Changing from AC to variable speed DC motor

[Foozer]

Being as I dislike cold, anything below 50 F the fingers refuse to do as directed, what should be a day project is now hit and miss.

Changing over the AC motor to a treadmill variable speed DC motor, we hope. Not a great wiz at electrics other than its like water thru a pipe. I always start out reminding myself; Do not stick your finger into anything than has a cord attached. Do not power up anything electrical until it has been triple checked, if you don’t know ASK someone.

So got this 2hp DC motor from a treadmill, controller and supply of tubing, If I can avoid the smoke test it just may work

Now there no reverse built in to this thing as received so of course the first try was just reverse the input, ah no, that doest work, never can be that easy. Time to map the motor and reverse switch wires out and I see that I have in the motor 2 big wires, 2 little wires and 1 green wire. As the green is attached to the motor frame it must be ground, gotta keep that one in play. The 2 big wires end up as such, into one side of the armature, out the other, into one end of the field and out the other. Hmm must be a series system whatever that is. The reverse switch is native to the lathe and its mapping is, well I don’t know what its called. Flip it one way and some contacts make while others break and so on.

From forum searching the solution to getting the motor to reverse was found

Reverse the direction in which the coils are energized and the motor reverses.
http://www.homemodelenginemachinist.com/index.php?topic=2740.msg25008#msg25008

So I dig into the motor and split the armature to field wire, splicing in extra wires (soldered and double shrink wrap) so I end up with 2 circuits as seen in view “B”

Ol Dukie giving his approval so I must be OK so far

. With this and the mapping of the FWD/REV switch its time to see if I can wire it up.
Got the plan mapped out

And the actual (the motions getting to this step are dull, cut and solder, wire ties are your friend)

Disconnected the motor power wires from the controller to allow testing with a small battery, Don’t want to smoke the board. Hooked it up and ran the FWD’REV switch thru its paces and YeeHaw, it rotates forward and reverse. Now its just mount it, dress it and use it.

Have to talk to that cat, seems even though the motor does the FWD/Rev bit it is stuck on slow speed. The controller does not alter the speed at all. So whats up with that? Back to the original motor wiring seems that the arm and field in series mean something, don’t know what but shouldn’t be hard to reconfigure the FWD/REV switch to alter the field polarity while leaving it in series with the armature rather than parallel as it now is.

Shorten the story of the last 2 months tinker it actually works as intended.
The 2 small wires mentioned earlier are for some sort of speed sensor attached to the motors armature, this in conjunction to a magnetic switch pulsed from a small magnet encased within the driven pulley (can see its wires in the shot) I guess regulate the controller read out. Mounted the original controller to the right side of the bench and with a push of a button (will grab a shot after I get the bench re-bolted to the floor) I can change speed at will. Ok so it reads in MPH, some Excel work as in =SUM((((4*(300/B9))*3.141)/12)*0.01136)*1.5 (1.5 is just a random pulley step up number, subject to change as experiments go on) may get me to the MPH to FPM realm for different materials and diameters, ya I’m bored. Still have to get within the infield of the speed controller to pulley relationship, but for now 0.5 MPH and I can count the spindle revolutions, At 10 MPH, well it’s a lot faster than I’m comfortable with, Good thing it will be bolted down to the floor.

Things to change, Motor brushes are mounted offset of centerline. Seems that its designed to favor one direction for brush life? To agree with the design need to remount motor 180 degrees. Can see why preferred method is mounting motor above lathe, chips don’t fall up as well as they fall down. Have to fabricate some sort of guard for that. Figure out the speed pulley relationship for the controller and dump the multi-step to a single. Actually make something other than modifications.

And No Honey, I dont know what happen to your Tupperware

 

[Kermit]

Slow and easy. Think it through, then think it through again.

You done good figuring out the wiring without the tedious tech schooling.

This proves that electrical work can be done by amateurs with proper caution and lots of safety checks by just knowing the basics of Ohms law and the mechanics of how switches work.

I started out about 7 or 8 years old, -after I was shocked the first time I just HAD to find out what that stuff was all about. ;D

Way to go Foozer,
Kermit

 

[Kludge]

From forum searching the solution to getting the motor to reverse was found

I'm glad my writeup helped, Foozer. That's a good part of why it was written. (The other part is that I'm a writeaholic.) IF you have any questions, please feel free to ask. I'm sure I can come up with something that almost sounds plausable.

And No Honey, I dont know what happen to your Tupperware

When it's no longer fit for the kitchen, it goes to the shop. When it's no longer fit for the shop then it gets cut up for patterns. What's left gets recycled. Repurposing at its finest.

BEst regards,

Kludge

 

[Bernd]

Interesting. All the tread mill motors I have have permanet magnets in them. Must be the newer motors they're using today.

Bernd

 

[Foozer]

Finally all back together, dog approves but its just a neighbor mutt over to steal another ball.

