 60HZ Ac to the chuck is a
non-starter. Because the chuck inductance is so high more than a
thousand volts would be needed. Using the dimmer and successsive
polarity reversals is a miserable business because it needs lots of
graded reversals.

The following kludges work pretty well:-

Remove the rotor from a fractional horsepower motor and remove the
piece slowly from on or near the stator teeth.

Restack the laminations of a power transformer so that a stack of"E"
laminations remain. Remove workpiece slowly from on or near the
exposed ends of the"E".

Raid the dump for a defunct colour TV and remove the demagnetising
coil that is located on the bulbous flare of the tube. Twist it back
on itself so that it forms a triple loop instead of the original
single loop (this the same twist as the one used for tidily storing
spare bandsaw blades). Pass the workpiece slowly through the triple
loop.

These are all short term rated demagnetisers - if power is applied
for more than 30 sec they'll get pretty hot.


Jim


Jim, I have a demagnetizer. The thing is, when parts are ground on an
electromagnetic they stick when power is removed. All the chuck
controls I've used have a demagnetizing button that helps to get the
part off the chuck. I have seen chuck controls without this feature
but have never used one. Maybe that's why chuck controls are so
expensive? It's because of the demagnetizing electronics?
Thanks,
Eric

"Eric R Snow" wrote in message
...
On Thu, 16 Jun 2005 22:23:58 GMT, "Pete C."
wrote:

Eric R Snow wrote:

On 16 Jun 2005 13:33:14 -0700, "
wrote:

I don't know what DC voltage a mag chuck needs. So you might need a
transformer in addition to the lamp dimmer and rectifier.
Dan
Oh. The mag chuck needs 100 vdc. Part of the reason for the dimmer is
to limit the voltage to the chuck. But I suppose a transformer would
be OK. I just want to know if a rectifier connected to something that
expects a resistive load will ruin the device.

The lamp dimmers use phase control dimming with triacs. They turn on the
triac part way into the half cycle of the AC, so they do not in any way
limit the peak voltage.

They actually eliminate the first part of the waveform rising (or
falling) from the zero crossing point, generating quite a switching
transient which is what causes filament buzz.

Try a variac (variable autotransformer), they will actually reduce the
voltage supplied to your rectifier.

Pete C.
So the dimmers keep more and more of the waveform on either side of
the peak as the power is increased? And they always reach peak
voltage? I thought that they started conducting at zero and used more
and more of the voltage until peak voltage is reached. But after
reading your post that doesn't make sense to me.
Eric

Nope -- the triac turns on some time after the zero-crossing. That
time is usually simply determined by a simple RC circuit that delays
the trigger (lags). You may not always get the peak -- if it is turned
way down, it may actually turn on sometime after the peak, but it
does not turn off until the next zero crossing. There are different
circuits used for things like heater control that do switch on at the
zero crossing to minimize spikes etc, but they work on a "burst" of
cycles as it were. They may use a 1 hz "cycle time" and vary how
many cycles during that 1 second period are actually turned on but
the typical light dimmer/speed control works with a delayed phase
angle firing of a triac - makes them electrically "noisy". They work
well for lights because you are varying the "average power" under
the portion of the curve (sine wave) that it is turned on - works well
with lights. Not so well for a rectified supply because until you delay
past 90 degrees, you are still getting the peak (and high current pulses
when it turns on).

mikey

"Eric R Snow" wrote in message
...
On Fri, 17 Jun 2005 13:52:37 +0100, wrote:

On Thu, 16 Jun 2005 14:52:25 -0700, Eric R Snow
wrote:

On 16 Jun 2005 13:33:14 -0700, "
wrote:

I don't know what DC voltage a mag chuck needs. So you might need a
transformer in addition to the lamp dimmer and rectifier.
Dan
Oh. The mag chuck needs 100 vdc. Part of the reason for the dimmer is
to limit the voltage to the chuck. But I suppose a transformer would
be OK. I just want to know if a rectifier connected to something that
expects a resistive load will ruin the device.
Eric


The fullwave rectified voltage delivered to an inductive +
resistive load is the mean value of the RMS input i.e 0.9 x RMS volts.
so rectified 110/120v AC supply will be fine.

