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Old 02-27-2008, 11:22 PM   #1 (permalink)
Ford Escort 2.0
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Location: Alameda, CA
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Electricar - '89 Ford Escort LX Hatchback
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Series Motor - Speed vs Torque

I came across a statement regarding the correct connection of the field and armature posts on a series DC motor. One thing that I found interesting was this:

"where a series field (S1 and S2) is provided, the polarity of this winding must always be connected for the same polarity of the motor armature"

"Apply + and - to the same number post. + to A1 and S1; - to A2 and S2.
It's A1, A2+S1, S2 for torque, but A1, A2+S2, S1 for speed"

So, from a line drawing perspective, it would look like this:

+ A1::A2>>S1::S2 - for torque (where :: is the motor internal wiring, and >> is either a jumper wire or a Forward/Reverse contactor)

+A1::A2>>S2::S1- for speed.

Turns out that my motor was wired this way -

+S2::S1>>A2::A1- (which would be a torque setting, forward rotation)

In order to test out the 'speed' theory, here was my plan. First step is to change to 'speed'

+S1::S2>>A2::A1- (ends same - speed) But this would reverse the motor rotation, so I reversed the polarity at the ends:

-S1::S2>>A2::A1+ (ends still same - speed, opposite polarity = forward)

Oddly enough, the car went BACKWARDS in this configuration. I checked it several times to make sure I wired it according to the diagram. I did.

Well, no harm, no foul - I just switched it to 'reverse' and drove home. Same acceleration, same top speed In 'reverse' it swaps S1 and S2, so:

-S2::S1>>A2::A1+ (torque mode... ends opposite.) Essentially the way it was.

Back at home, I changed the polarity on the ends to make it 'go' the other direction -


Again, the car went BACKWARDS

Anyone out there have a spare series motor on the bench that can tell me if their motor turns the same direction if polarity is swapped in these two cases? I may pull out my motor to see, but if someone has one out already, it would save me some confusion...

Seems no matter what I do, this setup wants to be in torque mode forward, and speed mode reverse (the opposite of what I want to test).

The saga continues!

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