DC Drive & motor questions

Ive got a Covell OD grinder, with a powered 5c collet work spindle. There is what appears to be a relabled Minarik drive controller mounted on the machine, with what appears to be around a 1/4-1/2 motor running the spindle.
The holidays have given me some time to catch up on my To Do List and this is next. When I brought this home, the motor had been disconnected from the drive, and I simply matched the colors of the wiring and turned it on.
It would run ok, at low range, pretty slow, no matter how fast the pot was set, though it would change speeds somewhat. It would not run at all at high speed, nor would it reverse. It ultimately blew a puff of smoke out of the louvers on the drive, blew the fuses then quit. Generally this is not a good sign........
Opening it up, there is a pair of old style bridge rectifiers made up of 4 diodes, and a medium sized veriac or pot. Nothing appears visibly blown on a quick inspection.
The data plate on the motor has been work smooth from years of operators resting their hands on it, so no data is available.
I know absolutely NOTHING about DC motors, or how they work, and even less about DC drives.
I can do a fast and cheap replacement of the diodes by replacing them with the common Rat Shack rectifiers, and I can ohm out the pot thingy..but what do I do next? Id rather not replace everything if po$$isble though the stuff on Ebay is sorta kida maybe affordable. The grinder is in good shape otherwise and runs smooth, and has a good coolant tank and pump.
Any ideas, suggestions, links to wiring diagrams, types of motors DC motors that need two bridge rectifiers and a pot...
This is one big hole in my knowledge base I really need to fill.
Thanks
Gunner
'If you own a gun and have a swimming pool in the yard, the swimming pool is almost 100 times more likely to kill a child than the gun is.'" Steven Levitt, UOC prof.

Odd, there should be no need for a Variac and diode bridges when a Minarik is there to run the motor. Is it a permanent magnet motor of does it have a field winding (two or four wires to the motor)? Did the smoke come from the area of the Variac/diodes or the Minarik? Answer these and we'll go from there. Respectfully, Ron Moore
Gunner wrote:
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So . . . . what is a "Minarik"?
Bob Swinney
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Minarik is a motor controller brand, like KB, Dart, etc. Used a lot in "company-brewed" machines. Respectfully, Ron Moore
Bob Swinney wrote:
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Minarik drives are common in the surplus channels too. Surplus Center had one the right size for a 3/4 hp motor for ~$40 complete. They are on Ebay pretty regularly for even less than that ($25+/-).
Sized for 1/4 to 1/2 hp is even cheaper.
Might be better off buying new surplus for that price...?
Gunner, if you want to know how well the Surplus Center drives work, I will pull out the one I bought and give it a try. Its been sitting on a shelf for a while waiting for me to find some time. Having just graduated I find myself with a nothing but time lately - job hunting. Know anyone who wants to hire a Mechanical Engineer with several years of product design experience? =)
The basic idea for speed control on DC motors is to rapidly (several khz on up) switch on and off a constant voltage power supply such that the motor responds to the *average* current in the windings as if a lower voltage were applied with a resulting lower winding current. The frequency stays the same, the percentage each pulse is 'on' is varied. The inductance of the motor evens out the pulses.
StaticsJason
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I did a Dykem spray and wipe off of the motor plate and got this info
Bodine 115vt Cont, 1726 M-2080D060
.43 1/8 NSH 54?7
The badge on the outside of the drive unit :
Carl E Holmes Co. 59988 Speed Control 115VAC Input 115 DC output
Opening the can of the drive, I find glued to the back wall a VERY oil soaked schematic thats barely readable that says:
SH32 Control and Minarick
The motor does have brushes, and there are two heavier wires, plus two thinner wires going into the motor,
I can take a picture of each and email them to you, including a couple of pic of the inside of the drive, if that would help
Gunner
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'If you own a gun and have a swimming pool in the yard, the swimming pool is almost 100 times more likely to kill a child than the gun is.'" Steven Levitt, UOC prof.

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Pictures would help, put them in the dropbox??
Sounds to me like they're running the field winding off of one of the bridges, maybe there should be a series resistor someplace to set the current.
And that they're running the armature from the other bridge, possibly though a variac. A photo would allow one to determine that it is a variac, indeed.
Are the diode bidges selenium plate rectifiers, ie a bunch of inch or so square plates all stacked up with spacers in between them?
Jim
================================================= please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com =================================================

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I emailed a zip file with pictures to several others. Drop me a simple email and Ill reply with the zip file. about .5 meg
gunner
'If you own a gun and have a swimming pool in the yard, the swimming pool is almost 100 times more likely to kill a child than the gun is.'" Steven Levitt, UOC prof.

