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Hi All,
I want to verify my stator is optimized and working as well as it can be for 60 year old technology. The bike is running okay, but the headlight and brake light are pretty dim and the horn is barely audible.

I don’t know if the system is charging the battery as I have been leaving it on a trickle between rides.

The regulator/rectifier tests fine.

I tried really hard to make sure the flywheel was oriented correctly during installation, but the instructions in the manual are not foolproof and the degree orientation seems spec like an approximation. I also don’t understand why this orientation should even matter. It’s just spinning to generate AC power and the points time the spark, not a trigger on the flywheel. Is the reason for this to time the power surge going to the capacitor (the one near the points)? Maybe because there is one area that doesn’t have a winding and that aligns during spark?

Anyway, can I just test the AC output on the two yellow wires coming from the stator? What would be the typical range considered normal? But that doesn't tell me about amps though, right?

I would rather not pay to have the stator rewound or re-magnetized if that isn't the problem.

I have kept the bike stock including the 6V system and would prefer not to convert to 12V or use non stock items.

Thanks!
Jim

With a battery ignition system, it normally wouldn't matter how the stator is timed.

I use these types of voltmeters on most of my old vehicles to confirm charging voltage.
https://tinyurl.com/25a6tz77
They are easy to wire in between any wire that goes live when ignition is switched on, and ground.

Thanks Jordan. That is really helpful… and affordable which is a big plus

Sounds like I buy one, put male and female bullet connectors on it, and plug it between one of the yellow wires and the regulator/rectifier and it should show voltage, right? Rev it up and get some numbers.

I’ll report back once I have some empirical data.
Jim

If you have a DC ignition and a decent alternator which keeps the battery in good health then it would not matter how the rotor/stator is timed . This is pretty much how the european range of singles worked. However this is sometimes not how it is. The early US bikes were not really considered as practical road transport that were likely to be ridden in the dark much if at all. Many were fitted with AC ignition or pathetic 28 watt alternators. In these bikes the rotor timing is important . Even those converted to a conventional Dc coil ignition could gain a benefit from a pulse at the crucial time . If you want a bike to ride with reliabilty I would think carefully about an up grade.

Sounds like I buy one, put male and female bullet connectors on it, and plug it between one of the yellow wires and the regulator/rectifier and it should show voltage, right?

Well, it probably will show voltage, just not the reading you need. And you would stop the system working altogether.

You should do as Jordan says;

wire in between any wire that goes live when ignition is switched on, and ground

Oh right. Just noticed that the component says DC. So just as I said about the bullet connectors, but put it between the regulator/rectifier and the battery. Thanks for pointing that out Max.

A battery on a bike without electric start seems unnecessary if the generator is sufficiently designed. I guess the battery can act as a bit of a buffer though. Maybe provides some juice for the initial spark at starting?

I did order a 6V P21/5W LED bulb for the tail light in hopes that it will be brighter than the filament. That should arrive soon. If that is an improvement, I'll look at an LED headlight bulb. I never ride this one at night so doesn't matter too much. I also put a clamp-on bicycle horn on it to pass the state inspection. I'd like to pull that back off if I can get the stock horn louder. I've been aiming to stay as stock as possible, but I'm okay with the quick swap out components as I can quickly put back the OEM type. Its not my daily rider so it doesn't need to be super reliable, but I am a little concerned about the upcoming 300 mile MotoGiro I committed to

Regarding fitting the voltmeter, I suggest making the wiring connections near to where it will be installed.
Presumably that would be at or near the handlebar, for the neatest and shortest wiring.
You could use a tester or bulb/wire to find what goes live when the ignition switch is turned ON. Attach/splice the red voltmeter wire at a convenient such point. That could be on the switch plate assembly.
Attach the black wire to any nearby earth point.

blaat! wrote: <snip> A battery on a bike without electric start seems unnecessary if the generator is sufficiently designed.

Not if you want your lights still working while waiting for the traffic lights to go green!
And I say that as a former Mobylette rider ...

But yes, in essence, you're right: with a magneto/coil-fired ignition, the battery serves to keep the lights shining. It doesn't do anything for the ignition.
And I say that as a Ducati SCR rider. No battery needed to make that one go!

blaat! wrote:I did order a 6V P21/5W LED bulb for the tail light in hopes that it will be brighter than the filament. That should arrive soon. If that is an improvement, I'll look at an LED headlight bulb.

Brighter they are, certainly. Also frequently more fragile, unfortunately.

blaat! wrote: ... if I can get the stock horn louder.

Horns draw a shedload of power - i.e. amps - especially as they age.
Best thing is to buy a new Chinese cheapo. This will lighten the load considerably. If it offends you visually, you can stick it away out of sight somewhere, leaving the Real Thing in place and visible, just disconnected.

Did some more testing:

I put the inline DC voltmeter between the regulator and the positive terminal on the battery. Since I didn't know which way the current was flowing (charging the battery vs running off the battery) I hooked it up both ways.

With the meter positive hooked to the regulator I get over 6.4v:

With the meter positive hooked to the battery I get 1.3v:

Any idea how to interpret this?

So I did more testing:
With the bike running on a fully charged battery and the two yellow stator wires disconnected from the regulator and hooked up to an AC tester I get 24V at Idle and 42V revved up a bit. That seems good to me although that is with no load on it. With everything hooked up and running my headlight is dim.

Currently the bike will also run with the positive lead disconnected from the battery so the stator is putting out enough power to make spark and the regulator is cooperating to some degree (see below).

With the bike off I tested resistance of the stator windings (across two yellow wires) and got 0.8 ohms. This seems reasonable to me. A trusted mechanic friend (who knows nothing about Ducati singles) told me to also check between each yellow wire and ground and I should NOT have continuity. He said that that would be a fault, but when I went back through the old Ducati documentation it says there SHOULD be continuity:

Each yellow to ground has continuity by design, right?

Okay, on to the regulator/rectifier. The values were all in range when I tested it six months ago, but something is definitely wrong here now. These are the values I get in RED:

I'm no EE so I have no idea how to isolate the problem within this component. Here is Jim F's schematic of the regulator/rectifier:

Any thoughts on what failed internal to the regulator?
I could buy another off eBay as they come up occasionally but I fear I will end up paying for another bad one. Ideally I would like to repair the regulator if it is as simple as disassembling and soldering in a new resistor or something. Inexpensive 6v regulator/rectifiers are available online but they only have four wires (two AC in, two DC out) and I wouldn't know how to integrate that into the rest of the system.

Thanks in advance for any help.
Jim

Is the engine running in the first photos with the voltmeter?
It needs to be, to see if the alternator is capable of charging the battery.
At around 2,500 rpm, 6.9V or more would prove it's OK.
With headlight on it might need more revs, but you will still need 6.9V or you won't be charging a lead-acid battery.

Why not just try as suggested? Connect the voltmeter at a SWITCHED part of the circuit.