Hooking up an ammeter

[llih]

I justed picked up a nice SW 100amp ammeter. It seems to be new. I was going to hook it up, but noticed that on the back it says to use with shunt. Would the gauge have had a specific shunt or bridge across the terminals? Can I make a replacement? If so, what would be the best material? Copper or brass? I never had a gauge that went this high. I really don't remember the rating of my alternator output. I am guessing the Delco is anywhere between 65-100 amps.

Thanks Brad

 

[John Smith]

Depending on what the alt came from it could produce over 100 amp. I would test the output before you fry your nice new gauge. My Delco alt puts out around 120amp.

 

[Otterav]

Hey,
A shunt refers to a specific part that you place inline from the alt main charge cable, or the battery positive cable. Either way it would be a SPECIFIC part from the mfg of the gauge.
eric

 

[theo]

Buy a shunt.

http://www.stewartwarner.com/Catalog/shunts.html

 

[llih]

Thanks guys. i thought there might be a specific shunt. i will get one ordered!
Brad

 

[Pin_Head]

External shunts are the cool way to rig an amp meter. One end of the shunt is connected to the battery + post. The alternator output and the chassis power feed attach to the other end of the shunt. That way both the current into and out of the battery are monitored (which it is supposed to).

You can also use the fusible link as an external shunt, but you have to calculate the lenght to use. You need to know the meter resistance, the current for full scale meter deflection and the maximum current you want to measure. You use this to determine the shunt resistance:

Shunt resistance / meter resistance = meter deflection current / maximum current.

One you know the shunt resistance you can look up how long the shunt needs to be on a table that lists the resistance per foot. the shunt resistance is a real low number, like .001 ohm.