TECH: Chattering Relay Problem Solved !!!!
Tom Diviney
************** Chattering Relay Problem Solved! *******************
I received several suggestions, which got me poking around again. It
turned out that nobody stumbled on the real problem. I discovered while
manipulating the relay arm that this particular relay seemed to have
little or no "float" where the contacts pass through the plastic insulator
which is connected to the moving arm. A close inspection revealed that
one of the contact leaves had adhered to the plastic (it looked like it
overheated at one point and slightly melted the plastic). I have
identified this point with an 'X' on the diagram below. All I had to do
was take an Xacto knife and free up the contact, and it now works like a
charm. I was surprised at how much the performance of the relay depends
on this float.
I have included the original problem description below for reference:
Thanks to all the rpg readers,
-Tom
*************** Original Description of Problem ********************
Symptom: While the ball is actuating any of the 100 point features,
the relay which actuates the solenoid to advance the 100
point wheel chatters wildly. When the ball releases the
feature, the chattering stops. The other score relays,
1K 10K are very "crisp", and no chattering is observed.
Relay coil is actuated with around 39VAC.
spring
,---//////------I
II================I===
II ,-----------, I
II | |+ I
II | Coil |+ I
II | |+ I ASCII Artwork of the
II |___________| I pivoting Relay in question
II I arm
II :|:|::|:X:::::::::
II > < > < I
II | | | |
II | | | |contacts
II | | | |
II | | | |
IIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIII
Tests Performed So Far:
1. Ruled out possible inadvertant feedback path by manually
activating the coil (connected 39VAC to coil with jumper).
Severe chattering while connected. Other score relays
behave well with this test.
2. Isolated all relay loads by inserting paper between
contacts so nothing is being switched. Relay still
chatters severely.
3. Measured coil current in "bad" and "good" relay:
"Bad" Relay "Good" Relay
Arm held open: 1.4A 1.4A
Arm held closed: 1.1A 1.1A
4. Replaced Coil -- Still chatters severly.
5. Swapped coils between 100 point and 1K point relay.
100p still chatters even with "good" coil, 1K point
relay is still GOOD even with "bad" coil!
(confused yet?)
6. Physically examination of good and bad relay shows no
differences. If I push the arms with my finger, I cant
percieve any difference in tension between the two.
HEEELLPP! --- 3 coils have produced the same result, it must have
something to do with the frame!??
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* Tom Diviney div...@sky700.bwi.wec.com *
* Westinghouse Electric Corp. (410)765-6606 voice *
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