[sdiy] Hall Effect transistor question

[Michael Bacich]

Hello guys,

I'm working on repairing an electric scooter that uses a linear Hall  
effect device as a motor speed controller  It's built into a little  
thumb-operated accelerator control on the handlebar.  Just to  
clarify, the Hall device doesn't connect directly to the motors, but  
is used to open some big pass transistors that are located inside a  
remote motor controller/heat sink box.  The unit runs on a  
rechargeable 36 Volt battery, and the two motors are rated at 150  
Watts each.

I'm trying figure out why the motors are not working, and it looks  
like there may be a problem in the little thumb speed control unit.   
I don't have schematics for any part of the scooter, but I'm going to  
reverse-engineer the thumb controller and draw my own tonight -- it's  
not too complicated.

Unfortunately, without schematics for the thumb controller or any of  
the larger system, I don't really know what kind of signals I should  
expect to be seeing inside the controller.  I don't have any  
experience with Hall effect devices, so can anyone fill me in on  
their basic function, and how they are typically wired?  Are the  
terminals analogous to Collector, Base, and Emitter in a bipolar  
transistor?  This device, BTW, has three leads.  I can't read the  
numbers on the device right now, since it's mounted in an  
inconvenient location -- I'm now working on removing it from the  
housing, hopefully without damaging it or  the cheap plastic housing.

Is it possible for me to do any testing on the Hall device without  
any biasing power connected to it?  That is, will my Ohmmeter show  
any change in reading if I read the device while moving the magnet in  
and out?  (without the power being applied)

BTW, I am only assuming that this is specifically a Hall effect  
device, since it is activated by small magnets that are moved by the  
thumb actuator.  I'm also assuming it's a linear device, and not a  
simple on/off device, since it's possible to smoothly and gradually  
change the motor speed from slow to fast.  Are there any other device  
types that might be used in something like this application that  
perhaps I am not yet aware of?

Also, there are actually two magnets in the thumb wheel:  one that  
rests next to one side of the device when the scooter is at rest, and  
which is pulled away from the device when you accelerate, and another  
which faces the opposite side of the device, and which is moved  
closer to it as you accelerate.  Thus, the two magnets would seem to  
have opposite effects -- possibly one magnet "pushing" the transistor  
open, and the other one "pulling" it closed?

And yes, this indeed Synth DIY -- the scooter is being used as a  
mobile platform for an electronic music performance setup.  It's  
going to be a lot of fun, once we get the motor problem sorted out.

Michael Bacich