20th May 2010, 5:49 pm | #1 |
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My Homebrew ESR Meter for testing el caps
I sometimes work in an outdoor workshop, and sometimes in a spare bedroom, so I tend to have tools and test equipment in one place when I need them in another! Hence, most items have been duplicated over the years rather than to have to trot back and forth, often asking myself “now what did I come out here for?”
One of the most useful items of test gear for renovation vintage radios and other eelctronic gear is an ESR Meter for testing electrolytic capacitors. Most people reading this will know that over time, capacitors can develop a high series resistance, and though they may read ok on a capacitance meter and exhibit low leakage, act as though there is a high resistance in series with the capacitor. (From experience, small low voltage electrolytics seem prone to developing a high ERS - cathode bypass caps etc, and I’ve cured a dim LED display in a VCR through changing a cap). ESR meters work by passing a low voltage AC current at 100 – 150 kHz through the capacitor under test, and measuring its ESR. Most electrolytic capacitor values have an ESR of much less than 10 Ohms which means good caps test at very close to full scale, and bad caps test at little or no deflection. Several years ago I built an ESR meter from a design in the now defunct ‘Television’ magazine, which has given a good account of itself, but I’ve long since lost the copy of the article and PCB artwork I decided it was time to make another ESR meter, so looked around for designs on t’internet. Three ESR Meter circuits caught my eye: The one I opted for is at this link. I favoured it because it is built on a PCB, uses easily obtained components, and unlike some designs, there’s no transformer to wind: http://www.members.shaw.ca/swstuff/esrmeter.html The designer (VE7IT) used four rechargeable batteries to provide the 5 - 6 Volts needed, but rechargeables soon self-discharge if not used, so are unsuitable for use in any low current device which is used infrequently, and then only for a few minutes at a time. I therefore modded the PCB artwork to incorporate a TS78L05 5V+ regulator so I could power the unit from a 9V PP3. These cheap and simple regulators need no external components, and as they have a 1.7V voltage drop, will provide a fixed 5 Volts even when the PP3 voltage falls to just below 7 Volts. As the meter only draws 25mA, a PP3 will last for a very long time. I also felt that many of the component pads on the PCB were a little small, so I beefed them up. I made a couple of other minor alterations to the tracks to make the pads of C5 fit the radial lead cap that I had, and re-routed one of the tracks (Pin 6 of the IC to R3) as there was little clearance from adjacent tracks. I used a 50 uA meter as specified, but found that to get full scale deflection I had to reduce the value of R17 from 10K to 3K3. I made a dial and calibrated the meter from zero to 15R, but in my experience capacitors either have a high ESR and hence are useless, or a very low ESR and are good, so the precise value isn’t all that important. The easiest way to check a capacitor about which you are doubtful is to see how it compares with a known good one. I etched my own PCB and had all the bits except the meter, which I bought cheaply from the aptly named ESR Electronics LTD, for under £5.00 + P&P and VAT. http://www.esr.co.uk/electronics/pro..._testequip.htm I’m not a fan of die-cast or ABS boxes, so I’ve taken to making my own enclosures from oak, with comb-jointed corners as they cost me nothing to make and are evocative of crystal set days. At least, I think so! I hope this is of interest, and have attached a few pics including my modified PCB layout, which might encourage others to have a go at this neat and cheap to build design of a very useful piece of test gear. The 5V+ voltage regulator can be seen at the top LH of the PCB, next to some soldered connections for which I apologise in advance if they're offensive to the eye. (Dire!) There are other ESR meter designs which I considered but rejected: This one: http://ludens.cl/Electron/esr/esr.html (A transformer to wind, and no PCB layout – built ‘ugly style’) And this one: http://www.qsl.net/iz7ath/web/02_bre..._esr/index.htm (Doesn’t need a transformer, but doesn’t have a PCB). David. |
20th May 2010, 6:12 pm | #2 |
Pentode
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Re: My Homebrew ESR Meter for testing el caps
What a beautifully-made piece of kit! Especially the box.
Have you ever considered a box-making service for those of us who are all thumbs at woodwork? Depending on the price I could well be interested in one (or more) like that... |
20th May 2010, 7:37 pm | #3 |
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Re: My Homebrew ESR Meter for testing el caps
Thanks for reading my posting and for your kind comments.
But in answer to your query - No! It's quite time consuming and hopelessly uneconomical. To make more than the occasional box, which I enjoy doing, I think I'd have to be banged up in prison with no other option but sewing mailbags, or it would drive me nuts. Really, I need to get out more But it keeps me occupied, exercises my mind, stops me from being put in a home, and is a way of my combining my twin interests of woodworking/turning, and electronics. It's not an especially difficult task for anyone with a cheap router to make a comb-jointing jig to make such boxes, but several fiddly time-consuming processes are involved. The wood I used was scrap, but needs to be planed to thickness, cut to size, the joints accurately cut on a router jig, then glued and cramped and a base fitted, then sanded on a belt sander, stained, given a coat of sanding sealer, sanded down to 400 grit, then treated with pastewax. Ridiculous really, from a cost/benefit angle, when the ESR meter would work just as well in a two quid ABS box. (I'm as mad, as a hatter of course). David. |
20th May 2010, 7:42 pm | #4 |
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Re: My Homebrew ESR Meter for testing el caps
Very nice.
