correct alternator AC ouput?

Paul LeClair

Paul LeClair

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Location
Calgary, Alberta, Canada
for any motorcyle charging system, what alternator alternating current voltage output is required for the regulator/rectifier to output say around 13.8 volts DC at correct engine rpm?

Paul LeClair
 
Not easy to answer as there are a number of different regulator designs. The most common way these days with a Laverda type alternator (no field winding) is the use of SCR's to clamp the AC voltage from the alternator. It is then rectified to get a DC voltage. The rectifier is losing about .7 volts so the alternator output is going to need to be about 1 volt higher than the DC output. So for 13.8 volts DC you need about 14.8 volts AC from the alternator. Also a number of new bikes these days use automotive type alternators and the regulation of the output voltage is entirely different.
 
Paul, do you mean from the alternator phase wires, disconnected before they get to the regulator.
From memory you generally measure around 90 to 120ACV between any two phase wires at revs.
 
thanks, Tippie and Keith

it is actually the two wire stator from the 81 Ducati 900 SS I am back working on, the thing doesn't charge, I replaced the regulator/rectifier with a known good Electrex unit I have, still no charge, then I tested the AC output between the 2 output wires and got 28 volts max at 4,000 rpm. All the wiring is good, and to be sure, I connected the r/r direct to the battery, bypassing the wiring harness completely.

what I expected to see was somewhere between a low of 75 volts AC and a high of about 90 volts AC, based on previous experience over the years with motorcyle electrickery... The Ducati manual is useless, says to take it to a Ducati dealer to test such a complicated item as a charging system......

the owner of the Ducati is reluctant to spend the money to have the stator rewound, which is about $200 around here, and won't spend the money for a stock Ducati stator at about $500. Odd with the existing stator (which I have removed) is that the two output wires are not soldered to the stator, they have some sort of mickey mouse clip setup, so as a further check I am going to solder heavier guage output wire and run a final output test, but I don't really expect to see any improvement in output, and if I don't, it is time for him to take the problem to someone else if he doesn't believe the stator doesn't need rewinding or replacing......

Paul LeClair
 
Ah, on a two wire single phase system you are looking for around 18 - 30 volts AC so your output is in the ballpark. Got to be a bit more specific with your questions Paul, thought a lawyer would know that....  :D



  Keith.
 
Burn it Paul.  Best outcome all round.

Furthermore, working (at a guess for free) for a guy who won't spring $200 to repair a dud part is a recipe for frustration and disappointment.

Cheers
Steve B
 
The Ducati singles I used to work on put out 85VAC between the phase wires from the simple single phase alternator. They needed only a 12v rec/reg and could run a 12v system no problems.
 
breganzane said:
Furthermore, working (at a guess for free) for a guy who won't spring $200 to repair a dud part is a recipe for frustration and disappointment.
Click to expand...

Couldn't agree more!

Currently working on a (sort of nice) bevel Ducati 750GT.  Nice original condition but the owner is too skint to have us make and replace the steering stop that he broke off in a minor tumble.  Prefers to use the fuel tank... :o :D

What is it with these guys?  Got horribly expensive bikes but are too tight to spend money on even the basics!  Bikes' value certainly won't appreciate with such an attitude...

piet   :-X
 
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