Re: Where are all the ESR meters?


"Winfield" <winfieldhill@xxxxxxxxx> wrote in message
news:1185103461.604452.53880@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Jim Thompson wrote:
Winfield wrote:

I'll post mine, when I get enough energy to transcribe
it from my paper scratchings, calculations and notes.
Remember, it must be four terminal, and handle high DC
voltages when probing in-circuit storage capacitors.

How high is "high"?

Perhaps a better question is, how big is big?

Several designs we've been considering have a
pair of diodes to discharge the test capacitor
and limit the circuit voltages, but I've heard
these can fail with large, charged capacitors.

I think the issue isn't necessarily how high
the voltage (tube amplifiers get to hundreds
of volts), or how high the current delivered,
but how much energy is going to be dissipated
in the protection components that discharge
the guilty capacitor.

I'd say the answer is, the size of two fists.
I think we're talking about ~ 100J of energy.
Isn't that more than enough to blow out a
common glass diode and/or a 1/4-watt resistor?


Protection is easy - read the voltage across the cap in question with a
comparator, if it is more then a few volts, have a indicator displayed to
discharge the cap first. If it is below a few volts, connect the cap to the
metering circuitry with a couple of low RDS on FET's.




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