Charging problems - bsa

[Bob bsa 500 68]

I bought the bike last year. Nice bike. runs well. I had installed new wiring and carburetor. Starts first or second kick. My problem is:

The bike charges but drains the battery. My repair man says I need to install a 3 phase alternator as I have a single phase alternator. We have not checked that.  So the bike has to run fast (rpm) to charge. It does not charge enough in traffic. The bike charges but drains the battery at low revs.  The lights have to stay on at all times by law and safety.

How can I check that?

What else could be the problem if it is not what is written?

[wetdog]

when the lights are on and bike is running does it show a discarge ? reduce the watage ,

[bikerbob]

You don't say what model you have or if it is 12v or 6v system. The problem could well be the alternator but it could also be the rotor or if you have a 12v system the zener diode  or if 6v then the rectifier or you may have a modern solid state control unit which may be failing all these things as well as the wattage of the bulbs being used need to be checked out before you go for a new alternator.