Electronics "guru"

Any non technical topic
RichardWallach
Posts: 340
Joined: Mon May 21, 2012 10:14 am
Name: Richard Wallach
Location: Melbourne, Australia

Electronics "guru"

Postby RichardWallach » Sun Oct 01, 2017 11:00 am

Does the AOC have an electronics expert who can work out the values for two capacitors in a Lucas Transistor Assisted Contacts circuit. Lucas provided all the service information but failed to list the value of each of the two capacitors. I can supply all the Lucas information.


Richard
Melbourne

NeilWillatt
Posts: 18
Joined: Sat Jun 16, 2012 7:35 pm
Name: Neil Willatt

Re: Electronics "guru"

Postby NeilWillatt » Tue Mar 06, 2018 3:35 pm

Hi Richard, Can you gain access to the capacitors separate from the rest of the circuit. If so, finding the capacitance of an unknown capacitor is a fairly standard problem for 17-18 year old school students. The procedure is as follows:

Connect one end of the capacitor to one end of a known resistor. Place a voltmeter across the resistor. Now place a 12V battery across the capacitor, positive to the end with a band round it if it has one. This will charge the capacitor. Disconnect the battery and connect the free end of the resistor to the free end of the capacitor so they form a circuit. The voltmeter should immediately rise to 12V and then drop, rapidly at first then more slowly. If this happens very quickly repeat with a larger resistor. If too slowly with a smaller resistor. Keep playing with different resistors until it takes about a minute for the voltage to drop to zero. Now repeat once more and record the time taken for the voltage to drop to 4.4 volts. (0.37 or 'e' x 12) This will give you the value of the 'Time Constant' for the circuit. The equation Time Constant = Resistance x Capacitance will give you the Capacitance.

NeilWillatt
Posts: 18
Joined: Sat Jun 16, 2012 7:35 pm
Name: Neil Willatt

Re: Electronics "guru"

Postby NeilWillatt » Tue Mar 06, 2018 3:37 pm

Hi again Richard,

Alternatively you could buy a multimeter with a capacitance mode for about £25 which will simply read off the capacitance directly.

Neil Willatt

durhamsmudger
Posts: 76
Joined: Thu May 31, 2012 2:30 am
Name: Alan Smith

Re: Electronics "guru"

Postby durhamsmudger » Sun Mar 25, 2018 8:07 pm

I agree with the multi meter route, but my experience has been that capacitors usually have the capacitance stamped on them .
Cheers
Alan


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