How do you do it?
For many classic motorcycle enthusiasts, the idea of upgrading from a quirky 6-volt electrical system to a more modern 12-volt setup is tempting. Brighter lights, more reliable starting, and the ability to run modern accessories are all compelling reasons.
However, the process can seem daunting, often shrouded in misconceptions about voltage, current, and power.
Let's demystify the electrical upgrade and shine a light on watt truly matters.
For many classic motorcycle enthusiasts, the idea of upgrading from a quirky 6-volt electrical system to a more modern 12-volt setup is tempting. Brighter lights, more reliable starting, and the ability to run modern accessories are all compelling reasons. However, the process can seem daunting, often shrouded in misconceptions about voltage, current, and power. Let's demystify the electrical upgrade and shine a light on watt truly matters.
Watts: The Real Power Player in Your Electrical System
When contemplating an electrical upgrade, it's easy to get caught up in the "volts" discussion. But here's the crucial takeaway: watts matter most for understanding your electrical system's overall power capacity.
Think of watts as the total 'strength' or 'output' of your electrical system, much like horsepower is the measure of an engine's total power output.
Just as an engine's 60 horsepower can be delivered through different gear ratios (affecting torque and speed), your alternator's 60 watts can be delivered at different voltages. At 6V, it pushes a lot of current (like a low gear with high torque). At 12V, it pushes less current for the same total power - like a higher gear with less torque but still 60 horsepower.
Triva. Horsepower of course is a term invented by the "marketing genius" James Watt! (also quite a good engineer!) And the SI unit of power, the "watt", is named in his honor, recognizing his contributions to power measurement! No other Adman will ever earn an acoloade like this!
The core challenge in a 6V to 12V conversion isn't about magically increasing your alternator's total power. It's about ensuring your existing alternator can generate enough watts to:
* Continuously power your new 12-volt ignition system components and lights.
* Have enough surplus watts left over to constantly charge your 12-volt battery
Your Alternator's True Voltage Output:
Here's a common misconception: many assume a "6V electrical system" means the alternator only generates 6 volts. This isn't accurate!
A healthy classic motorcycle alternator, even one designed for a 6V system, actually produces Alternating Current (AC) voltage that increases significantly with engine RPM. You'd typically see around 20 VAC (Voltage Alternating Current) or greater at idle, rising to 50-75+ VAC at higher RPMs.
This higher raw AC voltage is precisely what a 12V regulator/rectifier uses to create your new 12V DC system.
This means that, in terms of voltage, upgrading to 12V is relatively straightforward. The alternator is already capable of producing the necessary voltage; it just needs a different "governor" (the 12V regulator) to control it at the new, higher level.
You do not need an additional device to "upscale" the voltage between your alternator and the new 12V regulator/rectifier.
Balancing Your Electrical Budget: Every Watt Counts!
A typical classic motorcycle 6V electrical system often has an alternator rated at 60 watts.
When you upgrade to a 12V regulator, that same alternator will still only produce approximately 60 watts of total power for your new 12V system.
This 60-watt limit is your electrical budget.
The key is that while the total power (watts) remains the same, the voltage changes.
This means that all your new components (like 12V light bulbs and 12V ignition coils) must be designed to operate at 12 volts and fit within that 60-watt budget.
Here's a rough idea of typical 12V component power draws:
* Ignition Coil (12V):
* A 3-ohm coil: Up to 48 watts (peak draw)
* A 5-ohm coil: Up to 28.8 watts (peak draw) Recommended
* (Note: The average power consumption for the ignition system will be lower than these peak figures, typically 10-25 watts for a single cylinder.)
* Halogen Headlight: 35-60 watts (or more!)
*** LED Headlight: 15-30 watts (a great upgrade to save power!)
* Taillight/Brake Light: 5-21 watts (less for LED)
* Instrument Lights: 1-5 watts
* Hand Held Dyno® Ignition: < 1 watt
The bottom line: You need 'Watts In' from your alternator to be greater than your total 'Watts Out' to all your running electrical components and charging the battery.
If Watts In < Watts Out, your battery will slowly die! This is why opting for efficient components, especially LED lighting, is highly recommended for 60-watt systems.
