Blowing up capacitors

[invalid unparseable]

I don't see the number 3.7 for lithium-ion battery nominal voltage.

[Fredxx]

And??

[invalid unparseable]

I thought the poster, "The Natural Philosopher", implies the mathematical series he posted denotes all possible nominal voltages from all possible battery chemical reactions.

[Fredxx]

No, it's typical misinformation from him.

The series represent preferred numbers for component values, generally resistance or capacitance. Also zener voltages etc. The don't represent cell voltages that can vary from cell to cell as well as chemistry. Any similarity is a coincidence.

The idea of the E-series was historically associated with tolerance, where values would be selected on measurement and placed in the appropriate bin. The more accurate the higher the series.

These days most surface mount resistors are cheap. I would only now use

1% as the component price is dominated by the placement cost and it saves inventory. Capacitors tend to have higher tolerance, and most have a strong dependency on temperature.

[Joe]

No, they're preferred component values, varying approximately logarithmically as is correct.

Cells rarely have a particular terminal voltage exactly equal to the electronegativity difference of the chemical components. Secondary lithium cells, as an example, vary in voltage between 3V and 4.2V depending on the state of charge. They are sometimes described as 3.7V and sometimes as 4.2V.

A capacitor placed across a lithium cell would need to have a voltage rating of at least 4.3V, but would be more likely to be 4.7V or 5.6V. Many components still come in the old 20% tolerance values, even when they are actually 1% or better. Many types of capacitor come in 1, 2.2 or 4.7 multiples, as things like power supply smoothing capacitor values are not critical, and tolerances of most electrolytic capacitors are very wide.

[Peter Able]

Not so. For quite a long time, smoothing capacitors in gear using thermionic valves were 2, 4, 8, 16 and 32 microfarad. Some of these were

2-in-1 construction.

Us Oldies remember well the "red spot" !

PA

[The Natural Philosopher]

Exactly. A supercapacitor is not an electrochemical battery.

Oddly enough electrolytic capacitor and other capacitor voltage ratings are and always have been a mixture of the E series and simple

5,10,15,25,50, etc etc.

Since voltage rating only has to be 'high enough' the circuit does not depend on some precise value of breakdown voltage unlike say a Zener diode.

[The Natural Philosopher]

That is not a voltage rating.

[Rod Speed]

Yep

[Fredxx]

Cobblers.

series there of electrolytic capacitors:

2.5V 3V 4V 5V 5.5V 6V 6.3V 7V 7.5V 8V

While some of those might conform to the E24 or other series, most don't.

Get your facts right before spouting nonsense.

Yet in practise there are rules of thumb used for the voltage rating of capacitors depending on the type. Something I'm sure you won't have a clue.

[Rod Speed]

BULLSHIT

You have never ever amounted to a hill of beans, sniper.

[Commander Kinsey]

Fuck! I just connected a small one (25V 220uF) backwards to 14V. It was actually connected the same way round as a small fan I was powering from half wave rectified AC, so I thought I had it correct. But the fan was backwards. I wondered for about 10 seconds why the fan wasn't rotating, and was just about to check the voltage across it with a meter, when the capacitor blew it's top and shot me in the stomach. Gave me a f****ng fright and I made more noise than the capacitor. I didn't realise they hated reverse polarity quite so much, I thought it just wore them out. I've always used excessive voltage to deliberately blow one up.

[invalid unparseable]

It's a simple "power = voltage x current" formula.

If you connect an electrolytic capacitor in reverse polarity, the power going into the capacitor = VI. The longer the connection time, the more energy will build up to heat the oil inside, until it blows up.

If you use excessive voltage in a correct polarity connection, it might take much longer to blow one up because the over-voltage may not drive a large enough leakage current through the capacitor. You might get a fat, bulging, angry capacitor as a result.

[rbowman]

The + lead on an electrolytic never identifies as a - lead.

[The Natural Philosopher]

If it does, its in for a shock.

[Fredxx]

I agree, voltage ratings don't generally follow any E-series values.

I'm intrigued. The E-Series of values was invented circa 1950s:

So I'm surprised that valve systems would use non-standard component values.

Must have been before my time! :-)

[Commander Kinsey]

And anyway, the equaliser could be built in at manufacture.

[Commander Kinsey]

For a laugh, go into an electronics store and ask for a bisexual capacitor.

[Max Demian]

You can get bipolar integrated circuits. Are they mad?

[jon]

Sometimes you can get caught out with a polarised resistor.