Although the rectified voltage applied to chuck is half sine
waves, the inductance is so high that the current flow is close to
pure DC. No capacitor should be fitted as it is not needed and its
presence would upset the 0.9 Vin relation.

To avoid inductive arcing, switching should be on the AC side
of the rectifier. If you want to play with a lamp dimmer - it depends
on detail design. Some will accept an inductive load some will refuse
to dim and just deliver full output. Damage to the dimmer is
unlikely.

Demagnetising by applying 60HZ Ac to the chuck is a
non-starter. Because the chuck inductance is so high more than a
thousand volts would be needed. Using the dimmer and successsive
polarity reversals is a miserable business because it needs lots of
graded reversals.

The following kludges work pretty well:-

Remove the rotor from a fractional horsepower motor and remove the
piece slowly from on or near the stator teeth.

Restack the laminations of a power transformer so that a stack of"E"
laminations remain. Remove workpiece slowly from on or near the
exposed ends of the"E".

Raid the dump for a defunct colour TV and remove the demagnetising
coil that is located on the bulbous flare of the tube. Twist it back
on itself so that it forms a triple loop instead of the original
single loop (this the same twist as the one used for tidily storing
spare bandsaw blades). Pass the workpiece slowly through the triple
loop.

These are all short term rated demagnetisers - if power is applied
for more than 30 sec they'll get pretty hot.


Jim


Jim, I have a demagnetizer. The thing is, when parts are ground on an
electromagnetic they stick when power is removed. All the chuck
controls I've used have a demagnetizing button that helps to get the
part off the chuck. I have seen chuck controls without this feature
but have never used one. Maybe that's why chuck controls are so
expensive? It's because of the demagnetizing electronics?
Thanks,
Eric

I have not worked with one, but I would imagine that all you do
for "demagnetize" is to apply AC instead of DC to the coil.
They may make it a little smarter than that to make sure the AC
is turned off as it goes through 0 current so there is no residual
magnetism left. Very much like the degaussing coil in your TV or
computer monitor (when you first turn it on, there is a "hum" - that
is the degaussing coil which goes for a few seconds then turns off.

mikey

Whatever you build to power your mag chuck put an isolation transformer
between it and the mains, lest you become the best path to ground.

Eric R Snow wrote:

On Thu, 16 Jun 2005 23:53:58 GMT, "Pete C."
wrote:

Jeff Wisnia wrote:

Pete C. wrote:
Eric R Snow wrote:

On 16 Jun 2005 13:33:14 -0700, "
wrote:


I don't know what DC voltage a mag chuck needs. So you might need a
transformer in addition to the lamp dimmer and rectifier.
Dan

Oh. The mag chuck needs 100 vdc. Part of the reason for the dimmer is
to limit the voltage to the chuck. But I suppose a transformer would
be OK. I just want to know if a rectifier connected to something that
expects a resistive load will ruin the device.


The lamp dimmers use phase control dimming with triacs. They turn on the
triac part way into the half cycle of the AC, so they do not in any way
limit the peak voltage.

They actually eliminate the first part of the waveform rising (or
falling) from the zero crossing point, generating quite a switching
transient which is what causes filament buzz.

I don't see any inherent reason why a full wave bridge rectifier after
the dimmer won't work. Try it.

I didn't say it wouldn't work, just that it did not reduce the voltage.
If you want to try this approach, don't use a light dimmer, use a fan
speed control. Only a couple $ more and they are at least designed to
deal with an inductive load.


You could also use just a full wave bridge rectifier with an appropriate
sized light bulb in series with the chuck coil to reduce the applied
voltage.

A filter capacitor across the chuck coil might be needed if it acts a
little buzzy running on just the rectified AC waveform.


Try a variac (variable autotransformer), they will actually reduce the
voltage supplied to your rectifier.

Too expensive, unless you've already got a spare one. A 120 to 18 or 24
volt transformer wired up as an autotransformer to subtract its
secondary voltage from the 120 line will reduce the AC voltage to around
100 volts pretty cheaply.

I've got an entire milk crate full of 1 kw variacs. A few 2 kw kicking
around as well.

Pete C.
Pete,
How do the fan speed controls work? And, you wanna get rid of any of
those variacs for cheap?
Eric

I've not dug into the fan versions much. I believe they work in much the
same way as the lamp dimmers, but probably use higher rated triacs and
larger snubbers to deal with the inductive load. The may also use
reverse phase control with a switching device other than a triac. In
reverse phase control instead of turning on after a delay into the half
cycle, the device turns off after the delay which lets the voltage
gradually come up (or down) from zero crossing before being cut off.

