Estimate the steady-state maximum current (eg from the unit's normal
mains current) then search Digikey for "inrush current limiters".
Select values near or a little greater than your estimated mains
current in the 6th list-box (select multiple values), titled "Current -
Steady State Max", and click "Apply Filters".
Also make a guess as to the allowable voltage drop across the varistors
in steady state operation. Divide by the estimated current and select a
similar or lower value in the 7th listbox, and again click "Apply
Filters". That should leave you with a managable number of parts to
look thru in the table at the bottom of the web page.
Look at the R at 25C, which will be the major factor in limiting inrush
current. I would tend to choose a varistor with the largest R25, for
minimum inrush current.
(I have no pecuniary interest in Digikey, but I've been a long-term
customer, and I think their search capability is so much better than any
others.)
I hope you find this useful. Feel free to email.
Dave
On 3/13/2014 8:34 AM, David Smith wrote:
I need some help with repairing a Fluke 5100B Calibrator.
The capacitor support bracket fell into the power supply module and vaporized
both varistors, RV1 and RV2. A call to Fluke tells me they no longer can supply
these MOV's. According to the manual's parts list these varistors are in-house
parts by Fluke. I have no way of determining a substitute part. Is there anyone
that can help me identify what could be a useful replacement?
Thanks,
Dave - W6TE
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