Thread: A DC motor question.

I found a Reed Prentice 2v mill I couldnt pass on.... but now I come to the motor.


The 64 dollar question is how do I power it up?
And how do I test it before I buy a power source?

Lazz,

I sure haven't seen anything in my travels that would power that beast. I would focus on dumping the old DC motor and mating a modern three phase motor with frequency drive, if that is possible.

Stuart

I have a supply on my Sheldon lathe that would run that nicely, but of course I am using it. Do you want it variable or just run? At that time, a lot of St. Louis was supplied DC and it may have had a simple on off switch. In that case, a full wave bridge rectifier across a 240 VAC line would do it. Does the machine have changeable belts, gears, or whatever to change speeds?

Bill

Originally Posted by 9100

I have a supply on my Sheldon lathe that would run that nicely, but of course I am using it. Do you want it variable or just run? At that time, a lot of St. Louis was supplied DC and it may have had a simple on off switch. In that case, a full wave bridge rectifier across a 240 VAC line would do it. Does the machine have changeable belts, gears, or whatever to change speeds?

Bill

Variable would be nice but it has step pulleys.As you can see the step pulley is a little on the large side. There was a electrical box included that I thought had a bridge rectifier .

Originally Posted by lazz

Variable would be nice but it has step pulleys.As you can see the step pulley is a little on the large side. There was a electrical box included that I thought had a bridge rectifier .

The 4-terminal device at upper left, under/behind the brown tubular shape, with glossy black pastic filler and light-metal case showing around the edges, is indeed a packaged full-wave bridge rectifier. Type has been in use since the 70's and still common, so younger then the machine, but not necessarily new. Lumpy orange device appears to be a paper/mylar capacitor, probably intended primarily to reduce commutation noise. Too small for effective filtering of the 60 Hz ripple.

Expect about 230 VDC or higher unloaded when measured with a meter because of the capacitor.

Expect 180 VDC under load, not the 230 VDC the motor expects. Torque and RPM would be reduced proportionately.

You might want to see how well that works for you before spending any bigger bucks.

Bill Hacker

Upper RIGHT, Bill, not upper left, you must have dropped the rock.

To be a little more serious, Does the motor nameplate say 4.1 A or 41A ? The rectifier probably will supply 4.1 A, but the steel plate it is mounted on is not a good heat sink. I'm sure it was originally intended to be run on constant 230 VDC with speeds changed with the pulleys. As to voltage, between the motor inductance and back EMF generated, the motor will look like a huge inductor and smooth out the ripple. I suspect you will see more than 180 V when running. You can probably find a 4 amp Variac in a surplus store for less than a replacement motor and use the taps that will give you a bit of voltage increase at the top setting and you will have a variable speed machine with multiple ranges, a very useful setup. If the motor runs properly, I wouldn't change it.

Bill

P. S.

I forgot to mention that if you use a variable supply, you will have to separate the field and keep full voltage on it, only varying the armature voltage. If it has a cooling fan there may be some issues with cooling at low speeds. An external blower will take care of that if needed.

Bill

Originally Posted by 9100

P. S.

I forgot to mention that if you use a variable supply, you will have to separate the field and keep full voltage on it, only varying the armature voltage. If it has a cooling fan there may be some issues with cooling at low speeds. An external blower will take care of that if needed.

Bill

Yes, 'upper right'... mea culpa

To the OP .. separating the field winding leads may mean a bit of digging.

Note from the nameplate that there is no info on field voltage or current, ergo they'd have been shipped for the same voltage as the armature and wired accordingly .... within the connection box if you are fortunate (four leads, grouped into two) or 'below' it, deeper into the motor (two leads only in the connection box). For-sure field-windings exist, as it is not a permanent-magnet motor.

Either way, this particular motor appears to have been optimized for stability at its rated speed - not for ease of variable-speed, so I'd not try for a wide range - just the ability to shift a resonating cutter off-RPM enough to smooth things.

IF you go for a new 3 phase AC motor and VFD, I'd suggest 2 HP motor instead of 1 HP, and a VFD rated for 3 HP or more if to be fed off single-phase input. It isn't so much that you need more power, but rather that you give up some of it when moving away from the motor's 'natural' speed, and some of what is lost shows up as extra heat, so the 'reserve' reduces annoyances.

