Hi,
12V/23W Quartz Halogen in the pilot
It actually looks brighter than the headlight
The headlight bulb is a 12V, 45/40W.
Been using qh pilot bulbs since late '79 or early '80; yes, they're better than the Lucas 45/40 (or 50/40) BPF headlamp bulb, because the Lucas headlamp bulbs - and, as said, the standard lens/reflector - are crap.
In addition, because the pilot bulb is by definition off the focal point of the lens, the pilot light spreads in a wide arc - rather than being focussed ahead of the bike, as the headlamp is necessarily - which helps to make the bike more visible to others not so directly in front of it. :thumb
the 'Owners Handbook' states 'the motor should be maintained at a speed in excess of 2100 r.p.m.' to prevent discharging the battery. A local mechanic who got the bike running better than it has in years told me the r.p.m. should be kept above 3000 to 3500.
"r.p.m." is not a sensible measure of whether the battery's being charged or not. But your "local mechanic" is about right; whoever reckoned "2100 r.p.m. to prevent discharging the battery" either couldn't count or didn't know basic electrics (a sadly not-uncommon occurrence
).
Assuming the original RM21 alternator, Lucas rated that for 10.5 Amps @ 5,000 rpm, also 120 Watts. The original alternator is also single-phase; Lucas stated those produce 75% of rated output @ 2,400 rpm, so 90W or a gnat's under 8A.
Headlamp dip is 40W, coils draw about the same; unfortunately, unlike the pre-'71 headlamp toggle switch, the standard switch on your bike doesn't turn the pilot lamp off when the headlamp's on and
vice versa, so originally 6W for that; tail lamp is 5W, speedo. 'n' tacho. illumination are 3W each. Total 97W, or just over 8A (the calculation is Watts = Amps x Volts, aka P=IE).
As you can see, consumption and generation @ 2,400 rpm is about the same, generation falls/rises quickly particularly at low rpm, consumption essentially doesn't, the above calculation doesn't include intermittent consumers like 21W brake lamp, two 21W indicators and horn. Ime, at least an additional Amp over and above constant consumption is necessary to keep the battery charged for intermittent consumers.
Few additional things to bear in mind:-
. Headlamp main adds another 5W (~0.5A) to the consumption.
. While fitting a qh pilot bulb cuts consumption when its used instead of the headlamp, because the toggle switch doesn't turn the pilot off when the headlamp's on, it adds 17W (~1.5A) to the overall consumption when you must use the headlamp.
. An original alternator is now over forty years old, everything else being equal, how much a forty-year old alternator can generate depends on the forty-year-old magnetism in the rotor; magnetism attenuates with age; it can be really slow, or other factors can speed it up ...
. Even when the bike was new with original bulbs, there was very little spare between generation and consumption; you maybe want to consider LED and/or a more-powerful alternator? If you go for LED, ask questions
before you spend money, or you could end up wasting the latter.
12V/23W Quartz Halogen in the pilot and use that in lieu of running the headlight all the time (as required where I live).
With the standard wiring, the tail lamp is on too. In daylight, the standard rear lamp is not very good at displaying the difference between tail and brake. This gets worse the brighter the sunlight. As you must have a "headlight" on all the time, have you considered a simple wiring mod. that would turn on just the pilot lamp with the ignition switch and leave all other lamps to be switched on and off by the toggle switch? Simple plug-'n'-play, easily reversible?
Hth.
Regards,