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# Electrolytic capacitor ESR at DC (Zero Hertz)

## Electrolytic capacitor ESR at DC (Zero Hertz)

### RE: Electrolytic capacitor ESR at DC (Zero Hertz)

That is something that you can't measure - or even talk about. Even if you use the standard test method, discharge through an external resistor and calculate ESR from the initial negative voltage pedestal, that ESR is a result of the frequency spectrum contained in your discharge current and does not represent the DC ESR.

In other words, there is no such thing as DC ESR. And if it existed, you could not use it for any practical purposes.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

### RE: Electrolytic capacitor ESR at DC (Zero Hertz)

Don't quite understand the background for this question, but I could imagine the OP perhaps sees unexplained DC shift on the cap.
That's not an ESR issue, but dielectric absorption or "soakage" as National calls it.

Benta.

### RE: Electrolytic capacitor ESR at DC (Zero Hertz)

Perhaps one could determine the ESR at various frequencies and extrapolate the curve to zero Hz.

### RE: Electrolytic capacitor ESR at DC (Zero Hertz)

That would be an interesting excersise for a rainy day! If I know myself, I will probably do it in a near future.

Thought: Put DC on the capacitor and superimpose a square wave. FFT voltage and current. Calculate ESR at different frequencies from ratio Un/In, where Un and In means voltage and current value at the harmonics found.

That would also show if ESR varies with frequency or not. Has to be careful, though, so ESL doesnt show. That would ruin the measurements.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

### RE: Electrolytic capacitor ESR at DC (Zero Hertz)

(OP)
the reason for asking is that this capacitor will be charged up and then used to actuate a solenoid valve by discharging it through the coil.

...so its essntially DC.

But i fear that the Zero Hz ESR may be well high and poorly toleranced from part to part (or batch to batch?)

### RE: Electrolytic capacitor ESR at DC (Zero Hertz)

(OP)
sorry...forgot to say...."its a Latching solenoid valve"

### RE: Electrolytic capacitor ESR at DC (Zero Hertz)

I wouldn't say DC. If this is the latching coil you have discussed in other threads, the time spans involved are tens of milliseconds. That implies frequencies in the tens of Hz range and there, the ESR is essentially the same as at 120 Hz.

Also, it will have a very small effect on your circuit's performance. I think it would be a lot more productive to concentrate on real issues.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

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