A little more info:

http://www.lutron.com/technical_info...mingBasics.pdf

Seems to indicate that dimmers rated for magnetic low voltage lighting
might work as well.

Still more info:

http://home.howstuffworks.com/framed...ghtdimmer.html

As for the variacs, I have to track down where they are. I think they
are still at my other facility which I will not be at for a while (1,700
miles away). If I can get my hands on them I'd be happy to send you one
since I'll never use all of them.

Pete C.

On Fri, 17 Jun 2005 07:39:55 -0700, Eric R Snow
wrote:

Snip


Jim, I have a demagnetizer. The thing is, when parts are ground on an
electromagnetic they stick when power is removed. All the chuck
controls I've used have a demagnetizing button that helps to get the
part off the chuck. I have seen chuck controls without this feature
but have never used one. Maybe that's why chuck controls are so
expensive? It's because of the demagnetizing electronics?
Thanks,
Eric

I've never used one of these chucks so I can't be sure how
they're organised. Thoroughly demagnetising a workpiece on an
electromagnetic chuck would need a sequence of decaying amplitude
polarity reversals. This is could be carried out by sequencing two or
three Triacs or SCRs. Possibly a pair to control polarity reversal and
one to program the amplitude - sounds a bit expensive.

One posible kludge is to remember that much of the remanent
magnetism is a fixed amount as it originates from hysteresis in the
chuck iron. If this were entirely true (OK with mild steel workpiece -
not OK with a large lump of alnico) a carefully chosen single pulse of
reverse polarity would be enough to unstick the workpiece.

Don't know enough about your chuck to tell you how much but a
lot less than 100v - start with only a few volts and increase it bit
by bit until it does the job.

Don't forget to be certain that the chuck body is properly grounded.
Used dry, the insulation failure hazard is about the same as with an
electric motor. However, if you're going to use it wet with suds
coolant I second comment that an isolation
transformer is a sensible addition

Jim

In article ,
Leo Lichtman wrote:

"Eric R Snow" wroteclip)Also, for the demagnetization of the chuck isn't
the best way to achieve this is to apply ac and slowly decrease the power?
(clip)
^^^^^^^^^^^^^^^^^^
If you're talking about demagnetizing the chuck, meaning allowing it to let
go of its load, you may not have to be that elaborate. The technique of a
"tapering" AC field is needed when you need to get rid of ALL the residual
magnetization. And it is usually applied to the type of steel that holds a
field with the power off. Your chuck was probably designed not to hold a
residual field. Try just interrupting the power and see what happens.

On my Sanford grinder with the EM chuck, the "demagnetize"
position of the switch just applies pure AC to the coil, which does a
good enough job to release the workpiece.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 17 Jun 2005 16:05:58 -0400, (DoN. Nichols)
wrote:

In article ,
Leo Lichtman wrote:

"Eric R Snow" wroteclip)Also, for the demagnetization of the chuck isn't
the best way to achieve this is to apply ac and slowly decrease the power?
(clip)
^^^^^^^^^^^^^^^^^^
If you're talking about demagnetizing the chuck, meaning allowing it to let
go of its load, you may not have to be that elaborate. The technique of a
"tapering" AC field is needed when you need to get rid of ALL the residual
magnetization. And it is usually applied to the type of steel that holds a
field with the power off. Your chuck was probably designed not to hold a
residual field. Try just interrupting the power and see what happens.

On my Sanford grinder with the EM chuck, the "demagnetize"
position of the switch just applies pure AC to the coil, which does a
good enough job to release the workpiece.

Enjoy,
DoN.
Thanks DoN, That's just what I was looking for.
Eric

Although the lamp dimmer does not limit the peak voltage, they do
control the power and should work fine. If I were doing it I might
make a stop for the lamp dimmer so it could not be set too high. If
you use a lamp dimmer , fullwave rectifier , and a cap you can get 163
volts.

Dan

My experience with lamp dimmer has been that they work fine with
inductive loads. This does not mean that all lamp dimmer will, just
that all the ones I have used have worked.


Dan