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

["Robert" <euclid delhitel net>]

The Alltrax is basically an 'H' bridge generic controller. 'H' bridge 
controllers use all semiconductors to do the switching but you use twice as 
many drive transistors as a simple PWM motor controller so you pay a lot 
more for them, great for CNC stepper motors that have to change direction 
rapidly and often but even so there's no reason these things should cost 
$400. Now that my two tractors are mechanically restored I'm getting to the 
design stage of the controller which will be PWM driven by a uC that 
switches the direction through a relay when the motor stops so it's a 'dry' 
switch with no load on the relay. There's really nothing wrong with relays 
and they can last for decades if applied correctly. I expect my controllers 
to come in well under $100 each for the prototypes. Think about it how many 
times do you sit there and rapidly change direction.

Rob

-----Original Message----- 
From: elec-trak-request cosmos phy tufts edu
Sent: Sunday, August 28, 2016 12:00 PM
To: elec-trak cosmos phy tufts edu
Subject: Elec-trak Digest, Vol 14, Issue 113

Send Elec-trak mailing list submissions to
elec-trak cosmos phy tufts edu

To subscribe or unsubscribe via the World Wide Web, visit
https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
or, via email, send a message with subject or body 'help' to
elec-trak-request cosmos phy tufts edu

You can reach the person managing the list at
elec-trak-owner cosmos phy tufts edu

When replying, please edit your Subject line so it is more specific
than "Re: Contents of Elec-trak digest..."


Today's Topics:

  1. Re:  Elec-trak Digest, Vol 14, Issue 109 (David Roden)
  2. Re:  Elec-trak Digest, Vol 14, Issue 109 (Briggs, Michael)


----------------------------------------------------------------------

Message: 1
Date: Sun, 28 Aug 2016 06:31:18 -0400
From: "David Roden" <etpost drmm net>
To: elec-trak cosmos phy tufts edu
Subject: Re: (ET) Elec-trak Digest, Vol 14, Issue 109
Message-ID: <57C28536 779 99346B3 etpost drmm net>
Content-Type: text/plain; charset=US-ASCII

On 27 Aug 2016 at 22:38, Christopher Zach wrote:

> Sure, but if you constantly go from forward to reverse you start burning 
> up
> the contactors.

No, not at all.  If you're using an Alltrax (or almost any other electronic
controller) you have only one contactor, a main one for master power.  All
the motor current is managed by the controller's silicon.

There's never any of the arcing that used to trash the reversing relay my
E15 used to have.  I sure don't miss those days.  I fitted the Alltrax at
least 10 years ago, and I haven't had to open any of the ET's access panels
since.

To reverse the tractor, the controller silently and electronically reverses
the field.  Everything is done under control of a microprocessor.  If you
reverse your ET with the "throttle" on (which I usually don't do), it 
gently
reduces the armature and field current to zero, reverses the field, and 
then
re-applies the previous armature and field current settings.  Basically, it
does what you probably should have done yourself.  :-)

It also has a spooky "hill holding" function that will apply power to
actively hold the ET still when the potbox is at zero.  This makes me a
little more uneasy than the "active reversing" above, so I prefer using the
good old fashioned mechanical brake.


David Roden - Akron, Ohio, USA

= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Note: mail sent to the "etpost" address will not reach me.  To send
me a private message, please use the address shown at the bottom
of this page : http://www.evdl.org/help/
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =