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» Film-Tech Forum   » Operations   » Film Handlers' Forum   » Kelmar rewind blowing fuses

   
Author Topic: Kelmar rewind blowing fuses
Ken Lackner
Phenomenal Film Handler

Posts: 1885
From: Atlanta, GA, USA
Registered: Sep 2001


 - posted 05-09-2002 05:32 PM      Profile for Ken Lackner   Email Ken Lackner   Send New Private Message       Edit/Delete Post 
When I was building a print today, the fuse for the motor on my Kelmar rewind bench blew. It worked fine for 5 or 10 minutes, then all of a sudden the motor quit. Someone checked the fuse, and it was blown. I replaced it, and the same thing happened about 10 minutes later. Any ideas why?

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This one time, at Projection Camp, I stuck a xenon bulb....

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Gordon McLeod
Film God

Posts: 9473
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 05-09-2002 05:49 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
Probably bad brush in the motor or a shorting winding on the variac
At what wpeed was it running ? THere may have been too much drag (belts,bearings clutch) for the speed and the motor of course drew too much current

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Steve Kraus
Film God

Posts: 4068
From: Chicago, IL, USA
Registered: May 2000


 - posted 05-09-2002 08:12 PM      Profile for Steve Kraus     Send New Private Message       Edit/Delete Post 
If it's an old unit your motor's commutator may be shorting between segments from carbon dust. Someone familiar with motors can disassemble it and scrape the divisions clean. If the commutator is badly scored and the brushes worn it can be turned smooth and the brushes replaced but you get to a point where it is simpler just to replace the motor and be done with it.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12328
From: Annapolis, MD
Registered: Dec 1999


 - posted 05-09-2002 09:01 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
If this is the new UL listed rewind table...replace the motor fuse with a 3 amp slo-blo...your problems will vanish. If the motor shorts or draws too much current, the fuse will blow. Prior to the big UL listing, there was no fuse on the motor. The least they could have done is to make it a Slo-Blo rather than a fast blow.

Steve

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"Old projectionists never die, they just changeover!"

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Ken Lackner
Phenomenal Film Handler

Posts: 1885
From: Atlanta, GA, USA
Registered: Sep 2001


 - posted 05-10-2002 01:47 PM      Profile for Ken Lackner   Email Ken Lackner   Send New Private Message       Edit/Delete Post 
This is a brand new table, only a few weeks old. The fuse that came out was 2.5 amp fast acting, so a 2.5 amp fast acting fuse went back in. I generally believe the manufacturers have reasons for using specific parts that they use, although this may not always be the case. Why should I use a slo-blo? thx.

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This one time, at Projection Camp, I stuck a xenon bulb....

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12328
From: Annapolis, MD
Registered: Dec 1999


 - posted 05-10-2002 02:36 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
Ken,

I generally agree with your statement about manufacturers and fuses. Normally they are well chosen. In the case of the RTV-8900, the 2.5amp fast blow was a poor choice. I'm sure UL put the motor into a stall at full speed to see what current it drew and it had to blow it's fuse in a specified time. That has no practicality in real life. The slow-blow fuse will stop your fuses from blowing. The 3-amp will give you a margin. The 2.5 amp fast blow was simply a bad design and should be rethought.

Steve

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"Old projectionists never die, they just changeover!"

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