Can an alternator generate high current at low RPM?

Answer 1

good question

An alternator is effectively a small generator. Thus, what you know about generators will also apply to an alternator.

Generator windings are designed to carry specified amounts of current; and a generator is designed to output a given voltage (within a range). If we imagine a generator using field and stator windings that is spinning at less than nominal speed, you will see the terminal voltage begin to decrease. To hold terminal voltage up (thus keep current flowing at the same level at this reduced frequency), the field winding will need to be energized even more (ie, more current pushed through the winding acting as an electromagnet) to increase the mechanical power pulled from the rotating machine. This will overload the field winding at some point (highly dependent on the generator design), and terminal voltage will not be able to be kept at a nominal value without causing damage to the generator.

So the answer to your question is: yes and no. an alternator could provide "high"current into a very small resistance load, but not into a high resistance load (because the terminal voltage will be reduced). The more important thing here is the power your alternator will be able to provide will decay as the speed decays, due to a decaying terminal voltage.

This is one reason for using 60Hz over 50Hz, and 400Hz on ships - the lower the frequency, the bigger (physically) generators must be to generate equivalent amounts of power.

There are other factors that will come into play here as well, such as the reduced RPMs may also reduce the coolling of the alternator, effectively de-rating it.