KTM Pittman remotor question

1.13 amps running free, no load?……..that doesn’t sound right Gray, that Pittman should be sipping on energy running free……

Pat

Maybe a msicommunication.  motor installed on chassis running drive up on blocks with no load.

How’s the mechanism Gray??….is it smooth?…..I can usually get these to draw under an amp, dragging 20 cars via AC power and a bridge rectifier,…how does the gear box feel to turn it by hand? …..The KTM stock gear boxes although not the absolute best, are pretty good, …..

Pat

First, what you need to figure out is the stall current of two motors.  Keep the motor shaft from spinning and then apply 12 volts DC and measure the current draw.  This recorded value needs to be below the DCC decoder current rating.  The reason you measure stall current is because DCC motor speed control works on the PWM (Pulse Width Modulation) method.  PWM are pulses that are full on and off.  The higher percentage of on pulses versus off, the faster the motor spins.  This is a digital device, it only knows two states, full on or full off, so they employ PWM as a way to provide variable speed.  Even when the loco just starts out and not even rotating yet, it receives 1000s of full on /off pulses before the motor starts to even turn.  To the DCC decoder, this looks like a stall current situation and the electronic chips need to be able to handle this current draw at the "stall" situation or you will let the magic smoke out of the decoder motor driver chips.  Hence the stall current test on the motor that everyone talks about in the DCC world.  Old open frame motors can draw huge amounts of current in this stall test (in excess of 10 Amps) and more modern can motors generally draw a smaller stall current value, hence their wide spread use in the DCC world in order to keep the stall current as low as possible to stay within the DCC decoder current rating.

Here is a video from SoundTraxx on stall current:

https://youtu.be/7KbEVKZ2JhA?si=KzRzLetWg_yYaY1c

Next thing to realize is the magnet material in those old Pittman motors can lose their magnetism.  This is not evident until the motor has been run under load awhile.   Therefore, you can see the locomotive progressively run slower and slower and slower and if you feel the motor at this point, it will be hot to the touch to the point where you cannot keep your finger on it.  A properly running motor will never be too hot to the touch.  It might get a little warm, but not hot.  Something to consider before putting a lot of time in when doing a retrofit with an old Pittman motor.  Pittman switched to different magnet materials (such as neodymium) in their newer motors in the early 2010s to avoid this from happening, since their motors are mainly used in commercial and industrial applications.  The 3rd digit in your Pittman part number is a '1', which means you have the older magnet material.   A '3' in this location means you have neodymium magnet material.  A '2' can also be found here for an intermediate magnet material that was better than the original, but not as good as neodymium.  However, it can be difficult to find a motor with neodymium magnets in the secondary market, so sometimes you just need to try and see.

Scott

Seems to run free with no binding.  Ran pretty slow with just test leads on the pittman. slower than the CLW.  Maybe I misread a decimal point.  I'll try again.  If things are true, maybe that's why it not in someone else's locomotive.  Do you have a new equivalent pittman number?  I know Ametek wants a fortune for everything though. 

I'm running off an HO power pack, but that shouldn't have anything to do with anything except maximum output, which I would be nowhere close.

I never have been able to find or decipher Pittman numbers, even to try and find a newer version (which I would have to transfer the hex onto).

Another thing to check Gray, in addition to Scott’s comments, ….did you fiddle with the support bearing I’ve circled in your picture? ….if you have excessive drag on the drive line, that support bearing can get cocked easily if the screws got loosened for whatever reason,……

Pat

Only drive components touched were to motor to motor mount screws (obviously)  Nothing moved as far as motor mount or support bearing.

If the driveline is nice & smooth, and doesn’t require a lot of force to get it to start turning, then it’s quite possible that 9412 is trying to take a poop on you. ….if the 9412 size fits well in the shell, then a more modern equivalent would be 9432. Same size motor with better magnets ……almost impossible to find on the secondary market, and prepare for sticker shock trying to buy one from Ametek ( Pittman’s parent co. ) An alternative is a pretty decent motor available at mthpartsandsales.com …this is MTH’s equivalent to a 9432 type motor. …see the screenshot below for part number …

Pat

Bottom line up front: if you want DCC, just install a big decoder and leave the motor alone.

I'm guessing that the gear ratio is at least 24:1 (it would be useful to know for sure.)  A Pittman 9412 is a slow-turning motor, probably slower than the CLW motor that's in there now, so you're going to lose some top speed.  That may or may not be important to you.  The "1" in 9412 indicates that this particular Pittman doesn't have rare-earth magnets (which were probably introduced after it was made.)  You didn't mention if your Pittman has ball-bearings.  If the CLW is already a 7-pole motor, the Pittman may not be much smoother or more powerful, so there's no performance advantage in the swap.

A swap also introduces issues with form factor and driveline angle.  An open frame motor is asymmetrical.  Because there are no magnets nor motor case at the bottom gap between the poles, the armature shaft can lay down very close to the chassis and line up with that bearing support Pat pointed out.  If you install a can motor (*unless it's a gearhead motor) the output shaft is in the center and it's going to sit higher, which will mess with the alignment.  The gearbox itself will rotate to line up, but you'll have to make a new bearing support or a custom torque brace, etc.

Scott thanks for posting link to the video, but I don't agree with your logic 100%.  When a loco is starting out, even a heavy train on a grade with the slack stretched, it'll definitely be pulling some amps, but not "stall current" the way it's defined in the video.  Remember, Soundtraxx wants high sales revenue and zero customer claims of failed decoders.  So it's in their interest to sell you a bigger decoder than you can probably get away with.  In the video, the guy presses the loco into the track and forces the wheels to stop turning (it hurts me to watch this!)  In actual use that should NEVER happen!  A properly-designed loco should spin its wheels when it's overloaded.  This is a function of many variables: weight on drivers, gear ratio, motor torque, driver tire material, track cleanliness, etc.  USH are really well-engineered.  But if a previous owner packed extra lead in there, I would personally remove a little until you're confident that the wheels will spin when overloaded.

For decoder selection purposes, I would measure max current like this:  Hold the tender coupler or the boiler front and let the loco push against your hand.  SLOWLY increase voltage until the wheels alternately slip and grab.  Check your amps, and THAT's the max current that you're likely to see in use.  Your CLW is a permanent magnet motor, not a wound field "universal" motor, so my guess is that the DC current draw will still be well within range for DCC.  Plenty of space in the tender, so worst case stepping up to the next-larger size decoder might cost a few bucks more.  Think of it as cheap insurance.

If you had a ball-bearing Pittman 9434, or if you come back and tell me that the loco is geared at 16:1, then I would advocate for a Pittman swap.  But I'm guessing that your "Big Emma" is a pretty good performer already, and I don't see any reason that you can't convert her to DCC in situ.  My $.02.