Anyone out there ever work on or service a mag-chuck? I just won a
chuck on ebay, 8 x 24 for my grinder? seller states it plugs right
into the wall. Every one I've seen uses a control box. Can I build
my own? Anyone have a schematic?

Anyone know what happened to Hitachi? All my seaches come up with
nothing as far as a chuck goes.

Hitachi model # HU-824

Thank You,
Randy

Remove 333 from email address to reply.

Randy wrote:

Anyone out there ever work on or service a mag-chuck? I just won a
chuck on ebay, 8 x 24 for my grinder? seller states it plugs right
into the wall. Every one I've seen uses a control box. Can I build
my own? Anyone have a schematic?

Anyone know what happened to Hitachi? All my seaches come up with
nothing as far as a chuck goes.

Hitachi model # HU-824

Thank You,
Randy

Remove 333 from email address to reply.


The chuck runs on DC you have AC coming out the wall.
I've had good luck with Walker company for power supplies.

http://www.walkermagnet.com/products...-services.html


You could make your own too, the rating for the chuck voltage is usually
on the data plate of the magnet. It is nice to be able to demagnetize
the part by feeding ac into the magnet and then gradually decrease the
voltage, or on some power units they reverse the polarity of the dc as
they slowly ramp down the voltage. in an emergency, a variac and a
bridge diode block will work.

Make sure the chuck is good before you order a power supply. Hook it to
a 12 v car battery and see if it magnetizes the chuck and doesn't draw
too much current

John

On 2008-12-16, Randy wrote:
Anyone out there ever work on or service a mag-chuck? I just won a
chuck on ebay, 8 x 24 for my grinder? seller states it plugs right
into the wall. Every one I've seen uses a control box. Can I build
my own? Anyone have a schematic?

Anyone know what happened to Hitachi? All my seaches come up with
nothing as far as a chuck goes.

Hitachi model # HU-824

Well ... the one for my Sanford grinder runs (poorly) on AC, and
very nicely on DC rectified and filtered from the power line.


The original circuit in the base of the grinder was like this:

DEMAG Switch SPDT
+------------------------------------o
| OFF /______o-----------+
| resistor selenium \ |
120 VAC o----+-----WWWWWWW----------||-----+-----o 3 Mag
20 Ohms rectifier | HOLD 3 Chuck
10 Watts ___ 3 Coil
___ 8 uF 250 VDC Electo 3
| -lytic |
Neutral o-----------------------------------+-----o-------------------+

The capacitor was dead, and I did not trust the selenium rectifier
so I redesined it -- using a silicon bridge rectifier, and a 2000 uF
250 VDC capacitor. I replaced the SPDT switch with a DPDT switch, so I
switched both sides of the coil so the mag chuck was fully disconnected
when not turned on.

To hold, you switch to "HOLD".

To demagnetize (after holding) you switch to "DEMAG"

Then you switch to "OFF".

It does not do a complete job of demagnetizing the workpiece,
but enough so that it is easy to pull off the chuck. If you want better
demagnetizing, keep the switch on DEMAG while you slowly move the
workpiece away from the chuck, and only switch it fully off when you are
about six inches away.

I knew that my mag chuck could take line voltage and rectified
line voltage by looking at the circuit in the base of the grinder. I
just re-designed it to be a better system using more modern components.
(I kept the wirewound resistor, and (of course) the mag chuck. :-)

I actually just finished yesterday replacing it with a Permanent
Magnet chuck, because the manual for the grinder warned (quite
reasonably) to *not* use coolant with the electro-magnetic chuck. If
you wanted to do that, you would need an isolating transformer. The PM
chuck is also just barely smaller than the travel of the wheel in both
axes, so it is a better fit than the electromagnetic chuck.

Be warned -- if you use the circuit shown above, *don't* use
coolant.

You will need to make sure that the chuck is intended to run on
117 VAC in degauss (DEMAG) mode, and 170 VDC in "HOLD" mode. If not,
you may need to change the voltage -- either step it down for a lower
voltage one (in which case you have an isolation transformer anyway), or
step it up for a higher voltage one. The same applies there, except
that you will need to change the voltage ratings on the rectifier diode
or bridge, and on the capacitor.

