Mystery capacitor values

[Malcolm T]

Digging through some caps I find these, can someone help me with identifying the values please as the n designation is a bit of a mystery. I know its nano-farad but I'm still not clear on the actual value. Ta.

The multiplier, lets use "n" as it is the first one, is often used as a decimal point, n47F would be 0.47nF or 470pF and with a 350V rating seems more than plausible.

[Malcolm T]

Ah I took it as 0.47 Farads but thought that would be huge!
I'm really miffed by some of these new designations, why couldn't they keep things as they were?

[G6fylneil]

The F is the tolerance, 1% in this case.

[Skywave]

This might help.

First, prefixes denoting sub-units.
p = 10^-12; n = 10^-9; µ = 10^-6; m = 10^-3, where the notation 10^-n means 10 raised to the power of -n. Hence, pF, nF and µF. (For capacitors, mF is rare).

So, 100 pF = 0.1 nF
1,000pF = 1 nF = 0.001 µF
10,000 pF = 10 nF = 0.01 µF
100,000 pF = 100 nF = 0.1 µF

Therefore, 1n5 = 1,500 pF, as an example of a number after the n.

There is an alternative way of 'decoding' prefixes using basic arithmetic; example:
1,000 nF = 1 x 10^-3 x 10^-9 = 1 x 10^-6 = 1 µF

A few days ago, whilst having a tidy-up, I found a capacitor marked 15,000 pF. A quick bit of mental arithmetic converted that to 15 nF, which from the above, is 0.015 µF.

HTH,
Al.

[Skywave]

Originally Posted by Malcolm T

I'm really miffed by some of these new designations, why couldn't they keep things as they were?

The physical size of capacitors today is a lot less than those of the 1950s / 1960s. Consequently, if a capacitor is 1,500 pF, there will often be insufficient room to write that 1,500 pF on it, so 1n5 F - or just 1n5 - gets written instead, the 'F' being understood.

Al.

[Jolly 7]

I heavily rely upon my cheap component tester, when I am in the slightest doubt about component values. I have made mistakes with values in the past and also found that aging capacitors, both ceramic and electrolytic, can have significantly different values from their markings. Many multimeters struggle to read lower value capacitors, which is where the component testers come in handy.

Recently I got some modern 0.047 uF axial capacitors rated for 630 V. As Skywave observes, I was very surprised at their minute size compared to other similarly rated older capacitors in my parts box.

[Lucien Nunes]

I was very surprised at their minute size compared to other similarly rated older capacitors

The size depends as much (or more) on what dielectric is used, as on the age. So if you compare a modern polyester capacitor with an old paper one, yes it will be smaller. Just as a metalled polyester will be smaller than a film-and-foil version and much smaller than polypropylene.

But a modern paper-in-oil cap won't be much smaller than an old paper cap, and an old polyester (e.g. C280 or C296) won't be much bigger than a modern film-and-foil polyester.

Ultimately the size is determined mostly by the permittivity and dielectric strength of the dielectric, and these parameters haven't changed over time for any given material.

[Jolly 7]

Originally Posted by Lucien Nunes

The size depends as much (or more) on what dielectric is used, as on the age. So if you compare a modern polyester capacitor with an old paper one, yes it will be smaller. Just as a metalled polyester will be smaller than a film-and-foil version and much smaller than polypropylene.

But a modern paper-in-oil cap won't be much smaller than an old paper cap, and an old polyester (e.g. C280 or C296) won't be much bigger than a modern film-and-foil polyester.

Ultimately the size is determined mostly by the permittivity and dielectric strength of the dielectric, and these parameters haven't changed over time for any given material.

I am attaching a picture of one of my functioning old capacitors. What type is this ? Is it not metallised polyester ? It's approximately 35 mm long with diameter of 15 mm.

[Maarten]

That's likely a paper capacitor. Some are betters than others, I think this is a rubber ended industrial quality type but once the tiniest amount of humidity gets in, it is done for.

[Lucien Nunes]

I agree that is probably a metallised paper capacitor, I have seen these Matsushita parts marked 'No PCBs' in reference to the impregnant not being the nasty polychlorinated oil. It is rated for 450V AC mains duty, as shown by the safety approval marks and in certain applications ought to be replaced with an X-rated equivalent. Its non-safety DC rating might be as high as 1kV.

[Jolly 7]

Thanks for the responses. The capacitor is not too far off its rated value, I desoldered it to test. It's running between the on/off potentiometer and the internal/ external modulation switch of my signal generator. From the circuit it does not appear to have any high voltage across it and may solely be related to modulating the 400 Hz audio tone onto RF. I think I will probably leave it in situ as there are no problems with AF or RF signals at present.

I have attached a picture of the modern capacitor that might be a suitable replacement in case it's required in the future.