[GreenKeys] Smoke and Fire

[Bruce Gentry]

I am not yet familiar with the coil and magnet you mention in a 33, but 
have decades of experience with coils, magnets and relays of all sorts 
in elevator controllers. If the coil in question was disigned for 120 
volts, and designed to be energized for a reasonably long time-several 
minutes or more- then the failure was almost certainly an intra-winding 
short. These occur when a turn or so of the winding shorts out, almost 
always deep inside the winding where heat can not escape easily. One 
shorted turn creates heat, which causes more shorts, a vicious cycle 
begins and continues until the winding burns up and opens. Age is the 
main contributer to this, useage heats the coil and over the years the 
insulation fails. In addition, older insulating materials were not as 
robust as newer ones can be. Other considerstions can overheat the coil 
as well. Over voltage will cause overheating, and under voltage can as 
well if the plunger or armature the coil is pulling does not move all 
the way to it's seated position. AC magnet coils draw far more current 
if the plunger or armature (clapper) do not move all the way and "seal". 
As for not blowing the fuse, it's purpose is only to keep the device 
from starting a fire in the building. There is no consideration in most 
cases to preserve the equipment from damage as long as whatever happens 
inside does not start a fire outside. The safety codes are especially 
loose  for equipment that is not typically kept and operated in a 
residential setting.

        Bruce Gentry, KA2IVY

On 1/8/18 6:18 PM, Michael Zahorik wrote:
> Well...... it seems like only a few hours ago, I was talking about how 
> well my ASR33 unit was working. This evening I was reading a paper 
> tape into my PDP8E and half way through the read, I noticed smoke and 
> fire inside my ASR33. Turns out the distributor trip magnet caught 
> fire. Looking at the circuit I find that it is very simple. This coil 
> is 120 VAC, protected by a 3 amp slow blow fuse (which did not blow) 
> and the only control that I see is the tape tight/out or reader switch 
> off contact. I have removed the coil and it appears to have burnt in 
> mid coil, I can see red wire at the top and bottom. This coil reads 
> open and I see no short to the core. This magnet has a number on it, 
> 1800853. While the magnet is out, re energized the unit and there are 
> no problems, smoke and/or fire that is. I can read 120 VAC at J4 pin 
> 11 & 12, when the unit is in either local or line and there is paper 
> tape in the reader. If the tape is removed or the Local/Line switch is 
> turned off the 120 VAC goes away. I'm betting the coil somehow shorted 
> internally either to itself or the core (ground). What are my options 
> on finding a replacement magnet? Thanks for the help.
> Mike Zahorik (414) 254-6768
>
>
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