Bill

Just a though after looking at that electrica switch gear, spend a few dollars on e-bay or your fav. surplus house and get a new contactor and such, that things looks pretty clapped out.

Originally Posted by doug8cat

Just a though after looking at that electrica switch gear, spend a few dollars on e-bay or your fav. surplus house and get a new contactor and such, that things looks pretty clapped out.

Worse - it wasn't much to begin with!

Much of a fan of DC as I am, this animal would benefit from a total strip-out and replace, be it DC or AC.

Just too much blend of antiquity, accumulated wear and damage, and marginal prior mods for peace of mind...

Bill

I agree the wiring is a little past it's prime...I like the idea of using The original motor....But when I plug in the present birds-nest the 2 glass fuses go pop...

I removed the old controller and it still pops the fuses.... So as I looked for a "220vac to 220vdc bridge rectifier wiring diagram" it looks like the motor needs to be in the line up for anything to work....
You guys have been great help.... Im kinda ashamed I cant find a simple wiring diagram....

Do the orange wires go into the motor, or is there another junction box? There seem o be 3 orange wires, implying field and armature connections with a common. Visually check the internal wiring to see that the insulation isn't crumbling, then check continuity to the frame on all the motor leads, preferably with them disconnected from everything else. Make sure there isn't another lead coming out of the motor going to the frame. If you don't get a reading to ground, then check between various leads. If one pair is the field, the resistance should be somewhere around 500 to 1000 ohms. The armature should read dead short when motionless. Switch the meter to a low DC voltage range and turn the motor. You should generate a little voltage from the residual magnetism in the field. If it passes these checks, the motor has a good chance of being useable. If the motor turns freely and the field and armature are hooked up correctly, it should run on a car battery. It won't develop much torque, but it should motor. An insulation check with a megger would be a good idea, but you probably don't have one. A megger applies 500 volts to the circuit, which usually will show a breakdown that will not read on a regular ohmmeter.

Does the motor have a reversing switch?

Bill

None of the existing wires were connected to the motor. The previous owner never powered it up. But he thought the motor wired to the top connectors of the disconnect to the left of the rectifier. 2 of the (red?) wires went to the L1 and L2 then to the fuse holders in the pic. The 3rd red wire went to a hand/off/auto switch which was connected to the A1 terminal of magnetic switch.

The motor has 5 wires. Each has a metal band . Clock wise they are the 2 connected A & S ,then an unreadable tag ,L, and F.
L and the unreadable tag generate a small DC voltage while spinning the motor by hand. None of the 3 open wires appear to be connect to the motor frame.

Surprisingly the wires from the motor seem to be in good condition... The cloth insulation is a little frayed but the wires and underlying insulation seem flexible.

OK, here's a WAG.

If A was for armature and S for series field, it make sense that they would be tied together and not to anything else.

Are A & S just tied together without any connection to anything else? Then you should read very low resistance to two other wires, I am going to surmise L and Unreadable, which would be the other ends of the armature and series field.

If you separate A & S, you should read continuity from A to Unreadable and from S to L. These should both be very low resistance, close to zero on a normal meter.

If so, you should get a voltage generated between A and Unreadable and not between L ans S when you turn it.

That leaves F, which should show a higher resistance to one of the other pairs. I am going to guess it will be to the S & L pair. The second end of the shunt field would probably be connected to L, but you will not be able to tell with a standard ohmmeter. I have a low resistance Wheatstone bridge that I got from a former Century Electric engineer, who used it on motors that would tell, but that is not much help here.

Let me know how this checks out. Even if it is wrong, the answers are still useful data.

Bill

I forgot to mention no reverse anywhere I can find.
A&S together only... no other connections.

I think you have a good understanding of the situation... Your predictions look like they came true...

