# Rebuilding Mantua Pittman motors with rare earth magnets



## tkruger (Jan 18, 2009)

I have a large collection of old Mantuas and started to rebuild the motors with rare earth magnets. Just what I have found. I have an amp and volt meter on each of my main lines. When I tested the locos I did so on each track. Both are powered by a MRC Sound and Power 7000, all DC.

First I converted a Berkshire and a Pacific. Results were basically the same with each. Replaced the magnet with 8 1/8x1/4x1/2 magnets (two stacks). Note that the gauges on my panel may not be accurate to compare to anything but themselves.

Prior to upgrade: 
70% throttle was required to start the locomotive.
60% to maintain minimum speed.
Amp draw between 2 and 3.
Amp needle 'jumped' frequently as the loco ran.
Once moving the throttle could be decreased to slow the speed but not to the point that the updated motors ran at.

Post upgrade:
40% throttle required to start the locomotive.
40% required to maintain speed.
Amp draw between 1.5 and 2 amps.
Amp gauge remained steady. 
Start point was as low as the throttle could be operated.
Top speed was the same.
Easier throttle control due to the range that the throttle can be moved through.
Easier switching since the starting speed is less and better throttle control.

The cost to do this was ~$35 for 50 magnets on EBay, enough for 6 locomotives.
Time is about 15 minutes to change the magnets. Rest of the time is whatever is required to dismantle the locomotives. I am happy with the results for the cost. There is no flywheel action but there is a momentum option on the transformer I use that can simulate this.

Note that even though the locomotives were in good working order prior to changing the magnets since I had them apart I did a complete clean and lube job. I the past the clean and lube did not make this much of a change but did provide some improvement.

I have ordered a can motor replacement and when I receive it I will compare it with the rare earth magnets. The can motor did run $35. We will see if the cost difference is worth it.


----------



## gunrunnerjohn (Nov 10, 2010)

It stuns me a bit to see that a typical HO locomotive requires 2-3 amps to start, even with a fairly long consist! I can run 30 cars behind a typical Lionel Legacy dual-motored diesel and not pull that kind of current!


----------



## DonR (Oct 18, 2012)

My Bachmann HO DCC locos draw around .5 amps each,
no sound.

Don


----------



## Sasha (Jul 8, 2012)

Our locos run right around 300 milliamps and the Athearn DDA40X runs at about 500 milliamps. We have to run more than 3 locos at a time to draw over 1 amp.

- Dad


----------



## ggnlars (Aug 6, 2013)

The up grade results sound great. You need to understand the units the current meter is presenting. You did not indicate if it was loco only or with some kind of load. Most healthy HO motors from that era will ha a start current between 0.3 and 0.5 amps. The stall current at 16 volts could be as high as 3 amps. The max load current might approach 1 amp. If your amp meter is reading correctly, then I would check for binding in the valve assembly. If it is sticky then the motor will be running at a high load. 
The deltas you quote sound great. The amp level needs some more understanding.
Larry
Check out my blog: www.llxlocomotives.com


----------



## tkruger (Jan 18, 2009)

Sorry, I need to clearify the amp meter readings. My meters are not accurate for the number of amps. What they are accurate for is comparing the improvement from one test to another. I think the marks on the card are wrong but not sure. What I listed is what they read. Note that I can repeat a test and get the same results each time. I use them more as a 'on a scale of 1-10 your loco draws X' rather than the exact amount it realy draws.


----------



## tkruger (Jan 18, 2009)

Cannot improve all motors.

I recently purchased an 'well loved' MDC Atlantic. Unfortunately the motor did not move the loco. Removed the motor and tested it without the loco. Found it did run. Also found the running gear while not running perfectly was not binding. Rebuilt the motor with the rare earth magnets, cleaned the com and oiled the bushings. It now rand better with power applied. Oiled and lubed the chassis and it was moving smoothly. Added the motor and at 100% power the train only creeped along. Motor also started to get hot. I think the magnets may have helped the motor to actually turn but there is something eles not right.


