Re: NST filter failure?

[Terry Fritz <twftesla-at-uswest-dot-net>]

Hi Mark,

	Just to follow up on my last post...

The power resistors "normally" can run at 350 degrees C.  So unless they
are obviously melted down or something, they are fine and don't need to be
replaced.  You may want to at least check the resistance.

The MOVs save the caps on the filter too but visually check the cases of
the caps for obvious damage.  You can check the values too if you have a
meter.  The resistors across the caps should not be blackened.

However, the MOVs will "ALL" have to be replaced.  When they get really
hot, the internal solder connections melt and the solder flows across the
bulk material reducing their turn on voltage but providing even greater
protection when it is most needed (they don't give up easy ;-)).  You might
as well order a new set of MOVs.

Properly set the safety gaps and KEEP them set there ;-))  Normally the
safety gaps would protect the MOVs.  It can be argued that the MOVs really
are not needed, but things like this show they are! :o)

Cheers,

	Terry


At 10:13 PM 8/20/00 -0500, you wrote:
>> Original poster: "Christopher Boden" <chrisboden-at-hotmail-dot-com>
>>
>> >Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
>> >I would be interested in hearing what with wrong with the NST filter?
>> >
>> >snip...
>> >
>>
>> Mark?
>
>Yes?  ;-)
>
>Well, I actually just reassembled the base, and placed it in an out-of-the-way
>location in the laundry room (the only first-floor location that's out of the
>way).  I doon't have access too the tools required until next week.
>
>My filter is the exact one posted on Terry's page.  I'm running 15/90 
>currently,
>although I did have the 4th NST hooked up at teh beginning of the demo (Mark's
>law of life 157:  if it a lready works well, then do *NOT* make it better an
>hour before you need to use it).  This was not, IMO, a cause of the
failure, as
>the symptoms below occurred at least 20 minutes after I removed the 4th
NST and
>MMC bank, and it was running "normal" just after the removal.
>
>I surmise that I had a motor problem (lost sync when NSTs were running),
>combined with a too-wide safety gap, and a poor power supply (tried to run
20+A
>off a 15A (probably 14AWG romex) fuse).  The motor, FRT, I've had trouble with
>before (thermometer failed during first test run).  The resitors got MUCH 
>hotter
>than they should have (for ~5 minutes run time over 45 minutes).  The MOVs,
>which normally run cold to "bearly warm," were SEARING hot - hot enough to
turn
>the glossy epoxy a nice matte.  I fear that these are toast, and I will
need to
>replace all 14.  MOVs fail open, correct?
>
>It'll probably be about 10 days before I'll know anything more.  I'll post
what
>I find out.
>
>Mark
>
>
>