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    I would be interested, but that is too big a file. I've been fending off virii (only because of the nuisance value) by setting my mail system to reject delivery of anything over 50k in size, and this is ten times to big.
    However, if you post them to the dropbox, I can download them with no problems.
    From what I have read so far, it does sound like two rectifier circuits -- one direct to power the field, and the other through a Variac before the rectifier to power the armature to get variable speed. No attempt at regulation at all.
    Good Luck,         DoN.
P.S.    If the photo shows the rectifiers are selenium ones, then I     strongly suspect that is the source of the smoke. It has been     decades since they were last used in new designs. :-)

Gunner wrote:
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Looks like the earlier explanation of Pulse Width Modulation does not apply here. Instead of using a constant voltage power supply and chopping it with an adjustable control they just use the variac to make a variable voltage powersupply. It looks like there are no electronic brains to fry (that I can tell from your photos).
If I am reading it right, the non adjustable transformer in your drive supplies power through one bridge rectifier for the field windings (to generate the magnetic field in lieu of permanent magnets). The variac (biggest thing there attached to the knob on the front) just directly varies the voltage to the motor.
Cross referencing the old designation SH32 yields their replacement drive, not the same design but the theory of operation is similar.
Minarik's replacement model is an MM21251C and the manual is here: http://www.minarikcorp.com/PDFs/250-0100.pdf
The manual is 50 some pages and includes a sections on operation and calibration.
Again, it's not the exactly the same drive but some of the testing and calibration sections will apply here.
my 2 cents, StaticsJason Posted and mailed
PS: the Minarik cross reference table is here: http://www.minarikdrives.com/catalog/minarik-076.pdf
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It would be helpful if you could put up some pictures of the motor, and possibly the drive board(s).
You're familiar with how things come apart, so you could open the motor to see if it has a wound field (4 wires exiting the motor), and if the brushes & commutator are in reasonably good condition (some tension on the brushes and they're long enough to be useable, and the comm segments are fairly smooth and round). The motor shaft should spin easily, and there shouldn't be any burnt odor in the case.
I suspect that if the contents of the drive box only contains the 2 full wave bridge rectifiers that you mentioned, that 1 of 'em is for the armature, and the other is for the field winding. If this is the case, the speed control "pot" would most likely be a variac. Another possibility is that this type of controller is an improvised (not manufactured) controller circuit. It could be useful to note what the ratings of the fuses are.
If there's also a more sophisticated drive board in the controller, it could've suffered almost any kind of failure.
The Shack store isn't likely to have diodes that would hold up to 120V motor duty.. you'd probably want to get 400V 10A or higher rated diodes.
WB ...............
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To clarify, the item you are describing here is the sum total of all the electronic drives on the machine, the box with the two rectifiers and the other variac or pot item, is the one that's labeled "Minarek?"
First off how large is the pot/variac thing that the speed control dial is attacthed to? Ie is the total volume of the thing behind the panel about one cubic inch, or larger, about 100 cu inches? And does it have visible windings on it, around a large torroid, with a wiper on the shaft that rides on exposed copper of the windings?
Jim
================================================= please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com =================================================

Hey Gunner,
Another possibility is to just scrap that DC out and put a 3 phase and VFD in. Cheap and easy at lower horse powers.
That's what I did on my 10EE.
Merry Xmass.
Karl

On Wed, 24 Dec 2003 23:26:23 GMT, "Karl Townsend"
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yup..thats definitely a thought. Some VFDs on Ebay for cheap will run what is probably a 1/8 hp 3ph motor. I was just hoping to not have to adapt a new motor to the mount, new pulley, etc, vfd etc
Cheap is good. really really cheap is much better.
Gunner
'If you own a gun and have a swimming pool in the yard, the swimming pool is almost 100 times more likely to kill a child than the gun is.'" Steven Levitt, UOC prof.