----------



## ggnlars (Aug 6, 2013)

Magnets only work on outside flux. For the motor to run strong, the inside windings have to be creating a strong flux as well. The heat is coming from the inefficient operation. If the brushes are good, the communicated is clean, and the rotor turns easily, then the windings are faulty. The motor was likely run hot for long periods, without the needed lubrication.

If that is the case, then a new motor is the answer. 
Great info,
Larry
Check out my blog: www.llxlocomotives.com


----------



## gunrunnerjohn (Nov 10, 2010)

What usually happens when a motor runs too hot is one or more windings short. That will run up the current consumption a bunch and also drop the motor power a bunch. Result is the motor gets hot and has no power.


----------



## tkruger (Jan 18, 2009)

gunrunnerjohn said:


> What usually happens when a motor runs too hot is one or more winding short. That will run up the current consumption a bunch and also drop the motor power a bunch. Result is the motor gets hot and has no power.


I think you are right about the winding being bad. I did everything else I could for the patient, noting else left but that. Unfortunately I have found out the 4-4-0 was made in the mid 50s and there are not parts. Looks like I will be Magivering something to replace the motor.


----------



## gunrunnerjohn (Nov 10, 2010)

Just rewind the armature.


----------



## T.C. (Dec 13, 2016)

I realize this is a old post and I may not get and answer but I have to ask anyway.
I noticed that there were two stacks of magnets installed into one motor in this post.
My question is how well did that work and were they trying to force themselves apart ?
When I tried to do this the magnets would try to separate from each other and flip.
When I allowed them to do this I got a weird reading from my compass, I think because they were attracting north to south .
So when I put them into the motor I didn't get a good north / south reading, but when I forced them togeather I got a really good "N" "S" reading.
I glued them together in the forced position and put them into the motor and it definitely has a cogging feeling when turned by hand ?
Anyone know what is the correct way to do this?
Thanks for any advise or suggestions
T.C.


----------



## gregc (Apr 25, 2015)

T.C. said:


> My question is how well did that work and were they trying to force themselves apart ?


at least when there is a single stack of magnets as shown in the image below, the magnets easily stack when aligned N to S.




T.C. said:


> When I tried to do this the magnets would try to separate from each other and flip. When I allowed them to do this I got a weird reading from my compass, I think because they were attracting north to south .
> So when I put them into the motor I didn't get a good north / south reading, but when I forced them togeather I got a really good "N" "S" reading.


the metal frame acts as a conductor for the magnet field, so that the field on opposite sides of the motor armature. Don't know how you might measure this with a compass.



T.C. said:


> I glued them together in the forced position and put them into the motor and it definitely has a cogging feeling when turned by hand ?


shouldn't have to glue them together. The north side of one magnet is attracted to the south side of another magnet



T.C. said:


> Anyone know what is the correct way to do this?
> Thanks for any advise or suggestionsT.C.


they should be stacked and aligned as shown in the image.

if they are wrong side up, the motor runs in the opposite direction


----------



## T.C. (Dec 13, 2016)

Thanks for the reply Greg
Actually I probably didn't explain myself well enough.
I was talking about a double stack of magnets 4 on each side left and right instead of one stack on the end.
When you try to arrange the stacked magnets so you have both north poles the same direction they will try to swap ends so you would have a N-S situation on each end .
I did get them glued together and into the motor and it now works much better than the one stack, it has more pulling power and less amp draw.
I did a search on the magnets and mantua/pitman motors and found that I did it correctly.
How did I know it was wrong? I used my compass, when held up to the motor to check the N-S readings it acted all confused like it wasn't sure weather it was reading north or south. Now it about bends the pointer getting to the pole your reading.
What I would do different though is just buy the 1/2"x1/2" cube as it would be much easier than the 8 stacked magnets I used.
Terry


----------

