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Re: [Amps] Homebrew "Hi-Pot" design issues

To: "Jim Homer" <>, " AMPS" <>
Subject: Re: [Amps] Homebrew "Hi-Pot" design issues
From: R.Measures <>
Date: Fri, 9 Jan 2004 10:35:50 -0800
List-post: <>

>I am currently gathering components for a new amp project, and 
>would like to 'pre-qualify' my parts with a hi-pot assure that the 
>proverbial "one bad apple" doesn't blow up the whole bunch 
>when I apply HV power.   
>So, I am considering a simple hi-pot project using a small variac, a 
>7.5 kvac 30 ma neon transformer, 15kv rectifiers, .

**  7.5kV-rms produces 21,6k PIV in a halfwave rectifier circuit.   I 
would go with c.  a 30k-PIV rectifier.  Also, with a halfwave rectifier, 
a 120v MOV should be connected across the primary winding to preclude 
rectifier failure.  If a FWD or FWB circuit is used, the MOV is not 
needed.   A FWD would be useful for checking the 15kV vacuum caps that 
are commonly used in Ham amps.   For 60-Hz mains, 2, 0.01uF capacitors 
are suitable for use in a FWD high-pot tester.

>1 mfd 10 kv cap, 
>15KV HV 'tigerstripe' resistors and associated components to get an 
>adjustable output of about 0-10 kv.
>My current "Draft" design would limit direct-short current to 100 
>microamps max at 10KV and proportionately less as the adjusted 
>voltage is less (50 microamps at 5 kvdc and so on).
>However, I have been looking at commercial hi-pots and many have 
>adjustable "trip" values of from 1 to 50 milliamps or so, so I am 
>concerned that my current designed limit of 50 microamps at 5 KV 
>might be too low.
**  50uA is plenty, even to do the Funderberg gold-sputter test.  

>Can anyone experienced in this area tell me what amount of leakage 
>current would be considered "acceptable" or "typical" for components 
>such as vac variables

**  When you see 1uA of leakage, the breakdown point close.  When you 
hear a "tink", you have arrived.

>, large tubes, 

**  >10uA suggests that all is not well.  

>RF caps, HV power tranformer 
>insulation and the like? 

**  For ceramic caps, I check 'em at the rated-V.  Going to the 
breakdown-V   causes a short.  .  
cheers, Jim
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