SAE rating for alternator


Ford gives my 2019 Superduty an alternator rating of 377Amps (dual alternators). Is that the actual ISO or SAE rating? If not, how would I find that? And at what RPM? Thanks in advance


Expedition Leader
On a Super Duty I'd have to think an alternator is stated per SAE.

The specification for alternators is SAE J56. It's basically a standardized way to test and mark so the current is given at uniform RPM, voltage and temperature. For the purpose of marking the SAE temperature is defined as 23°C ± 5ºC, test voltage is 13.5, the "idle" is defined as 1,500 RPM and "rated" is 6,000 RPM.

So a hypothetical alternator would be marked like 200/377/13.5V in your example, meaning idle/rated/test voltage at the test temperature.

The typical way to show an alternator is to give an ambient (23ºC) and hot (93ºC) curve over a range of RPMs and probably at a higher voltage.
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