Using a PS1 Board Pullmor open frame AC motor: UPDATE: Success!

Wow, you're treating Lionel's universal series wound motor like a prototype traction motor. Traction motors used in locomotives are DC universal motors are very similar in construction and operation to Lionel's motor. From what you describe is separate excitation of the armature and field rather than having the armature and field windings in series. 

Does the field winding rely on the resistance of the series circuit from the armature to reduce voltage to the field, so am I applying too much power to the field with it wired directly to the pickups through the bridge?  I thought the bridge would provide a bit of voltage reduction. 

Yes.

You could wire the motor in series from the PS1 board. Often the motor leads are red and black, but it looks like yellow and white from the PS1 board in your picture. For example, you can attach the yellow wire from the board to the left brush holder. Then run a wire from the right brush holder to the center lug which the field winding also attaches. Then the other side of the field wire will attach to the white wire. In this case, the motor will be wired in series and operate off of DC fed from the PS1 board. Problem is that the motor will not reverse. 

I think the easiest way to have the motor reverse is to wire only the armature into the PS1 board. That way the PS1 board will change polarity fed to the armature. You would have a separate rectifier for the field. You would wire the rectifier to the track which will feed the AC from the track to the rectifier. Then you would wire the field to the rectifier which will feed DC to the field. Polarity to the field is fixed while polarity to the armature can be reversed thus allowing the armature to spin in both directions depending upon the polarity fed to the armature. The problem is that you do not need 18 V to the field. You probably only need 6 V or so to the field so you will need to find a way to drop the voltage down from the track to the field winding. You could put a resistor into series with the field but that may produce a lot of heat at the resistor. Another issue that even when the motor is "off" the field winding is still being powered. 

Cool project. 

The series winding diagram is correct.  The shunt winding diagram will draw too much current, 2-3 times what it was designed for, causing an overload on the power supply and overheating of the armature & field.

Wire it up w/o the PS board 1st, as in the diagram, to see what you can expect from it operationally, powering the entire circuit from a transformer through a second full wave bridge rectifier.  switch the - & + leads on the transformer rectifier to switch direction.

@WBC posted:

...I think the easiest way to have the motor reverse is to wire only the armature into the PS1 board. That way the PS1 board will change polarity fed to the armature. You would have a separate rectifier for the field...

This would work if you had a twin motor loco, powering the fields in series from a full wave bridge, and the armatures wired in series to the PS board.

With just one motor, you need the field & armature in series.

Ok so before I saw these replies, I tried reversing the position of the bridge, so now the armature is wired directly to the rollers through the bridge (so armature polarity is constant) and the PS1 motor output leads go to the field, so I can regulate field DC voltage and polarity using the throttle, and armature DC voltage is always based on rectified track voltage.

And... So far so good! Motor runs MUCH cooler, and all PS1 functions work great! Starting and accelerating is almost as smooth the can motors in my real PS1 engines.

So now, given the above responses, (thanks guys for the tips) am I over-powering the armature by having *it* go right to the bridge? I wouldn't think so, since the armatures pull non-rectified AC current right from the track. What's the relationship of AC voltage to DC through a FWBR? Just don't want to damage the motor, but I'm going on about 20 minutes constant running at 11 volts from the transformer (which is pretty fast) with no performance issues! I suppose if the rectified DC voltage can get too high, I can just be sure to limit throttle to something less than what the KW outputs.

Also, I measured the running current pulling the train seen in the video. With the two incandescent bulbs in the engine, two bulbs at the track (one at a switch and one at a lockon location) I'm pulling like 5.2 amps (with some spikes at around 6 when I start and accelerate). Seems like a lot for only 11-12 volts, so maybe I need to limit it there.

@ADCX Rob posted:

The series winding diagram is correct.  The shunt winding diagram will draw too much current, 2-3 times what it was designed for, causing an overload on the power supply and overheating of the armature & field.

Which exactly describes what I was seeing. But when I tried the series connection like your original from the older thread, I could NOT get it to behave. There was something that introduced a DC bias (had to be the bridge, right?) That would cause the engine to start normally, blow continuous horn in forward, go to neutral and start ringing continuous bell, go into reverse and horn would stop but bell would continue, go into neutral and all sounds stopped, then repeat with horn blowing continuous in forward again.

Since the PS1 boards are programmed to blow horn in positive DC bias and bell at negative, it makes sense that when the polarity of the motor lead outputs switched, something in the bridge diodes produced a constant bias depending on which side of the "AC" leg of the bridge was being fed. 

Would be nice to know where I messed up because if I can get them hooked up in series like you say, I'm guessing I run less if a risk of feeding too much voltage.

Very cool experiment indeed!  I'm going to print this thread and save it because I had been meaning to explore these alternatives myself!  I think, five to six amps is abnormally high.  If it got much higher, you wouldn't be able to start the train at all.  For comparison, an unmodified 8551 would probably draw 2 amps cruising with that train, maybe spiking at 3 to 3.5 on initial acceleration.

