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I have an old Walker electromagnet chuck and I really need some help figuring out how to wire this thing..

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marino1310

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#1
So I have an old walker 220-240v chuck, no idea how old it is and walker refuses to respond to my multiple emails asking about it. Its mounted to an old Norton surface grinder from the 40s. The original power supply was spliced off the motors 3ph 240v and goes into two large tube rectifiers and a large isolation transformer. None of the old tech works anymore. The isolation transformer is fried as are the 2 tubes. I just want a way to wire this up to its own power or from the machines power, I just want it to work. I went to my friend who is an electrical engineer and he told me Id need an isolation transformer so I dont get shocked and apparently a 1:1 240v isolation transformer is hard to find and very expensive... I was wondering if you guys knew any other way to wire these things
 

Ulma Doctor

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#2
i suppose a possible go around would be to use a step up transformer,
or running a step down transformer, in reverse, to achieve the end.
it would still need to be rectified to get the dc to make the magnet work
 

benmychree

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#3
Look into a Neutrofier type of magnetic control, I bought a Chinese unit that is very compact, this was on a 12 X 36" chuck, it has variable hold and neutralizes the residual magnetism so parts are easy to remove from the chuck face and it neutralizes any residual magnetism in the part. I do not know if they are available in 200+ volts, most chucks seem to require 100 V current; I think I got it from KBC or MSC. The machine came with a vacuum tube rectifier, which failed, and the replacement was satisfactory in every way, for over 10 years time.
 

marino1310

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Look into a Neutrofier type of magnetic control, I bought a Chinese unit that is very compact, this was on a 12 X 36" chuck, it has variable hold and neutralizes the residual magnetism so parts are easy to remove from the chuck face and it neutralizes any residual magnetism in the part. I do not know if they are available in 200+ volts, most chucks seem to require 100 V current; I think I got it from KBC or MSC. The machine came with a vacuum tube rectifier, which failed, and the replacement was satisfactory in every way, for over 10 years time.
Ill look into that. But they seem to be very expensive as well. Chinese ones on ebay seem to average $300
 

JimDawson

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#5
Usually the transformer is about the last thing to fail. While it's possible that it is gone, it is less likely than other components.

As near as I can tell those old chuck controllers are a full wave, 2 diode rectifier circuit. This would mean a center tapped secondary on the transformer. If the center tap isn't grounded, then it would be a full isolation system. It would also output about 120 VDC max with that wiring configuration.

1543006684448.png

If you were to more or less duplicate the circuit above and use SCRs as opposed to diodes, then drive them with a basic light dimmer circuit it would give you an adjustable output DC supply for your chuck.

This might be worth a read https://www.hobby-machinist.com/thr...ntrol-circuit-wanted.57733/page-2#post-477868
 

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#6
Hi Marino,

Just to add to Jim's post, you definitely need to use an Isolation transformer ! Don't even think about running without one.

If you cannot get one then you could use a pair of identical transformers wired back to back, that is 240 in low volts out into the other transformer low volts in high volts out. That will give you the isolation.

However there is a major problem with doing this, whilst it will work, you don't know how much power is involved. If the transformers cannot handle the amount of power needed they will get hot and burn out.

Then you will need to rectify the AC to get DC in order to turn the electromagnet on ! A simple bridge rectifier will do that easily. But again you need to know the amount of current that the electromagnet requires to produce the needed magnetic field. If you are lucky that information will be on a rating plate attached to it.

From there on its just a matter of getting the right rated components and building the power unit to supply the device.
 

Be_Zero_Be

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#7
A 120 to 240 step up transformer would probably be easier to find. (Or a step down transformer used backwards).
 

benmychree

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Ill look into that. But they seem to be very expensive as well. Chinese ones on ebay seem to average $300
They are expensive, but they are well worth the price!
 

markba633csi

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#9
Baron is correct, once you know how much current the chuck requires you just build an ac to dc power supply using a transformer and a modern silicon rectifier. Add a variac to adjust the power. Less than 100 $ in parts if you shop around. Marlin P. Jones (www.MPJA.com) is in Florida, they have lots of electronic parts. Ebay too.
Like this:
acdcsup1.jpeg
 
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Ulma Doctor

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Baron is correct, once you know how much current the chuck requires you just build an ac to dc power supply using a transformer and a modern silicon rectifier. Add a variac to adjust the power. Less than 100 $ in parts if you shop around. Marlin P. Jones (www.MPJA.com) is in Florida, they have lots of electronic parts. Ebay too.
Like this:
thanks for the parts source Mark :grin:
 

markba633csi

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Digi-key and Mouser are also good for new components, but MPJA often has lots of surplus goodies
Also American Science and Surplus has some neat stuff
M
ps I recommend trying to find large transformers locally because of the high cost of shipping
 
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MozamPete

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BaronJ

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Hi Guys,

After sleeping on it and re-reading the OP, the thought occurs to me, if the original transformer is burnt out and so are the tube rectifiers, what caused that to happen ! The chances are that the magnetic chuck has shorted windings and unless it can be safely tested and rewound if it has, then whilst all the above information is correct, it could be for naught !
 

KBeitz

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#14
Just put a set of jumper cables off your car to it.
I will work enough to try it out.
 

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warrjon

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Hi Guys,

After sleeping on it and re-reading the OP, the thought occurs to me, if the original transformer is burnt out and so are the tube rectifiers, what caused that to happen ! The chances are that the magnetic chuck has shorted windings and unless it can be safely tested and rewound if it has, then whilst all the above information is correct, it could be for naught !
Just put an ohm meter on the chuck

E=I/R so 110V / 10 amps = 11ohms (R)

Check the label on the chuck for its current rating and you should be able to determine what R the chuck should be
 

Bob Korves

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#17
FYI, a typical 6x12" mag chuck draws about 125 watts at full saturation.
 

markba633csi

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#18
Light dimmers are designed for resistive (incandescent) loads, they may not last long with inductive loads like mag chucks.
Worth a try though, worst case you fry it and lose 6 or 7 bucks- no big deal
mark
 

JimDawson

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#19
Light dimmers are designed for resistive (incandescent) loads, they may not last long with inductive loads like mag chucks.
Worth a try though, worst case you fry it and lose 6 or 7 bucks- no big deal
mark
Ceiling fan controller maybe? They are designed for inductive loads.
 

warrjon

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#20
Inductive loads with DC works exactly like a restive load until the power is switched off, then it will provide a back EMF depending on L and R (inductance and resistance) a flyback diode across the coil will fix this if it is an issue.
 

MozamPete

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#21
That exactly the circuit I used to test my magnetic chuck when first playing around with it (dimmer and a four terminal rectifier). Horrible waveform, mainly as I was switching 230Vac (325V peak) down to 110Vdc so a very short firing angle, but it worked.

Until I just turned off the supply (as opposed to ramping the voltage down with the dimmer) and I believe that is when the back EMF killed my first rectified. So a free wheeling diode or varistor or other snubber circuit is probably a good idea.
 
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