<The E-15 doesn't have a stupid shunt, why does the E20 have
one??>
Different approach to controlling things.The early E-20 made
an attempt to prevent field weakening at a inopportune time by
measuring armature draw. The E-15 had time delays to try to do the same
thing.The E-20 approach actually DID work,(Although I've disabled it on
mine.), the way things were done on the E-15 never struck me as being
worth the bother. :)
RJ
Ben Griffith wrote:
I had to replace both transistors on my card 4 when I got
my E20 last summer. I got the replacements at Radio Shack. Both
replacements had the pins in a different order than the board calls
for, so I had to twist them around to get them in correctly. Q401 was
replaced with a 2N222 (from a 15-pack of generic NPN transistors) and
Q402 was replaced with a TIP31.
And they do work... I kept getting bumped out of the higher speeds
until I cleaned up the shunt connections.
-Ben
On Sat, Sep 11, 2010 at 10:55 PM, Chris Zach
<cz alembic crystel com>
wrote:
Ok,
so I took card 4 out, replaced the blown resistor, cleaned it up, and
put it back in the tractor. Decided to check to see if the shunt was
showing 0 ohms resistance.
The sense wires showed 64k. Oh brother.
Took off the plate, turns out when I assembled the shunt a few years
ago I used 10 gauge crimps on the cables (now melted), spaced the lugs
with copper bolts (all overheated) and the sense wires were far away
from the shunt (and covered with carbon).
So I cut off all the crummy crimps, cleaned up the shunt and bolts,
then put new screw-down 8 gauge copper lugs on all the main wires.
Instead of putting things between copper bolts everything is right
against the shunt on the bottom and top.
Fired up tractor, moves faster, go figure. However speeds 6,7,8 are
still out.
Checked the shunt, it's ok now the strip of metal gets hot under heavy
load but the lugs are cool. Which is good. However why does that metal
strip insist on getting hot? The E-15 doesn't have a stupid shunt, why
does the E20 have one?
Anyway, checked the voltage on the relay output of card 4, it's only
putting out 9 volts or so. I think the first amplifier transistor is
shot. So does anyone know what types of transistors they used, and if
Mouser has a replacement?
Overall this has been one of those "clean up a lot of things" type of
project. In the meantime I bypassed the relay so I can have the higher
speeds (and be able to stop cruise control by blipping the throttle).
I'll get back to this next week.
On a side note: I noticed my MOV was once again blown to bits. This
time it looks like it might have caught fire as well. Just how big of a
MOV does one need to provide surge supression on the motor armature?
Should I put 3 or 4 of them in parallel?
Chris
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