advise on ESR meter project ?

If it's a really old piece of kit , and has electro caps in it, just replace the lot. They guys who built it probably didn't know what ESR was in those days, it's only become obvious with modern smps IC's, needing miniohms of ESR

martin

Don't bother with that one, get what everyone else in the industry has:

Bob Parker hangs out on the aus.electronics group, so you can ask questions there.

There is also this one, which even Bob himself has heard good reports about:

Dave.

"robb"

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hello martin, thanks for reply. i understand your point and i will likely do that however the trouble as pointed out on that ESR schematic website is that even brand new caps can have numerous ESR failures. So i was thinking before i invest all that time changing out all those caps i should at least test the new caps for ESR failures ?

thanks for the advice, robb

OK, nothing wrong with having an ESR meter, but repairing old bits of kit, say over 10 years old, just recap the lot, no need for a meter, and the caps today are a lot better than the 80's.

Are you really going to remove a 20 year old cap, measure it and then say " that's s*it, that one is s*it as well, so's that one", then stuff the occasional good one back into the pcb...., just replace them all

martin

Couldn't cope with the graphics on the web site, but in the old days, you would just stick 10uF here, 10uF there, and a splattering of a

And I don't think that a site selling ESR meters would say that Quality Control in modern factories is quite good.... a bit of FUD maybe

martin

My opinion, It does not come close to actually giving you a true ESR reading. All the design is doing is relying on high valued capacitors assumed to still have life and hoping to display the effective series resistance in them by assuming the Xc to be at a very low value with the 50khz referenced used. In practice, that isn't a real ESR meter.

When I worked at Semco, the preferred method used on the automation line for ESR testing was to apply a 1 us pulse to the cap via a low value R from a stable pulse source. Both the pulse source and net result reference from the cap under going a test were being monitored via a high speed comparator. When the pulse source reached it's max peak it would force another comparator to briefly update a sample and hold circuit for a generate voltage offset difference;

Theory of operation was that most caps when discharged (shunt shorted) would exhibit virtual 0 (Xc)with a fast raise pulse, and the net results of the resistance formed by construction and leads would then not allow for an absolute short to common which would give you a reference to work with that could then be translated into Ohms. Part of the components were mounted in the probe assembly arm to reduce induction in the equation.

Using this method, it did not matter if the cap was a small or large value type. it simply only did the acquisition of readings on a single positive transition.

This method was check against other equipment in the lab that was designed for Q testing of small and medium value and found to be very accurate.

"robb" wrote in news: snipped-for-privacy@corp.supernews.com:

I built and use it. It is adequate for good/bad/questionable diagnosis. It is also simple to assemble, I built mine from "junk" parts. I don't think I could beat it for the price...

The kit is from Vancouver BC We make some stuff out here.. :)

D from BC

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so this luden's ESR gives no useful info about a cap ? and its a waste of time design ?

Thanks for advice Jamie, robb

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Thanks for reply chuck, That looks alot like those Bob Barker ESR meters

Thanks for help, robb

I built this one

Chuck Olson W6PKP

from what I can see, it's not fully implemented to give you an accurate reading. If you were to have a failed cap due to loss of capacitance, it will give you the conclusion that it has a high ESR but that isn't true how ever. A circuit like that could work much better if it was modified. the idea of pumping in a square wave of 50khz into that xformer most likely generates +/- pulses if the induction is low enough.

My self, I would of used a bridge type sensing circuit from the source and from the cap test point with a low (R) between the source and test cap to measure the offset on the transition period. With this type of config, the cap would be in as a shunt and not as a series component. all one would need to do is cross the leads for 0 calibration before test begins.

If you don't know enough to mod this unit, maybe you should look for a simple LCR meter with that function on it.?

I haven't really seen to much on the net for a stand alone ESR meter. I think most just get a unit that does LCR/ESR. something like the below link. THat's a bench model how ever, they make a hand held also.

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Hi jamie speaking of using a bridge circuit how does this design look ?

If it is not obvious i am looking for cheap (free) ESR schematic/plans to build thanks for the help , robb

now you're cooking with GAS! :)

yes, That one will do just fine!

I built that one, the cost is low, and it works fine for what you want to do. If you want a laboratory grade instrument, look elsewhere.

Ed

On a sunny day (Fri, 21 Dec 2007 18:44:29 -0500) it happened "robb" wrote in :

I have no ESR meter, but many times if I wanted to know about caps I just used 2 scope channels, substract, and in that way monitor the voltage over the cap, and IF it shows fast transients the cap is defective. This method works nice in switchmodes. And indeed the applying a pulse method is likely the best, and can be used in the same way. I hope you have an analog scope :-)

For quick go/nogo indication, those simple ESR meters are handy and useful. If you happen to have access to some simple equipment, you can measure ESR and Self Resonant Frequency as follows: Connect a signal generator output to the capacitor under test. Connect the trigger output of the generator to scope trigger input. Connect 1 scope channel across cap under test. If a current probe is available, monitor cap current with it. Otherwise, connect a low value resistor in series with the ground lead of the cap under test and use a 2nd scope channel to monitor the voltage across this sense resistor. With the signal generator set at a low frequency (where Xc is high compared to the sig gen's output Z), increase sig gen output and scope chan sensitivities for clean waveforms. Increase frequency and observe decreasing voltage across cap and increasing current through cap, along with changing phase relationship. Readjust scope controls as necessary. Eventually, you will reach a frequency where voltage and current are in phase, and further increases in frequency cause decreases in current. The ratio of voltage to current at this frequency is a good estimate of ESR, and the frequency is near the SRF. This procedure can be time consuming, but, if you have already have scope and sig gen, you'll learn a lot about each cap you test. Paul Mathews

I bought recently this one :

nice kit, and with the esr meter you have for the same price of most of esr meters kits , a precise LCR meter !!! this is a valuable instrument I really enjoy mine !

regards.