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

Chances are that any SCR that you purchase today will have performance specs that are light-years ahead of the "Apollo Era" units that were in their infancy then. Even ones from RadioShack® will fill the bill.Just make sure to get the terminals in the correct places.{A heatsink would be a plus, too. } Again, an analog VOM on the low ohms scale would likely provide enough current to the gate to bias it ON.You can observe gate closure with you sand based meter. I don't have any of those cards here, since any of those tractors that found their way to my doorstep ended up getting 'updated' to the more primitive all switches. relays, and contactors type control scheme. :) 
    And I think that you're beginning to see WHY.
----- Original Message ----- From: "Michael S Briggs" <msbriggs alberti unh edu> 
To: "RJ Kanary" <rjkanary nauticom net>
Cc: <elec-trak cosmos phy tufts edu>
Sent: Saturday, August 05, 2006 5:55 PM
Subject: Re: (ET) new relay in- now no reverse




RJ, yup, it's a DC relay. See
http://www.surpluscenter.com/item.asp?UID=2006080216301211&item=11-2382&catname=
 I'll check the resistance in both directions to make sure it's not
directional though - will need to borrow an old analog ohmmeter from work.
 Interesting point about the SCR on card 1 being what would be
taken out - see the post I just sent just before yours - I think I've
narrowed it down to the SCR being the problem, just trying to make sure
I'm looking at the right SCR (since they aren't labelled on my card. Based
onlocation and trying to look at the etchings on the backside without
removing the card, I think the one just under pin 8 is SCR 106, the one
its directly connected to, but I'm not positive).
 If SCR 106 is dead, the plan then becomes:
1. Temporarily jumper pins 8 and 9 together, with a 10A fuse between them
(I've put a 10A fuse on wire 11 coming out of the reverse relay to protect
it also) so I can mow the lawn tomorrow. Be very careful to wait a while
before going between forward and reverse.

2. Order a replacement SCR (is this something Harrold carries, or should I
just go through Newark?), remove all wires from card 1, remove card 1,
replace the SCR and while the card is out, check every other component on
there and "freshen up" the connection points.

3. Order a REAL reverse relay instead of a replacement part that (1) isn't
very well built (now that I think about it, I'm pretty sure the first of
these relays I put in was shorted across the coil connections, and
presumably is what fried SCR 106 or something else on card 1), (2) is
HUGE, and thus very difficult to fit in the same spot the real relay goes,
(3) uses screw on connections instead of spade connectors. Ugh.

4. Put everything back in, and hope something else doesn't fry. :)

Mike

--

--------------------------------------------------------------
Michael S. Briggs
UNH Physics Department
(603) 862-2828
---------------------------------------------------------------

On Sat, 5 Aug 2006, RJ Kanary wrote:


Are these DC rated relays? Before you try another
relay..........get your analog VOM out . Use the X1 or X10 resistance scale . Measure the coil resistance in BOTH directions of an uninstalled relay.If it is different in one direction, those relays have a clamping diode across 
the windings to keep EMF from the collapsing magnetic field from killing
delicate components downstream.{Your sand based DVOM can't perform this test 
reliably. }
     You have a 50 / 50 chance of hooking it up wrong and taking out the
SCR for the Reverse relay on Card 1.
      Glad I could brighten your day. <VBG>

Anyone else following along may wish to take note of this when using
"upgraded" components. Know what you are using.  :(



RJ Kanary  Bandi Bros. Inc.
Member TRNi  Since 1998
ASE® Certified Master Auto Technician

rjkanary nauticom net