Replacing open frame magnets with new rare earth magnets

[emdmike]

Thought I would start a new thread for this topic as it kind of overtook a previous thread of mine about something else.  I got new rare earth magnets from Micromark to replace the weak Alinco magnet in a Pittman motor in a brass steamer.  The motor was ok other wise.  But was weak torque wise and ran hot.  Running them hot to long breaks down the varnish around the wires in the armature.   I had a can motor and in fact tried in in the model, believe it or not, the open frame is quieter once tuned along with fresh magnets.  I put 5 of the magnets up against the center bulkhead. I tried 10 magnets to totaly fill up the space taken up by the old magnet.  It actualy ran poorly and was noisy.  Five magnets is the perfect amount IMHO.  You will need to use a piece of metal, in my case half of a washer to take up any open space above the magnets.  This way when you tighten up the screw to clamp them down, the magnetic circuit is complete.  One of these little magnets has more ummph then the one it replace.  So 5 of them really have some stick to them.  On the club layout, she drew 1/5 amp at 10 volts pulling 12 Atlas propane tank cars(the long 60'ish foot ones).  if I held onto the caboose so she slipped out, she only drew 3/4 of an amp.  Both well within range for DCC if I wanted to install a decoder.  This is also with a constant lighting circuit installed in the locomotive.  This will work with any open frame motor.  Most older steamers have such steep gear ratios that flywheels do not really help all that much if at all.  Motor brush isolation is all that is needed for DCC to be installed, normal just putting a piece of wire insulation over the brush hair spring to isolate it from the motor frame is the only modification.  The only other modification I preformed on the motor was to highly polish the communtator with a polishing ruby stone.  You can also fill the slots in the communtator with epoxy and file smooth to help quite brush noise.  Here is a pic of the rear of the motor peeking thru the cab.  Locomotive is a PFM/United AT&SF 2-8-0.    Mike

[mlehman]

Nice work. New technology that makes old tech even better. I don't have any need for this fix currently, but it's good to know it's around in case I ever have enough cash to dabble in brass again.

[hon30critter]

emdmike

I've replaced the magnets on a couple of steam locos and had similar positive results. I also experienced the same thing that you did when you tried to put in 10 magnets.

Here is where I got my magnets. I don't know what Micromark is charging but this source seems to have fair prices. EDIT - I just checked Micromark's prices out of curiousity. These are about 30% cheaper and you can buy the quantity that you need:

http://www.forcefieldmagnets.com/catalog/index.php?cPath=23_37&sort=0a&page=3&osCsid=9421e594d526d832ef6116c77e9d48fe

Dave

[bruce22]

Found mine at an electronics supply store at

[emdmike]

I got mine from where I did as it was more of an experiment to try and keep costs down when reworking brass or when the owner wants it to run, but not replace the original motor.  I am very pleased with the results. There used to be articles on how to tune open frame motors for the best performance, setting brush spring tension and getting your magnets remagnetized.  That last step really isnt an option anymore, espicaly with these little magnets.  If the open frame runs smooth without excess vibration from a tweaked armature, I will rebuilt rather than replace it unless the owner wants the new can motor and it can be installed.   Many modelers think replacing these older motors is required for DCC or for good slow speed operation.  I can call that myth busted!    Mike

[dstarr]

I replaced the tired Alnico magnet in an old PFM Mogul with the neodynium super magnets.  Worked like a charm.  The original motor ran hot to the touch and lacked torque.  With the supermagnets it ran cool and pulled hard.  It's an easy job, much easier than swapping in a can motor, and just as effective.  The only thing that makes can motors better than open frame motors, is a stronger magnetic field.  The magnetic path inside the can motor is shorter (it just runs around the can) which makes it stronger, and most can motors came thru from the factory with ceramic magnets which are stronger than Alnico. 

   The only trick to the job is to install the new magnets with the North pole pointing in the same direction as the old magnet.  If you get the magnet reversed the locomotive will run backward.  I used an old magnetic compass to determine the directions of the magnets. 

[trainnut1250]

Sounds like a good solution.  One question:  has anyone measured stall current after installing the magnets?  I have fried decoders with open frame motors that drew too much current at stall.

 

Guy

[emdmike]

The genuine Pittman DC70 in the connie draws 3/4 amp with the engine slipping out.  If you can stall the motor without spinning the drivers, then the motor is overloaded and any extra weight needs to be removed or a larger motor installed.  From 10 volts slipping thru 12volts full throttle it stayed at 3/4 amp on the meter.  Mike

[Ron High]

I have used the magnets in Hobbytown drives with DC 70 motors and their substitute motors. They work very well. I reduced current draw,got more power.and even better slow speed performance. Of course the Hobbytown drives are great performers any way ,now even better. I get my magnets from K&J magnetics they have 2 grades N42 and N52. The latter are stronger and a few cents more.I am not sure if I can determine how much performance difference between the 2 grades.

Ron High

[twhite]

Like Mike, I've used the Micromark magnets on quite a few of my open-frame older motors, and the difference is astonishing.  I've had good luck loading 10 into the motors, though it takes a little adjusting once you get the first stack in and working.  The photo shows the magnets in the motor of an old 1964 Akane AC-8 SP cab-forward.  The loco is so quiet all you can hear are the rods clanking, and the control in the speed range is superb--especially the slow speed control.  But I will agree with Mike, if 10 seem too much, 5 will work just as well.  I have 2 older PFM Rio Grande 2-8-8-2's that I've re-done, one with 10 magnets, one with 5.  Both have excellent control response.

It's seriously like installing a new, quiet can motor.  The difference is that you're getting much more power.  At least it seems so.  I really recommend them for extending the life of your open-frame motors (and quieting them down to practically nothing).

Tom