Re: (ET) 4QD Pro 120 controller

["David Roden" <etpost drmm net>]

Lots of interesting discussion on this.  Sorry I'm late entering the fray; 
I 
was on vacation.

First, I'm surprised to hear that a 4QD failed in only 10 years.  I 
haven't 
yet used a 4QD though I have one sitting on the shelf here, but they have 
an 
excellent reputation.  I've had other name-brand EV controllers that ran 
for 
15-20 years and more, and I'd expect that from a 4QD as long as it was 
used 
well within its ratings.

In the early 2000s I recall seeing some cheap Chinese 4QD knockoffs 
offered 
on Alibaba.  I wonder if you might have accidentally gotten one of those 
instead of the real thing.  Did you contact 4QD to ask what they might be 
able to do?

FWIW, the main failures I've seen in controllers have been caused by the 
input electrolytics (they get old and their ESR goes up).  

The early PMC controllers (Curtis forerunners) had a quirkly failure mode. 
 
They had bipolar transisitors and used voltage drop across the E-C 
junction 
to determine current limit.  As the transistors aged, the voltage drop 
increased, so the controllers' max current would drop.  The users would 
open 
the case and twiddle the trimpot to get back to original factory current, 
and the transistors would then release their smoke.

As for transistor controllers vs the old GE contactor iron, most folks 
who've been here a while know I stand on this issue.  For others, I bought 
one of the first Alltrax ET-specific controllers, and have never regretted 
it.  That was about 10 years ago.  It works fine as of today.  

I understand the visceral satisfaction of having a machine with no magic 
boxes - where you can work on ever part.  I also agree that many times a 
simple solution is the right one.  

However, I really like being able to move my tractor by centimeters, 
thanks 
to having a more subtle controller.  I appreciate that fine level of 
control, especially for manuvering the tractor into my jam-packed garage.  

The Alltrax improved the reliability of my E15 by an order of magnitude.  
I 
had the usual hassles with the original control - bad card edge 
connections, 
exploded diodes and resistors, failed capacitors, and of course the 
infamous 
reverse relay problems.  Some of these are just normal age-related 
failures, 
but they got downright annoying.  After the snow plowing session I had to 
do 
with the hood and component panel open so I could reverse the tractor by 
pressing the reverse relay, I decided I'd had enough.  

Someone mentioned "the E15's moronic use of a relay to switch the field."  
That's not moronic at all; it's a sensible way to do it. Eeversing the low 
current field is normally more economical and practical than reversing the 
high current armature.  I'm not an EE, but I think it's just that GE's 
implementation wasn't up to snuff.  In any case, reversing the E15 isn't a 
problem for me any more, and I'll never have to dress the contacts on the 
relay again.

Although the reliability gain might be less or nonexistent with an E20, 
I'd 
still probably make the change if I had one of those instead.  

Overall, I'm very pleased with the Alltrax.  Its driving character is 
admittedly different from the original - the speed isn't as stable up/down 
hills, for example - but that doesn't bother me.  Ironically, that just 
makes the tractor work more like an ICE-powered machine.  


David Roden - Akron, Ohio, USA

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