Back in its home all bolted to the floor, Kid tried to get me to place the controller on the left side, we had a bit of a discussion about rotating objects and arms getting not so gently removed. The right side position does block the tool board a bit. However it will soon enough be grown accustom to. Small learning curve is well worth keeping the body parts intact.

To those to whom within their prior postings, have taken the time to explain details of the various niches surrounding metalworking Much Thanks.

Now to work on the MPH to FPM math

 

[Kludge]

Interesting. All the tread mill motors I have have permanet magnets in them. Must be the newer motors they're using today.

Well, universal motors are easy and cheap to produce and, as a rule, tread mills only go one direction so they are a logical choice. A PM motor has the advantage of a fixed field where the universal motor's changes with the power supplied to the motor and the load. Increasing the load increases the current demand which, in turn, increases the field strength (Good old ampere-turns at work!) which with the increased armature current (more ampere-turns) should maintain a more or less constant speed.

Ah, but then there's the speed control which will sense the decreased voltage drop which also occurs (along with the actual shaft speed most likely) and should bump the voltage up to everything's all happy and the sun is chirping and the birds are shining.

The speed control on a PM motor should work the same way with the main difference being in what's it's driving and the details of how it does the sensing majique.

Best regards,

Kludge

 

[Foozer]

So after playing with the little lathe with its newly adopted variable DC drive a few items have come up.

From the link to the Siemens site http://www.homemodelenginemachinist.com/index.php?topic=4213.msg43734#msg43734

It is mentioned that series wound motors (which this one is) are not so stable at slow speed. Now this gizmo’s control head is equipped with a clock, so counting the tics against the second hand gives about 100 RRM spindle as the slowest obtainable stable speed. But after chucking 3 truck loads of stuff to the dump being bombarded by that little bird’s voice saying “Get a Tach” I looked at what other features the original treadmill had. Ah a heart rate monitor, now there’s possibilities. All I need to do is make a heart beat. OK. Took a piece of vacuum tubing, plugged one end with a shot from the hot glue gun, filled it with water and hot glued the other end. Stuck it in a tool holder in such a way that the face plate dog would give it a whack each revolution.

Clipped the earlobe monitor to the other end and let it go round. “Repurpose” as it has been said

Its Alive

We have a pulse and at 102 compared to my 100 count I call it good. Did the repeatable test a few times and it came to the same speed +/- 2 RPM

Scaling up till the pulse monitor gave up counting (about 190 beats) the relationship between RPM and MPH seemed linear. Doesn’t mater much as the metal tells what it likes.

Total time of testing 43 minutes 05 seconds, Clock has got to go, if the bride knew how much time I spend on my pride watching shinny things . . .

 

[Kludge]

Finally all back together, dog approves but its just a neighbor mutt over to steal another ball.

That he's comfy there says a lot about you - all good. Dogs are excellent judges of character.

Best regards,

Kludge

 

[Kludge]

It is mentioned that series wound motors (which this one is) are not so stable at slow speed.

This is true which is one reason why separating the field and armature windings is a Good Thing. Feed the armature with a steady current and vary the armature voltage to control the speed for a lot smoother operation. This is pretty much the same as a PM motor (but with a controllable magnetic field) and will improve low end performance.

BEst regards,

Kludge

 

[Noitoen]

One easy way to reverse a dc series motor by just reversing the input polarity is to install a full bridge rectifier to supply the field.

View attachment Field.bmp

 

[Foozer]

This is true which is one reason why separating the field and armature windings is a Good Thing. Feed the armature with a steady current and vary the armature voltage to control the speed for a lot smoother operation. This is pretty much the same as a PM motor (but with a controllable magnetic field) and will improve low end performance.

Got a PM motor 1hp to try first but it looked just to dinky, the treadmill was cheap and with it having a 2hp motor (at least it looks substantial) I figured it would dump the slow speed heat better. Slowest stable is around 650 motor RPM with a 100 RPM spindle rate. Dug into that hunk of steel perty good, lot more than the tailstock liked, to test it out, 'round .100 @ .002 pre rev.

So a bit more fooling around with the pulley ratios to find a comfortable motor speed that is stable (stable being constant RPM holding capacity and sufficient rotation for its cooling fan to function while maintaining enough top end for small dia soft metals) It still has the back gears for low end but that brings into play the overpowered question. Hmm perhaps I should just quit thinking about it and run 'er.

That he's comfy there says a lot about you - all good. Dogs are excellent judges of character.

Ya he found a sucker, I go to the thrift store and get a box of old soccer balls, I buy em and he eats em. Leaves me thank you's hiding in the grass for my soles to find. Something wrong with that equation

Care

 

[Foozer]

One easy way to reverse a dc series motor by just reversing the input polarity is to install a full bridge rectifier to supply the field.