The resistor is there only to keep the surge current to a
minimum when the system is plugged in -- or when the switch is set to
"HOLD" if you re-wire it so the switch is before the rectifier, which
would be a good idea.

Good Luck,
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 ---

If I understand your circuit correctly, there is current flowing through the
resistor only during the half cycle that the rectifier is conducting. I'm
guessing that with the original circuit, half cycle conduction, resistor,
and 8uF capacitor, the voltage at the chuck was probably closer to 120VDC
than 170VDC. Without knowing the resistance of the mag chuck I'm only
guessing but a 20 ohm 10 Watt resistor could drop up to 20V for 50% duty
cycle giving a 150V peak and the 8uF capacitor most likely won't hold this
voltage very well during the reverse half cycle. Just guessing I'd figure
the resistor, diode, and capacitor combination probably supplied close to a
120VDC equivalent.

I did a project one time making a pick and place system that palletized
metal parts. I used a McMaster Carr electro magnet and when we switched off
the current, the part stayed stuck to the magnet. With a little research,
we found out a momentary reverse current would release the parts. I ended
up using a relay wired to reverse the power to the magnet, there was a
capacitor that charged and caused a momentary reverse current through the
magnet. When the relay was on, forward current would flow through the
electro-magnet, when off, enough reverse current would flow to charge the
capacitor, releasing the part.

RogerN

"DoN. Nichols" wrote in message
...

Well ... the one for my Sanford grinder runs (poorly) on AC, and
very nicely on DC rectified and filtered from the power line.


The original circuit in the base of the grinder was like this:

DEMAG Switch SPDT
+------------------------------------o
| OFF /______o-----------+
| resistor selenium \ |
120 VAC o----+-----WWWWWWW----------||-----+-----o 3
Mag
20 Ohms rectifier | HOLD 3
Chuck
10 Watts ___ 3
Coil
___ 8 uF 250 VDC Electo 3
| -lytic |
Neutral o-----------------------------------+-----o-------------------+

The capacitor was dead, and I did not trust the selenium rectifier
so I redesined it -- using a silicon bridge rectifier, and a 2000 uF
250 VDC capacitor. I replaced the SPDT switch with a DPDT switch, so I
switched both sides of the coil so the mag chuck was fully disconnected
when not turned on.

To hold, you switch to "HOLD".

To demagnetize (after holding) you switch to "DEMAG"

Then you switch to "OFF".

It does not do a complete job of demagnetizing the workpiece,
but enough so that it is easy to pull off the chuck. If you want better
demagnetizing, keep the switch on DEMAG while you slowly move the
workpiece away from the chuck, and only switch it fully off when you are
about six inches away.

I knew that my mag chuck could take line voltage and rectified
line voltage by looking at the circuit in the base of the grinder. I
just re-designed it to be a better system using more modern components.
(I kept the wirewound resistor, and (of course) the mag chuck. :-)

I actually just finished yesterday replacing it with a Permanent
Magnet chuck, because the manual for the grinder warned (quite
reasonably) to *not* use coolant with the electro-magnetic chuck. If
you wanted to do that, you would need an isolating transformer. The PM
chuck is also just barely smaller than the travel of the wheel in both
axes, so it is a better fit than the electromagnetic chuck.

Be warned -- if you use the circuit shown above, *don't* use
coolant.

You will need to make sure that the chuck is intended to run on
117 VAC in degauss (DEMAG) mode, and 170 VDC in "HOLD" mode. If not,
you may need to change the voltage -- either step it down for a lower
voltage one (in which case you have an isolation transformer anyway), or
step it up for a higher voltage one. The same applies there, except
that you will need to change the voltage ratings on the rectifier diode
or bridge, and on the capacitor.

The resistor is there only to keep the surge current to a
minimum when the system is plugged in -- or when the switch is set to
"HOLD" if you re-wire it so the switch is before the rectifier, which
would be a good idea.

Good Luck,
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 Dec 2008 05:26:12 GMT, "DoN. Nichols"
wrote:

On 2008-12-16, Randy wrote:
Anyone out there ever work on or service a mag-chuck? I just won a
chuck on ebay, 8 x 24 for my grinder? seller states it plugs right
into the wall. Every one I've seen uses a control box. Can I build
my own? Anyone have a schematic?

