My Heathkit cap checker has power factor % reading- anything much over 10
% and i scrap it. Russ.
From: "Donald Chester" <[EMAIL PROTECTED]>
Reply-To: [email protected]
To: [email protected]
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
_________________________________________________________________
The new MSN 8: advanced junk mail protection and 2 months FREE*
http://join.msn.com/?page=features/junkmail
_______________________________________________
AMRadio mailing list
[email protected]
http://mailman.qth.net/mailman/listinfo/amradio
_________________________________________________________________
Protect your PC - get McAfee.com VirusScan Online
http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963