On the junk meter I have the data is as follows....
S to A returns OL on the meter
S to L returns 0 (zero) on the meter
S to Unreadable returns OL on the meter
S to F returns 1.07 on the meter

A to L returns OL on the meter
A to Unreadable 0(zero) on the meter
A to F returns OL on the meter

Between A and Unreadable with the motor turned by hand gives DC voltage . With a simple flip of the wrist it peaks at nearly 300 and falls off to 0 .

Between S and F the same spin bounces the meter from mid 3's to mid 9's... 3.45 to 9.61 vdc for example.... That could be from my cheapo meter.

Originally Posted by lazz

I forgot to mention no reverse anywhere I can find.
A&S together only... no other connections.

I think you have a good understanding of the situation... Your predictions look like they came true...

On the junk meter I have the data is as follows....
S to A returns OL on the meter

Not sure what meter you have (make and model helpful - the ranges are probably on line somewhere)

But... Bill? I think we can take 'OL' as 'Out of Limit' IOW infinite resistance.

S to L returns 0 (zero) on the meter

Which I take as Zero Ohms

Where 'infinite' and 'zero' are, of course within the design limits of the meter, not the Universe.

You are on the right track. In-motor wiring being in better shape than that of the kludge box is a good sign.

Bill

Originally Posted by thermite

Not sure what meter you have (make and model helpful - the ranges are probably on line somewhere)

But... Bill? I think we can take 'OL' as 'Out of Limit' IOW infinite resistance.

Which I take as Zero Ohms

Where 'infinite' and 'zero' are, of course within the design limits of the meter, not the Universe.

You are on the right track. In-motor wiring being in better shape than that of the kludge box is a good sign.

Bill

See what happens when someone ... Me..... Tries to talk about a subject I know only enough about to be dangerous.

Yes sir "Out Of Limit" and "Zero Ohms" would be correct .... I think....

Originally Posted by lazz

See what happens when someone ... Me..... Tries to talk about a subject I know only enough about to be dangerous.

Not so. You have asked, and your ignorance is being dispelled, and safely. No one was born with an RPE certificate.

Someone who knew only enough to be dangerous would have simply 'rectumfried' himself WITHOUT asking, 'stupid' being more amenable to Darwinian selection than correction.

Run a search on 9100 Bill's posts and discover that the aid is coming from a world-class expert at that.

Me? Mere dilletante as far as motors go. I just like DC power 'coz logic circuits are happiest with it....

PM in action again...

Bill

"World class expert"? In an alternate universe, maybe.

Anyway, The readings look right on. This is a compound wound motor. The F lead is to the shunt field winding composed of a lot of turns of relatively fine wire. It is connected directly across the 230 V line and supplies the magnetic field for the armature to work against. The S lead goes to a series field winding that is connected so that the armature current flows through it also. When you load the motor, the armature draws more current, which increases the magnetic field contributed by the series winding and helps reduce the drop off in speed. The shunt and series fields are always connected in the same polarity, so both can be connected to one lead, L (for "low" maybe?). To reverse the motor, switch A and U. Since A and S were tied together at the motor, there was no reverse operation on this machine.

To run it, reconnect A and S, connect U and F together and one power connection goes there and the other to L. To test it, hook it to your car battery with jumper cables. Remember to hold the motor down, because reaction torque can make it roll right off the table. It will not produce much power, but it should run smoothly.

The rectifier unit will have two diagonally opposite corners marked with a ~ symbol, denoting AC voltage. Your power line goes there. The other two corners are marked + and -. These go to the motor, polarity doesn't matter, it will run the same direction ether way because reversing polarity reverses both the armature and field polarities cancelling the change.

Add such switches and circuit breakers as desired and that is about all there is to it. Since these components can generate large voltage spikes, surge protectors on the rectifier would be a good idea. I don't have part numbers at home, but I will look them up and let you know.

It would be a good idea to slide some sleeving over the motor leads. I use a silicone fabric material. I haven't bought any for a long time, so I don't have a source. I will look around.

Happy milling,

Bill

Success....
I would like to thank you all for your input....
And now I come to an internet down fall....
IF I had bugged you at some local hang out I would now be able to buy a round....
Since we are all spread out around the place I will now offer a sincere
Thank you gentlemen...

now to clean up the mill.....
to paint or not to paint....
that will be the next question/decision....