Anyone know what happened to Hitachi? All my seaches come up with
nothing as far as a chuck goes.

Hitachi model # HU-824

Well ... the one for my Sanford grinder runs (poorly) on AC, and
very nicely on DC rectified and filtered from the power line.


The original circuit in the base of the grinder was like this:

DEMAG Switch SPDT
+------------------------------------o
| OFF /______o-----------+
| resistor selenium \ |
120 VAC o----+-----WWWWWWW----------||-----+-----o 3 Mag
20 Ohms rectifier | HOLD 3 Chuck
10 Watts ___ 3 Coil
___ 8 uF 250 VDC Electo 3
| -lytic |
Neutral o-----------------------------------+-----o-------------------+

The capacitor was dead, and I did not trust the selenium rectifier
so I redesined it -- using a silicon bridge rectifier, and a 2000 uF
250 VDC capacitor. I replaced the SPDT switch with a DPDT switch, so I
switched both sides of the coil so the mag chuck was fully disconnected
when not turned on.

To hold, you switch to "HOLD".

To demagnetize (after holding) you switch to "DEMAG"

Then you switch to "OFF".

It does not do a complete job of demagnetizing the workpiece,
but enough so that it is easy to pull off the chuck. If you want better
demagnetizing, keep the switch on DEMAG while you slowly move the
workpiece away from the chuck, and only switch it fully off when you are
about six inches away.

I knew that my mag chuck could take line voltage and rectified
line voltage by looking at the circuit in the base of the grinder. I
just re-designed it to be a better system using more modern components.
(I kept the wirewound resistor, and (of course) the mag chuck. :-)

I actually just finished yesterday replacing it with a Permanent
Magnet chuck, because the manual for the grinder warned (quite
reasonably) to *not* use coolant with the electro-magnetic chuck. If
you wanted to do that, you would need an isolating transformer. The PM
chuck is also just barely smaller than the travel of the wheel in both
axes, so it is a better fit than the electromagnetic chuck.

Be warned -- if you use the circuit shown above, *don't* use
coolant.

You will need to make sure that the chuck is intended to run on
117 VAC in degauss (DEMAG) mode, and 170 VDC in "HOLD" mode. If not,
you may need to change the voltage -- either step it down for a lower
voltage one (in which case you have an isolation transformer anyway), or
step it up for a higher voltage one. The same applies there, except
that you will need to change the voltage ratings on the rectifier diode
or bridge, and on the capacitor.

The resistor is there only to keep the surge current to a
minimum when the system is plugged in -- or when the switch is set to
"HOLD" if you re-wire it so the switch is before the rectifier, which
would be a good idea.

Good Luck,
DoN.


The chuck is marked 115VDC 1.8 AMP. so a variac and full wave bridge
with cap should work. I'll need to make a panel up with switches and
relays to switch in AC power. although with the switch after the diode
and cap no relay would be needed. I kind of like the power switch to
be the first thing in the circut, but the above way does simplify
things.

How do the "other" guys do it. The factory B & S control panel has
what looks like a 1watt pot to contol the power.

see ebay Item number: 130270640953

would like to see a schematic for one of these.

Thank You,
Randy

Remove 333 from email address to reply.

On Wed, 17 Dec 2008 13:19:39 -0500, Randy wrote:

On 17 Dec 2008 05:26:12 GMT, "DoN. Nichols"
wrote:

On 2008-12-16, Randy wrote:
Anyone out there ever work on or service a mag-chuck? I just won a
chuck on ebay, 8 x 24 for my grinder? seller states it plugs right
into the wall. Every one I've seen uses a control box. Can I build
my own? Anyone have a schematic?

Anyone know what happened to Hitachi? All my seaches come up with
nothing as far as a chuck goes.

Hitachi model # HU-824

Well ... the one for my Sanford grinder runs (poorly) on AC, and
very nicely on DC rectified and filtered from the power line.


