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Jeff Root
2012-Nov-19, 09:32 PM
I need help figuring out how the electric motor in a
handmade model train locomotive works, so I can get
it running again. My dad made it in the 1930's. I think
he got the motor from somewhere, but he made the
rest of it from scratch.

I don't know whether the motor is AC or DC, nor do I
know where to apply the power. There are some broken
wires. There are strong clues the locomotive was designed
to work on three-rail track, but the old track my dad has
that the locomotive does fit on has only two rails.

Here are six photos of the locomotive, plus more details:

http://www.freemars.org/jeff2/motor/motor1.htm

Anything you can tell me about what I need to do to get
it running again?

Thanks!

-- Jeff, in Minneapolis

Hornblower
2012-Nov-19, 09:48 PM
I need help figuring out how the electric motor in a
handmade model train locomotive works, so I can get
it running again. My dad made it in the 1930's. I think
he got the motor from somewhere, but he made the
rest of it from scratch.

I don't know whether the motor is AC or DC, nor do I
know where to apply the power. There are some broken
wires. There are strong clues the locomotive was designed
to work on three-rail track, but the old track my dad has
that the locomotive does fit on has only two rails.

Here are six photos of the locomotive, plus more details:

http://www.freemars.org/jeff2/motor/motor1.htm

Anything you can tell me about what I need to do to get
it running again?

Thanks!

-- Jeff, in Minneapolis

If you so wish, I can e-mail the link to my fellow model railroad club members. We have some pretty sharp technical people who might be able to help. That motor is a complete mystery to me.

Jeff Root
2012-Nov-19, 09:59 PM
That would be good. I am just about to search for the
website / contact info for the model railroad club here,
in St. Paul, too.

If you'd rather e-mail than PM, I'm jroot at freemars
dot org.

-- Jeff, in Minneapolis

Trebuchet
2012-Nov-19, 10:08 PM
The key may be in the device forward of the motor, which appears as if it may be a transformer. If so, AC. I'm seeing five terminals on it, three on top and two on the left side. Perhaps it's putting out two separate secondary voltages. I'd be taking a voltmeter to it and seeing what's connected to what.

Jeff Root
2012-Nov-19, 10:20 PM
Can you tell me more about that? I've never heard of
a transformer so small until the last few years, so I'm
flabbergasted that my dad made one in the 1930's.
It fits what he said about it. How would it work?

I'll bring my multimeter when I visit for Thanksgiving.

-- Jeff, in Minneapolis

cjameshuff
2012-Nov-20, 12:05 AM
What you have here is a reversible DC motor.

The stack bolted up front is a selenium bridge rectifier. You will probably want to replace it...it's likely gone bad, and the failure mode of selenium rectifiers was an infamously smelly and rather unhealthy one. It's delivering DC of fixed polarity to the field coil. (They did this before strong, long-lived permanent magnets became cheap...permanent magnets made of iron were too weak and tended to demagnetize.)

The motor commutators are split into the common thirds arrangement used to switch current between the coils of a DC motor, and I can't see for sure, but I'll bet the brushes aren't hooked up to the rectified power from the bridge rectifier. This lets you reverse the motor by reversing the applied voltage...otherwise, the field coil would reverse too, and the motor would turn in the same direction regardless of the polarity.

Strange
2012-Nov-20, 12:38 AM
selenium ... infamously smelly and rather unhealthy

"Nauseating beyond description" and seriously toxic too. What's not to like? :)

Antice
2012-Nov-20, 12:40 AM
Hmm.. After studying all the pictures for a while and noting down some detail i think i can give you a pretty good answer.
I give no warranties tho.

First I'l shed some light on a few of the known components there. this is indeed a very very nice engine. notice the sandwiched metal plates? those are parts of an electro magnet. they are in fact the iron core of a horseshoe shaped electromagnet. been a while since i saw one of those. modern engines generally use a pretty different design.
Notice the copper winding's that is mounted across and around the stack of plates? that is the coil that generates the magnetic field in the horseshoe magnet. this coil should have 2 wires going into it if i am right.

In the last picture you can actually see one of the brushes that connects to the rotor coils. This rotor has 2 coils it seems (as opposed to having only 1). and as the motor rotates the coils are alternately powered for the time they spend in contact with the brush.
I wonder if there is another brush on the other side as well? I think there should be one. if not then it must be replaced before it will work

The next item. the black coil like thing that all the wires emanate from I am much less certain off. It might actually be a solid state DC voltage regulator. if so it's basically a resistor with multiple outputs.
one can make such a circuit by using a bolt, wrap it in paper an put washers on it. the more washers between the connections the higher the resistance measured between terminus's.
The more resistance that is coupled in parallel with a coil the more amps will pass into the coil instead of trough the resistor.
I noticed that the big coil was connected at both of the ends of the black thing. that makes sense for this theory since the electromagnet is a bit of a power hog.
I bet that the smaller coils on the rotor is connected somewhere in the middle of it as well as on one of the ends. the chassis itself should also be connected to one of the ends, with the pickup being connected on the other side of it.

