Trying to run a treadmill motor

[Rick A]

Hi, all; I'm new here and more mechanically than electronically inclined, but hope I can get some advice. I was powering a milling machine with a treadmill motor when the controller failed. I want to simply run the motor at full speed and achieve speed control mechanically. It's a 95v. 18a. permanent magnet motor. Can I simply build a bridge rectifier and use a resistor to cut the 115v. house current down to 95? The controller has a choke, which, I understand, helps to even out the current. Is this necessary? Do small fluctuations in the DC current have a deleterious effect on the motor? Thank you for any help.

Rick A

 

[Ubergeek63]

Hi, all; I'm new here and more mechanically than electronically inclined, but hope I can get some advice. I was powering a milling machine with a treadmill motor when the controller failed. I want to simply run the motor at full speed and achieve speed control mechanically. It's a 95v. 18a. permanent magnet motor. Can I simply build a bridge rectifier and use a resistor to cut the 115v. house current down to 95? The controller has a choke, which, I understand, helps to even out the current. Is this necessary? Do small fluctuations in the DC current have a deleterious effect on the motor? Thank you for any help.

Rick A

a choke that would even that out would be 6 inch cube, you either have an EMI or a switcher filter choke.

depends. a low frequency variation can resonate with the motor speed to unevenly wear the bearings.

the are only 95 or 100V so that the equipment can run at full speed at low line voltage

dan

 

[Rick A]

Dan:

Thank you for your reply. The amount I use the motor, I can probably accept the bearing wear. Do you mean I can rectify the current and go directly to the motor? Would not 115v hurt the motor?

Rick A

 

[Ubergeek63]

Dan:

Thank you for your reply. The amount I use the motor, I can probably accept the bearing wear. Do you mean I can rectify the current and go directly to the motor? Would not 115v hurt the motor?

Rick A

a variac will slow it down as would a phase controller, though a phase controller will make it even more noisy. most of the motor controls use inverter rated motors and PWM after a rectifier and filter capacitor.

A lot depends on how well you want it to work. DC motor speed is related to load as well as supplied voltage.

dan

 

[Rick A]

It has a PWM controller, which failed (there are three circuit boards- power board, PWM board, and control board, and I don't know where the failure is). Being unable to fix it and trying to avoid the cost of all new electronics, I'm going the route I mentioned (when the mechanical variable speed acts up, I can deal with it!) I'd suspect it'll slow down enough under the load of cutting. Thank you again for your advice, Dan.

Rick A

 

[Ubergeek63]

wow that is complicated for a consumer mill! we build those all in one, though the display electronics is obviously separate.

dan

 

[Rick A]

It's a Proform, which, I gather, is a widely produced brand. this is the third or fourth treadmill motor I've adapted like this and the electronics always give out, don't know why- maybe because I run it for just a couple of minutes at a time, several start/stop cycles per use?

Rick A

 

[bobledoux]

After my treadmill motor controller burned out I went the easy way: I fed a variac autotransformer through a bridge rectifier. It provides 0 to about 130 volts on the AC side.

It works well under the variety of loads on my metal lathe. Speed isn't quite as constant as a commercial drive unit when used under variable loads.

DC motors can be run above their rated DC voltage. However, there are limits. Be careful about power draw and look for a motor getting too hot under continuous load.

 

[Rick A]

Does it have good power at low speeds, like for parting off and drilling big holes? I'd be interested in going that route (simpler than building a variable speed friction drive), but the 20a variacs I've seen on E-bay start at $100 or so, plus shipping on something that heavy to HI. The higher voltage might not be a problem on a mill because I don't often run it for long periods under high load. It's a vertical attachment to a horizontal mill, and if I need to seriously move metal I use the horizontal mill.

Rick A

 

[Ubergeek63]

Does it have good power at low speeds, like for parting off and drilling big holes? I'd be interested in going that route (simpler than building a variable speed friction drive), but the 20a variacs I've seen on E-bay start at $100 or so, plus shipping on something that heavy to HI. The higher voltage might not be a problem on a mill because I don't often run it for long periods under high load. It's a vertical attachment to a horizontal mill, and if I need to seriously move metal I use the horizontal mill.

Rick A

that is a problem. there are three things...

1 the need to be running at a reasonable speed to keep the motor cool so add a fan.

2 they are not easily controlled at low speeds.

