Thread: DC motor conversions

I have a couple of 2.5HP DC motors and wonder if there are any advantages to be gained and how complex a project it would be to repower a lathe or drill press and especially a 2" wide belt grinder with one. I know I would need some kind of variable voltage power supply but really do not know much about electrical stuff. Can anbody offer any advice or maybe plans for the power supply? Thanks for any comments.

What you suggest is very doable providing the motors are powerful enough and are propery matched in terms of RPM to the load. Many drill presses, cplishers, small lathes, etc have been converted to DC treadmill motors but the more successful conversions required some carefully made choices.

You can get a good idea of the available control to run your DC motor from AC by looking under "DC controls" and "motor controls" on eBay. Look especially under Dart control and KB control. These are tiny (about 4" square) but quite sophisticated devices that require only switching and a spped control to make them operate a DC motor over a wide range of RPM with good regulation and built in current limit. Naturally whatever control you select has to be suited to your motor.

The "2.5 HP" makes me womder. Are they from treadmills? Can you tell us some nameplate data? Volts? Amps? RPM? Whether the motor has permanent magnets, is shunt or series wound? Does the motor case fully enclose the motor? Are there air vents? Is the motor's case "skeletonized" that is so that much of the motor's internal parts are visible?

This info will be helpful for the rest of us to advise you.

If the motors are indeed reasonably rated at 2.5 HP they could run a drill press or a small lathe. If they have open construction they have to be mounted in an enclosure or located very much out of the way of chips and dust.

You got it - they are from treadmills. They almost appeared to be totally enclosed, until I looked at the end where it is open and I can see the rotor. The spec. tag on one of them reads;
Nordic Trac
P.M. D.C. Motor Model C3464B3185
ICON P/N M-160927
17.6 AMPS 3050 RPM CW Rotation
INS Class H 25 (degree) Ambient
Open Const. External Fan
2.5HP @ 130VDC E62788
Icon Health and Fitness
Logan UT 84321

The other one is a bit buried at the moment so no specs on it but if I remember correctly, it looks the same and I do know that it came from a treadmill since I'm the one who took it out.
I can't tell you if it is shunt wound or series -I think I know what series is but have no idea what a shunt is. I checked on eBay according to your suggestions and it seems that controlers are not to expensive which is encouraging. Some of them do not appear to have any "controls" as in knobs and such to control the speed. Your comments about dust are a big concern. I do lots of welding and grinding and everything in my shop does get covered with iron grit. I do keep my lathes/milling machine covered though. I am thinking the that the belt grinder would be the first tool for a conversion since having the variable speed on that would be sweet.

I coverted an old Chinese built mill/drill from AC to DC.It originally came with a 1/2 HP AC motor long burned up before I got the machine, for free.I acquired this machine with the intentions of using it as a drill press and liked the idea of having X/Y travel.I took the burned out motor off and replaced it with a 1HP 90 Volt DC from Pacific Scientific.I used a Minarik(spelling) controller and couldn't be happier with it as a drill press.I've not tried even the smallest milling cutters on it and have no intentions of using it that way since I have two full size milling machines to do that work and another on the way.I've used a 1 and 1/32 inch drill in it(my largest)at slow speed and it worked great.The RPMs will vary from zero to 2000 although I've not tried it in the upper RPM range.I say go for it.BTW this thing was originally a 12 speed with three three step pulleys so I can really play around with the speeds if need be.

I have a couple of those treamill motors too. I plan on using one on a spindle for my cnc router. It has similar ratings as yours bt made by Magnetek. The other one is rated 2.5 HP at almost 25amps! somewhere around 4500rpm. I havnt found controller big enough to drive that one.

Note that these are "treadmill duty" Meaning they were not designed to be ran for more then a couple hours at a time. Usually all they have for cooling is a snall external fan blade attached to the shaft. I wonder if adding a nice high flow fanducted to one of the end bells would help that.

There is site where someone hooked one of these too their 9x20 and it works fine.

Well one problem will be the controller. Make sure it can handle the motors you got. If I remember correctly on my setup for my mill, I have a 1.5hp motor but with the controller I use I,m really only getting 1hp which is plenty for me. And the same will probably work for you as I doubt you will find a cheap controller that will let you get 2.5 hp out of the motors.

