2 motor loco - serial or parallel?

[tebee]

If I build a loco with 2 motors, like a diesel with a motor in each bogie, am I better having two 12 volt motors in parallel or two lower voltage motors in series ? 

 

I see to remember that series is better from an electrical load  point of view, but can't remember why and have failed to work it out again from first principles.

 

So what do you think folks and why ? 

 

Tom

[Andy Reichert]

From a motor protection POV, if you place two lower voltage motors in series and one is stalled, the running motor will get almost double its rated voltage applied across it.

Andy

[kevinlms]

If I build a loco with 2 motors, like a diesel with a motor in each bogie, am I better having two 12 volt motors in parallel or two lower voltage motors in series ? 

 

I see to remember that series is better from an electrical load  point of view, but can't remember why and have failed to work it out again from first principles.

 

So what do you think folks and why ? 

 

Tom

It depends on what motors.

 

For example, I've previously double power bogied Lima diesels in the past. Those I wired in series and this dramatically improved the running & gave a very controllable top speed. There was no shortage of hauling power. In this case, this choice overcame the inherent problems of the standard Lima drive train. I would use this method if the motors used tended to run too fast.

 

But given the choice, I would prefer to use a central motor to drive both bogies, which of course is the method currently used by most R-T-R locos.

[SRman]

As Kevin said, Lima motors (and gearing) tended to run too fast and to not be very controllable at lower speeds, so wiring in series makes a lot of sense in taming them.

 

On the other hand, I double motored a Triang Hymek, with the earlier, pre-ringfield motor bogie design. These tend to use a lot of power and don't run all that quickly, so parallel wiring was the way to go - it works beautifully for me with one decoder controlling both motors, and will go down to the slowest crawl, has a good top speed and will pull the side out of a house!

 

I also have several Underground trains with two Black Beetles wired in parallel (again with one decoder for both). The Black Beetles have excellent slow speed running but don't have a very high top speed, and wiring in series would make them even slower, so parallel wiring was again the way to go.

 

Short answer, it depends on the motors you are using and their characteristics, as well as their maximum voltages, plus the gearing.

[34theletterbetweenB&D]

I would make the choice pragmatically, as answers 3 and 4 suggest. With the two bogies on track, and ideally the pick ups linked with slack flexible wire for most reliable current supply, try the motors wired for both series and parallel. Go with whichever performs best for you. If there is any mismatching between the motors, that needs to be fixed before installation in a single body, or you will only have to dismantle and sort it out to cure erratic performance.

 

But unless you already have the motors and/or there is some pressing reason for this choice of layout, I would be right there with KevinLMS in using centre motor and shaft drive to both bogies as the better solution.