Author Topic: Yet another cap question from a noob.  (Read 1124 times)

GCUZakalwe

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Yet another cap question from a noob.
« on: March 16, 2015, 09:05:42 PM »
I'm a little confused by the letters in the materials list next to the capacitor values.  When I go the sites to buy caps  I see uF and pF and mF but no n caps.  Do I need to convert the values?  And what is the values for the ones listed as 2n2 or 1n8 and such.  I'm just starting to study this sort of thing and what I am seeing in the stores don't seem to match the stuff on the list.

mgwhit

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Re: Yet another cap question from a noob.
« Reply #1 on: March 16, 2015, 09:36:42 PM »
I'm a little confused by the letters in the materials list next to the capacitor values.  When I go the sites to buy caps  I see uF and pF and mF but no n caps.  Do I need to convert the values? 

Yep.  Some sites like to use nF (nanofarads), others don't and will use thousands of pF (picofarads) for lower values and thousandths of uF (microfarads) for higher values.

1000pF = 1nF = .001uF

And what is the values for the ones listed as 2n2 or 1n8 and such.  I'm just starting to study this sort of thing and what I am seeing in the stores don't seem to match the stuff on the list.

When you see values like this, treat the unit indicator like a decimal point.  So 2n2 = 2.2nF (= 2200pF ;) ).  You'll see that in resistor values, too, sometimes with k, as in 2k2 = 2.2K.  Sometimes you will see the unit indicator preceding the value, as in u22.  Again, just treat it like a decimal point.  So u22 = 0.22uF (= 220nF).

Edit to add: And just for the record, in this context u is just the Roman alphabet stand-in for when you need to represent the Greek letter μ (mu) for micro.
« Last Edit: March 16, 2015, 09:41:15 PM by mgwhit »

Jebus

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Re: Yet another cap question from a noob.
« Reply #2 on: March 17, 2015, 05:06:33 AM »
You can calculate them, but you can also just print a chart like this: http://www.justradios.com/uFnFpF.html

Also this is useful until you memorize the order: http://en.wikipedia.org/wiki/Metric_prefix

midwayfair

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Re: Yet another cap question from a noob.
« Reply #3 on: March 17, 2015, 06:33:02 AM »
uF and mF

These are the same. It's older terminology to use "m" for micro (not milli) in microfarrads. (Millifarrads never appear in audio electronics except once in a while you might see a 1 millifarrad cap as part of the power filtering.)
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GCUZakalwe

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Re: Yet another cap question from a noob.
« Reply #4 on: March 17, 2015, 11:38:31 AM »
Thanks guys that really helps.  The texts I have been reading mostly only mention the picofarad and microfarad values.  I didn't realize that out in the real world there were so many different ways to say the same thing.  I'm sure the more I do this I'll get to the point where I won't have to think about it much and it'll be much easier.   
And that chart will really help a lot.

pricklyrobot

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Re: Yet another cap question from a noob.
« Reply #5 on: March 17, 2015, 12:13:23 PM »
The fact that what's supposed to be a Mu = μ, is most often (but not always) written as a U = u, for convenience's sake, makes everything extra confusing;)

I like this chart: http://www.hamradio.cc/electronics/capacitance_conversion_chart.php because it has the actual component codes as well.

And this is an excellent resistor code calculator, while we're at it: http://www.hobby-hour.com/electronics/resistorcalculator.php
« Last Edit: March 17, 2015, 12:16:36 PM by pricklyrobot »