How to measuring output AMPs from an Alternator?

[69ChargerRT440]

Is it possible to measure the number of AMPS my alternator will produce if I have a Voltmetter gauge?


I have a 2 Field Alternator.

[beepbeepsrule]

Not really. Amps are a product of Volts run thru resistance. Raise the volts for the same resistance and amperes go up. Same with resistance, raise it with the same volts and amperes have to go up to keep up. That is what the voltage regulator does, keeps the volts the same for added resistance by telling the alternator to add more "power" which is measured as amperes.

You have to know the resistance and the volts to calculate the amps. Resistance also changes under load for components with coils and magnets and the like, that is called reluctance. Almost impossible to measure or calculate. Ammeters are in-line, actually part of the circuit, that is how they work.

You could turn everything on and measure voltage as you increase RPM's but you would still have to know the exact resistance/reluctance encountered over the entire circuit to calculate the amperes.

[dave571]

Voltage is the most accurate way to see what the charging system is doing.

If your system voltage is low (like battery voltage) then the alternator is not making any amps.

The amps, forced into the system, make the voltage.

If your thinking like plumbing, amps=flow, volts=pressure

What is the voltage across your battery terminals, when the car is running?

[dewme5]

there are clip on amp meters, and even some old school ones that look like a stock ammeter, but you just press it against your charging wire.

we have a Mac high current inductive amp probe that will measure to about 200amps. swing by the shop, and I'll let you know..

[cgraff]

Not sure if you have the alternator on or off of the car. Perhaps an alternator shop can perform this?

[Bigdog340]

Some auto parts stores can check the amp rating or a rebuild place.

If you get 13.9-14 volts at the battery when the car is running its charging, less than 12v its not. If its just over 12v its broke. Turn on everything you got and recheck. If the alt cannot maintain that same 13.9-14V then you need a bigger model alt.

71 Duster 340
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