Re: (ET) Elec-trak Digest, Vol 14, Issue 113

["David Roden" <etpost drmm net>]

On 30 Aug 2016 at 13:10, Briggs, Michael wrote:

> why would you now prefer to go with a 4QD compared to something like a
> Curtis 1204 ... 

Good question.

As I understand it, and I am not an EE, so please correct me if I'm wrong, 
but otherwise similar series motors generally have more inductance than 
either PM or sepex motors.

On the stage of motor design, you have  PM and sep-ex motors sort of 
milling 
around between center stage and stage left, while series motors are way 
over 
there on stage right.

Series ---------------------- PM --- SepEx

The Curtis 1204 is a series motor controller.  That's OK for golf cars, 
because most of them have series motors.  However, ETs don't have series 
drive motors. They have either sep-ex or PM motors.

It will work, people have done it, but a series motor controller isn't  
really designed to run PM or sep-ex motors.  At least, it should probably 
have an extra inductor in series with it.  Without that, the current 
limiting circuit may not do its job right.

OTOH, 4QD make PM motor controllers.  

In all fairness, with a 4QD and a wound-field ET, you still need to have 
some way of turning the field power on and off.  As it turns out, some 4QD 
models considerately provide a brake release output.  It turns on when the 
vehicle is supposed to move.  This is exactly what you need to energize 
the 
motor field, though you might need a relay if it can't sink enough current.

Also, 4QD make, as the name suggests, true four quadrant controllers  That 
means they can control 2 motors in 2 directions.  This is the way power 
chairs work (joystick forward, go forward; joystick right, go right) and 
it's exactly what you'd want for a ZTR tractor, if ETs were that.

ETs aren't ZTRs (duh), but 4QD also make true two-quadrant controllers.  
That's what I'd use.  With these, center on the potentiometer is off.  
Pull 
back to reverse, push forward to go forward.  You don't need a reverse 
switch, not even a microswitch hidden inside the lever like GE had on 
their 
original design.  I like that.  

Finally, Curtis controllers are made in China, and 4QDs are made in the 
UK.. 
I like that too.  (And Alltrax are made in the USA, or were last time I 
was 
paying any attention.)

But 'tis true that Curtis 1204s are cheaper, and VERY easy to get your 
hands 
on.


David Roden - Akron, Ohio, USA

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