two led esr meter kripton depository

[pete g]

hi all, I found an esr meter that I want to build. can anyone tell me if it can be used in circuit?

http://www.belza.cz/measure/ctst.htm

[SeanB]

Most ESR meters are not meant to be used in circuit, as there can be parallel low resistance paths that give an erroneous pass indication. However generally if you use it in circuit it will in most cases be somewhat reliable in showing faulty, but the one linked is not exactly great for ESR, only giving a pass fail reading, and the ESR of most capacitors really is low, and the line between working and fail is very small for low ESR capacitors, typically well under 0.5 ohm is reasonable, over 1 ohm is generally a fail, and this one has a pass fail resistance of around 5R.

will work for most general purpose non low ESR capacitors, and for pretty much all high voltage capacitors which in most cases have a high ESR, but for low voltage and SMPS electrolytics it will only show you grossly failed capacitors, not those on the way out only.

You probably want one with a scale showing you the ESR in ohms instead.

[kripton2035]

I referenced this one on my repository , well for reference
today, you can build the jay-diddy-b ones (I reference too)
they are meant to measure in circuit, and have a small coil output that gives a better idea of the esr than just 2 leds.

http://kripton2035.free.fr/analog%20esr/esr-5-transistor.html
and also this one that is protected from high voltages on capacitors :
http://kripton2035.free.fr/analog%20esr/esr-dmm-adapter-.html

[pete g]

hi guys, thanks for your replies. actually I have made the jay diddy meter, it works great. I realize the 2 led meter is not for low esr caps, such as found in computers and switch mode p/s. I was just curious if this meter could be used in circuit allowing for its limitations. it puts out about 250mv pp at 500kc. so it shouldn't turn on anything but shockey diodes. is this correct?

[kripton2035]

yes if it puts less than 300mV on the probes, it could be used in circuit.
nothing is better than a try...

[Conrad Hoffman]

ESR meters give you some information and people do use them in-circuit, but my first choice is still a conventional bridge or capacitance meter. As long as the voltage is kept low (and that's automatic when checking aluminum electrolytics at 1 khz or more whatever instrument you use, lest you need a power amp to drive it- try putting a volt of AC across a large cap) they can be used in-circuit.

With a proper cap bridge or meter you get both capacitance and loss, so you actually know something useful. Unless you're specifically interested in switching supplies, dissipation factor is a better measure of loss than ESR. ESR only has popular appeal because everybody knows what an ohm is. Dissipation factor is just a simple ratio, but is, IMO, handier because the value of the cap is already factored in. Building a traditional cap bridge is incredibly easy, just as easy as most ESR meters.