With a 1-wire alternator the "turn-on" speed is the speed you have to get the alternator up to before the charging circuit will engage or "Turn-On". Once the alternator is operating you can run it at lower speeds although if it de-energizes it will need to hit the minimum "turn-on" speed again.
Basically, the alternator won't start outputting voltage until it initially hits 2500-rpm. After that, you'll need to keep the alternator above 1000-rpm for it to keep working. Once it falls below 1000-rpm it will de-energize (turn-off), and need to be spun back up to 2500-rpm to start working again.
From some guesswork we did previously, top speed on the axles would be around 27mph or 400-rpm. With a 10:1 pulley driving the alternator, you'd have to get up to around 17-mph for the alternator to turn on, and then maintain at LEAST 7-mph for it to keep working. Once you drop below 7-mph it will turn off until you get back up to 17-mph for it to turn back on.
The alternator will also drain 0.4 mAmps at all times regardless of whether it's operating or not. This is why you need a disconnect on the battery when you store the gokart. A plug in battery trickle charge is also a good idea when you have it sitting in the garage.
The ripple current is the output pulse of the alternator's stator and rotor. This is what makes the lights in cars look like they are pulsing when diodes go bad. The pulse is usually smoothed out by the battery and sometimes a capacitor in the rectifier. But basically 63-amps is an average reading, with actual output being somewhere between 51-75 amps depending upon the rotor position at that time.