Very close DerryUK
. Think about it. You ALWAYS
want positive readings (lights ON or OFF) at road speeds. Positive readings indicate the battery is being "charged". Zero or negative readings mean you are "discharging" the battery as you ride down the road. 3 guesses how far you'll get with a Brit bike and a dead battery.
All electrical systems vary from each other. There is NO one single hard and fast answer. Rotor magnetism drops with age, thus affecting the alternator output. Any number of loose or corroded electrical connections might decrease charge rates. Then of course the condition of the battery itself plays a part.
But no matter what...
► Idle lights OFF
will be negative (a "discharge") This simply checks the connection of the ammeter!
► 3000 RPM lights OFF
should be in the positive region. If there is not
a modern regulator (Podtronics and the like), you might see currents as high as a battery-cooking
7A. This is why you never drive on the expressway without the lights turned ON.
► 3000 RPM lights ON
Should also be positive. By how much will depend upon the condition of your system. Dropping back into negative readings is usually too much wattage in the HL bulb. The system was designed for a 35W bulb. For open country riding most riders can use 45W. You really never want your battery to be continuously
charged by more than 2A. If you know how and where the bike is ridden, then you can "tune" the charging system with the wattage of the HL bulb.
• An interesting experiment is to see exactly what RPM the meter goes into positive ("charging") territory with lights ON. That is the minimum RPM you can ride if you expect to charge your battery.
Hope this helps!