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Megger Help needed

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Boater Sam
(@boater-sam)
Posts: 495
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I have a Megger in the mottled Bakelite case that I have never used. 
I need an instruction leaflet and some leads, the side holes for the leads look unusual.
The needle is drifting around in the middle,should it?
Has anyone managed to fix one of these?

Boater Sam

 
Posted : 24/03/2017 7:20 pm
turretslug
(@turretslug)
Posts: 567
Honorable Member Registered
 

The wandering needle is normal and part of the design- it has been explained to me why, but I forget! There's not much to using- connect, crank and read, just keep small children and animals away from the DUT....

These are good little beasties, and something of a classic- one problem that can occur with them is that there is an RC snubber across the generator output with a 50nF capacitor that, you've guessed it, goes leaky and limits the maximum output voltage. A quick test is to stick a decent high-impedance meter like a standard 10M DMM across the terminals and crank away- if it's the "usual" 500V version, the output will peak at, er, around 500V- much lower than this and the capacitor is a suspect. You'll also find cranking much easier if the capacitor was leaky and is replaced....

The standard capacitor is labelled 1500V TEST- I take the liberty of assuming that this means 1.5x normal working and use a 1kV type.

We used these at work, although they were superannuated, as they could deliver enough energy to "fry out" slightly damp and leaky (low tens of megs) TV camera triaxial cable that otherwise gave PSU start-up problems- a bout of 20-30 seconds cranking and hey, presto. Eventually, the powers-that-be withdrew them from service, as this energy capability was deemed dangerous. Some of us wink simply secreted one and continued using them stealthily....

I've mentioned the 4mm plug dodge on UKVRRR.

 
Posted : 24/03/2017 9:15 pm
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