Interpreting Electrolytic Capacitor ESR readings. Any ESR aficianados out there?

Thread Starter

RAMBO999

Joined Feb 26, 2018
244
Hello all

Merry Christmas to you all even though it will probably be wel over if you get around to reading this.

Just got myself an ESR meter and have spent a few hours going through the caps on a TV power board that I know has issues.

Seeing how it works.

I am not using the small ESR table that is attached to the device to interpret the output.

Instead I am using the cap manufacturer's datasheets for the appropriate cap series which are pobably more reliable.

In this case the manufacturer is CapXOn and their datasheets give impedance values in Ohms.

One example: CapXOn GF Series.

470 uF 16 V capacitor has Max Impedance at 20C / 100 KHz = 0.095 ohms

My ESR meter reading for this cap in situ on the board is 0.22 ohms.

Which is way over the max figure of 0.095 ohms on the datasheet.

Now here's the thing. When I look at the "Typical ESR values" table on the meter the "typical" value
for that cap is 0.21 ohms which is pretty much spot on. In other words it's fine leave it alone.

So I ask myself : Why the difference between the "typical" values and the datasheet max values?

Does anyone have any idea how these "typical" ESR values that you find scattered about are caculated?

They also vary from chart to chart I have noticed.

I know that there is an cap impedance ratio that is temperature dependent, and the rated temperature of
a typical cap is 105C, and I am wondering if that has any part to play in determining these typical values.

Is there a formula or some kind of approximation rule based on capacitance, voltage, impedance ratio etc?

How far away should an ESR reading be from the typical reading to be considered a failure? 10%? 20%?

Any thoughts?

Cheers

Ray Pooley
 
Last edited:

Papabravo

Joined Feb 24, 2006
14,412
Are you removing the capacitors from the circuit before taking the readings? I would not expect reliable results if the device is still on a circuit board.
 

Papabravo

Joined Feb 24, 2006
14,412
The whole point of an ESR meter is so that you don't have to remove capacitors from the pcb.
If your meter can measure the capacitor in circuit without being affected by the remaining circuitry then I have no idea what your observations mean. None of my meters can do that. In fairness, I have to say that I almost never work on ancient equipment that needs repair or refurbishing.
 
Last edited:

Thread Starter

RAMBO999

Joined Feb 26, 2018
244
If your meter can measure the capacitor in circuit without being affected by the remaining circuitry then I have no idea what your observations mean. None of my meters can do that. In fairness, I have to say that I almost never work on ancient equipment that needs repair or refurbishing.
Some modern multis do have ESR capability. It is nothing to do with "ancient equipment" . Quite the opposite in fact.

Alternatively you can supplement your meter collection by buying an ESR meter that offers ESR on its own, but usually including resistance, diode and transistor testing features.

ESR stand for Equivalent Series Resistance. There are two ways to assess the health of an electrolytic capacitor.

By measuring its capacitance using a multi that has the capacitance option. For accuracy it is best to remove the capacitors
from the pcb. Fine when you have one or two caps to assess. A ball ache if you have twenty caps, for example, to deal with.

By measuring the cap's resistance in the circuit and comparing that resistance to the resistance of a healthy cap as detailed
in the cap's datasheet. You can do this with an ESR meter without having to remove the cap from the pcb. This is the more modern way to assess caps in situ. Saves alot of time.
 
Top