KB is good. I have used their stuff. At least on the older KB controllers, you need a current programming resistor, which is sized per the motor.

Cooling at slow speed will be rotten. Keep motor speed up.

The motors as you show are high speed, 3000 rpm. They will need a lot of speed reduction to get to useful speeds, twice what a regular 1725 rpm AC motor would, more if you have 1150 motors on the machines now (like my DP).

Belt grinder might be a good application. Speed isn't so widely variable, and you rarely use full power, and then not usually at full duty cycle. There is always slack time moving the part to deburr another spot, etc.

Anyone use golf cart motors?
Seems to me they would be a lot better.

It is amazing how many times fitness realted equipment shows up at town dumps - and in virtually new condition! I have seen exercise bikes with only 1 or 2 "miles" on the speedometer (and I doubt they "rolled it over"). Treadmiils show up a lot as well and I have yet to find one that didn't work.
When you score a treadmill at the dump (or by the side of the road) first plug the unit in and see if it works. If it does, you not only have a working treadmill motor, you also have a working speed control unit (as these treadmills have an electronic speed adjust control module). When you pull the motor, also pull the control module and the interconnecting wiring. Somewhere on the treadmill there will be a schematic of the interwiring, pull that as well (may take a saw) as it will make it MUCH easier to reconnect everything afterwards. In this manner, you get not only a motor but also the speed control for it (don't forget the speed pickup - usually a small unit mounted on the frame near the flywheel).
You should measure the diameter of the treadmill belt driving shaft and the reduction ratio (if any) from the motor to the drive shaft to obtain the design motor RPM range. This is the RPM range at which the motor is at its best and the range you should try to work within as you design in the motor to your application (may take different set of reduction ratios).
Good luck.

Pete

Thanks for all your comments!
The first motor that I scored at the town dump was from a treadmill that the bulldozer guy had beat me to - it has some of the elecronics as I figured it was the power supply that the motor needed. I think the one problem with them is that the speed control is not infinite, which seems to me to be a huge advantage of that kind of power. The second one was just a motor that somebody else had ripped out - probably thinking they could just plug it in and away they would go. (Ihope they didn't try to plug it in - can't imagine that it is good for them) Lot's of treadmills at the dump as well as other exercise equipment as you have noted. Maybe I'll try and get a complete one.
As far as using it on the grinder, I am not using my grinder to deburr. I grind knives and such and so the machine is on for a bit, but probably not longer than somebody would have been if using it for treadmill.

Does anyone know what the "treadmill" rating actually means in % duty cycle?

Also what difference does shunt versus series mean on a DC motor?

Thanks

TMT

Not to hijack your discussion but what has anyone built out of an old exercise bike?

Thanks

TMT

There are 2 types of DC controllers:
1. SCR (Silicon controlled rectifier): common, less $, very durable, and generally output 90V max for 120V input (or 180V for 240V input)
2. PWM (Pulse width modulation): newer, more $, not as durable, a little more accurate speed control, more efficient for the motor, quieter, and generally output 130V max for 120V input. OEMs like these because they can spec a smaller DC motor and the overall cost is less.

DC motors can output constant max torque at all speeds. Current is proportional to torque. Speed is varied by changing the voltage. So the motor and controller need to be matched for both current and voltage. There is no harm in using a controller with less voltage and/or current than the motor rating, except that you have less max speed, torque, and/or power than the motor nameplate rating. There is likely harm in the opposite config. Overcurrent and heat are the main risks of failure for DC motors.

For metalwork, SCR is preferred since it is ~bulletproof. But treadmills are often PWM (130V rating is the giveaway), so if you run them with a 90V control your power is 70% of max. Or, get a 180V SCR control (230V input) and turn the max speed to 130V (there is usually a pot to control this).

I've heard good things about KB, less good things about Minarik.

Treadmill motors are rated for "intermittent duty" which unfortunately can mean whatever the mnfr wants it to mean. The main issue is cooling, so if you are running the motor a lot at low speed, or continuously, use an external fan to blow air on it / through it (w/ filter).

