Shunt for amp metter, to mach with alternator

[Pan Meibers]

I'm rewireing a motor. want to put in a shunt for an amp meter. the alternator is 80 amps. I know that the meter has to mach the shunt, not really sure how, but how do you match the alternator to the shunt? Any one?

[barnakiel]

Simple. Get a shunt specced so that it will not melt at full current. If you use a shunt that is not up to the job, it will melt like a fuse.

Rate for continuous, not intermittent.

Mind how things are wire for if starter juice goes via the same shunt then it WILL melt it (unless you sized the shunt to allow for starter currents).

There is some good info at bogart engineering www.

b.

[Tristan]

You can use one of Allegro ACS756 family current sensors. They work on the Hall effect principle -no power lost. If you are interested I might have a few of them for 100 Amps range.

[pbiJim]

I'm not quite sure what you are asking. If you want to wire in a low resistance shunt that lets you use a voltmeter to measure amps, then you would normally buy a power resister, typically 0.1 ohms or less, that is rated for enough amps to handle the maximum load, wire it in series with the load & put a volt meter across it. Amps through a 0.1 ohm resister will be 10 times the voltage read across it. Amps through a .01 ohm resister would be 100 times the voltage across it. A 1 ohm resister would read amps to volts directly, but it would chew up a lot of energy & waste it as heat. Amps times volts = power in watts.

If you are buying a remote reading ammeter that uses a shunt, then the proper shunt should come with the meter when you buy it.

These days, inductive pick up ammeters are much more common than they used to be. They do not require direct attachment to the load. The cheap ones only read AC. More expensive ones are frequently capable of reading AC or DC.