Another cap meter worthy of mention, is Cyril Bateman's Tan Theta meter from Electronics World 10-12 years ago, sadly, I never did get round to building one. |
21st May 2010, 9:24 pm | #5 |
Heptode
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Re: My Homebrew ESR Meter for testing el caps
Lovely job David ... as always!
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Colin Armstrong |
21st May 2010, 10:22 pm | #6 |
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Re: My Homebrew ESR Meter for testing el caps
Thanks Colin - maybe I can at last get on with the wobbulator!
There's been a bit of slippage on the homebrew programme, ("mission creep"?) and I'm itching to get on with the Dave Gingery coil winder. (I've got the talley counter, so it's a start!). Hard work this retirement malarkey - I don't know how I do it for the money David. |
21st Jul 2010, 6:21 pm | #7 |
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Re: My Homebrew ESR Meter for testing el caps
Hello David, I like your ESR meter any chance of component value, some are obvious.Also in Radcom or ETI some years ago there was circuit diagram and details of how to measure the resistance of a moving coil meter by connec ting a linear pot in parallel with the movement I think, not sure, I have any knowledge in that area.Ted
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21st Jul 2010, 7:59 pm | #8 |
Octode
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Re: My Homebrew ESR Meter for testing el caps
If you look at the first link there is a circuit diagram and all other details.
Nice unit, well done. If anyone fancies knocking up a few PCB's I'd be more than willing to buy one. Just don't have the facilities to do my own. |
21st Jul 2010, 8:37 pm | #9 |
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Re: My Homebrew ESR Meter for testing el caps
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5th Aug 2010, 12:06 am | #10 |
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Re: My Homebrew ESR Meter for testing el caps
I built the same esr meter as David some months ago but couldn't get a reading on the panel meter. As I was busy, I left it till now before returning for a another look. The stripboard was inspected for shorts and the BF194 transistor replaced by a 2N4401 (higher Hfe).
Success! Maybe it was the transistor substitution that did it but the meter worked as it should. The movement was a bit stiff towards fsd so I had a go at oiling it when disaster struck. I managed to 'magnetize' it resulting in a very dead panel meter so it looks like I'll have to buy a new 50uA panel meter. At least I know it all works, so when it's finished it'll be part of something bigger which will get a write up from me. Back to the hot iron for now! |
5th Aug 2010, 9:04 am | #11 |
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Re: My Homebrew ESR Meter for testing el caps
Just a reminder from my original posting, I found that to get full scale deflection I had to reduce the value of R17 (the series meter shunt) from 10K to 3K3. Different meters may need a diffrent value of R17. I found that value by experimentation by temporarily substituting R17 with a 10k pot, which I adjusted downwards until I got full scale deflection on the meter - in my case, 3k3 - a third of the value specified in the circuit. Thus, I removed the pot and fitted a 3k3 resistor as R17.
The meter that I used was - as I stated, from (aptly named!) ESR Electronics, order code 124-116 'Analogue meter - 0-50uA'. It has an internal resistance of 6,500 Ohms. The current price of the meter is £5.31 + P&P and VAT. http://www.esr.co.uk/electronics/pro..._testequip.htm ESR (with whom I have no connection) can supply the other bits too. I explained that I didn't like the idea of using rechargable batteries (as used by the designer), they soon self-discharge in equipment that's used only occasionally, and for a minute or two at a time. The meter isn't heavy on battery consumption anyway - just a few mA. Hence, I preferred to feed the 74HC14N IC - which is rated at 2 - 6V, with a regulated 5V from a 9V PP3 battery, which will last for ages. The simple and cheap TS78L05 5V+ regulator is no larger than a transistor, needs no heat sink and if the amended PCB layout that I showed in my posting is used, fits easily on the board. In terms of de-bugging the project if it doesn't seem to work, a scope (and/or a frequncy counter) is helpful. At pin 2 of the IC, there should be an AC (spiky!) waveform of 156kHz or thereabouts - the actual frequency isn't important. This waveform is fed into the other 5 gates of the IC, which comprise a low pass filter, and from there outputs, via the five paralleled 680R resistors, the AC signal is fed to the AC amplifier - a 2N2222 transistor. At the base of that transistor there should be 0.0V p-p with the test terminals OPEN circuit, and when the test terminals are SHORT circuit, about 180mV p-p 156 kHz (or thereabouts). This AC signal passes from the output of the transistor (the collector) via C3, to the meter rectifier, which rectifies the AC voltage to DC and presents it to the 50uA meter, via a 22k pot, which is adjusted to zero the meter at FSD. There is no DC output at all until approx 75 Ohn (ie, equivalent to a high ESR from a duff cap), is present. Mid scale should be about 10 Ohms, and full scale 0 Ohms.). The scale isn't linear and is cramped towards the lower end. In my case, the right hand third of the meter scale was 0 - 3R, the mid third was 3 - 7R, and towards the lower end, was from 10R - infinity. Frankly, the precise value of ESR is unimportant. Most good caps have an ESR far below 10R - mostly below 0.5R, so a old cap which has an ESR of more than a few Ohms is highly suspect. The best way to verify that is by comparison with a known good new cap. I hope these notes - which should be read alongside the circuit, are of help, and might encourage a few other forum members to make an ESR meter - arguably, the cheapest and most useful bit of test gear in our armoury! Best of luck! David |
6th Aug 2010, 8:02 pm | #12 |
Pentode
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Re: My Homebrew ESR Meter for testing el caps
i myself would gladly buy the pcb or a kit if it was made available..