The original circuit in the base of the grinder was like this:

DEMAG Switch SPDT
+------------------------------------o
| OFF /______o-----------+
| resistor selenium \ |
120 VAC o----+-----WWWWWWW----------||-----+-----o 3 Mag
20 Ohms rectifier | HOLD 3 Chuck
10 Watts ___ 3 Coil
___ 8 uF 250 VDC Electo 3
| -lytic |
Neutral o-----------------------------------+-----o-------------------+

The capacitor was dead, and I did not trust the selenium rectifier
so I redesined it -- using a silicon bridge rectifier, and a 2000 uF
250 VDC capacitor. I replaced the SPDT switch with a DPDT switch, so I
switched both sides of the coil so the mag chuck was fully disconnected
when not turned on.

To hold, you switch to "HOLD".

To demagnetize (after holding) you switch to "DEMAG"

Then you switch to "OFF".

It does not do a complete job of demagnetizing the workpiece,
but enough so that it is easy to pull off the chuck. If you want better
demagnetizing, keep the switch on DEMAG while you slowly move the
workpiece away from the chuck, and only switch it fully off when you are
about six inches away.

I knew that my mag chuck could take line voltage and rectified
line voltage by looking at the circuit in the base of the grinder. I
just re-designed it to be a better system using more modern components.
(I kept the wirewound resistor, and (of course) the mag chuck. :-)

I actually just finished yesterday replacing it with a Permanent
Magnet chuck, because the manual for the grinder warned (quite
reasonably) to *not* use coolant with the electro-magnetic chuck. If
you wanted to do that, you would need an isolating transformer. The PM
chuck is also just barely smaller than the travel of the wheel in both
axes, so it is a better fit than the electromagnetic chuck.

Be warned -- if you use the circuit shown above, *don't* use
coolant.

You will need to make sure that the chuck is intended to run on
117 VAC in degauss (DEMAG) mode, and 170 VDC in "HOLD" mode. If not,
you may need to change the voltage -- either step it down for a lower
voltage one (in which case you have an isolation transformer anyway), or
step it up for a higher voltage one. The same applies there, except
that you will need to change the voltage ratings on the rectifier diode
or bridge, and on the capacitor.

The resistor is there only to keep the surge current to a
minimum when the system is plugged in -- or when the switch is set to
"HOLD" if you re-wire it so the switch is before the rectifier, which
would be a good idea.

Good Luck,
DoN.


The chuck is marked 115VDC 1.8 AMP. so a variac and full wave bridge
with cap should work. I'll need to make a panel up with switches and
relays to switch in AC power. although with the switch after the diode
and cap no relay would be needed. I kind of like the power switch to
be the first thing in the circut, but the above way does simplify
things.

How do the "other" guys do it. The factory B & S control panel has
what looks like a 1watt pot to contol the power.

see ebay Item number: 130270640953

would like to see a schematic for one of these.

Thank You,
Randy

Remove 333 from email address to reply.

Hey guys,

Any I've seen used a 20 Amp DPDT Center Off non-shorting
spring-loaded-one-side, with a full wave bridge and an in-line cap.
Switch markings as ON-OFF-RELEASE, with the RELEASE being the
spring-loaded side of the DPDT. Not sure why they would require 20
Amp, other than to be physically more robust and therefore a bit
longer lasting.

I do believe that I have seen, but never used, some VERY old models
that were just AC, some of them without even a switch. Jes plugger
in! If they are AC, they won't really want to run DC, nor vice-versa
I would think.

Take care.

Brian Lawson,
Bothwell, Ontario

On Wed, 17 Dec 2008 18:51:17 -0500, Brian Lawson
wrote:




Hey guys,

Any I've seen used a 20 Amp DPDT Center Off non-shorting
spring-loaded-one-side, with a full wave bridge and an in-line cap.
Switch markings as ON-OFF-RELEASE, with the RELEASE being the
spring-loaded side of the DPDT. Not sure why they would require 20
Amp, other than to be physically more robust and therefore a bit
longer lasting.

20A may have been the AC rating. Or a physically larger switch may
have been necessary to get enough separation in the contacts to
control arcing. With AC you get 120 chances per second to quench any
arcing that occurs on opening the switch. Not so with DC. Switching DC
that's supplying a large inductive load is very hard duty for a
switch.

