But, the old engineer understands more, after seeing Kerry's post from yesterday. He was just saying that the DC output of the charging system must be greater than 20W, because the DC load he showed was 35W. The calculations are correct, except he neglected to include the bulb, which is what we're trying to power.
Power delivered=(12^2) /(0.96 + 3.2 + bulb resistance)
Bulb resist= (V^2)/55W= 2.6
Therefore, if the system can maintain a 55W bulb, and maintain battery charge, it must have 21 Watts available for the light circuit, inc the wire resistances, Kerry suggests (not 35W). Since we have neglected many other system losses, in these calculations, the actual power demand, to power this 55W bulb, is less than 21W. Therefore, I think it is entirely reasonable that a "20W" charging system could power a 55W bulb successfully.
(the 150Watt thing is not correct, because the calculation assumes that the stater output remains at 12V with the 0.96 Ohm stator shorted.)