Modern Vespa

ok i have a 2007 mp3 250. Battery voltage is dropping fast whenever the engine is running, measuring <12v with the engine idling. Gotta keep a battery tender on it all the time.
The "hidden" fuse is good.
With the engine off, unplugged the alternator from the regulator. All 3 coils measure ~ .3 ohm.
Started it. All 3 coils, disconnected, measured 19.5 - 20.5 VAC while idling.
Shut off, disconnected regulator from battery. All 6 diodes were 530 - 540 mV forward voltage.
Reconnect alternator to regulator and start. Alternator measures 8.5, 9, and 9.2 VAC idling, and regulator outputs 1.65 VDC.
Reconnect regulator to battery. Kick tires and Cuss.

So are they both dead?

I'd suspect regulator before stator for one simple reason.

Piaggio used a bunch of Ducati regulators until a certain point (circa 2010???) that failed pretty much without exception.

Besides, accessing the regulator is a lot easier than the stator.

I don't know who is the current supplier to Piaggio for the regulator, but it is probably some Chinese outfit. At least those are far more reliable than the old Ducati regulators.

well that's good to know, it definitely changes the diagnostic implications that are presenting.
I've found 2 plausible replacements:
one is $36 but has female plug termination,
https://www.amazon.com/Arashi-Regulator-Rectifier-Motorcycle-Accessories/dp/B07P2D5M46/ref=sr_1_16?crid=LPU7PKC1JMCD&keywords=Voltage+Regulator+Rectifier+piaggio&qid=1669953974&s=automotive&sprefix=voltage+regulator+rectifier+piaggio%2Cautomotive%2C342&sr=1-16
the other is $50 with the correct male plug termination,
https://www.amazon.com/Areyourshop-Regulator-Rectifier-Voltage-Atlantic/dp/B00RB38C6I/ref=sr_1_5?crid=REL5G4V5B3JK&keywords=Voltage+Regulator+mp3+piaggio&qid=1669954182&s=automotive&sprefix=voltage+regulator+mp3+piaggio%2Cautomotive%2C408&sr=1-5

So i'm wondering about just how generic are the regulators for this type of vehicle. Does it have to really match the make and model of my bike? Can i save some money with a little bit of work?

Get the right part. It is a Italian vehicle after all, designed and assembled by the inventors of electricity who perfected the art of electrical failure.

If this were Honda then I'd be more inclined to gamble.

easyparts.nl is the best site for scooters that I have found and used so far.

that is a good point, considering the experience i've had with Piaggio. It doesn't seem to be a very user friendly brand, so i did shell out for the more pricey part. i'll find out in 3 days.

easyparts.nl is fine for those in the EU. Here in the US use scooterwest, AF1racing or scooterpartsco, e.g.:
https://scooterpartsco.com/ricambi/080-oem/oem-voltage-regulator-for-vespa-250-300-piaggio-aprilia

Do NOT use Amazon or Ebay for parts.

Regulators are one of the most general piece of motorcycle electronics you can find. On the other hand. How much time are you willing to spend (and money to risk) to save 10-20 bucks?

By the way. Good work on the diagnostics. Most people would not do that before asking for help. Did you check reverse voltage on the diodes?

yeah they were all open circuit in the reverse direction. So now i'm thinking that the bypass-to-ground circuitry is fried, and i hope the stator has not been damaged as a result (another $75).

The problem with finding the "right" part is that there are occasions when i don't have the option/money/time to get it and have had to make do, and i have never regretted it later. Besides, nobody can say that they've never substituted little things like hoses, tires, relays n such, but you just have to know when to play it safe.

i don't think it's a hard n fast rule. For example, Scooterpartsco sells parts on ebay, but i notice they do not accept returns on electronic parts, while Amazon does. And i have returned parts before, i'm willing to waste some time and effort if my options are limited.

FYI, a voltage regulator from g.aigisill (ebay) is reliable and high quality. I had 250cc'2006, so my stock VR died in 2015. And I never had any problems with the one from Greece (it was Japan-built according to seller's info) until a truck destroyed my mp3 with VR (it cracked).

But! My advice is to remove the connectors. They get rust quite easily, so I prefer soldering. Some say that soldered wires fail because of vibrations, but I can't say it is true.

Last edited by Jah on Tue, 13 Dec 2022 03:45:11 +0000; edited 1 time

thanx that's valuable information. it's all about who you know.
and it may be possible for soldered connections to create a weak spot at the point where the flexible wire meets the hard solder, if the solder joint is anchored to some rigid part like the frame or cranckcase. Or if it's a cold joint. Never had that problem because i'm anal AF about connecting wires. I'm like a nazi with my wires.

for Voltage Regulators, Piaggio still uses Ducati for a lot of the European production, as well as Shenzhen and Kokusan. The newer Ducati components seem to hold up as well as the Asian sourced ones.