Treadmill Motor

[nhengineer]

Lots of great ideas about re-purpose of treadmill motors on this forum. I've found they can be from 90 to 130VDC and more that 2½HP. The last treadmill I took the motor from had a transformer choke wired to it and maybe the others did too but I missed them.

Question:

If I re-purpose the motor do I also need the choke even if I used the homemade SCR drive described in other threads?

Point of Interest:

The treadmills with incline have a boss 120V gear-motor with pinion, small rack and one I found even had a photoelectric position sensor on it. I'm sure to find a use for that. Does anyone know how to find out what the pinion pressure angle so I can get a longer rack?

You all would be amazed at the treadmills that are scrapped. One was still in the original box, not even assembled yet. I love rich people.

[bruce.desertrat]

I have been told that including the choke makes the motor run more smoothly when powered via a basic diode bridge "DC" power source or SCR controller.

[Crusty]

Yup. A bridge rectifier typically outputs a lot of ripple so a filter capacitor or a choke is usually used to smooth out the ripple for a more constant DC voltage and a more constant running motor.

[Eaglewood]

I tried the scr/bridge rectifier route but the brushes arced badly. Didn’t try a choke or cap.. I found a treadmill with a controller that has terminals that output 80/160 dcv so I am waiting for a $20 dc controller to arrive to see if that cleans up my act.
Dick

[Frank S]

I have 2 treadmills that I am currently disassembling 1 is an older unit with a 1750 RPM 120/240 volt cap start cap run 1 1/2 Hp with a variable pitch drive pulley the other has the 130vdc 2hp magnet motor in it I don't know how much any of the electronics in it will be of any use as it sat out in the weather for several years but both machines have quite a bit of useable steel in them as well as the rollers and bearings so like butchering a hog I will try to save everything but the squeal.
the 1 1/2 Hp AC motor runs as I've already tested it too bad it wasn't a 5 or 6 hp as I need 1 of those to build a belt grinder which will wind up being a combination centerless grinder / flat face sander and pipe notching machine but I have a couple of 8 hp 3 ph motors that I was planning on making a 16 hp rotary phase converter out of

[DIYSwede]

It isn't just the scr's/ regulators or whatever is upstream that put out ripple -
what really arcs and fries the commutator is the back-EMF from the turning rotor coils themselves,
who give a nasty HV return spike when the brushes releases,
thus necessitating the caps from each terminal to ground & also between the terminals.

Then quite a few manufacturer's don't even install them, as they're more into selling than the longevity of their products.

AFAIK a single "ferrite donut" is merely trying to protect the motor controller from that HV hash & RFI compliance,
whilst letting the motor fry itself to to death, to the lively cheer from the motor producers & service staff.

Personally, I cram in as big caps, as close I can as possible, on any DC motor I use -
but then I'm only just another DIY cheapskate.
Caps: <10 muF total non-polarized small ceramics and biggie plastic, max VDC at least twice the applied.

Cheap idiot test to see if your snubbing caps are adequate:
1) Run motor naked (without suppression) and listen to an AM radio tuned between stations. Behold the arcing!
2) Install caps and watch if/ when the arcs fade out - listen for less noise on the radio.
(If you're into scientific method, measure comparatively the radio's speaker output with an AC voltmeter!)
3) Try adding, or even bigger caps.
4) Rinse and repeat the steps above 'til satisfaction, or you reach "the diminishing returns point".

2 cents

[Carnel]

Tricky stuff. A choke keeps the current running at the moments the SCR or the bridge diodes are closed. But where does this current came from? If there is no suitable source, very high voltages surges will occur and your electronics will die. So in a well designed circuit a flywheel diode is a must. For 50 or 60 Hz supply voltage I would recommend to use the choke for a more smooth and silent running. Connect a diode between the choke input connection (at the SCR/bridge side) and the mains return, with the cathode to the positive pole and anode to the negative pole. So for the normal motor voltage the diode is not conducting. The result is that the current is kept alive through the diode when the bridge or SCR is closed. Of course the diode must be specified for the peak voltage of the grid and the maximum motor current. Take ample margins!

[nhengineer]

Yup. A bridge rectifier typically outputs a lot of ripple so a filter capacitor or a choke is usually used to smooth out the ripple for a more constant DC voltage and a more constant running motor.

Crusty, is the transformer choke wired in series with one of the DC legs or what? I'm an ME and some of this electrical stuff is mystifying.

[nhengineer]

Tricky stuff. A choke keeps the current running at the moments the SCR or the bridge diodes are closed. But where does this current came from? If there is no suitable source, very high voltages surges will occur and your electronics will die. So in a well designed circuit a flywheel diode is a must. For 50 or 60 Hz supply voltage I would recommend to use the choke for a more smooth and silent running. Connect a diode between the choke input connection (at the SCR/bridge side) and the mains return, with the cathode to the positive pole and anode to the negative pole. So for the normal motor voltage the diode is not conducting. The result is that the current is kept alive through the diode when the bridge or SCR is closed. Of course the diode must be specified for the peak voltage of the grid and the maximum motor current. Take ample margins!

Carnel, would you be so kind as to provide a schematic?

[tonyfoale]

Others have commented on the current smoothing effects of a series choke and parallel capacitors for voltage smoothing and arc suppression so i will not go into that again.
i just want to point out an aspect that I have never seen mentioned and which depends on the use to which the motor will be put. Many applications do not require perfectly smooth velocity over a revolution, these include tools like a drill press and lathe for example. However, if you want to drive a grinding wheel and achieve great results then you need the motor to spin as close to constant speed during a revolution as possible. If you use an SCR or thyristor controller then at less than full speed you will have a very spikey supply which requires a lot of smoothing. On the other hand if you use a PWM controller then the higher carrier frequency will be much easier to filter and you will need a much smaller choke with minimum iron in it. Of course a PWM controller is also fine for a drill or lathe.
So why are SCR controllers used at these power levels? It is simpler older technology and until relatively recently was cheaper, but nowadays PWM controllers are cheap enough so I see no reason to not use one.