Battery Ah size for 3 phase alternator

I'm putting a Lucas 3 phase alternator (180W?) on a friends 750cc Commando with a Podtronics rectifier.
Will the alternator put out 15A maximum at 12V?
Or is the Amperage lower because the alternator is putting out over 14V to charge the battery?
The Podtronics is rated for 200W & 20A maximum.
With all this extra Watts / Amps do you need to increase the Ah size of the battery?
What Ah size battery would you use for the above arrangement?
The overall electrical load of the bike hasn't gone up, just the higher charging rate.

Should be ok with a margin of 20W.
They only create their max power at high rpms so most of the time the pod unit will have an easy time. If in doubt use the headlight all the time. What strains a reg rec is dissipating unwanted power.

I have used that alternator on my 850 with a 5 AH battery without problems, and 8 AH battery is better though. I leave the headlight on all the time and I have a 55W headlight. The balanced charging starts at around 2000 RPM when you have a good rotor strong rotor. Get a new rotor because the old ones loose their magnetism and also the blow apart sometimes. The best thing about the 3 phase alternator is it starts to charge at lower RPM than the single phase ones.

It is not often that you would run the engine less than 2000 RPM so the characteristics of this alternator really suit the Norton. Even around town with frequent idling the alternator seems to keep up. Usually when I go out on the highway after about 1/2 an hour the battery is fully charged and the ampmeter goes down to zero.

The size of the battery has no effect on the alternator.

Think more about power consumers vs. recharge time. If you have 150 watts of consumption (100w headlamp, incandescent running lamps, CDI electronic ignition) and a 200 watt alternator, you have 50 watts left to charge the battery. If you turn the headlight off, you have 150 watts and 1/3 the recharge time. The equations for calculating the *actual* recharge time are not too hard to find and use, but determining your usage and actual recharge rate are subjective to your riding style. The easy way to know for sure whether you're winning or losing is to install a remote AMP gauge temporarily.

BMW and Moto Guzzi are famous for having enormous batteries, yet being on the trickle every night. Mine was, as the daytime headlight requirement in FL coupled with a Dyna electronic ignition demanded to be run over 3000rpm to charge meaningfully-even a 50 mile ride with 30 open road miles each way to work left me weak after 3-4 days. Ducati upgrade resolved it.

I just bought a 3-phase alternator for my '71, and absent an electric start I expect zero charging issues-I will check the voltage when it's finished and if it's good, I'll run it until it proves otherwise.

Whether the battery is minimally sufficient, or greatly over capacity to run the starter (if you have one) doesn't affect how much work the alternator does to replace consumed capacity. You just have more or less reserve remaining.