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

["RJ Kanary" <rjkanary nauticom net>]

              Pages 5-2 and 5-3  of the Homeowner's Service manual of the 
cover the basic theory  of the control system for the AA- E-15 and its less 
endowed stepchild, the E-12 S.
        One of the things that is unique about an SCR is that once it is 
on, it is ON. Remove the gate current, and it is STILL on.You have to 
interrupt current flow to the anode the make it unlatch.{More sophisticated 
gated devices came later to address this shortcoming.}
          This is what the RTN circuit does for the PTO and the 'L' 
contactor.
           As far as using a bipolar transistor to do the 
job.................... Why reinvent the wheel? <VBG>
         In (tongue in cheek) view of your other misadventures, maybe we 
should just stick to getting this unit to back up without making sacrificial 
smoke. <VVBG>
         BTW, have you found out if those relays have clamping diodes in 
them yet ?

ABTW
{PNP......Points iN, Please.
NPN..Never Points  iN. }

RJ

----- Original Message ----- 
From: "Michael S Briggs" <msbriggs alberti unh edu>
To: "RJ Kanary" <rjkanary nauticom net>
Cc: <elec-trak cosmos phy tufts edu>
Sent: Sunday, August 06, 2006 7:27 PM
Subject: Re: (ET) new relay in - now no reverse


> 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