"DoN. Nichols" wrote:

On 2012-09-26, Michael A. Terrell wrote:

Jon Elson wrote:

Michael A. Terrell wrote:


The winding may have opened & arced, causing plasma which ignited the
oil. I used to see hundreds of bad clock motors a year, when one shop
did school clocks & fire alarms. Most had bad gears, but some had open
coils and burn marks.

Yup, I agree. An impedance-limited motor can't get hot enough to
ignite oil. But, if there was internal or external arcing, that could do
it. I'm still a little surprised internal arcing could do it, as these
motors are usually pretty well closed up. Either it arced internally
for quite a while, or until an outside wire burned off and dropped into
the usual oily mess on such pumps. It really seems a properly-sized
fuse should have cut this off before it got to that stage. Might be
something to install while rebuilding.


Some have vents to cool the coils, or open windings. Older motors
were often built with a brass or aluminum deep drawn cover that was
friction fit to the steel body, and could work loose. Some would pull
off with your fingers, and had enough gap to let a flame out if it was
in the right spot.

This is one of the teardrop shaped ones which contain the gear
train. The usual deep drawn cover was over the actual motor part, the
teardrop likely also had some enclosed lube, and I remember others of
the type had the whole gear train solder sealed into the teardrop, but
the motor winding was a different matter.

This is based on drawings downloaded. I'll have a better idea
when I get a chance to pull it out and take it apart outdoors. (If
there is enough left to judge from. :-)


Post some photos before its removed, and to show the damage after its
removed?


Since the motors were designed for another use, the
thought of starting a fire likely wasn't considered. I once found a
particle board speaker cabinet that was set on fire when the wirewound
two watt 20 ohm pot caught fire. Someone had removed the line
transformer to get more volume, rather than find a short in the building
wiring. When I found the bad wire, the speaker could be heard all over
a 40,000 Sq foot room, for about a second. It had shorted to the
ceiling grid, which was grounded to the steel building and support
posts.

Ouch! I presume that the cone was tatters, as well as the voice
coil being toast. :-)


Actually, the speaker survived. The entire control was burnt,
though. Just the metal parts & ash. It was still in use when I was
laid off, several years later.

The Merlin phone system, was another story. It was non Y2K
compliant, and caught fire a week before it was to be replaced. It set
the equipment room on fire, and smoke damaged 40,000 Sq. feet of office,
warehouse & stockrooms. You would still get a whiff of smoke, two years
later. We were working the next day in production, with the doors
propped open to be able to breath. That was a Saturday. Monday morning
Sprint was there to run temporary lines to the main office & reception
for single line phones, and started replacing all the 25 pair cable with
yellow cat five to each new phone.