Model Boat Mayhem

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: AlanP on September 10, 2008, 07:13:49 PM

Title: Capacitors
Post by: AlanP on September 10, 2008, 07:13:49 PM
I have been given quite a lot of capacitors but I am having trouble identifying them.

They are from Rapid Electronics Ltd and a look at the site has not made it any clearer to my simple mind.

They are ceramic disc capacitors (cos it says so on the packet) I have picked three at random  4n7   1n    180p is there a way of turning them into uF as I was hoping to find some 0.047uF and 0.1uF for motor suppressing.

Perhaps I am way off track and they are really hens teeth  {-)
Title: Re: Capacitors
Post by: chingdevil on September 10, 2008, 08:17:44 PM
Try Googling a converter program, or see if this one answers your question:-
http://www.electronic-supply.com/capconversion1.htm

Brian
Title: Re: Capacitors
Post by: barry park on September 10, 2008, 08:23:30 PM
A few 4n7 across motor terminals will do,with one 1nf or 4n7 from each terminal to motor case.
Earth the motor case to stern tube.
You will find hens teeth in an old transistor radio or similar electronic equipment.
Barry Park
Title: Re: Capacitors
Post by: AlanP on September 10, 2008, 09:45:18 PM
Thanks Barry and Brian, I have googled capacitors and found out that it is a cheaper way of getting a headache than buying beer

I think the n stands for nanofarad, so on one marked 4n7 I think the n is a decimal point making the value 4.7 nanofarad but still need to find out how to convert this to uF

I think the p is for picofarad, so one marked 180p, zero being the multiplier would be 18 picofarad, also need to convert this to uF

I think I am getting another headache. {-)

Alan
Title: Re: Capacitors
Post by: wideawake on September 10, 2008, 09:57:43 PM
Thanks Barry and Brian, I have googled capacitors and found out that it is a cheaper way of getting a headache than buying beer

I think the n stands for nanofarad, so on one marked 4n7 I think the n is a decimal point making the value 4.7 nanofarad but still need to find out how to convert this to uF

I think the p is for picofarad, so one marked 180p, zero being the multiplier would be 18 picofarad, also need to convert this to uF

I think I am getting another headache. {-)

Alan

Hi Alan

You're right.  It's conventional in capacitor labelling to use the p or n instead of a decimal point partly I think as on tiny cap's the decimal point can easily be misssed.

In terms of microfarads the n or nanofarad is 1/1000 of a microfarad ( 1 X 10-3) and the p or picofarad (often referred to as a puff) is 1/1000000 (1 X 10-6) of a microfarad.

If you're trying to make up a value from more than one capacitor you need to remember that the rule is the opposite of that for resistors.  ie Two capacitors in parallel add together C3 = C1 + C2 like two resistors in series.   Capacitors in series are calculated like resistors in parallel.

HTH

Guy

Title: Re: Capacitors
Post by: chingdevil on September 11, 2008, 10:16:06 AM
Alan
This one works even better
http://www.translatorscafe.com/cafe/units-converter/electrostatic-capacitance/calculator/picofarad-%5BpF%5D-to-microfarad-%5B&%23181%3BF%5D/

4n7 = 0.0047uF
180pF = 0.00018uF

Brian
Title: Re: Capacitors
Post by: FullLeatherJacket on September 11, 2008, 12:17:19 PM
Brian
What a useful link that is! It'll help save what's left of my brain cells.

Alan
0.22uf is OK across the brushes, as is 0.1uf (marked 104). 0.01uf (marked 103) from the brushes to the case is the norm.

Works for me; suit yourself.

FLJ
Title: Re: Capacitors
Post by: AlanP on September 11, 2008, 01:59:49 PM
That's a cracker Brian, thanks a lot  O0 even I will be able to manage with that.

FLJ
Thanks for your words of wisdom, I will now go and look for them at the back of the drawer where I threw them  ::)

Alan
Title: Re: Capacitors
Post by: malcolmfrary on September 11, 2008, 02:18:33 PM
When suppressing motors,a factor of plus or minus X100 makes little difference, the important thing is that they should be ceramic.  This ensures good performance at the frequencies involved and  makes sure that for our purposes the voltage rating is appropriate.  There are other construction materials that work just as well, but it is best to stick with something cheap and fairly universal.