I think that Alan J means 180 watts or otherwise he could do a bit of welding while out and about. The standard Walkernator can produce up to 30 amps, and an experimental one on test now can produce 40 amps, and although a 12 volt system is nominally 12 volts in reality while running the volts tend to be about 14.3 thus over 400 watts can be available. However, so far no one has found the need to fit a 30 amp ammeter. What happens is that once the bike is started the ammeter tends to go right over to full charge. If one then hold the bike on tick over for a few seconds the output from the alternator is sufficiently low, due to the low engine revs, that the alternator is not able to produce the high rate of charge. The amps drop progressively down as the battery volts build up to the 14.3 volt level. Typically this takes seconds, or if the battery is really flat then a charge of about 6 amps continues to be shown. Once the amps reading has dropped to this level then one can use as many revs as one wishes and the 8, 10 or 12 amp ammeter being used is well able to take care of any passing charge. The rather small batteries used on bikes charge up very quickly when a few amps are fed into them and very quickly achieve a sufficiently high voltage that the charge rate drops. What can cause trouble is a dud battery. If you have a worn out battery which cannot attain its full voltage of 14+ volts then the system continues to belt out large numbers of amps to try to bring up the battery voltage and if the ammeter cannot cope with these then something will fail.
B’knighted’s comments above are correct in that when using an ammeter all the charging current has to go up to the front of the bike and then back to the battery. It is better practice to feed the battery direct and then use a volt meter, or LED system, to indicate battery volts. My trouble is that having been brought up in the era of ammeters I find it very comforting to be able to glance at the front of the bike and see at once just what is happening with all those electrons which I cannot see, but can feel if there are enough of them!!