I know it is preferreable to run a volt meter instead of an Amp meter, but I want to use the stock gauges. My question is when running a high output alternator 100+ amps, is there a point at which the gauge can't take the load? If so, what can be done to prevent problems?
I suppose that exceeding whatever the full scale reading on the ammeter is would be as much load as you'd want to run through it. There are ways to add a secondary shunt around an ammeter so that a lower capacity ammeter can be used with a high output alternator. Do I sense another ammeter/voltmeter debate brewing?
The ammeter should be measuring how much current goes into or out of the battery. If you need to run a high current alternator to power high current loads (compressor, stereo, electric fan, power windows, etc) then the high current mostly won't be running thru the ammeter.
What squirrel says is true, the ammeter only measures battery charge or discharge - BUT - after a long cranking session on a cold morning that alternator is capable of pushing way more charging current into the battery than the ammeter is designed for. A shunt is an easy and safe way to insure you won't peg your ammeter permanently.
while i agree, my alternator spiked and the ampmeter melted and so did the wires. I was young and did really know what happened but the shop put in a volt meter instead. Since then i dont really use amp meters.
I just have the idiot light on my 55. Does all I need. I keep the engine working right so I don't need to crank it long, and I change the battery before it starts acting up (five years is typical).
Can anyone elaborate on the use of a shunt? Maybe even toss up a diagram? I have the same interest as the OP.
A shunt is just a thick piece of wire, and you use a meter that measures the voltage drop across the shunt. This tells you how much current runs thru the shunt. I dont know an easy way to convert an original ammeter to a shunt type. I do know that by the mid 60s, GM was using shunt type ammeters in their trucks and performance cars, instead of the normal full current type.
Had an Amp gauge burn up on a 56 Chevy once including the wiring. It left about a 2 1/2 inch burn mark on the top of a nicely pin striped dash. Lucky I didn't lose the whole car. Voltmeter's only since.
A good example of how to calculate a remote resistor to measure current without bringing the high current inside the car. http://www.allaboutcircuits.com/vol_1/chpt_8/4.html The resistor labeled Rshunt would go in the feed wire on the positive post of the battery. On later cars that is the thinner wire coming off the + battery connector, usually tied into the starter cable connector. It would read the total charge or discharge to/from the battery, not total alternator/ generator output. Depending on the shunt resistor you can make a 30 Amp meter read 100, 200 or more amps.
Thank You. Since I have been into electronic gadgets from the time I was a kid (about 65 years ago) I like to know what is going on with my machinery. A little time doing instrumentation on test rigs, space program and others, didn't hurt. I like to have a voltmeter, an ammeter reading alternator output and another one for battery charge/discharge. But, that's probably overdoing it.
DONT SUGGEST USING FACTORY AMMEMETERS ON HIGH OUTPUT ALTERNATORS.... BAD IDEA.... Shunt Resistor is the only way as described above.... aftermarket ones and even factory meters were always in series withthe charging wire.... So your stock was 30 amps and you have 100 to 150... peg it 1 time time and its toast.... Volt meters are the easiest way to keep up with how things are going... Also for 100 amp alternator make sure your using 4 gauge wire for your charging cable to your battery...
A redneck trick that was used on some of the old Mopars that were converted to higher output alternators was to run a second (shunt) wire from the output of the alternator directly to the + battery post. You are effectively shunting some of the current around the ammeter, and reducing the load that has to go through the firewall connector. The gauge of wire you use will determine what percentage of the current is shunted. The heavier the "bypass" wire, the smaller the current running through the ammeter, with a corresponding drop in the ammeter reading.
Here's some more info on how you can build a shunt: http://millpower-race-engineering.piczo.com/?g=43218292&cr=5 (scroll down to the Ammeter article) This set-up will work with up to a 70-amp alt., I think by adding 1 more resistor to the group it would work for your 100-amp alt.
I suggest having the ammeter serviced. They were not designed to last this long. In addition you could add a fusable link for insurance. As far as shunting is concerned, you can easily add one, but dialing it in takes a bit more time/effort. In any case the ammeter will tell you more about your charging system than a voltmeter.
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