Capacitor Leakage, and ESR Explained

[ppppenguin]

....The cause of a high ESR will, be as already mentioned, allow DC current to flow through the capacitor even after it is charged.

Mike, while much of your explanation makes sense, this bit does not. ESR and leakage are different things. Leakage can be often be modelled as a parallel resistance, but cannot, by its nature be a series one.

This article isn't bad: https://www.avnet.com/wps/portal/abacus/...apacitors/ but I haven't yet found anything online that gives a concise explanation of ESR and why it matters to us when restoring vintage equipment.

The article I cited has a nice diagram showing the imperfections of a real capacitor. Series and parallel resistance, plus series inductance. How perfect does a cpacitor need to be? Depends on the application, there isn't a single short answer. Behind this lies questions like "Why do we mak such horrible capacitors?" The answer is nearly always because we want a lot of capacitance in a small space at low cost. And we're prepared to trade off other things against that.

An example...
A reservoir capacitor will often be 100s or 1000s of microfarads. Totally impractical other than as an electrolytic. But electrolytic must be conencted the right way round, are leaky by their nature and will have series resistance which tends to increase with age. A small leakage won't matter -  what of the odd milliamp when you're dealing with amps. But that cap has a lot of current flowing in and out of it. The series resistance may be called "equivalent" but it will still make heat when current flows through it. Heat isn't good for capacitors, expecially electrolytics. So you need low ESR in this role.

So we all need to understand the whys and wherefores of capacitors when we're working on vintage kit. Or modern kit for that matter. I've got a lot of experience and I still run into capcacitor problems. See this thread: https://golbornevintageradio.co.uk/forum...p?tid=8219

So don't be ashamed of not understanding, please ask for help and we'll do our best. Even if we're not always right.