--
Ned Simmons

On 2008-12-17, RogerN wrote:

If I understand your circuit correctly, there is current flowing through the
resistor only during the half cycle that the rectifier is conducting.

Yes -- but very little current once the capacitor is charged.
Its primary function is to keep the initial charge surge from frying the
selenium rectifier, which were rather more sensitive to excess current
even for short times than the Silicon ones. I kept it once I saw how
much of a spark plugging in the grinder caused with the full wave bridge
and the 2000 uF capacitor. I figured that would also shorted the life
of the switch if I didn't keep the resistor to lower the surge current.

I'm
guessing that with the original circuit, half cycle conduction, resistor,
and 8uF capacitor, the voltage at the chuck was probably closer to 120VDC
than 170VDC.

I think that it was closer to the 170 VAC. The chuck never felt
warm, even after a long time holding a workpiece (unless I was grinding
too heavily, which was uncommon.)

Without knowing the resistance of the mag chuck I'm only
guessing but a 20 ohm 10 Watt resistor could drop up to 20V for 50% duty
cycle giving a 150V peak and the 8uF capacitor most likely won't hold this
voltage very well during the reverse half cycle. Just guessing I'd figure
the resistor, diode, and capacitor combination probably supplied close to a
120VDC equivalent.

O.K. Time to check the resistance of the chuck. Back in a few
minutes ... how about 36K? I don't think that there will be much
ripple, or drop in the resistor once the cap is charged.

That would be 4.7 mA at 170VDC -- or a bit less than 10mV drop
across the resistor. If it were drawing enough to drop half of the
voltage across the resistor, we would need a 360W resistor or so. :-)

But for the short cap charging period, even with the cap bumped
from 8 uF to 2000 uF, the high current is short enough so the average
power in the resistor is well within specs.

I did a project one time making a pick and place system that palletized
metal parts. I used a McMaster Carr electro magnet and when we switched off
the current, the part stayed stuck to the magnet. With a little research,
we found out a momentary reverse current would release the parts. I ended
up using a relay wired to reverse the power to the magnet, there was a
capacitor that charged and caused a momentary reverse current through the
magnet. When the relay was on, forward current would flow through the
electro-magnet, when off, enough reverse current would flow to charge the
capacitor, releasing the part.

O.K. With a selected capacitor value. Too little would not
demagnetize it enough, too much would re-magnetize it in reverse, before
the stock could start to fall. :-)

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 ---

"DoN. Nichols" wrote in message
...
On 2008-12-17, RogerN wrote:

If I understand your circuit correctly, there is current flowing through
the
resistor only during the half cycle that the rectifier is conducting.

Yes -- but very little current once the capacitor is charged.
Its primary function is to keep the initial charge surge from frying the
selenium rectifier, which were rather more sensitive to excess current
even for short times than the Silicon ones. I kept it once I saw how
much of a spark plugging in the grinder caused with the full wave bridge
and the 2000 uF capacitor. I figured that would also shorted the life
of the switch if I didn't keep the resistor to lower the surge current.


I'm
guessing that with the original circuit, half cycle conduction, resistor,
and 8uF capacitor, the voltage at the chuck was probably closer to 120VDC
than 170VDC.

I think that it was closer to the 170 VAC. The chuck never felt
warm, even after a long time holding a workpiece (unless I was grinding
too heavily, which was uncommon.)

Without knowing the resistance of the mag chuck I'm only
guessing but a 20 ohm 10 Watt resistor could drop up to 20V for 50% duty
cycle giving a 150V peak and the 8uF capacitor most likely won't hold
this
voltage very well during the reverse half cycle. Just guessing I'd
figure
the resistor, diode, and capacitor combination probably supplied close to
a
120VDC equivalent.

O.K. Time to check the resistance of the chuck. Back in a few
minutes ... how about 36K? I don't think that there will be much
ripple, or drop in the resistor once the cap is charged.

