Magnetic Chuck Control Circuit Wanted

My mag chuck has one figure on the name plate stamped '66' but I can no longer make out what the value is for. Now I'm thinking it may be a de-mag voltage rating. 110Vdc operating, 66Vdc reverse for demag. Would sort of tie up with what this circuit is doing using only a half wave rectifier for the demag function.

It is pretty much similar to the curcuit I was trying to develop - triac feeding a rectifier with some reduced voltage for demag. I was trying to changing the triac triggering for the reduced voltage but the full to half rectifier is a nice approach.
 
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It seemed quiet elegant. If you'd like I can take the cover off and post a picture...
 
Sure why not? I'd be curious to see if there's a pcb or if they wired it point to point. Also the heatsinking.
Mark S.
 
Here are some pictures, at least you can get the idea...

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Do I see a burned resistor over on the right near the orange caps?
MS
 
Good catch! It is the resistor that is used in the voltage divider circuit... The unit is working fine, but I should check that it isn't 'open' and near its specified resistance.... hmmm...

-- Thanks for noticing!
 
Look closer I think it's the 150 ohm 1/2W resistor in the triac circuit, R7- the color code (or what's left of it) looks like brown green brown = 150
M
PS maybe it's not burned and it's just a shadow on the picture-
 
I'll still check it out before turning the machine on! Frankly there's problems with all 18 Bijur flow control devices. I may have to replace almost the entire lube system - the chuck is 2nd priority at the moment...
 
OK ... I finally received my order of PTCs from China (thru Alibaba). Tried one in my homemade magnetizer/demag, but initially with unsatisfactory results. So I measured the "cold" resistance of the PTC - about 20Ω. The motor stator I'm using has about 3Ω resistance, so the issue was one of impedance matching. I wired four of the PTCs in parallel and tried again. This did the trick. Holding down the switch, I can feel the "buzz" start at a good power level, then dissipate in about ½ to 1 second. It does a good job of demagnetizing things like screwdrivers. If I want to magnetize, I just blip the switch very briefly.

I think these devices will work well to control the demag circuit of a magnetic chuck. Just wire a set of paralleled PTCs in series between the demag switch and the coils. I have quite a few of these left, and will be more than happy to send some to anybody who asks (until I run out). Just measure the DC resistance of the coil and decide how many of the 20Ω PTCs it would take to approximately equal that resistance. PM me with your mailing address and how many you'll need.

PS - Don't try to test your circuit immediately after soldering to the PTCs - let them cool for about ½ hour or so, or the residual soldering heat will have them in a high resistance state. I'll let you guess how I discovered that little tidbit of info :)

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Very nice John- so the parallel ptc group you have now is about 5 ohm cold. If you had to order them again I'm guessing you would order a lower resistance value.
Come to think of it, did anyone post the cold resistance of their chuck? Anyhow, it looks like the chuck and ptc ohms should be about equal. Good to know.
Mark S.
ps it might be good to point out that resistances divide in parallel = 4 X 20 ohm devices in parallel =
5 ohms. 2 X 20 ohm devices = 10 ohm and so on...
 
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