Another Treadmill DC Motor Controller Question

Thread Starter

m98lee

Joined Nov 19, 2020
4
Hi All,

I'm not going to pretend to know anything about electronics. My hobbies revolve around motorcycles and cars ... so I could really use some help.

I've been restoring an 1944 metal lathe that currently has a 3/4 hp AC motor. I would like to be able to use lower spindle RPMs speeds without engaging the rattly back gear (and to be able to reverse the spindle occasionally). To that end, I've picked up a treadmill. It's PM DC motor is 90V, 4800 RPM, 15A.

I have read just about everything I can find here and elsewhere on the web, but I'm still confused. Here's a KB KBIC-125 controller I think might work (specs here) -- especially if I use the auxiliary heat sink -- but I wonder if you knowledgeable folks could confirm this. The treadmill was advertised (in 1994) as "2.5HP", which exceeds the maximum spec for the controller, but that may not be an issue -- am I right? Also, what resistance "horsepower resistor" should I get for that motor?

Thanks a million for any help!
 

MaxHeadRoom

Joined Jul 18, 2013
22,671
The only problem with the low end KB controllers is they are triac bridge controller and do not give the best control, especially at the low rpm ranges.
KB have PWM versions, which although a little pricier are the better choice.
There is also the option of picking up a T.M. controller that uses the MC2100 versions, around here, there is at least one T.M., not working, given away for free that is often the source of one of these boards, The earlier MC-60 is the same type of control as the KB-125.
IIRC If you pursue the KB , you will need the lowest resistance for that motor, you may only rarely use it in the high current, 2.5HP range. (current).
Any higher resistance value will limit motor capacity.
Max.
 

Thread Starter

m98lee

Joined Nov 19, 2020
4
Max, thank you for your quick reply. Just to be clear, I don't need all that horsepower (3/4 was fine), although given the current gearing, I would probably be operating the motor in the 500 - 2000 rpm range most of the time. If 500 rpm is too low a motor speed, I can correct for that somewhat with pulley sizing (am retaining the countershaft pulleys, and the back-gears work if I need to go super slow). I did look at the PWM KBWT-112, but it seems like this motor is beyond its range. Should I worry about that? Can I use the settings to protect it (and/or the motor)? Also, the KBIC-125 referenced above looks like it can be set up for some "braking" effect. I wouldn't want too much (screw-on chucks), but I would love to have a fairly quick stop if possible. In the KBIC series, would a slightly-higher resistance plug-in help with protection at the cost of lower power?
I see no reference to braking on the KBWT series. Wish I understood more about electronics!
 

Attachments

MaxHeadRoom

Joined Jul 18, 2013
22,671
The dynamic braking circuit needs some extra components as shown in P20/21 of the manual.
In conjunction with I1 I2 Inhibit terminals.
Max.
 

Thread Starter

m98lee

Joined Nov 19, 2020
4
Thanks, Max. If I went that route, I think I could wire that braking circuit up, possibly with a little help regarding the values. But I would love to know if you think the KBIC-125 can handle the size of that motor, and whether a slightly higher resistance on the "horsepower resistor" would add a safety cushion to the electronics. If so, what value would you choose?

I do appreciate that this is free advice, and I am *extremely* grateful for any help!
 

MaxHeadRoom

Joined Jul 18, 2013
22,671
You could probably get away with the 1hp 0.1Ω to be on the safe side, also you have a current limit adjustment, just that if you do alot of heavy machining, the controller may fold back on you, if so try the 1.5HP value (max).
The motor current is generally on the fairly low side unless really bogging it down with a heavy load.
Max..
 

Thread Starter

m98lee

Joined Nov 19, 2020
4
You could probably get away with the 1hp 0.1Ω to be on the safe side, also you have a current limit adjustment, just that if you do alot of heavy machining, the controller may fold back on you, if so try the 1.5HP value (max).
The motor current is generally on the fairly low side unless really bogging it down with a heavy load.
Max..
Thanks, Max! I'll give it a try.
 
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