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ibmapc
November 8th, 2017, 10:01 PM
Anyone here have experience with this ESR Meter? (https://www.ebay.com/itm/MESR-100-LCD-Auto-ranging-Capacitor-ESR-Ohm-Meter-100KHz-In-Circuit-Tester-O2C4/112354008915?epid=688962484&hash=item1a28d21f53:g:KNwAAOSwXYtY3hSX) I'm thinking of buying one to test for bad caps. I'd like to be able to test in circuit and this one claims that it can. Are there limitations when testing a capacitor in circuit? Any recommendations greatly appreciated. I don't want to spend more than 50 bucks.

Thanks

Greg

Chuck(G)
November 9th, 2017, 05:59 AM
An ESR meter won't tell you the in-circuit capacitance of a device, just its series resistance. It can be useful if you know how to use it and know what the readings mean.

There are some caveats--you don't use one on a powered circuit and if there are several capacitors hooked in parallel (common on computer PSUs), it can only measure the composite ESR, not that of any particular cap.

Basically, a low-voltage (so as not to involve semiconductor bandgap) AC signal is applied and the current flow is measured. All the other stuff is refinement and window-dressing. If you're of a mind to "roll your own", here's a popular DIY ESR meter project (http://ve7it.cowlug.org/esrmeter.html).

The whole theory hinges on the fact that wet electrolytics dry out with age, which causes the effective internal resistance to rise, which also (remember I2R?) causes self-heating to increase and accelerate aging.

Unknown_K
November 9th, 2017, 06:27 AM
For on board testing you probably need some expensive industrial equipment.

dabone
November 9th, 2017, 08:41 AM
I've got this one, and it's been decent for in circuit testing. I've found it worth the money.

Remember it only tests esr.

Later,
dabone

David_M
November 9th, 2017, 07:57 PM
In circuit testing will rarely work and it will never be clear if the ESR is accurate, so unless its 100% reliable its 100% useless.

Save yourself cash and headaches... and get something useful that works.
https://www.ebay.com/itm/Digital-Combo-Component-Tester-Transistor-Diode-Inductor-LCR-Capacitor-ESR-Meter/201588666635?epid=607602869&hash=item2eef9ef10b:g:rHQAAOSwxj5XQCXN

Chuck(G)
November 9th, 2017, 09:08 PM
An ESR tester is useful for a 'go/no go' type of test, but if you're looking at accurately measuring the ESR of a 68,000 uF electrolytic in-circuit, forget it. Remember that in-circuit ESR testers put out only a couple hundred millivolts AC, which would make the AC drop across a big low-ESR capacitor in the microvolt range.

retro
November 13th, 2017, 05:23 AM
I built the Altronics (http://www.altronics.com.au/p/k2574-esr-meter-kit/) kit. I get good use out of it. Works well for in-circuit testing.