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Tech Square Technical and speculative discussion of amps, cables and other topics. |
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Tech Square Technical and speculative discussion of amps, cables and other topics. |
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In Reply to: RE: Resistor for power transformer voltage drop posted by clifff on November 19, 2008 at 05:53:27:
Hi Clifff,
Thanks for your reply, much appreciated. The application is a phono amp. All measurements that have been taken (two different parts of town and three sets in total) indicate that its not mains variation but is down to the transformer. A variac would do the job nicely but is going to cost a lot more!
An engineer friend estimated a current of 200ma and a required drop of 10v.
Therefore R=V/I, R = 10/.2 = 50 ohm
Having tried a 47 ohm on the transformers live input last night I got the following results:
Ideal V, Without resistor, With resistor (47 ohm)
15, 17.79, 17.44
6.3, 7.46, 7.33
300, 353, 346
12.6, 15.01, 14.76
So therefore the resistor has only given approx 1/8th of what was expected (and required).
Does this indicate that a resistor of approx 375 ohms would do the job?
If so then how does this relate to the above equation (V=I/R)?
Thanks for any help. As I posted originally I am new to all of this (and dearly wish that I paid more attention when I was young and at school!)so do find it all a little confusing.
Also for the value of V being the p.d. across the resistor. I take it that the p.d. is the voltage drop and not the 240v going through it? The books that I have are not at all clear on this point.
Many Thanks,
Simon
Edits: 11/19/08
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Follow Ups
- RE: Resistor for power transformer voltage drop - amos 06:50:09 11/19/08 (2)
- OK, now we know what we are dealing with! - clifff 14:56:21 11/19/08 (1)
- RE: OK, now we know what we are dealing with! - EchoWars 19:07:32 12/02/08 (0)
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