Instructables

how do i connect a shunt to an analogue ammeter?

how do i connect a shunt to an analogue ammeter?
can some please draw me up a diagram (even crude paint one will do ) of how i wire up an ammeter to a device such as a motor or something with one input and one output (+ and -) while using a shunt?

shunts really have me confused and i havent yet been able to figure out how they work logically


caarntedd3 years ago
Connect the shunt in parallel with the ammeter, then connect them in series with the load. Or connect the ammeter in series with the load and the shunt across the ammeter terminals. Or connect the shunt in series with the load and the ammeter in parallel with the shunt. Make the connections before switching on the supply. All the same, whichever makes the most sense.... I think.
jpoopdog (author)  caarntedd3 years ago
how about a crude labled paint diagram? please?
none make much sense compared to the other
Crude enough?
shunt.bmp
jpoopdog (author)  caarntedd3 years ago
excellent, thankyou!. also framistan, i think that is how the ammeter works. i already have orderd the ammeter so i dont plan on buying a voltometer too.

but thaqnkyou everone for your help. my next question is, what kind of shunt should i look for (specs if possible) to use with an ammeter which will read up to 20 amps, on a current which runs at 5v with an absolute maximum (before tripping the surge protector, its a pc atx) 30A?
The value depends on the ammeter you have, since you need to know its terminal resistance.
framistan3 years ago
A shunt is a VERY LOW resistance resistor. It is connected in series with the load. The resistance is so low that the voltage to the load is not affected. A volt meter is connected across the shunt resistor (not an AMP meter). Each millivolt you read from the shunt indicates a number of amperes. For example, your reading might be 52 millivolts. This would represent 52 amperes of current flow through the shunt. The actual reading and conversion depends on the shunts resistance. so my example is just an example. This (sort of) makes your voltmeter into an ampmeter because it is reading VOLTS but they are related to the AMPERES flowing through the shunt.
A shunt provides a parallel path for MOST of the current to pass through, and leave a little bit for the meter. Think of it as a very fat pipe, next to a very thin one - where does most of the flow go ?

Steve
jpoopdog (author)  steveastrouk3 years ago
i would suppose it would flow into the device!
though this troubles me as it would mean less current will pass through the ammeter, and wont give me proper results!

or will the ammeter still work it out?
will i also require such a setup to properly work out current using a multimeter? because i cant work out current with the multimeter, when i try passing current through the multimeter and into the device, no current come sout and nothing happens, and when i do it parralel, essentially just shorting out the powe supply, i dont get the actual usage .
The fuse has blown in the ammeter section of your meter, or you have blown ITS internal shunt !!

If you use a voltmeter, rather than an ammeter, measuring the voltage across the shunt is a direct measure of the current, since I=V/R

Steve