3 consumer mills often have crappy controllers.

it would cost less if you get a gear motor rated for your use instead of using treadmill motors at 1/10 capacity. you probably have a 1HP motor and only need a 0.1 or 0.25HP

 

[Rick A]

What you say suggests I'd do best to stick to my plan to build a mechanical variable speed and run the motor full rpm. It's a 1.3 continuous hp motor (I understand these motors are rated VERY optimistically) which is not too much power when turning a 1" endmill or larger fly cutter. You need a wide speed range for a mill- I plan for 100-2000 rpm so it'd suffer at the lower speeds, like you say. I plan to slow down the motor with a 10:1 worm & pinion, then the variable speed drive. The two things I like about the treadmill motor are: I already have it and it's small size. The vertical miling attachment clamps to the overarm of the mill and a large, heavy motor is a disadvantage.

Rick A

 

[Ubergeek63]

What you say suggests I'd do best to stick to my plan to build a mechanical variable speed and run the motor full rpm. It's a 1.3 continuous hp motor (I understand these motors are rated VERY optimistically) which is not too much power when turning a 1" endmill or larger fly cutter. You need a wide speed range for a mill- I plan for 100-2000 rpm so it'd suffer at the lower speeds, like you say. I plan to slow down the motor with a 10:1 worm & pinion, then the variable speed drive. The two things I like about the treadmill motor are: I already have it and it's small size. The vertical miling attachment clamps to the overarm of the mill and a large, heavy motor is a disadvantage.

Rick A

that is a big range... you call a treadmill motor SMALL? what i was saying is that the treadmill motor that you have is probably a 1HP motor. you did not tell us about the speed range before... only about low speeds.

here is another thought: 5 Speed Drill Press

 

[Rick A]

Sorry I didn't make the situation as clear as possible, Dan. You're always looking for a certain number of feet per minute at the tips of the cutter teeth for a given material being cut, so a .125" cutter would run at eight times the speed of a 1" cutter, hence the wide speed range. When manufacturers used to make vertical milling attachments, they had large AC motors with stacked pulleys like the drillpress in your link. It made for a quite bulky unit, compared to which the treadmill motor and drive I plan is quite compact. There are times when I want to remove this attachment and it's about all I can handle with the treadmill motor on it.

 

[Ubergeek63]

Sorry I didn't make the situation as clear as possible, Dan. You're always looking for a certain number of feet per minute at the tips of the cutter teeth for a given material being cut, so a .125" cutter would run at eight times the speed of a 1" cutter, hence the wide speed range. When manufacturers used to make vertical milling attachments, they had large AC motors with stacked pulleys like the drillpress in your link. It made for a quite bulky unit, compared to which the treadmill motor and drive I plan is quite compact. There are times when I want to remove this attachment and it's about all I can handle with the treadmill motor on it.

well there are a number of alternatives and the most compact would be a manually changed gear ratio. production equipment would have automated tool changes so could not use that method. like it or not, the treadmill motors are not rated properly for what you are trying to do. you will at the very least need to add cooling fans.

the torque is proportional to the drive current ... unfortunately so are the copper losses in the motor and at low speeds there is no airflow from the integrated fan blades.

 

[Rick A]

Actually, the horizontal mill on which this attachment mounts has a 13-speed gear transmission which is fairly compact for the range it covers- it drives the table, but I'll never see another- the mill is near a century old and there aren't many others like it out there. What I intend to use is opposing cones with an idler wheel between them; it's a design that was used on some drillpresses long ago. Since the motor will be turning full speed all the time and won't run under load for long periods, I'd think it'll run cool enough. When I used it before the controller quit, it never seemed to get even warm. Usually, it's not loaded up all that much, but occasionally I need it to work pretty hard. Picture the head of a Bridgeport mill scaled down and you can envision what I'm doing. In fact, Bridgeport started in business making vertical attachments like this.

Rick A

 

[Ubergeek63]

Actually, the horizontal mill on which this attachment mounts has a 13-speed gear transmission which is fairly compact for the range it covers- it drives the table, but I'll never see another- the mill is near a century old and there aren't many others like it out there. What I intend to use is opposing cones with an idler wheel between them; it's a design that was used on some drillpresses long ago. Since the motor will be turning full speed all the time and won't run under load for long periods, I'd think it'll run cool enough. When I used it before the controller quit, it never seemed to get even warm. Usually, it's not loaded up all that much, but occasionally I need it to work pretty hard. Picture the head of a Bridgeport mill scaled down and you can envision what I'm doing. In fact, Bridgeport started in business making vertical attachments like this.

Rick A

sounds reasonable... as i said, if you are using a full drive size your motor for max load and you will have a lighter result

 

[Rick A]

It'll take awhile to put the whole thing together, but I'll post a pic of it if it works. Thank you for all the helpful suggestions.

Rick A

 

[Ubergeek63]

It'll take awhile to put the whole thing together, but I'll post a pic of it if it works. Thank you for all the helpful suggestions.

Rick A

not a problem