I wrongly assumed that all A127 V pulleys were the same. If you wanted a higher power unit you need the poly-vee belt.
So I need to ask the question next time I buy the A127 and get the biggest amperage for a reliable transfer over a 10mm belt. I have a 25mm2 cable from B+ to battery, so output amps are not a problem. I need the amps to charge my leisure battery quickly as I plan on installing a lot more loads before winter comes.
PS. After belt snapped in Colne, I still managed to drive an extra 15 miles to work and fitted a new 10mm belt at lunch time. 12.1 v on battery and started first time.