That would be 4.7 mA at 170VDC -- or a bit less than 10mV drop
across the resistor. If it were drawing enough to drop half of the
voltage across the resistor, we would need a 360W resistor or so. :-)

But for the short cap charging period, even with the cap bumped
from 8 uF to 2000 uF, the high current is short enough so the average
power in the resistor is well within specs.


Wow, I would have never guessed the chuck resistance to be that high.
Another poster said his chuck was rated for 115VDC at 1.8A. His chuck is
over 200W and your is 0.8W. I was guessing your chuck to average maybe 0.7A
or so. If I'm calculating correctly, you have less than 1 mW power
dissipation in the 10W resistor, they could have used a 1/2W resistor and
still been 500X oversized.

The design you made sounds more like a DC power supply. The half wave
rectifier and 8uF capacitor sounded like something that was suppose to
deliver less than the peak voltage. Thinking about it a little bit here,
are you sure that wasn't 0.36K Ohms?

RogerN

On 2008-12-18, RogerN wrote:

"DoN. Nichols" wrote in message
...
On 2008-12-17, RogerN wrote:

[ ... ]

Without knowing the resistance of the mag chuck I'm only
guessing but a 20 ohm 10 Watt resistor could drop up to 20V for 50% duty
cycle giving a 150V peak and the 8uF capacitor most likely won't hold
this
voltage very well during the reverse half cycle. Just guessing I'd
figure
the resistor, diode, and capacitor combination probably supplied close to
a
120VDC equivalent.

O.K. Time to check the resistance of the chuck. Back in a few
minutes ... how about 36K? I don't think that there will be much
ripple, or drop in the resistor once the cap is charged.

That would be 4.7 mA at 170VDC -- or a bit less than 10mV drop
across the resistor. If it were drawing enough to drop half of the
voltage across the resistor, we would need a 360W resistor or so. :-)

But for the short cap charging period, even with the cap bumped
from 8 uF to 2000 uF, the high current is short enough so the average
power in the resistor is well within specs.


Wow, I would have never guessed the chuck resistance to be that high.
Another poster said his chuck was rated for 115VDC at 1.8A. His chuck is
over 200W and your is 0.8W. I was guessing your chuck to average maybe 0.7A
or so. If I'm calculating correctly, you have less than 1 mW power
dissipation in the 10W resistor, they could have used a 1/2W resistor and
still been 500X oversized.

Except during the time of charging the cap. I guess that if you
turned it on and off frequently, you might overheat a 2W carbon
resistor.

The design you made sounds more like a DC power supply. The half wave
rectifier and 8uF capacitor sounded like something that was suppose to
deliver less than the peak voltage. Thinking about it a little bit here,
are you sure that wasn't 0.36K Ohms?

I'm sure -- but what I am *not* sure of is whether there are
problems in the existing winding. It may have been intended to draw
more in the past. I've got to try re-flowing the solder on the
connector and measure again. It is still apart form my looking inside
it when trying to verify the observed resistance.

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 Tue, 16 Dec 2008 16:54:58 -0500, Randy wrote:

Anyone out there ever work on or service a mag-chuck? I just won a
chuck on ebay, 8 x 24 for my grinder? seller states it plugs right
into the wall. Every one I've seen uses a control box. Can I build
my own? Anyone have a schematic?

Anyone know what happened to Hitachi? All my seaches come up with
nothing as far as a chuck goes.

Hitachi model # HU-824

Thank You,
Randy

Remove 333 from email address to reply.

Got the chuck today, had to take the little box apart. hooked up as
follows:

120v (hot) to fuse than switch SPST then full wave bridge
120v (n) to full wave bridge

positive from bridge to DPDT switch top contact
negitive from bridge to DPDT switch top contact

common (center) contacts DPDT switch to chuck

DPDT switch top contact left to bottom contact right (AKA diagonal
jumper)

DPDT switch top contact right to pushbutton NO, other NO contact on
push button to a 2200 ohm resistor 1/2 watt ( red, red, red) the to
bottom left contact on the DPDT switch.

DPDT switch is magnatize in one position and demag in the other when
the push button is pushed, not sure if that will do much, if anything,
with that resistor in there.

If this confused the hell out of you I can draw it and scan the dwg
and post it somewhere.

Thank You,
Randy

Remove 333 from email address to reply.