You can generally tell the price of the treadmill motor by its max speed rating. If it is 6000rpm, it is probably a $25 motor. Your 3050rpm motor sounds like a decent one. The cheap motors actually work quite well but the speed reduction can be an issue depending on the app.

I believe the rotation rating mainly describes the cooling fan. I have run "CW" DC motors CCW successfully, at least for short periods.

David

Was surprised when I started up the shop( old precor) treadmill and have it start at full speed.What to look at first?It shuts itself off with defective speed control warning.

Does the motor have an optical feedback for speed regulation? Tht might give an error is it is dirty.

www.surpussale.com lists treadmill motors and they say treadmill duy means 2-4 hours at full load. If that is true I bet you could run these all day on a manual lathe.

I use a DC drive to run a lathe, though it's probably not a treadmill motor. The setup consists of a 1.25 HP, 130V, 2700 rpm motor belted up at a 3:1 reduction. That's 3" on the motor shaft, 9" on the countershaft. The motor housing is fully ventilated i.e. mostly open. It's also rated for continuous duty. I made up a plexiglass shield to go around the motor and keep out stray chips. So far, so good.

That motor is run by a KB Electronics drive. It's a NEMA-1 enclosure with a big heat sink on the back. The drive is capable of 1 HP max. I've run this setup for 8-12 hours at a stretch with no problems at all. The only time the drive gets warm is when taking heavy cuts for more than a few minutes at a time. Not sure which type of drive it is, but I'm very pleased with the setup overall. I take pains to keep the motor speed no less than 50% if taking a heavy cut. It cuts down on belt shifting but doesn't eliminate that.

A treadmill motor would probably work fine with the considerations already listed. If belts and pulleys don't provide enough reduction, you might consider a gearbox, though the motor you have ought to be fine. If you were running a belt grinder, one of the 5000+ rpm motors would make it mighty effective.

I have a couple of those treamill motors too. I plan on using one on a spindle for my cnc router.

Note that these are "treadmill duty" Meaning they were not designed to be ran for more then a couple hours at a time.

Those treadmill motors are quoting "peak" or "stall" power, not operating power.

The $20 Asgord "2 1/2 HP" Treadmill motor that is very popular at ******* is 2 1/2 HP Peak, 1 1/2 actual, and weighs 10 lbs.

http://www.surpluscenter.com/item.as...tname=electric

A "real" 2 Horsepower DC motor weighs around 45 lbs:

http://www.surpluscenter.com/item.as...tname=electric

I've been looking for a high-quality (Bodine, Leeson, ...) 2 Horsepower DC motor for my Burke knee mill, but they run between $500 and $1,200 on Ebay, and a lot more than that at Graingers, McMaster, etc.

I've been looking for a high-quality (Bodine, Leeson, ...) 2 Horsepower DC motor for my Burke knee mill, but they run between $500 and $1,200 on Ebay, and a lot more than that at Graingers, McMaster, etc.

Are you watching this one:

http://cgi.ebay.com/ws/eBayISAPI.dll...m=200009031466

This one is interesting too as it comes with a nice controller + heatsink:

http://cgi.ebay.com/2-HP-DC-motor-an...temZ7622840544

Another good one:

http://cgi.ebay.com/PERMANENT-MAGNET...mZ220009112159

And another:

http://cgi.ebay.com/DANFOSS-ELECTRON...mZ120013136503

If you think you might be able to get by with only one HP:

http://cgi.ebay.com/Reliance-DC-Elec...mZ330009270241

These items were found in a 'quick' search. More sneaky search tactics will bring up even more and better results. Most buyers will not bother (or just don't know how) to do a really detailed search on ebay and will therefore miss out on the really good deals. Both buyers and especially sellers should take a lesson from this fact.

If you want to sell your items for top dollar on ebay, make sure people can easily find them!

Jimbo

(ebay search wiz)

A question...when these treadmill motors need parts like brushes...are they available?

If so, from where?

TMT

Those treadmill motors sell for $20 at SurplusCenter (and are resold by the dozen on Ebay).

Just throw it away and buy another motor [img]smile.gif[/img]