voltage drop across resistor ?

[exxos]

Hi all,

I built a current sence circuit which trips out at about 5amps using a a
0.1R Ressitor, Which should give around 400mV, which works fine. The problem
is I can't for the life of me remember how I worked out the resistor value.
I would assume that 0.047R would give me 400mV drop at 10amps though thats
only a guess. So how do you work it out ?

thanks,
Chris

 

[dirk]

R (ohm) = U (volt) / I (amp) = 0.4 V / 10 A = 0.04 Ohm

The power that is used by the resistor can be calculated as follows:

P (watt) = U (volt) * I (amp) = 0.4 V * 10 A= 4 Watt

In this case at least a 5 watt resistor should be used.

hope this helps,
Dirk

 

[exxos]

thanks, was about the same as my guess

Chris