[AMRadio] DRIVER XFMR UPDATE

[russ dworakowski]

My Heathkit cap checker has  power factor % reading-  anything  much over 10 
%  and i scrap it.    Russ.






>From: "Donald Chester" <k4kyv at hotmail.com>
>Reply-To: amradio at mailman.qth.net
>To: amradio at mailman.qth.net
>Subject: Re: [AMRadio] DRIVER XFMR UPDATE
>Date: Sat, 22 Feb 2003 17:41:26 +0000
>
>
>
>> > If it's impossible to find 125 mfd's (which I doubt...they can
>> > be found
>
>I see loads of recently manufactured electrolytics both used and unused, 
>about 125 mfd @ 450 volts, at hamfests.  Many of these are packaged as 
>"computer grade".  They usually measure above the rated capacitance.  I 
>always test for leakage before using them.  The simplest test is to put 
>them across a HV supply at near their maximum working voltage and charge 
>them up.  Disconnect them and let them sit for a few minutes.  A good cap 
>will retain the charge (I have found that out the hard way, by getting a 
>jolt from charged electrolytics that have been lying around for a week or 
>more).
>
>The next test, if the cap appears to hold  charge, is to put it back across 
>the high voltage, fully charge it, then read the leakage current by placing 
>a milliammeter or microammeter in series with it.  Be careful; if the 
>capacitor shorts you can ruin an expensive meter that way.  Make sure the 
>cap is fully charged before placing the meter in series, as the charging 
>current can ruin a sensitive meter movement.
>
>Since the internal resistance of even a marginally good electrolytic is 
>likely to be several megohms, it wouldn't hurt to place a current limiting 
>resistor in series with the meter - just calculate, using ohm's law, the 
>resistance needed to make the meter read approximately full scale at the 
>power supply voltage.  This resistance will be much lower than any leakage 
>resistance (unless you are using a fractional microammeter), and will have 
>little effect on your leakage resistance reading.
>
>Don K4KYV
>
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