The reformer has proved very useful and effective, and the article is very informative on the topic of reforming electrolytic caps. For example, the author puts forward a formula for working out the time to reform a cap, as follows: T (in minutes) = 5 + M, where 'M' is the number of months that a capacitor is believed to have been in storage, either in an unpowered set, or N.O.S. So for example, if the cap has been stored for 40 years the total time to reform it is 5+ 40x12 = 485 minutes - about 8 hours.
In use, the voltage and current are set to the lowest settings and the reformer set to the 'Reform' oposition, then the current observed on the 10mA analogue meter, which should be much less that the maximum 10mA. The voltaage is slowly increased over time, keeping the current below 5mA. The author suggests that over a period of several hours, the voltage is increased in stages of a quarter, half, three-quarters and finally, the full working voltage of the cap, check at all times to ensure the the cap remains cool and the leakage current low.
That's just a brief precis of a seven-page article.
Just one important point to note:
In the circuit, the 6V winding of T1, which is rectified to provide 9V DC to power the digital panel meter, is shown as connected to ground. I've used several of these meters and the instructions that come with them make it clear that the power supply to the meter MUST NOT be connected to the equipment that the meter is measuring. Thus, the inut that powers the meter must be kept floating, and not share the ground that the rest of the equipment into which it is built. I've copied the circuit from the Winter 2008 Bulletin article (a sketch, as it appeared in the magazine), to show the error, and have attached an amended circuit showing the corrections.
I'm not sayng the author made an error - it may have been permissible to connect the digital penel meter that he used, in the manner depicted in the article. I'm simply saying that - to quote the instructions which came with the meters I've used they say 'power input must not share equipment ground or meter will damage and die'.
I've attached a diagram which came with the meters I've used which makes it very clear. These meters, which have a clear backlit display, are now quite cheap - as cheap if not cheaper than analogue meters, and can be used in all sorts of applications. I've used one in a homebrew zener diode tester for example, and am presently using a 9999 Hz frequency counter module (with a seven segment LED display rather than the more usuual LCD display), which cost about £12.00, to build a digital lathe speed indicator. (Of course one RPM is 60 times slower than 1 Hz, so for each rev of the lathe, 60 counts are called for to convert from Hz to RPM otherwise, if the lathe was running at 600RPM, the digital readout would only be 100. This conversion is made by fitting a disc on the lathe headstock with 60 slots in it, which interupts a beam in an opto interrupter).
That's another story, of which, more another time, but it illustrates just how versatile and useful these cheapo meter jobbies are, with a little imagination. The only downside, is that depending on the postal services from the PRC, they can take a few weeks to arrive, but hey - under the radar of VAT, and free post and pack - who's complaining!!?
Hope that's useful info, particularly to anyone contemplating building this cap reformer or using these meters in other applications. (They also sometimes have different power voltage requirements - my digital panel meter needs 12V for example).
David
In use, the voltage and current are set to the lowest settings and the reformer set to the 'Reform' oposition, then the current observed on the 10mA analogue meter, which should be much less that the maximum 10mA. The voltaage is slowly increased over time, keeping the current below 5mA. The author suggests that over a period of several hours, the voltage is increased in stages of a quarter, half, three-quarters and finally, the full working voltage of the cap, check at all times to ensure the the cap remains cool and the leakage current low.
That's just a brief precis of a seven-page article.
Just one important point to note:
In the circuit, the 6V winding of T1, which is rectified to provide 9V DC to power the digital panel meter, is shown as connected to ground. I've used several of these meters and the instructions that come with them make it clear that the power supply to the meter MUST NOT be connected to the equipment that the meter is measuring. Thus, the inut that powers the meter must be kept floating, and not share the ground that the rest of the equipment into which it is built. I've copied the circuit from the Winter 2008 Bulletin article (a sketch, as it appeared in the magazine), to show the error, and have attached an amended circuit showing the corrections.
I'm not sayng the author made an error - it may have been permissible to connect the digital penel meter that he used, in the manner depicted in the article. I'm simply saying that - to quote the instructions which came with the meters I've used they say 'power input must not share equipment ground or meter will damage and die'.
I've attached a diagram which came with the meters I've used which makes it very clear. These meters, which have a clear backlit display, are now quite cheap - as cheap if not cheaper than analogue meters, and can be used in all sorts of applications. I've used one in a homebrew zener diode tester for example, and am presently using a 9999 Hz frequency counter module (with a seven segment LED display rather than the more usuual LCD display), which cost about £12.00, to build a digital lathe speed indicator. (Of course one RPM is 60 times slower than 1 Hz, so for each rev of the lathe, 60 counts are called for to convert from Hz to RPM otherwise, if the lathe was running at 600RPM, the digital readout would only be 100. This conversion is made by fitting a disc on the lathe headstock with 60 slots in it, which interupts a beam in an opto interrupter).
That's another story, of which, more another time, but it illustrates just how versatile and useful these cheapo meter jobbies are, with a little imagination. The only downside, is that depending on the postal services from the PRC, they can take a few weeks to arrive, but hey - under the radar of VAT, and free post and pack - who's complaining!!?
Hope that's useful info, particularly to anyone contemplating building this cap reformer or using these meters in other applications. (They also sometimes have different power voltage requirements - my digital panel meter needs 12V for example).
David
