how many watts or amps a stock 73' 850 commando alternator can maintain.
Assuming it's a RM21, which was standard for those days, Lucas quoted 10.5A @ 5,000rpm. Obviously, it produces less at lower revs., although the correlation isn't linear.
At http://atlanticgreen.com/images/lucasrm24.jpg, Dave Comeau reproduces an ad. that Lucas ran when they launched the RM24 three-phase alternators in 1978. The ad. included two lines on a graph of Amps vs. revs. supposedly showing the difference between the 'high-power' version of the RM24 and an RM21; however, although the RM24 line is correct, for some bizarre reason, the RM21 one isn't! Nevertheless, at least it'll give you a rough idea of what Amps are available at your preferred revs.
Bear in mind also that Norton offered the higher-power (14.5A @ 5,000rpm) single-phase RM23 as an option. Iirc, a RM21 stator should have the number '47205' somewhere on it, while a RM23 should have '47239'.
thanks for your answers. I could not find specifications for the alternator in my service book, just testing methods. I was hoping more, the booke does say it takes about 4-5 amps for ignition. Throw in some lights and ........I guess i ride cold.
the booke does say it takes about 4-5 amps for ignition.
Nah, too high.
Your bike has 6V coils supplied through a ballast resistor? A Lucas (or pattern PVL) 6V coil has a low-tension resistance of 1.8 Ohms (give or take). By definition, the ballast resistor is about the same (at least, it should be). So let's say 3.5 Ohms total. Insert that and '12 Volts' into Ohm's Law (E=IR or Volts = Amps x Ohms) and you get 3.5 Amps (give or take). The Amps will be pretty much the same if the bike has an electronic ignition like a Rita or Boyer-Bransden; a more-modern e.i. like a Trispark will reduce the current consumption still further.
Originally Posted By: nert
Throw in some lights
If you ride mainly in daylight and either prefer lights-on or are required by local law, have you considered a QH pilot light? These draw around 20W, rather than the 40W of an original dip or 55W of a modern QH. I've used QH pilot bulbs for decades and they actually have advantages over a headlight for daytime riding.
http://www.norbsa02.freeuk.com/goffybulbs.htm for information but bear in mind the guy's across The Pond from you; he'll supply you but it'll cost. However, I'm pretty sure I've read on BB.C in the past of US suppliers of QH pilot bulbs.
Okay, i took a chance. Its been 38 degrees in the am when i leave for my daily morning 32 mile treck. Damn Norton started on (1) kick. Good thing. Don't now how many i had left in me. This thing easily holds my weight (185lbs) on the compression stroke. I wasn't shy with the ticklers. Sun light enough to keep the headlight off. I replaced the park light bulb with a Hella 5 watt map light bulb. Pretty bright. I thought i could be seen. I kept the heated vest on medium. No apparent performance problems, or net negative electrical power drain, (that i could tell). Signal lights worked fine, but i reverted to hand signals as not to invite trouble. The vest really keeps one toasty, and eliminated the bulk of layered clothing. The collar is even heated. The only thing cold at 65 mph on the interstate (8 miles) was my face. The cold was pretty well piercing, and starting to sting my hands through my gloves near the end of my journey. I just can't bring myself to putting the Vetter Hippo hands on a Brit bike. I've run them on my zuki's and they really work great. Fortunatly i got home before it was so dark that i would need to turn on the headlight. Hmm, let me think about this, heat or see. Tuff choice.