I think I will go introduce my head to the business end of the wall for not thinking of that, should be less of a headache than it was trying to wire the FWD/REV switch. I like it.

Care

 

[Stan]

Got a PM motor 1hp to try first but it looked just to dinky,

I don't know what size of lathe you are working with but I have a 10" Logan that I drive with a 1/2 HP Boston DC motor driven by a Boston Ratiotrol.

I run the lathe between 2 and 2000 RPM and never run out of power. Your 1 HP PM motor should be more than adequate for most home shop lathes although a PM motor is not as versatile as a shunt wound motor.

 

[Foozer]

I don't know what size of lathe you are working with but I have a 10" Logan that I drive with a 1/2 HP Boston DC motor driven by a Boston Ratiotrol.

I run the lathe between 2 and 2000 RPM and never run out of power. Your 1 HP PM motor should be more than adequate for most home shop lathes although a PM motor is not as versatile as a shunt wound motor.

Its only a little Atlas/Craftsman 109 6", older than dirt and for what I have spent on getting it usable, well that does seem to be a habit, taking the long way around the fence. Its so cute tho.

The 1 hp would of run it, but for the price of a controller I picked up the working treadmill complete for $50 bucks. Yes it is overpowered and the thought of some sort of shear pin in the pulley drive has crossed my mind. Off the cuff thinking is a 1/16 inch soft al pin might do. Need to cut a pulley anyway so just might travel down that road and see what happens. I don't know what if any torque control mechanisms are used in small machines other than bust a plastic gear or belt slip.

Care

 

[Kludge]

Got a PM motor 1hp to try first but it looked just to dinky, the treadmill was cheap and with it having a 2hp motor (at least it looks substantial) I figured it would dump the slow speed heat better. Slowest stable is around 650 motor RPM with a 100 RPM spindle rate. Dug into that hunk of steel perty good, lot more than the tailstock liked, to test it out, 'round .100 @ .002 pre rev.

Stan has the right of it; 1 hp would easily be enough to turn your 109. So, since you don't want to use it, how about tossing it my way to put on my Taig. ;D

Ya he found a sucker, I go to the thrift store and get a box of old soccer balls, I buy em and he eats em. Leaves me thank you's hiding in the grass for my soles to find. Something wrong with that equation

So what started this, him chewing the balls or you buying them for him? If it were really all that bad, you'd quit buying the soccer balls so his presence can't be all bad. But then, I'm a dog person in an apartment where I'm not allowed pets. That is frustrating so I "adopt" any dog I come across for a few minutes just to get a "canine fix".

Best regards,

Kludge ... *woof*

 

[Foozer]

Stan has the right of it; 1 hp would easily be enough to turn your 109. So, since you don't want to use it, how about tossing it my way to put on my Taig. ;D

I got a 1/2 hp PM motor sitting right here doing nothing

So what started this, him chewing the balls or you buying them for him? If it were really all that bad, you'd quit buying the soccer balls so his presence can't be all bad. But then, I'm a dog person in an apartment where I'm not allowed pets. That is frustrating so I "adopt" any dog I come across for a few minutes just to get a "canine fix".

Have 2 of my own both named Sh$t Head, at least they, like me answer to it, both Shepard/Lab mixes. Good rodent hunters and too big, 90+ lbs for them overgrown flying chickens (Eagles) to cart off.

I'll PM you the little motor specs

 

[RICHARDDV]

hi there--i am new to this group but i have been running my 109 with a pm treadmill motor for several years now with excellent results . i used the complete wiring from my donor treadmill to utilize the pm motor since the pm motors need some feedback to stabilize the speed and torque .this way the speed encoders on the treadmill are used to sense speed and the pulse modulation is increased or decreased as needed. another advantage is i kept the safety interlocks intact so the machine can be shut down immediately and it cannot be started at speed --everyone has their own methods so think the problem and make it work-- richarddv

 

[Foozer]

another advantage is i kept the safety interlocks intact so the machine can be shut down immediately and it cannot be started at speed --everyone has their own methods so think the problem and make it work-- richarddv

Found that out quick enough, it will start at speed and rather abruptly at that. Getting the arm accustom to the new motion of hitting the pause button will cure that. I take the safety interlock key out to insure my fingers always stay connected to the end of my hands when fiddling around with the 109

 

[Stan]

The 1/2 HP PM motor would do great on your 109.

Motor controls are always on ebay. I have never had to pay more than $30.00 for a good one. Sometimes you have to be patient if there are a lot of bidders out there.
Something like this one has all the features you could possibly need on a lathe motor.

http://cgi.ebay.com/New-Beel-DC-Mot...ryZ97184QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

If that long link doesn't work, just search ebay for DC motor control and it is on the first page. HTH Stan

 

[Kermit]

http://www.electronickits.com/kit/complete/motor/ck1400.htm