On the first picture you can see one wire coming out of the assumed voltage regulator and into both what appears to be a brush as well as one end of the big coil. I believe this is the ground return line. for the coil and rotor. I cannot say for certain without fiddling with the thing myself unfortunately... (I would really loved to do that, but alas. I'm just so far away it's not possible)

Going by what one can see in the pictures this is definitely a DC motor if my hunch about the black coil like item is indeed correct.
you can test that by measuring the resistance between the different connectors. it should go from low to somewhat higher the further apart you measure. I do not know if your father made this one part himself or not. but if it's very old it might have dried out so much that it is short circuited. try running the engine with a modern voltage regulator circuit to test if the motor rotates at all when powered before attempting to run the train with this old one.
Do not use it if it is fully shorted out tho. A short circuit here will make the motor run amok and maybe even do a rapid self disassembly if you don't stop it in time.


ETA: The selenium rectifier thing seems intriguing. but one that small back then? in both cases putting power to it is a bad idea tho. take it out and have someone with old time experience with these items look at it.

cjameshuff
2012-Nov-20, 12:47 AM
Another note...there's no need for a close replacement in this application. Any silicon bridge with sufficient current capacity ought to do as a replacement. Radio Shack carries some with a hole for bolting to a heat sink (unnecessary here, but useful for mounting) for a few dollars, generally with max current ratings that you won't come anywhere close to...that little selenium bridge likely couldn't handle more than 100 mA.

Also, it's possible the rectified voltage is going to the rotor coils with the field coil changing polarity to switch direction...either way will work.

cjameshuff
2012-Nov-20, 01:17 AM
The next item. the black coil like thing that all the wires emanate from I am much less certain off. It might actually be a solid state DC voltage regulator. if so it's basically a resistor with multiple outputs.
one can make such a circuit by using a bolt, wrap it in paper an put washers on it. the more washers between the connections the higher the resistance measured between terminus's.
The more resistance that is coupled in parallel with a coil the more amps will pass into the coil instead of trough the resistor.

The setup you describe would be practically a dead short...maybe a current shunt, but not a resistor for controlling current through a motor. I suspect you are thinking of a wire wound resistor, not stacked washers. Carbon disks would be a possibility, though I've never seen a resistor constructed that way. Or an actual rectifier, as some applications use the forward voltage to provide a voltage reference or low-current regulated supply.



ETA: The selenium rectifier thing seems intriguing. but one that small back then? in both cases putting power to it is a bad idea tho. take it out and have someone with old time experience with these items look at it.

They only needed to be really big when they had to dissipate significant power, and then it was mostly radiator fins. It might be a copper oxide rectifier, which used the same construction with different materials, but that's a quite standard bridge rectifier design...a 5 terminal stack of plates, the outer two terminals shorted together to make a 4-terminal bridge.

ShinAce
2012-Nov-20, 02:22 AM
At first glance it looks like an induction(AC) motor, but the brushes in the last photo are a giveaway that it's a 3 pole DC motor. In which case, change the rectifier. You will need to buy a bridge rectifier to replace it.

Jeff Root
2012-Nov-20, 02:46 AM
This is terrific! At the very least, I'm in a better position
to ask my dad questions about it and possibly make sense
of any answers. I can ask him if he remembers making the
black round thing, and if so, how he made it. I can look
at it more closely to try to see how it was made and what
materials are in it.

He said something about it taking ten volts. I have a
transformer and rheostat that, if I recall correctly, goes
up to twelve volts. Any suggestions about connecting it
without burning anything out? What should I test with
my multimeter before and during application of power?

-- Jeff, in Minneapolis

Jeff Root
2012-Nov-20, 02:55 AM
To paraphrase Brent Spiner in 'Independence Day':
I've learned more about this motor in the last five
hours than I have in the last fifty years.

-- Jeff, in Minneapolis

Hornblower
2012-Nov-20, 03:16 AM
I just e-mailed the link to the club. I just noticed something else. The trailing truck appears to be upside down. The frame could snag the rails anytime you go over a switch.

Jeff Root
2012-Nov-20, 03:56 AM
I don't know if it's upside down, but I've often got that
impression from looking at it myself. It does fit on the
straight track okay, but is *very* fussy. I figure that will
sort itself out when we get to it. I'm still wondering if
there are pieces missing. At the front end, in the first
photo, you might notice that the "cow catcher" is turned
90 degrees out of position. It is broken off and I just
left it sitting there on the little platform as I started
taking the photos.

-- Jeff, in Minneapolis

nota
2012-Nov-20, 07:28 PM
looks like a pitman motor
they were big in trains
and early slot cars esp drag race slot cars
but used a solid magnet by the 60's

tashirosgt
2012-Nov-27, 04:33 PM
My dad made it in the 1930's. I think
he got the motor from somewhere, but he made the
rest of it from scratch.


Ask him if he got the idea from plans in a magazine. There might be plans in an old edition of Popular Mechanics or in publications for Boy Scouts.

Hornblower
2012-Nov-27, 09:07 PM
Ask him if he got the idea from plans in a magazine. There might be plans in an old edition of Popular Mechanics or in publications for Boy Scouts.

I would try Model Railroader, which started in 1934.

baskerbosse
2012-Nov-28, 06:06 AM
Three rail trains do not have insulated wheels.
If there's a short between left and right side wheels, then 3-rail..