Re: (ET) new relay in - now no reverse

[Michael S Briggs <msbriggs alberti unh edu>]

On Sun, 6 Aug 2006, RJ Kanary wrote:

>       Since the time delay is likely inoperative, just using the Reverse 
> switch in the throttle eliminates more things to go wrong.I suspect your time 
> delay isn't working, since you have experienced reversing relay issues.

It's definitely not working right now :) - but that's almost certainly due 
to the surplus relay with a short across the coil, that fried something on 
the time delay circuit (now that I managed to mow the lawn (without 
reverse), I'll pull card 1 out and take a look at it). I guess the 
question is whether to try fixing the time delay circuit, or just bypass 
it - which would mean I'd need to remember (uh oh) in the future to never 
switch between forward and reverse quickly. And if I do bypass it, should 
I jumper the wires that go to pins 8 and 9 with them also connected to the 
card, or just pull them off the card and jumper them off of it? Reason 
being that from the schematic, it looks like the line coming in from pin 8 
(from the reverse switch) also connects to some of the other stuff on card 
1 - not sure what those parts are for though.
	I'd *like* to get card 1 working I think. Hopefully the only 
problem is that a trace at the beginning of card 1 burned up, and I can 
just make a new solder trace, or solder in a wire jumper over the burned 
trace. If that SCR is fried, then my question becomes - what should I 
replace it with? I'm not all that strong on transistors and rectifiers and 
such, but it seems that a PNP (or NPN, crap, I always have trouble 
remembering which is which... I think PNP is the normally open one that 
closes when you have a certain current coming into the gate?) transistor 
would be a nice replacement, if I understand the time delay circuit 
correctly.
	Is this how the time delay works? : when you move the speed lever 
into reverse neutral, the reverse switch closes, connecting pin 8 of card 
1 to 36V (or whatever batt voltage is). Pin 8 feeds into the anode of the 
SCR, which seems to be functioning essentially like a PNP transistor in 
this circuit. There's a little RC circuit connected between pin 8 and the 
gate of the SCR, such that the gate doesn't have enough current coming in 
until the capacitor in that RC circuit has charged up to a certain point - 
which is creating the time delay. Once enough current is going into the 
gate, the SCR closes (which I think is how PNP transistors work?), and pin 
8 then becomes connected to pin 9, which powers the reverse relay, causing 
it to flip the direction of the current in the field coils in the drive 
motor.
	Is that essentially how it works? If so, if I want to replace that 
SCR with a more modern PNP transistor, I'd need to pick one that would 
trigger with the "right" current coming into its gate (which means I'll 
need to analyze that circuit some... unless someone else has?).
	Anyway, I managed to mow the lawn by putting in the old, original, 
fried relay, just rewiring it so I only have forward instead of only 
reverse. Mowing with only one direction is kind of a pain, but easier with 
no reverse than no forward. :)
	Overall it was a rough day for the E15, mostly due to my 
carelessness. After installing the new capacitor, I was topping off the 
tractor this morning, and wanted to see what voltage the charger was 
putting out. Being lazy and careless, instead of putting the positive end 
of the voltmeter to a well chosen spot such as the + terminal of the most 
positive battery, or where it connects to the power disconnect, I chose to 
put it on the spot on the Landis controller where the red wire connects to 
the PC board (the red wire that connects to the power disconnect, and 
hence is connected to the uppermost battery + terminal). Of course, those 
solder traces are really close together, and the probe of my multimeter 
shorted across the solder spot where the red wire connects, and the trace 
connected to the 47 uF capacitor, shorting across them, and making a nice 
"pop". Right now I'm trying to assess whether it only took out solder 
trace, or if it also fried anything else.
        Bah!

Thanks,
Mike