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Title: Megger for checking electrolytic cap leakage Post by: W4AMV on January 13, 2020, 07:44:47 PM Sorting some capacitors and weeding out the not so good ones. I have a hand crank megger which at full crank produces 500 V. Testing ceramic disks it appears to perform fine. Checked out large R values for HV application, fine as well.
However, in testing some 330 uF/450 V electrolytic caps, it gives near ZERO ohms and a false BAD cap reading. As I have taken the same cap, applied near rated V from a supply and see nearly zero current. Yes, as the supply V is dialed up, the current spikes and then quickly steady states to zero. I have placed a series diode in line with the cap under test. No change, indicates faulty cap. Any ideas? I should mention, the unit I have is noted as a O H M M E T E R A N / P S M - 4 3 INCLUDING ZM-21C/U SO... it is called a OHMMETER but in every respect operates like a hand crank megger. Manual attached with the clever meter schematic. Thanks, Alan Title: Re: Megger for checking electrolytic cap leakage Post by: W4AMV on January 14, 2020, 01:00:29 PM After more careful review, I suspect this unit does not have the energy to sufficiently deliver the required charge to a large capacitor. See schematic. Fine for the measurement of insulation resistance. Hence, not all megger units are comparable for function. For small disc and mica units, probably fine.
Title: Re: Megger for checking electrolytic cap leakage Post by: iw5ci on January 14, 2020, 04:19:17 PM While the megger is fantastic for finding bad paper caps , ceramic, black beauties and and Kind of non polarized caps, it is not suitable for detecting leakage in electrolitics. You can damare low voltage caps, if you crank it fast. I used a loro my megger, but Now i prefer a vintage heathkit capacitor tester with neon lamp for detecting leakage.
It works fine with elrctrolitics. I also use a small chinese component analizer for measuring esr. Title: Re: Megger for checking electrolytic cap leakage Post by: W4AMV on January 15, 2020, 10:56:22 AM Thanks for your reply. Agree! Yes, that is in line with my observation and a different instrument is required.
Title: Re: Megger for checking electrolytic cap leakage Post by: WU2D on January 18, 2020, 10:50:49 AM I got this military surplus job from a ham who was cleaning out his basement. I use it to death. Of course it is a capacitance meter. And does leakage in two ranges, 0-60V and 0-600V. And other interesting capacitor measurements.
Title: Re: Megger for checking electrolytic cap leakage Post by: KD6VXI on January 18, 2020, 11:06:42 AM I got this military surplus job from a ham who was cleaning out his basement. I use it to death. Of course it is a capacitance meter. And does leakage in two ranges, 0-60V and 0-600V. And other interesting capacitor measurements. Recently calibrated, too! 👌😎 --Shane KD6VXI Title: Re: Megger for checking electrolytic cap leakage Post by: AG5UM on January 18, 2020, 07:55:54 PM I use the 1950's Sprague Tel-Ohmike, TO-4, which I really like. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Your Sig-Corp ZM-3/U looks great, I didn't know they made that, very COOL. AG5UM |