A question on salvaging capacitors from junk boards (trouble reading them)

[Kevin Mitchell]

I apologize if I'm in the wrong section or even if this topic is not appropriate for this site. But I'm having trouble figuring this out on my own.

So at my work place there is an endless supply of junk circuit boards. Most (if not all) are made in china and these are typically parts of printers and/or copy machines. I would like to salvage some parts for my pedal making hobby and I keep coming across film capacitors (greens and reds) that read something like ".015J400" That particular one being a green film cap by appearance.

Can anyone explain to me how to tell the what these values are and if such capacitors could be used for pedal circuits.

Sorry if anything I've said is unclear. Thanks in advance for any insight.

[Seljer]

0.015 = .015uF = 15nF, usually when you see the number with a decimal point it means its specified in uF, otherwise you sometimes might see them marked "153" denoting 15 * 10^3 pF = 15000pF = 15nF

the letter is most likely the tolerance, J being +-5%

400 = 400V voltage rating


Capacitance is capacitance in this case, go ahead and use them in your pedals, the voltage rating (and hence physical size) is a bit overkill but they'll still work

[R.G.]

In the case of that particular cap, it is 0.015 uF, 5% tolerance, probably 400V.

There are several ways cap makers label their products, and it may vary from manufacturer to manufacturer. The markings are mostly described in the maker's datasheets.

They all loosely follow the E12 or E24 numeric series of preferred values, and letter mark the tolerance: F=1%, G=2%, J=5%, K=10%, M=20%.

You're often on your own to guess a value from the marking. Generally if there is a leading zero, as in "0.1" or "0.015", it's in microfarads. Sometimes they use a "Mu" symbol, the long-legged "u" for uF and follow the Euro resistor styling: u22 = 0.22uF. Sometimes they use the pF code: the value is the first two digits of the three digit code, and the third digit is the number of zeros to add, and that all interpreted as picofarads. So 104 = 0.1uF; 223 = 0.022uF; 102 = 0.001. This gets confusing when you're dealing with 100pF. Should that be labeled as "100" for the number of pF, or "101", following the practice? Or does it mean 10pF, there being zero 0's after the first two digits.

Experience with caps to guess an approximate value from the size and shape, or the maker's datasheet may be needed. Even better, get a capacitance meter.

[Kevin Mitchell]

Thanks guys that really clears this up! I wasn't sure if there was some sort of Chinese mind game going on with their labeling and Google wasn't of help.

I feel as if I hit the jackpot here. Very happy. Thanks again! 

[GGBB]

As Simon alluded, the physical size of a typical 400V film cap can be a limiting factor affecting usefulness in pedals.  In addition to sheer body size alone, if you are going to be using pre-fabricated pedal circuit boards or following an existing vero or perf layout, the lead spacings of higher voltage caps are often wider than what the layouts will have, and since you won't have much lead length to work with due to them being salvaged, they probably aren't going to work.  If you are doing your own layouts, then size won't be a problem as long as you accommodate during design.

[bool]

ehhhhh ... as if size was ever a limiting factor

everybody knows that bigger=better, more mojo and of course "more tone"

besides, a 15n/400V shouldn't really be the same size as some 2uF/400V caps are

more probably it's a R10mm part, rather than a R5mm part, but hey, that should be still perfectly manageable.

[Kevin Mitchell]

Well here's the thing. The cap I used as an example really isn't that big physically compared to some orange caps I already have on let's say my Neo Vibe board I'm working on (R.G.'s layout) which has extra pads to fit your cap choice.

Capacitors physical size should never be an issue unless it's getting in the way while boxing it. It could be crud and ugly but it'll work. Luckily these green and red caps are half the size of some of the orange ones I've been using even though the voltage rating is higher.

Oh, and I don't use vero or premade pcbs. I enjoy printing my own boards (toner transfers on copper clad). Or at least that's what I've been doing sense I've started a few months ago. I've become such a fan of R.G.'s layouts anything that isn't on his site I'd rather make myself. I've gotten use to small pads and traces. Seems more professional by my amateur standards.