# Shunt

Discussion in 'General Electronics Chat' started by allcircuit, Jan 14, 2009.

1. ### allcircuit Thread Starter Active Member

Jan 7, 2009
31
0
For a battery source of 9V for measuring watt, what is the most appropriate shunt value can be used (to get the measured current)? I just knew that V,I and R could be variable to each other depending on what values of R and I will be against the load.
Thanks for giving advice and guidance.

2. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
Can you expand on your question? I am not at all clear about what it is that you want to measure and how.

3. ### allcircuit Thread Starter Active Member

Jan 7, 2009
31
0
Well, i was building a simple meter to measure watt. Inside the meter, there is a component where I need to measure the current (the current will go through the a shunt resistors). As I know there is power dissipation for the shunt, lets say if i use a 0.005 Ohm shunt, with 2A of current, there will be an xtra dissipation power of 0.02 Watt.

Now, i use a 9V battery, how can i decide the shunt range where i can use? What will be the possible range of current varies?

4. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
I'm still unclear about the function of your 9 volt battery. They are not able to supply 2 amps of current.

The function of a shunt resistor is to provide a low resistance path in parallel with the measuring voltmeter, which has a high resistance. The shunt lets the normal circuit current pass with minimal effect, and also gives a voltage drop that the meter can respond to.

The down side of this is that as current decreases, the shunt has to be either larger in value in order to develop measurable voltage - seriously affecting the current - or must remain at a low value and be amplified by an active device.

5. ### allcircuit Thread Starter Active Member

Jan 7, 2009
31
0
Yup,
thats the function i wanna implement. Just curious to ask, for a 9V battery source, around how much current will flow through the load, so that i can have the minimal voltage drop on the shunt.

6. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
A 9 volt battery is pretty limited. Something like 15 ma is the largest recommended load.

Of course, you have not yet defined "the load", so all we can say is that I = E/R. The shunt resistor is in series with the load, so heavy currents will result in a maximal voltage drop across the shunt resistor.