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Re: Odd Resistor Electrical behaviour
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Posted by JB on January 19, 2004 at 19:48:05 from (24.157.143.220):
In Reply to: Odd Resistor Electrical behaviour posted by Dave Craft on January 19, 2004 at 19:11:26:
Hi, the resistor probably requires a load to cause it to fail. Connect a 12V light bulb from resistor to ground and see if it glows dimmly or not. Problem reading the load end of the resistor with a volt meter is that the volt meter draws so little current that the voltage drop across the resistor is almost 0 and hence you read 12V. This is especialy true for digital volt meters as they require only micro amps of curent to read voltage. In math terms Voltage across Resistor = Current x Resistance. If current require for digital meter is 10 micro amps (10 x 10-6) and resistor is 5 ohms then voltage drop across resitor would be (10 x 10-6) x 5 = 50 x 10-6 or 50 micro volts.
So if you had a 12V battery connected to the resistor and a digital volt meter on the load side of the resistor the volt meter would read 12V because the -50 micro volts is to small to read.
This is the reason to connect a 12V light bulb on the load side of the resistor and it should draw 1 or 2 amps and the voltage drop across the resistor should be from 5 to 10 Volts. Sorry for the ramble but was an electronics troubleshooter for many years. JB
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