Capacitor question (nf, pf, uf...)

stolenfat

Heyo, trying to build an atari punk box, i was wondering if pf caps, could be substituted for nf caps? The schematics i found from getlofi called for nf caps, but all radio shack carries if pf and uf caps.

Whats the difference here? I know uf generally refers to electrolytic caps, pf are generally ceramic caps, but thats about as far is i go.

Most of my circuit knowledge is anti-theory, im a long time circuit bender and am now trying to move into build circuits from scratch instead of just modifying them.

Thanks for any help!!!

And if your so inclined to enlighten me further, what difference will a 1/8 watt resistor have on circuit compared to a 1/4 watt resistor of the same ohm value?

Hoooo!

asafnetzer · Joined: Jun 16, 2007 Posts: 112 Location: Israel

Hi stolenfat,

Regarding capacitors, you do not need to substitute just to use a Conversion Chart, theres a nice one here http://www.justradios.com/uFnFpF.html

most non electolytic caps reach up to 2.2uf, thats as far as I could find.

hope this helps

Asaf

blue hell · Posted: Thu Apr 17, 2008 2:02 pm Post subject:

Th uF, nF and pF things do not denote a capacitor type but they are scaling suffixes for the value, just as 1 kilometer is 1000 meter.

So 1 Farad is equal to 1,000,000 uF (micro farad)

1 uF = 1000 nF (nano farad)
1 nF = 1000 pF (pico farad)

Sometimes mF is used for mili farad, and 1 mF would be 1000 uF

The reason that u is used for micro is that the greek letter μ (mu) that should be used is not so easy to type on a keyboard and the m was in use for mili already.

For resistors the qualification in Watts (as in 1/4 W or an 1/8 W) tells you how much power they can convert to heat before they blow, the lower the number the sooner they blow. So when 1/8 W is specified you can safely use 1/4 W, but not the other way around.

blue hell

Inventor · Posted: Thu Apr 17, 2008 2:05 pm Post subject:

Welcome stolenfat! The wattage rating on a resistor refers to how much power it is capable of dissipating before it fails. Calculate the power dissipated by a resistor as either of P=V*I, P=R*I*I, or P= V*V/R. You can use any one of those three formulas depending on what you know about the circuit. You want to make sure that the power dissipated by the resistor is well below its wattage rating. That way you won't let the smoke escape out of the resistor!

stolenfat · Posted: Thu Apr 17, 2008 10:44 pm Post subject:

dude, thank you guys so much for the help!!

:DDD

françois · Posted: Fri Apr 18, 2008 1:23 am Post subject:

Hello,

And to make things a bit more confused... in SPICE simulation, upper- and lower- case letters are not considered different. So if you have a 1 mega-ohm (1 MΩ) resistor and enter it as "1M" you end up with a 1 millli-ohm (1 mΩ) resistor, which is one billion times smaller... Smile

You should have entered "1 MEG" !

-- françois

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

GlassX · Joined: Jan 27, 2008 Posts: 50 Location: Brazil

françois · Posted: Sun Apr 20, 2008 2:10 am Post subject:

Oh, yes... I can't understand why SPICE is so touchy with abbreviations. I always (like many others, probably) use "1M" to mean "one mega-ohm". And milli-ohm resistors are by far unlikely to be found in real-life designs. I can understand that upper- and lower- case letters are not distinguished (this is true in LISP, ADA, Pascal...) for portability issues, but, milli-ohms as a default interpretation bashes me !

OTOH, "M" for "milli" does make sense for inductors (milli-henrys) but those animals are not very common, or even capacitors (milli-farads, 1 mF = 1,000µF, already a big one but not irrealistic). Probably they did not want to have different conventions for different components.

-- françois

Inventor · Posted: Sun Apr 20, 2008 2:41 am Post subject:

I have a *guess* at why capacitors are marked in uF and pF, but not mF or nF. Electronics grew primarily out of radio communications and power systems. Power systems used uF capacitors primarily. radio used uF capacitors for the audio section and pF capacitors for the radio section. Capacitors in the mF and nF ranges just weren't used that much in the early days, so when a nF capacitor was required, it's value was simply denoted in the familiar uF range as 0.000X uF or whatever. The standard stuck with us til today.

Also I noticed over the years that technicians use uF and pF, while engineers often use nF in addition to uF and pF. I suppose that was because technicians are more "hands on" and their familiarity is with the parts vendors, while engineers are taught all the suffixes right off the bat in school.