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This Dynamic Braking Tutorial may be helpful. It has a good deal of information on controllers and links to other articles you might find informative.

At present the technical explanation of braking is overly simple but not inaccurate, technically. It simply doesn't mention current. Braking is actually caused by the magnetic field induced around the rotor windings from the current flow created when you short circuit the motor while it is running as a generator. The field produces a developed torque in the generator that is identical to the developed torque that spins the armature in normal operation as a motor.

Since the formula for developed torque gives some good insight on motor characteristics of importance to rewinders I have decided to go ahead and expand the tutorial to include a precise electrical explanation with at least one more diagram in the near future.

If all this is gibberish, that's why I kept it simple to start with, take a look.

Paul
Circuit TrustChrist
 

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Edo,

If you want to use electronic controllers they MUST MATCH the polarity of your track wiring. Swapping the controller leads around at the driver's station will not make an electronic controller work if the polarity of the controller does not match the polarity of the track wiring.

As for your PM controller with the reversing switch I wouldn't worry about it too much just yet. Just set it aside until you can get to a track that you know for sure is wired with positive polarity and test it there.

Is this the controller you boght from Philippe de Lespinay at www.electric-dreams.com? I am surprised the page does not state what polarity track wiring the controller is designed for. If this is the controller it is clearly not resistor based so polarity will matter. I would contact PdL, I've spoken to him a few times and he has always been very helpful and gracious.

The same is true for Andy aka Professor Motor.

Between the manufacturers and the custom home tracks there just is no standard for the polarity of track wiring and probably won't be as long as people wire their tracks to work with the controllers they have. Most experienced racers that have expensive controllers are probably equipped to handle whichever polarity track they encounter, either with two controllers - one for each polarity - or a controller that is dual polarity or has a reversing switch. Less experienced racers will probably be happy if you have a decent controller - like the PMs - for them to use when they come over. Unless there is some reason you haven't mentioned, it probably isn't necessary to change the polarity your track normally uses.

Sorry for your day of frustration, seems like we always learn the most about stuff when it breaks.

Paul
 

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Hi Edo,

That's a beautiful controller! You do have a good reason to change your wiring - making your layout match the club tracks is a good idea.

I only see two possible reasons why your PM controller with the polarity switch will not work after you rewired your track to positive polarity. The first reason is maybe the switch is broken. Switches normally have a long life time but maybe this is the occassional one with a defect.

The second reason is maybe there is a mistake in the track wiring. I am not familiar with Carrera track - I use Scaley Sport. If you are still using a Carrera power track could there be something inside the power track that is causing the problem? With Scaley Sport there is a rectifier circuit in the powerbase so even if you changed the input polarity of DC to the powerbase the rectifier would always pass it with negative polarity, the way Scaley track is wired. To truly change the polarity you have to get rid of the Scaley powerbase and build your own wiring harness and driver's staion. Have you tested your track since you rewired it with a positive polarity controller to be sure the track wiring is correct?

I would do two things:

1. If you think there may be a problem with your conversion from negative to positive polarity wiring post your question about how to rewire Carerra track from negative to positive again, both in Tracks and Scenery and in the Master Class forum. You need to find somebody who has done this before, ideally somebody near you who could look at what you've done and make sure it is right. In your new post maybe you could include some pictures of your power track and driver's stations to show how you have run the wires.

2. Contact Andy at Professor Motor either by phone or by email, tell him about your rewiring, and describe in detail how the controller with the polarity switch is working now. He might be able to pinpoint whether the problem is in your track wiring or controller. If you go to Professor Motor's website you can find his email address at the link for joining the Professor Motor Club.

Good luck, Edo, don't give up and I'm sure you'll get everything working, it just takes time.

Paul
 
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