I honestly wonder how Lionel arrived at the comparative resistance of the armature and field.  Bob Hannon compiled a must-have reference book on Lionel motors that would give you values for comparison.  These trains were toys for children so I'm guessing Lionel's priorities 70 years ago were cool running (for longevity) and plenty of RPM.  As an adult I like my trains to run slowly and accelerate realistically.  If performance improvements are possible from these old motors, what's a few amps between friends!?    

Slightly off-topic but I once installed a 3-position E-unit into a loco with a double-wound field  (needed for a 2-position e-unit.)  The instructions said to leave one field winding disconnected.  But I wondered what would happen if I connected both field windings in series, so I tried it. 

The performance didn't improve, but it got me thinking about whether better control could be obtained by exciting the armautre and field separately.  In fact, I wonder whether the Electric Rail Road (ERR) AC commander and some of the solid-state E-units that are purpose-built for AC motors (such as those by Dallee) use this very technique to achieve improved motor control?

One way to experiment with relative voltage for armature and field would be to use a pair of Lionel No. 95 rheostats in series with the rectified DC.  One in the armature circuit, and the other in the field circuit.  Eagerly following this thread!

Bringing this one back...

Now that we've got an operational layout, I'm taking another look at this issue.

Although the engine runs OK, I'm still bothered by the excessive current.

I had the engine apart yesterday, and I measured about 1 ohm resistance through the field and 2 ohms through the armature. Since I am regulating the field voltage through the PS1 board, is there any current limiting that would keep the field current from going haywire? Then I could just put a 1 ohm 5 watt resistor after the bridge that powers the armature from the track voltage is and cut my current that way?

I ordered some 5Watt 1 ohm resistors with the aluminum heat sink housings that I could attach to the frame. Should I put one in line with the field (in one of the yellow or white leads from the PS1 board as well?)

I figure if I'm pulling 6 amps at 18V, then my resistance is around 3 ohms, right? So by increasing the net resistance by 1 ohm, I could cut the current to 4.5 amps? If I put a resistor in line with the field as well, could drop it even more?

@Jeff_the_Coaster_Guy posted:

I figure if I'm pulling 6 amps at 18V, then my resistance is around 3 ohms, right? So by increasing the net resistance by 1 ohm, I could cut the current to 4.5 amps? If I put a resistor in line with the field as well, could drop it even more?

With a corresponding drop in performance, yes.

@ADCX Rob: When you say drop in performance, I assume you just mean net power available to pull a train.  The thing ran really fast as it was and would pull as long of a train as we wanted.  I'm thinking a slower max speed pulling the same consist is acceptable, if it lowers the demand form the KW transformer and keeps some power available for me to run my other trains.  Or are you talking about some other drop in performance that should concern me?

Am I on the right track with the resistors?

Pulling power and top speed. Using resistors is just converting available energy/power into heat, so there will be a loss no matter what.

Alright I think I've got a winner. This weekend I put two resistors in, one in-line with the field that is controlled by the PS1 board, and one in-line with the armature.

I only bought 1 ohm resistors, even though I was measuring closer to 2 ohms across the field windings. And I couldn't fit more than two of them into the chassis.

In any case, I figured that some additional load for each circuit would more closely mimic the net resistance that the Pullmor AC motor would normally have when wired in series add originally intended.

I measured the draw at the transformer posts prior to adding the resistors. I was getting about 4.9 to 5 amps when pulling 15 MTH premier freight cars. After installing the resistors, it dropped to around 4.2 to 4.5. Not as much reduction as I expected, but maybe enough to allow the field and armature to run cooler for longer and leaves a little extra power on my KW to run the B side train.

So I closed it all up and let 'er rip for a while to see how well she runs. I can tell you, slow speeds and starts under loads are WAY smoother than running this guy on the original E-unit and feeding AC to the motor. It really behaves much more like my dual-can DC PS1 locos in the rest of the fleet now. You wouldn't know it's got an old growling open frame motor from the 70's in there!

After running for more than an hour continuously pulling that big 15 car freight consist, and a significant part of that running up the incline (which it had no problem with, BTW! ) I took it apart to check internal temps. It was warm, bordering on hot but still just cool enough to touch for a couple seconds before it got unconformable. The board itself was very warm, the resistors were hot as expected, but the motor was a pleasant warm without burning my fingers.

I'm calling this project done! Now I have a cheapo Lionel EP5 from the 70's that sounds and acts like an MTH EP5 from the 90's!

Photos attached so you can see how I crammed the resistors in. I also cleaned up my wiring a bit. Video showing a slow start and some running.

Thanks for the help @ADCX Rob and others! I now know how to convert an AC series wound motor to work with full functionality on a PS1 board!