Series wired motors. Lesson learned.

If you're using command control, series winding really doesn't accomplish anything.  For conventional operation, that's a different story.

Hi Guys, when I use RailPro with it's full load current detection in MTH and Weaver engines that have the China drives, I always wire the motors in series.  The biggest advantage is reduced current draw which is half compared to parallel wiring.

Parallel draws twice the current draw but does have a higher top end speed.

If I am missing something please inform me.

Specifically, if you're using back-EMF speed control, the series wiring of the motors confuses the speed control logic.  In truth, parallel wiring does not have twice the current draw for the same given speed.  The difference is, you don't have the option of the higher speeds with series wiring.  That frequently isn't a concern, but it's worth mentioning.  The major reason most folks wire motors in series is to avoid the jackrabbit starts in conventional with standard train transformers.

@Don Sweet posted:

Hi Guys, when I use RailPro with it's full load current detection in MTH and Weaver engines that have the China drives, I always wire the motors in series.  The biggest advantage is reduced current draw which is half compared to parallel wiring.

Parallel draws twice the current draw but does have a higher top end speed.

If I am missing something please inform me.

Series wiring is poor engineering for the reason Chris discovered. If one wheelset looses traction, power is directed to it rather than the one that needs it. Reason, the faster a motor turns the greater the back emf which makes it appear as a higher resistance. Higher resistence equates to a higher voltage drop if you remember ohms law and resistors in series. 

As long as both motors are encountering the same load then voltage drops will be near equal. If your traction tires are in good shape and your layout is fairly level than you can get away with series wiring. Otherwise you may have find another solution.

Pete

Traction tires?

Dale Manquen came up with this nifty solution several years ago.  I thought it was common knowledge.  Like a limited-slip differential in a car, the circuit tames the tendency for a slipping motor to hog all the voltage.

I'm pretty sure you can find one or more threads dedicated to this subject here on the Forum.  I hope this helps but I've never been a fan of the "China Drive" diesels, especially the way MTH, Weaver, etc., geared them.  You can pack them full of fancy electronics, heck, you can even put a corrective lens on the Hubble telescope.  But it would be better if they had been designed right the first time!

yes, dual motored 'china' drives are problematic. but in a club layout environment where you run for hours during an open house. that setup is worthwhile. particularly with the long trains we run.

Series wiring cuts the voltage to each motor in half essentially limiting the speed of those "slot-car" type drives that come in some locos to about half over the whole throttle range.

I have used series wiring in 2 rail DC on my layout and been quite pleased with the results.   It does tame the speed and smooth the starts and stops.    My grade is about 1 1/2 percent on my main line.    I never had a problem with downgrades.    I did sometimes see the stall behavior on upgrades if the train was too heavy for the loco.    This would be prototypical.    If a train is too heavy, the real locos stall and spin the wheels.    

The solution is to add a second or third  unit to the consist - just like the real ones.   

Now on mine one unit could easily pull 12-15 cars on the grade.     So 2 units could do 20-25.    On my home layout, that is a long train.     I do have free rolling trucks on all my cars,    My grade is on a curve with 52 inch radius.   

I never had the issue with the locos stalling or running strange going down grade.     I have a pair of MTH AS616 locos that are wired series and they can work my mine branch which had about 3.5 % grade too.

@Ted S posted:

Dale Manquen came up with this nifty solution several years ago.  I thought it was common knowledge.  Like a limited-slip differential in a car, the circuit tames the tendency for a slipping motor to hog all the voltage.

I'm pretty sure you can find one or more threads dedicated to this subject here on the Forum.  I hope this helps but I've never been a fan of the "China Drive" diesels, especially the way MTH, Weaver, etc., geared them.  You can pack them full of fancy electronics, heck, you can even put a corrective lens on the Hubble telescope.  But it would be better if they had been designed right the first time!

Not sure how you'd integrate that with the "reversing circuit" that's just represented by contacts there.  It would obviously depend on the specific reversing circuit.  It's an interesting idea, but I think it would have to be "tuned" in conjunction with the reverse board to actually be practical.

In the case of Williams engines where most folks apply this series wired "fix" their E units do use relays so Dale's circuit should work. 

Pete

I'd beef up the transistors, those are 1A rated units.  I'm presuming the 1A rating is with an appropriate heatsink, so I'd be looking at something considerably more robust.

KSE44H11 TRANS NPN 80V 10A TO-220

KSE45H11 TRANS PNP 80V 10A TO-220

You still need a heatsink, but they won't die the first time you have a motor stall.

Traction tires and reversing units?  Did this slowly become a 3-rail scale thread?

@bob2 posted:

Traction tires and reversing units?  Did this slowly become a 3-rail scale thread?

...  ...

I've been meaning to ask you Bob; how do I install traction tires on my Varney Ten Wheeler?  

Mark in Oregon

@gunrunnerjohn posted:

I'd beef up the transistors, those are 1A rated units.  I'm presuming the 1A rating is with an appropriate heatsink, so I'd be looking at something considerably more robust.

 

John, would you be a hero (as you usually are!) and please redraw this schematic with the beefed up parts.  The one I posted was the best scan I could find and it's pretty crummy.  This circuit is part of Dale's legacy and it could be a valuable resource for some people.  Even with the lower-rated transistors I do believe it will solve the OP's problem, as wheelspin will prevent the motors from reaching their stall current.  (No rubber tires here!)  Thanks!!

If I am reading the diagram correctly, Dale’s torque balancing circuits are polarity sensitive.  That is why he shows the reversing circuit down stream from the balancing circuits. To use this circuit in a modern loco, would it not have to be incorporated into the motor control board so the reversing was done between the balancing and the motors?

Correct David, hence my comment about integrating it into the specific reversing board.  It's an interesting idea, but not "fully formed".

What are traction tires?    I have never seen them on a 2 rail loco.    I don't think they are necessary - just opinion.    I think if your loco won't pull the train, you put another loco on it just like the prototype.    And if your grades are too steep, make them less steep, just like the prototype.    over 2 % is steep on a model in my  opinion.    4-5% is way too steep for mainline modeling.    That is getting into logging RRs and shays and climaxes etc.

As for reversing boards,  you don't need them in straight DC.    However,  if you are using DCC, the decoder does polarity reversing because there is a chopped AC wave on the rails.    so 2 rail with modern electronics does have reversing boards in a way.