Here is a Circuit for a Capacitor Reformer, old style that really does weed out the bad ones.....Alan
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This is the one i am making at the moment, i will let you know when its done, its at the bare bones stage yet, pics below, meter to put background on and calibrate etc
.....Alan.
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Thanks for posting the article Alan - most interesting.
You've made a good start on your reformer - a very handy bit of kit! The neon light is a useful indication of leakage and the general condition of a capacitor. I built the reformer that was in Radio Bygones, June/July 2008, and later, also featured in in the BVWS Bulletin, Winter 2008. I won't clutter up this post by referring any further to that, but I'll put another post out, which might interest somone on the forum.
I look back the the 'Radio Constructor' years with fond memories, and built many circuits from RC. Indeed, one of the projects on my 'list of things to build' was in 'Suggested Circuits' in RC - a 'coil test unit' which enables you to test the coverage of a home-wound coil. It gladdens my heart to see so much Radio Constructor stuff archived on internet. I always have to restrain myself from delving into my spares box to start yet another project, despite having so many on the go already.
Best of luck with your reformer project Alan!
David
Hi David, yet another usefull gadget for all the capacitors i have, these will be put under a realistic voltage, and the neon shows what is going on, so does the meter, all housed in a smartish, metel case, with handle, and trivet underneath to give the right angle. It is quite an old fashioned circuit, but thats what i need its then inkeeping with the components/radios. I have a few 1930,s sets that are run, but if a capacitor was to fail, its nice to have a replacement, that works, like you i find home-made projects fascinating. The Avo information you sent was spot on, for the signal generator and avometer, thanks for your help, i follow your projects with interest.....regards....Alan.
A while ago I put this device together. It uses constant current to reform caps and I have had a lot of success with it (despite a few negative comments when posted elsewhere!).
Constant current means you can just leave it on overnight and let it reform gently, knowing nothing can go bang. Working voltage is also limited so no overloads.
Also, you can set the acceptable current leak (say 500uA for a very old cap) and watch to see that it does indeed finally take the full stress voltage (I allow working plus 10-20%).
In addition it is a very useful checker for all "those" capacitors eg the anode couplers. Wind up the voltage to working level and see what current flows (again, limited so no bangs!)
And yes, I know that real men only use a resistor a mercury arc rectifier and a variac but I am a wimp!
Provided to encourage discussion and kick off development ideas, not to trigger debate over "best" methods.
Total cost of bits would be about £20-£30, incl the dvm module. Far less if you have a good bits box.
all the best
Jeremy
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far better than mine basicly a variac the same voltage doubler circiut as yours ,with just a 10k curent limiting resistor and a ma meater to the cap under test using an avo across the cap to monitor voltage
rob t
(08-05-2011, 11:16 AM)Pamphonica Wrote: [ -> ]A while ago I put this device together. It uses constant current to reform caps and I have had a lot of success with it (despite a few negative comments when posted elsewhere!).
Provided to encourage discussion and kick off development ideas, not to trigger debate over "best" methods.
Total cost of bits would be about £20-£30, incl the dvm module. Far less if you have a good bits box.
all the best
Jeremy
Beautifully designed and drawn Jeremy! What software did you use to draw the circuit please? I'm not familar with the IRFBC40, but I've checked the datasheet and see that it's a hefty power MOSFET - 600V, 6 Amps, so it's well in spec in your application. When I was poking around searching for suppliers, I found this firm, which I've not come across before, but they seem to have lots of useful stuff and claim to be the main UK supplier of repair kits for LCD TVs etc. (I didn't check their P&P charges or whether they have minimum order quantities or values):
http://www.ohmsupplies.co.uk/epages/6202...ucts/TRT01
As to the little digital meter modules, who'd have though just a few years ago, that they'd become as cheap or cheaper than analogue movements? Neat idea to switch the meter with shunts to read Voltage and current. The only thing about these meters - certainly the ones that I've come across, is that the supply voltage that powers them must not be derived from the circuit that is beaing measured, but you've catered for that with the 6V winding on the transformer, rectified to provide the 9V for the meter. Some of the meters use a 5V or 12V supply, but that could easily be catered for.
The nice thing about homebrew, is that you can design and build geaer which is simply not avialable at any proce commercially, and over time, it susprosing how so much of what's needed can be found in an ample spares box. EG, a mains transformer from a scrap AC radio would suffice for the transformer, which would be the major expense in this instance.
As to negative comments from critics and sundry pedants, the one common feature they tend to have is that they're reactive rather than proactive - good at finding fault with the efforts of others, but never being creative themselves. And you're right about there being no 'best' or preferred method. The bassic priciple is invariably the same - build up the voltage as leakage current subsides, until the rated voltage of the cap is reached, by which time, hopefully the cap will be reformed, or consigned to the bin!
David
David,
thanks for the comments. Sometimes these sorts of posts result in a deafening silence and you wonder why you bothered!
I think I used MS Visio (which I had an old copy of) for the circuit diagram. Then pasted into Word.
Absolutely any old enhancement-mode N-channel MOSFET will do - They just need a decent voltage rating.
I certainly didn't pay more than £1 for mine.
FWIW the main switch was a 3-position toggle/lever switch, one position spring-biased. That means that you can flip the switch briefly to the "discharge" position, make sure the discharge LED goes out then release and you are ready to go again. I regularly do this during reforming sessions, even if the cap looks good.
Jeremy
Thanks for the reply Jeremy.
I've tried various ways to draw neat circuits, and invariably revert to floundering around using MS Paint. I've tried 'Express Schematic', which is a freebie, but as with all software packages, there's a steep learining curve to get into it.
Presumably the switch used for the resistor bank is just a standrd rotary switch of the sort that Maplin sell - the cotacts are rated at 6A continuous, despite their flimsy appearance.
Happy constructing, and thanks once more for the posting.
David
I used a standard rotary - it sits right at the low-voltage side and passes very small currents so anything will do.
PM me if you need any help constructing, or need the Visio original circuit.
BTW I used an old DVM module I had to hand but one of the newer ones with backlight would have been a LOT better in dim workshop light!
Jeremy