[Sneap] Current sense resistor, Varian 6004 power supply

[David Weisser]

Dear Allan,

We did have a problem with the sensing resistor in an identical power
supply, Spectromagnetics 6004. I quote from Tank Opening Report No. 25 page
7, (1981).

"About two weeks ago, instability on the ion source inflection magnet power
supply (Spectromagnetics) was traced to failure of the reference resistor.
The post to which the voltage sensing connection is made was corroded off
and inspection inside the resistor housing showed the resistor assembly to
be badly corroded in general.  A new connection post was silver soldered on
and the resistor and its connections were nickel plated.

Because of this failure, the equivalent resistor in the analysing magnet
power supply was inspected.  In this case corrosion was less severe but the
sensing connection post had been poorly soldered and fell off when it was
poked not too vigorously.  The assembly was cleaned and resoldered. then
painted with marine epoxy paint. (The inflection magnet resistor was plated
because there wasn't time for the epoxy paint to set.) Both supplies are now
operating stably."

We have had no further trouble with these resistors since 1981 though there
might have been a problem with the external connection at the voltage
sensing post.

Good luck,

David



********************************************
D.C. Weisser
Nuclear Physics Department
Research School of Physical Sciences and Engineering
Australian National University
Canberra A.C.T. 0200
AUSTRALIA

Tel:    + 61 (0)2 6125 2080
Fax:    + 61 (0)2 6125 0748
Mobile: + 61 (0)414 249 209

david.weisser at anu.edu.au

  -----Original Message-----
  From: sneap-bounces at tunl.duke.edu [mailto:sneap-bounces at tunl.duke.edu]On
Behalf Of kerna
  Sent: Wednesday, 5 March 2008 10:02 AM
  To: sneap at tunl.duke.edu
  Subject: [Sneap] Current sense resistor, Varian 6004 power supply


  Dear Sneap community,



  This resistor failed today.  It is .0316 ohms.  760watts of power at 155
amps.



  Does anyone have an old Supply not in use that I could scavenge this part?
This resistor has opened up.  I have not yet tried to fix it.  Has any one
had experience fixing it?  I haven't had a chance to locate a replacement,
as I have just discovered what was wrong with the supply a short time ago.



  I have left a mess with someone at Varian, but I don't hold much hope they
will be much help with a supply that was built back in the 1660's



  Thank you.



  Allan Kern



  Western Michigan University

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