# Why connections to both A and S on series motor controller?



## chansen (Mar 13, 2009)

Anyone know why controller (mine is a curtis) have connections to both the A and S terminals on a series motor? You would think that since the rotor and stator would be in series (duh) that only two connections to the motor would be required.


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## frodus (Apr 12, 2008)

A1 and A2 are for the armature, S1 and S2 are for the field. You have to connect them in series yourself. This way the user can determine what direction they want to spin the motor by wiring A2 to either S1 or S2 and have M+ go to A1 and M- go to S2 or S1 respectively. This is the only way to change the direction in a series wound motor. Changing polarity does nothing.

If there are B-, B+, M- and A2 connections on the controller, it means that the controller utilizes plug braking.

Have you read the manual for your controller?


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## chansen (Mar 13, 2009)

Thanks - that was what I was thinking, but looking at the Curtis schematics got me thinking that there might be some feedback to control the PWM frequency or current.

I have not set my car up for plug braking.


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## frodus (Apr 12, 2008)

oops, reread my post, I changed it a little to be more clear.

Just an FYI, when asking questions about motors and controllers, it always helps to provide a part number/model so we know what we're helping with.

What controller and motor?


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## chansen (Mar 13, 2009)

curtis 1221C and warp9.


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## frodus (Apr 12, 2008)

Yep, thats for plug braking. I don't think you have to connect the A2 connection, read the manual for more info.

FYI, manual is here:
http://curtisinst.com/index.cfm?fuseaction=cProducts.DownloadPDF&file=1209%2Epdf

read section 3, it fully explains the plug braking feature.


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## rmay635703 (Oct 23, 2008)

There are a couple controller that use both to perform automatic field reduction (though not curtis that I know of)


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## Woodsmith (Jun 5, 2008)

I pondered the same thing myself with my Curtis 1214 controller and series motor.

The manual didn't really say much about what the connections to the motor do. The plug braking was only mentioned in the programming and signal connections side.

I will be using plug braking on my tractor project and motor reverse controlled from the controller. 

I will probably use all the controllers features at some point including pedestrian control just to see what it all does.


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## EV-propulsion.com (Jun 1, 2009)

here's an official answer I received from a curtis engineer a while back:

"_Although the controller manual shows an A2 connection between the controller and motor, this connection should not be included. Plug braking on the 1231C at high voltages is not stable. Even if it were stable, plug braking while driving on a road is a dangerous maneuver. Reverse should be handled via the vehicle’s transmission. The manual has been in need of an update for years."_

_M_ike
www.EV-propulsion.com


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