Your 12V Conversion Shopping List (Charging System)
For the core 6V to 12V charging system upgrade, your shopping list is simple:
* 12-volt Regulator/Rectifier (designed for single-phase alternators)
* 12-volt Battery
Remember, you will also need to replace all your 6V bulbs (headlight, taillight, indicators, instrument lights) and your 6V ignition coil(s) and horn with 12V equivalents.
Confirming Your Alternator's Health:
The Dynamic Stator Test:
Before embarking on your conversion, it's always wise to test your alternator's actual AC output to confirm it's healthy and capable of supporting the new 12V system.
How to Test Your Alternator's Raw AC Output (VAC), Dynamic Stator Test:
* Disconnect the alternator (stator) wires from your existing regulator/rectifier.
* Set your multimeter to AC Volts (VAC), on a range that can read up to 100V or more.
* Connect your multimeter probes to the two output wires coming directly from the alternator.
* Start the engine (ensure your battery is fully charged, as the charging system won't be connected during this test).
* Observe the AC voltage at idle (it should be 20+ VAC) and then as you increase RPMs (it should rise significantly, 50-75+ VAC). This confirms your alternator is generating power.
By understanding these key principles, you can approach your classic motorcycle's 6V to 12V electrical upgrade with confidence, ensuring a reliable and brighter future for your ride!
What if one's alternator has 3 wires? Such as my 6V 450 Desmo?
3 wires means you might be sporting a three-phase alternator on your classic! Many bikes, especially the later models in the "classic" era, went this route because, frankly, it's a better way to make power.
In the article I talked about your alternator being capable of putting out serious VAC. With a single-phase system (two wires), you’ve got one set of alternator coils doing all the work. A three-phase system has three sets of coils, each pumping out its own AC voltage, slightly out of sync with the others. When your regulator/rectifier gets hold of these three AC waves, it smooths them out into a much more efficient and powerful DC punch for your battery and components.
The three wires coming off your alternator, they’re the individual AC outputs from each of those three phases.
Testing Your Three-Wire Alternator:
The Three-Phase Dynamic Stator Test
You'll need your multimeter set to AC Volts (VAC), ideally on a range that can read up to 100V or more.
Here’s the drill:
* Find & Disconnect: First, locate those three wires coming directly out of your engine case – they're the ones that usually plug into your regulator/rectifier. Disconnect all three of them from your regulator/rectifier. We want to test them raw.
* Pair Up & Probe: Unlike a two-wire system where it’s just one simple connection, with three wires (let’s call them A, B, and C), you’ve got to test them in pairs.
You'll do three separate tests:
* Test 1: Connect your multimeter probes to Wire A and Wire B.
* Test 2: Connect your multimeter probes to Wire A and Wire C.
* Test 3: Connect your multimeter probes to Wire B and Wire C.
* Fire Her Up & Watch the Numbers: Make sure your battery’s got enough grunt to start the engine, as you won't have a charging system connected for this test.
* Start the engine.
* At idle, you should see around 20-30+ VAC across each of those three pairs. The exact number can vary a bit between bikes, but the crucial bit is that all three readings should be very, very close to each other.
* Now, gently increase the RPMs. You should see that AC voltage on all three pairs climb significantly – we’re talking 50-80+ VAC or even higher as the revs build. And yep, you guessed it: all three readings should still stay tight together.
What the Readings Tell You
* All Good: If all three pairs show similar, strong, and rising AC voltage with RPM, then you're good to go! Your alternator stator is healthy and ready to feed that new 12V regulator/rectifier.
* Trouble in Paradise (Common Scenarios):
* One or two pairs are dead or super low, but the others are good: This usually points to a cooked coil (or coils) inside your stator – either an open circuit or an internal short. That means your total "watts in" budget is seriously compromised, and you won't charge properly.
* All three pairs are low or non-existent: This is a sign of a more widespread issue, possibly a totally fried stator, or even an issue with the rotor (the magnets) spinning inside.
* Voltage doesn't climb with RPM: Another red flag for an internal stator or rotor problem.
By doing these three quick tests, you'll know exactly what your three-phase alternator is truly capable of, confirming if it's got the "watt power" to handle your 12V conversion.