Thanks-Roger. |
6th Aug 2010, 11:15 pm | #13 |
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Re: My Homebrew ESR Meter for testing el caps
I might well have a go. It's AGES since I made anything.
I reckon 156Khz should be OK on Veroboard. Just!
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7th Aug 2010, 9:39 am | #14 |
Octode
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Re: My Homebrew ESR Meter for testing el caps
Years ago I made up a little FM transmitter on Vero, was about 4 CM square, worked like a charm ! Could tune over most of the FM band on my Dad's Pioneer Tuner Amp much to my amusement and his amazement ! 150 KHZ should be no problem.
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8th Aug 2010, 12:06 am | #15 |
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Re: My Homebrew ESR Meter for testing el caps
Thirded
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8th Aug 2010, 7:55 pm | #16 |
Pentode
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Re: My Homebrew ESR Meter for testing el caps
Well I have well and truely caught the bug...
researching the supply of parts,If I can construct it,and it looks half as good as David's then I would be a happy chappy.. David's workmanship is second to none,and this shows in the quality of his projects.. Obviously a person who takes pride in his work... I'm in awe mate.. Do'nt ask me to post pictures of it though lol. |
9th Aug 2010, 3:36 pm | #17 |
Heptode
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Re: My Homebrew ESR Meter for testing el caps
Hi David,
Thanks for the info regarding the 75L05 (now on order). I do have question regarding the PCB layout though. I copied this as per your layout but is this the correct orientation as the one I printed does appear reversed? I finally got to grips with some press on peel off material that I purchased from Maplin and had left in a draw and forgotten about. I was pleased with myself with the result that I had achieved (etching still to be undertaken) when I noticed my error. Regards Rob |
11th Aug 2010, 6:50 pm | #18 |
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Re: My Homebrew ESR Meter for testing el caps
Hi Rob,
Yes - sorry, the layout I posted is indeed reversed as you will see by reference to the component layout, so that the printed side of the mask (when printed onto inkjet acetate as a mask) is direct to the glass to minimise 'undercut' when the board is exposed. If anyone is using any other method of making the PCB than UV exposure (EG press n peel, laser printer onto photo paper ironed onto the board) it will be necessary to 'flip the layout in 'Photoshop' or whatever. Sorry for any hassle for not having made that clear. David. |
11th Aug 2010, 9:01 pm | #19 |
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Re: My Homebrew ESR Meter for testing el caps
I've taken another look at Rob's board, and in fact what Rob has printed onto his PCB is a mirror image of that which I showed in my posting. My posting follows the same orientation of the original artwork so if the tracks are etched as in my posting and (if the 5V regulator that I added to the layout is to be omitted) the original artwork as shown, the board will be correct.
However, if a copy of that artwork is used not simply for a UV mask, but for any iron-on techniques, then what is ironed onto the board will be a mirror image of the artwork, as Rob had. Thus, with such techniques, the image will need to be reversed. Hope that clears up any confusion! (I've been in touch with Rob by PM, and he tells me he's reversed the image and is well on the way to etching two boards - one for him, and one for a chum). David |
12th Aug 2010, 12:22 am | #20 |
Heptode
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Re: My Homebrew ESR Meter for testing el caps
Hi David,
Many thanks for the update. I must admit that I was confused by the 25k resistor (R10) thinking 'where on earth I am I going to get one of these?'. It appears that you used a 22k 10% resistor and I was suprised that these are not readily available from RS. All remain components are readily available. With the amount of parts that I have ordered (e.g. transistors in packs of 10's etc.) and if the PCB's etch well I might consider offering a 'kit' to others but I'll see how it goes at the moment. Regards Rob Last edited by Guitarist28; 12th Aug 2010 at 12:22 am. Reason: spelling correction |