Originally posted by Rico Delrosado: Thanks, yeah, I meant the twins.
My friend has a 1965 650cc project. In order to convert the alternator to put out 12 Volts, would he have to replace both stator and rotor, or just the stator?
Neither!! The alternator puts out what the battery sets the system voltage to.
1) He need only add a 12V battery, 12V bulbs and 12V coils.
2) He SHOULD add some kind of regulator to keep from cooking the new battery. I might suggest a Typanium or Podtronics 12V regulator unit in this instance, since they are so simple to install.
Installation would simply be installing male connectors to the new regulator, then unplugging the existing rectifier and plugging the female harness connectors up to the new regulator. He could simply lay the new regulator in his tool tray until he decides where to mount it.
Now, you also need to understand some background information. 12V system use "electronic" regulation; 6V systems used "mechanical" regulation.
Whereas the 12V systems used an OEM Zener or later 3rd-party electronic regulators to keep from cooking the battery, back during the 6V days there were no such wonders. 6V regulation was achieved using 3-wire stators; a single stator with 2 outputs (1 Low, 1 High).
So during the day (headlamp OFF) your bike ran on the Low alternator output. At night when you switched ON the HL, that same switch also turned on the High alternator output. The loads on the electrical system were simply matched to the alternator output and that kept the battery OK. You can easily spot these systems; they're the ones with rotary HL switches.
Now the problem is that because the load was matched to the requirements, you could never charge your dead battery... there was never any excess, day or night. So if you convert to 12V using the same mechanical regulation, the same thing will happen. Back in the day, this was OK because you rode everyday. Nowadays, people ride their "classics" maybe once a week and the batteries need a little extra charging from time-to-time.
That's why I suggest you physically rewire your alternator stator to the later 12V specs. It's very simple to do, probably take you less than 5 minutes.
BTW... Before some "whiz kid" follows me and starts chiming on about how Lucas is trash and the Japs are light-years ahead in design, know this. Lucas stopped using mechanical regulation on all bikes about 1966. The Japs continued to use this design well into the late 70's and early 80's. Every Honda vertical twin (305, 350, 360, 450) used the same system, and I believe some of their dirt bikes still use this same system today.
I took the Direct Current part of an Electronics course in high school, but bailed out before the Alternating Current part. So what I am left with is a basic DC "water pipe" understanding of 'lecktics. I do pretty well with wahring from the magic box to the headlight and the coil(s) and switches and stuff, but I often get confused when the electrons aren't all going in the same direction.
Well, brother... that's the great thing about updating to the later 12V design. All that two-way AC stuff is kept to a minimum, traveling on 2 wires between the alternator and the rectifier only. The old design had it running up to the HL switch which meant the main harness had AC and DC in it. When one of those babies rubs the wires bare onto the steel frame you'll have some headaches!
"Now the problem is that because the load was matched to the requirements, you could never charge your battery... there was never any excess, day or night. So if you convert to 12V using the same mechanical regulation, the same thing will happen. Back in the day, this was OK because you rode everyday. Nowadays, people ride their "classics" maybe once a week and the batteries need a little extra charging from time-to-time."
I don't really agree. The 6V system does work and does charge the battery. It doesn't charge the battery as fast as a system with excess power, regulated as needed. The unregulated 6V system's power has to be limited "at source" to a level that won't destroy the battery in use.
What I really don't like about 6V Brit alternators is the many opportunities for bad connections in the shoddy switches and connectors. 6V systems don't like resistance! Also, people are tempted to fit bigger bulbs in their lights, which causes the battery to run flat.
Triton thrasher mentioned the "R" word, and this is what people don't understand about 6 volt systems. For a given load (35 watt headlamp bulb) a 6-volt system will draw twice the current a 12-volt system draws.
Now we should understand that wire does have resistance. It is not only corroded switches and connections that we have to worry about. The smaller the diameter the wire, the more resistance it has.
With resistance of any kind in an electrical circuit we will get a voltage drop as current passes through the resistance. Corroded switch, kill button, connection, ground circuit or using too small a wire for the amount of current you will draw through it, all produce a voltage drop. And the voltage drop can be significant.
Now this can be explained with ohm's law, but too many eyes seem to glaze over when it is mentioned. Let just say that a 12-volt system will be quite happy with 16 or 18-gauge wire for most motorcycle applications (exception 75 to 100 watt quartz bulbs, etc).
A 6-volt system will need 12 or 14-gauge wire for typical motorcycle applications (typically 14 gauge works for all but the wires from the charging system through the ammeter to the battery, where I like to use 12 gauge).
This is something that people seemed to have forgotten. Even some of the people I buy wiring harnesses from who supply 6-volt harness with very small guage wire. If you want a bright headlight bulb you cannot have a significant voltage drop in the wires, let alone the switches and connections.
Now for those who have a 6-volt system and would like brighter lights take a look at the wires going too and from your hi-lo beam switch. If it is for a 12-volt bike it will be fitted with quite small wire. Small enough, that if you use it on a 6-volt system, you will experience a pretty good voltage drop. Put a 45-watt, or higher, quartz bulb in the socket and you will get better light from a couple of fireflies.
This is why when you bought accessory lights and horns for your 6-volt car or motorcycle they included heavy wire to run from the battery and ran it through a relay that you controlled with a on-off switch or hi-lo beam switch. They new all about voltage drop through wire.
Originally posted by triton thrasher: I don't really agree. The 6V system does work and does charge the battery. It doesn't charge the battery as fast as a system with excess power, regulated as needed. The unregulated 6V system's power has to be limited "at source" to a level that won't destroy the battery in use.
Obviously it charges a battery. What I should have said to be more accurate was that it's enough charge to keep a healty battery healty, but not enough to charge up a dead battery.
Pretty much if you take off with 6V you'll arrive with 6V. If you take off with 5V you may arrive with 6V depending on the length of the ride. However if you take off with 3V, you'll most probably arrive with 3 to 3.5V.