[cnc2]

if SBE, ex Motronics, doesn't find an old data sheet on it, post physical size and voltage/speed you got no load again in 1 single post. from that, various of us will be able to compare it to similar rated motors we design, build, sell, service, and be able to make close guess what its current, continuous torque, and max speed ratings are for you.

Hi mike_Kilroy,

Look at this pic, it's the motor on the right side of the pic:
http://img137.imageshack.us/img137/5914/cimg4044.jpg

It's a PMDC NEMA 34 size motor, voltage is 24 VDC but it has no current rating marked on it...its shaft is round & smooth with no key or flat surfaces, the end of the shaft is conical.

This motor seems to be quite powerful, I did try to stop it by holding the shaft with a thick piece of cloth it barely slowed down with little rise on the amp meter, I don't think it reached 3A, I couldn't stop it & the end of the shaft got hot from the friction with the cloth.

I couldn't measure the speed under load.

you'll find more pics in the first post.

Thanks !
cnc2.

[mike_Kilroy]

nice heavy duty looking motor.

the ticking may be result of its previous life maybe running in 1 direction all the time; that would seat the brushes in a way that if you run backwards they will click across the commutator bars. I would not be worried about the sound.

Answer these questions and I will give you a best guess of what your motor is rated:

- diameter?
- full length?
- rpm at some voltage?

OK, ur tach checker thing cannot measure speed. do it a different way then. is 24v on it too fast to count rotations of shaft in a given time like 10 seconds? then use jumper cables and put it on your car battery at 12v - can you count revs in given time now? still to fast? put a 1.5v D cell across it surely you can count revs in a given time now!!?? the longer the time the more accurate the result so see if u can count revs for 60 seconds. if possible give us the revs/time for multiple voltages if you want morre accurate motor specs; say 1 d cell, 2 d cells (3v), maybe a 5v power supply, etc. With multiple readings we can solve V=IR+Kb*N and get u better ratings!

[cnc2]

nice heavy duty looking motor.

the ticking may be result of its previous life maybe running in 1 direction all the time; that would seat the brushes in a way that if you run backwards they will click across the commutator bars. I would not be worried about the sound.

Will it disappear if I replace the brushes ?

Answer these questions and I will give you a best guess of what your motor is rated:

- diameter?
- full length?
- rpm at some voltage?

OK, ur tach checker thing cannot measure speed. do it a different way then. is 24v on it too fast to count rotations of shaft in a given time like 10 seconds? then use jumper cables and put it on your car battery at 12v - can you count revs in given time now? still to fast? put a 1.5v D cell across it surely you can count revs in a given time now!!?? the longer the time the more accurate the result so see if u can count revs for 60 seconds. if possible give us the revs/time for multiple voltages if you want morre accurate motor specs; say 1 d cell, 2 d cells (3v), maybe a 5v power supply, etc. With multiple readings we can solve V=IR+Kb*N and get u better ratings!

Well, motor's diameter is ~78mm length is ~124mm from plate to plate (these measurements were took using a plastic ruler but it should be accurate enough)

The mounting plate size is NEMA 34.

Why do you say that my "tach checker thing cannot measure speed" ? I used the RPM function which measures the wheel's RPM by counting every pass of the magnet by the sensor.

A quick test at 2.5V using a 1000mA power adapter, revealed that the motor is very slow and ticks & turns at a non constant speed, and voltage drops down to ~1V ~1.3V

At 3V the motor spins at a constant speed without ticking & the voltage drops down to ~2.5V ~2.6V sorry, i could not count the RPM accurately, it looks like it is between 1 & 2 rev per second....the bike's tachometer shows ~166 ~177 RPM ~3.1V becomes fluctuating between 3V & 3.1V

Edit: when I find more time I'll try to do some testing with my battery charger which has 6V, 12V & 24V at 10A & 5A

Thanks !
cnc2.

[mike_Kilroy]

if it is brush wear in 1 dir issue then yes, replacing them will stop the noise. it also could be worn down brushes but that should make the noise i both dir. also just running it for a while in the noisy direction should reset the brushes - no need to replace if not worn out. prob best to take then out and look to be sure they are not worn out.

OK for rating.... let me convert to english: 4.9" long, 3" dia. The torque rating of a motor goes up by the SQUARE of the diameter so this is pretty important to get right. The torque rating of the motor goes up only linearly with the length so that can be less accurate

Size comparison will get us close to TORQUE rating (nothing to do with speed or amps).


I am comparing it to a Kollmorgen TT-2031 brush motor of similar size )3"dia x about 5" long: .5/.6nm (4-6#-in) rating continuous.

MCG model ID3301 is 3.25"dia x 4.78" long rated .5nm (4.7#-in) cont.... similar....

So I'd say your motor is rated about .5nm or 5#in continuous.

Now for top speed. At 2.5v you got unsmooth motion, so most of the voltage went toward making torque instead of speed to overcome friction. V=IR+Kb*N. so we want it to rotate fast enough that the IR (torque producing portion) is small compared to the speed producing portion. So we will ignore the 2.5v run for now. somewhere around 3v you got somewhere around 120-160rpm; lets say 150. so the motor constant Kb is 3v/(.150krpm) or 20v/1000rpm. So being rated 24vdc on the nameplate, I would venture this motor is rated about 1500rpm top speed. If you do run it at the higher voltage with the bike tach, this can be made a bit more accurate.... but not sure if tht is so important to you...

motor Kt rating is same as Kb just in different units, so we can now find the motor current rating from Kb and cont torque rating. Take on faith that Kt=Kb* .085 in our units. so your motor Kt is 1.7#-in/amp. Since it seems rated around 5#-in torque, its current rating is 5*1.7=8.5amps.

So you have an 8.5amp cont, 5#-in, 1500rpm max speed, 24vdc brush motor.

If you want to check some more, you can put a torque wrentch on the shaft (or use pulley and weight like Al's link) and measure the current into the motor as you load it upto 5#-in torque; you should get around 8.5amps. If you leave this on it and watch the motor temp, it should not get too hot to keep your hand on it for about 3 seconds; if it does, our torque and amp rating is a tad too high. If it does not get this hot then our torque and amp ratings are a tad too low. But for cards I think if you used a 8amp cont/16amp peak 24vdc output drive like a small AMC you would run this motor very well.