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My 1973 750 GT has the original 150W alternator and is getting very tired. When I added the Dyna electronic ignition, it increased the draw at low RPM's as you would expect. I have to recharge my battery after every ride. Does anyone have recent experience with alternator replacement options? Has any one purchased the rotor and stator from MDINA ITALIA recently?

I installed an Electrex ST2 ~400W stator with rare earth rotor & their regulator about 4 years ago when I restored my GT. The regulator failed within months (internal failure causing parasitic load that would drain the battery) & was replaced with a MOSFET type unit from Rick's Moto Electrics. About a year later the stator failed. Ricks did not have a replacement stator on hand, but offered to re-wind mine, which I did. No problems at all since.

Oddly too, my sealed AGM battery failed to pass a load test within a bit more than a year & one of the trigger coils failed on my Dyna S after only 3-4 months.

The bike also has a Motogadget M-Unit powere distribution / circuit protection unit & it has been totally reliable. Same for the one in my Guzzi Loopframe.




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Although I have a background in basic electronics and understand alternators and different types of rectifiers, I have decided not to modify my existing stator and instead to try the simplest replacement alternator that is still uses a center tap stator. I ordered the Mdina Italia replacement rotor and stator which will pair up with the stock old center tap rectifier. The price is fairly reasonable and the unit is inbound from the UK. I will post the results when installed, including some before and after charts.

If you can find one, the ST2 alt. rotor by itself is supposed to upgrade the output to acceptable levels.

Yes, I had investigated the ST2 rotor option but they are hard to find and I have had some bad luck recently buying used Ducati parts off the internet. I had also heard that ST-2 alternator reliability was an issue, although I cannot imagine that a rotor by itself could be come unreliable, other than slowly losing some magnetism. In any event, I ordered the MDINA ITALIA alternator and it is inbound and in the hand of the USPS and should arrive in a couple of days.

I suspect the reported unreliability of the ST2 alternator stems from over accessorizing the ST2 for touring, i.e. heated grips, driving lights, heated suits, gps, etc. all running at once along with the marginal connector security Ducati is famous for.

Finally received the MDINA ITALIA alternator - it was misdirected by US Postal Service to Florida and took 4 days extra. Should get points for mileage. Installed today and it works well. Accidentally discharged battery to zero V. a couple of days earlier by leaving key on and could not get it to charge above about 11V, so installed a new battery and fully charged offline first. I then took readings with the old alternator. The new battery starting voltage was 12.9V With the new battery and DYNA ignition on, the battery voltage was 12.3V. With the engine running at 1000RPM, the battery voltage stayed about the same until about 2700RPM, when it hit 12.9V. This essentially says the battery was slightly discharging below 2700RPM. Note that turning on the LED headlight required 3100 RPM to break even. So, more than 3100 RPM to expect any charge at all. NOW FOR THE NEW ALTERNATOR: The battery hits 12.9V somewhere between 1500 and 2000RPM and by 3000RPM is pumping out over 14.1V. Definitely putting out a lot more juice. I did not have time to test to make sure the (original) regulator is controlling the charge. I want to make sure there is no overcharging situation. A couple of points: Exactly 36 inches of wire needs to be added to the three wires between the supplied alternator stator cable and the regulator. I soldered my connections and used heat shrink tubing. Rosso is red and Giallo is Yello. I had two spacer washers between the old rotor and bevel drive gear. I measured carefully and determined both could be removed. I tried removing just one, but there was inadequate thread left for the 30mm nut to hold down the rotor.

In any case is it better then the readings we got twentyfive years ago with the Original setup, having to rev it to 4000 to get some charging and 5000 to run the (Original) lights.
So You've got a double bonus : between 3K and 5K your clear with the lights AND preserving your bigends.

Enjoy the bike

ciao
ducadini

Thanks for the comments Ducadini. Yes, the original alternator was very weak. I discovered the wire insulation was severely cracked on the yellow wires as they exited the engine case and also one of the wires near the regulator. I am surprised the old alternator was working at all. This US model 1973 750GT was built in late 1972 and has the regulator under the left side cover.

I completed a test ride of about a 30 mile loop with lights on and plenty of stop and go and idling. Only issue was very slight oil leak around the case plugs where the stator wires exit the case. The rubber o-ring sort of thing (called a rubber) around the cable sheathing had cracked. Note that the new wire sheathing is slightly bigger in diameter than the old stator sheathing and stretching it caused it to crack. RTV to the rescue. The good news is that the alternator is working fine and the regulator seems fine too. Battery voltage at end of trip exactly the same as start of trip.

My suggestion to anyone replacing their alternator is to buy a new "rubber" that seals the sheathing as the old one is prone to cracking.

that part number is: 0400.46.030

I did not take the time to look for a source.

Looks like Steve has that part in the Bevel Heaven store - although it looks slightly different than mine does, it should do the job

What I used.

Electrex RO93 - Rotor Approx $200 Canadian shipped
Arrowhead Electrical ADC6000 - Bridge rectifier-regulator Approx $80 Canadian shipped

Modified stator as stated in 1974 GT Alternator Mod thread.
viewtopic.php?f=19&t=3834

Total cost $280 Canadian.