I am currently working on a project that requires a 24v alternator, which is powered by a mower engine.
This engine in particular runs around 3,000 rpm, give or take, and does not exceed 3,200 (based on a few quick tests with a cheap tach).
The main reason for this question is that I am trying to understand the power output relationship between the alternator, pulley, and engine.
I did a bit of research and see that alternators, which conform to ISO 8854, are rated as
IL/IRA VTV. Where
IL is the idle amperage output,
IR is the rated amperage output, and
VT is the test voltage.
However, when looking at alternators online, these metrics are often left out, which leads me to believe I may be incorrectly interpreting their meaning.
For example, take this Delco 10SI (1102916), which is rated for 40A @ 6,000 rpm.
If you know the engine runs at 3,000 rpm, with a max of 3,200 rpm, and will never hit 6,000, can you just linearly extrapolate and say @ 3,000 rpm the alternator will provide half (20A)?
Or, given the alternator rating in the example above with 40A @ 6,000 rpm, do you gear your alternator pulley in such a way that maps the running engine rpm (3,000) to the alternators rated rpm (6,000) to provide the 40A regularly?
From an application standpoint, the 24v alternator will be used to charge 2 12v 55Ah (wired in series @ 24v). The expected engine run-time is around 1 hour. The goal being to charge the batteries, as the engine is running, for that hour duration. I am trying to figure out the basics in terms of the alternator output power, in relation to engine RPM. Then I can I can size the alternator and accompanying pulley appropriately to charge the batteries.