Re: (ET) My First Mow Job

["Christopher Zach" <czach computer org>]

> When they short you lose your upper speeds. I
> haven't figured out why yet.

That's pretty easy to answer: That whole card assembly is basically there 
to
monitor current going across the shunt. As long as the current is below a
certain value the card does not short the field weakening resistor banks 
and
high-speed is availible.

As soon as the armature current exceeds the value (say you're climbing a
hill), the transistors turn off and the field weakening resistors are
effectively shorted. This brings the field to full current and slows down
the motor. It also has a side effect of bringing the motor to full power.

Really great idea IMHO.
Chris


----- Original Message ----- 
From: "Humphrey, Timothy" <HumphreyT neads ang af mil>
To: "Discussion List Electrac tractor" <elec-trak cosmos phy tufts edu>
Sent: Friday, May 09, 2003 12:25 PM
Subject: (ET) My First Mow Job


> Well, I had my first ET Experience last night!
>
> In the few weeks prior I was busy putting in new batteries and trying to
> straighten out some of the electronics while I waited for my grass to
grow.
>
>
> I had originally picked this tractor up last December. It had no
batteries,
> and the mower deck had been dismantled. The motors were rebuilt by Bill,
so
> I was pretty confident that they would work. Thanks to this list and
> especially to the documentation available on the web-site I was able to
> reassemble the deck without too much hassle.
>
> This is the I-5 Tractor. My card 4 needed some work. Q401 had an
> emitter-base short. Diodes 402, 403, 413,414 were all short and the edge
> connectors at pins 17 and 19 were missing (they were either burnt off or
> someone in the past had used rosin flux to repair this card, I'm thinking
> burnt). Bill sells this card for $45.00. I'm ordering one from him, but
also
> decided to attempt a fix on the one I have.
>
> I'll tell you, some of these components are hard to find. I used 1N5408
> diodes in place of the originals. The replacements have a 1kv PIV vice
500,
> and have a 6.25w dissipation, so should hold up better. I replaced both
> transistors with same part number replacements, got lucky there.
>
> My varistor on Card 3 was also vaporized, I couldn't find the exact part
> number for this, Bill has it though. I replaced it with a V39ZA20 device.
> The original was a V36ZA80. I expect it to fail, but hasn't yet.
>
> My cruise control doesn't work. The lights and horn didn't work and after
> about a half hour troubleshooting I figured out that the fuse wasn't
making
> good contact in the holder. (How many times has fuse holder connections
been
> discussed on this and the EV list? ;-). )
>
> I got the cards all put together and plugged them in woo-hoo I now have
all
> of my speeds, Still need to troubleshoot the cruise circuits though.
>
> After mounting the motors to the deck, I plugged the in and the all 
> worked
> fine, although the very loud roar was a little disappointing considering
how
> everyone is always saying how quiet the Elec-Traks are.  Of course it
> probably didn't help that I was in the garage with the doors closed :-)
>
> Picked up a can of Krylon Rust Stop in Implement Orange, it is almost a
> perfect match for the original I-5 paint. This can was anyway, who knows
> about the next one. At first I thought nothing was coming out of the can,
it
> was that close.
>
> I mowed Thursday afternoon, did about a quarter acre, then put it on the
> charger. Remember, battery break in period. The grass does a wonderful 
> job
> of muffling the blade noise. It was in fact a very quiet experience. I
also
> figured out at this time just what those springs and chains are for. One
of
> mine was missing. I picked up some replacements at the local hardware
store,
> and put them on.
>
> QUESTION: During battery break-in is it necessary to get a full charge, 
> or
> are we just looking to exercise the batteries. i.e.. discharge 'em, bulk
> charge 'em, then discharge 'em, repeat.
>
> After a few hours of charging my wife wanted to try it out. So I let her
mow
> another 1/4 acre. The middle mower stopped. It was a loose connection.
Then
> she continued, until she ran the batteries dead. I had to bring a cord 
> out
> to revive it. Let it charge for 2 hours then drove it into the garage to
> charge all night. During the time it was charging in the field I checked
> some things out. Unfortunately I found that I had once again shorted out
> diodes 402 and 403. I replaced them while it was charging (I bought a bag
of
> 25 diodes for 6 bucks). When they short you lose your upper speeds. I
> haven't figured out why yet.
>
> Anyway, it was a much anticipated, enjoyable moment.
>
> Stay Charged!
>
> Hump
>
>
>
>
>
>