From: "David Roden" <etpost drmm net>
To: elec-trak cosmos phy tufts edu
Sent: Wednesday, June 18, 2014 2:26:03 PM
Subject: Re: (ET) 4QD Pro 120 controller
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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