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yup..thats definitely a thought. Some VFDs on Ebay for cheap will run what is probably a 1/8 hp 3ph motor. I was just hoping to not have to adapt a new motor to the mount, new pulley, etc, vfd etc
Cheap is good. really really cheap is much better.
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I've got two 10EEs, and I'm going to keep the dc drive system ... although not necessarily with the original drive unit, perhaps just the dc drive motor, headstock (or ELS) direction control, and speed control pot!
There are some really good dc drives, such as the Emerson.
For single-phase operation, you've got to go to 277 volts, in order to get the full 230 volts armature and full 115 volts field.
With 240 volts input, the drives will only do 180-200/90-100 volts.
With 277 volts input (yes, 277 volts single-phase), the drives will do 230/115, and up to 10 HP, too.
But, of course, only 3 to 5 HP is needed for a 10EE, if the drive is dc.
OTOH, if the drive is ac, through a VFD, then 7.5 HP plus the backgear, or 10 HP without the backgear, is necessary to equal the capability of the 3/5 HP original machine.

Yeah, but not so cheap at the 10 HP level of the 10-EE. I haven't priced any but I'd guess a 10 HP VFD would be around $1000 or more.
Bob Swinney
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Yeah, but not so cheap at the 10 HP level of the 10-EE. I haven't priced any but I'd guess a 10 HP VFD would be around $1000 or more.
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Well, Monarch gets around $6000 for their kit, and a good portion of that is the drive.
Since almost no one wants dc drives, they are pretty cheap.
I bought several brand-new Emerson drives for around $100 each, for 5 HP drives. Less for 3 HP drives.
The only thing prventing such a drive from outputting 230/115, as needed by the 10EE, is the fact that the driver section and the power section are supplied by the same source.
If you power the driver section by 240 and the power section by 277, then these drives will produce 230/115 rather than 180-200/90-100.
Since the only connection between the driver section and the power section is a pulse transformer to the SCR gate, the isolation is complete, and there is no problem in such operation.
One Reliance model works on 277 only, but that is principally because the drive has a 277:240 control transformer in order to power the driver section. This driver section is identical to those in all other models, including those which are powered from 120 volts.
Probably the best dc drive conversions for the 10EE were made by Joliet. Imperial was another 10EE replacement drive manufacturer.
If you have 240 three-phase, 230/115 is possible with many off-the-shelf drives. Otherwise, for single-phase operation, 277 is a must.

I've viewed the pics and see some potential repair possibilities. The motor is fairly old, so investigating the condition of the brushes, brush springs and commutator would be where I would start. If there is a problem in the motor, this would affect my judgement of the route to proceed. I figger you know how to check the field windings for a short to ground with a trusty ohm meter. The leads should be removed from the Minarik control, and checked for continuity too.. maybe 100 ohms, probably less.
In the Minarik wiring diagram, most of the components are easily recognizable, except for the circular symbol at the lower left, which I think is probably the fwd/rev selector switch. It appears to be a DPDT switch with a resistor mounted on it.
The big speed control knob is on a variac, and it should be checked for overheated spots, open turns and that the brush is in good condition, and that brush wiping surface is clean. There's probably a good chance that these areas will need to be cleaned. There's another contact (ring near the shaft) that connects to the brush.
Most of the components can be checked with an ohm meter (checked only means a basic check for failed/shorted, not that an ohm meter will determine if the parts are good). That big paper (tubular shape) capacitor would be a primary suspect.. this style indicates a fairly old part, subject to failure from age, becoming internally shorted. These will also emit smoke when they fail.
The diodes will most likely show shorted (almost zero) if they've failed (most often failure mode), and when they go completely open, it's fairly obvious because you can usually see that the center is split open or missing. If the epoxy body is blistered, cracked, or ruptured, you can be sure they're bad. Another less noticable sign is a dark stain near the body (vented out the bottom). If a diode reading looks suspicious, you can recheck it after unsoldering one of it's leads from the board.
The resistors are probably marked with their values, or you might be able to read their values on the parts list. The one on the fwd/rev switch is probably marked with a value, and the one mounted to the panel appears to be marked. It looks like there's another resistor associated with the power on switch (off/lo/hi), and it might be the one that appears like it has been wired in with wire nuts. If this resistor has been changed, it might not be the same as the original part.
I don't see where the inductor (looks like a transformer in pic 5) is located on the wiring diagram. Maybe between the resistor and capacitor on the FLD lower line. The ohm meter should show low ohms, probably less than 10, for a definitely-maybe-good check.
The diodes appear to be 6 Amp devices. If some of them are shorted, you'll want to note the position of them before you snip them out. The band indicates their proper relationship to the others. The capacitor probably has + signs on it for the positive lead. You might be able to get more information from the parts list for the diodes and the capacitor. Hopefully, you can still read the original fuse ratings from the parts list.
Good luck with this, it looks like a nice grinder.
WB ...............
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