|
Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE! |
|
Thread Tools |
22nd Dec 2011, 12:23 pm | #21 |
Dekatron
Join Date: Jan 2006
Location: Ramsbottom (Nr Bury) Lancs or Bexhill (Nr Hastings) Sussex.
Posts: 5,817
|
Re: Testing capacitors with a 'Megger'
This is interesting. My ex-father-in-law (a former electrician) died recently at 91 and I was presented with some test gear he had squirrelled away without anyone knowing. Included is a very nice brown mottled Bakelite Megger in a leather case and complete with handle. I'd never seen this before even when I used to help out on the occasional job! (in those long ago days when you could!). I didn't realise that there was this application apart from testing wiring and giving people electric shocks .
Dave W |
16th Jan 2012, 12:43 am | #22 |
Dekatron
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,748
|
Re: Testing capacitors with a 'Megger'
I also use a BM8 battery Megger and have been surprised at how good some very old metal-clad capacitors are, compared with any NOS Hunts which are only worth throwing in the bin. I have a drawer full of ex-equipment or NOS capacitors, which I use occasionally but I always test them for value and leakage prior to use. About 75% turn out to be leaky when tested at or near their working voltage, and I throw quite a few away.
The current available from the BM8 is only about 0.8mA, but enough to make leaky Hunts capacitors crackle a bit! On a related note, a very cheap source of high voltage for test purposes can be obtained by dismantling and retrieving the inverter from one of those electronic fly-swatters, available for a few pounds. I measured mine and it generates around 1.8kV DC from a pair of AA batteries The output voltage can be controlled by varying the input voltage.
__________________
Phil Optimist [n]: One who is not in possession of the full facts |
6th Feb 2012, 5:00 am | #23 |
Retired Dormant Member
Join Date: Feb 2008
Location: Auckland, New Zealand
Posts: 631
|
Re: Testing capacitors with a 'Megger'
I have used electronic 'meggers' since the mid 1970's and have found them to be by far the best means of checking reliably capacitor leakage and/or susceptibility to breakdown, and for leakages between transformer windings etc.
My current instrument is a Kyoritsu 3132 (with analog meter) which gives a choice of 250, 500 or 1000 volt output and also does medium current low-ohms testing which is great for suspect contacts etc. As a nice finishing touch, it discharges capacitors after testing , which saves you the time searching for the little creature after you have inadvertently hurled it across the room. They are also great for checking the condition of that most obscure and obdurate of components, the high voltage VDR as used in elderly televisions. With three voltages to choose from, a series of performance points can be recorded for a known good component and that makes checking of suspect VDRs much easier. However, it has been my experience that VDRs are generally one of the more reliable components! Cheers Billy |
21st Feb 2012, 11:22 pm | #24 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,935
|
Re: Testing capacitors with a 'Megger'
Inspired by this thread, I decided to dig out my old Comark 1905 megger and check out a few capacitors. I had not used it for ....13 years or so and was not too surprised when I could not get it to zero. I suspect that... the capacitors have gone - how can I tests them now
This model has a transistor oscillator running on the secondary of an RS audio output transformer, then taking the output from the transformer and quadrupling the voltage to 1000V. The oscillator is running and producing some voltage, but I'll see what happens when I replace the 5 caps in the multiplier and output circuit. |