Regulator/Rectifier

Ducati single cylinder motorcycle questions and discussions, all models. Ducati single cylinder motorcycle-related content only! Email subscription available.
Moderator: Morpheus

Moderator: ajleone

frankfast
Posts: 231
Joined: Wed May 05, 2010 12:35 pm
Location: New York (upstate)

Re: Regulator/Rectifier

Postby frankfast » Tue May 05, 2020 3:08 pm

I connected only one of the three wires from the alternator (yellow) to the bridge rectifier and abandoned the other two. I connected the battery to the plus terminal and grounded the negative terminal and left the other AC terminal abandoned. The battery was connected to a toggle switch as was the lead from the coil and fuse block for the lights and horn. I thought that if I connected the two yellow leads from the alternator that I would over charge the battery especially without running the lights. With this setup my only concern is not getting enough charge to the battery.
Does your alternator have three wires or is it the earlier model?

tobydmv
Posts: 88
Joined: Wed Apr 16, 2014 4:59 am

Re: Regulator/Rectifier

Postby tobydmv » Tue May 05, 2020 5:06 pm

frankfast wrote:I connected only one of the three wires from the alternator (yellow) to the bridge rectifier and abandoned the other two. I connected the battery to the plus terminal and grounded the negative terminal and left the other AC terminal abandoned. The battery was connected to a toggle switch as was the lead from the coil and fuse block for the lights and horn. I thought that if I connected the two yellow leads from the alternator that I would over charge the battery especially without running the lights. With this setup my only concern is not getting enough charge to the battery.
Does your alternator have three wires or is it the earlier model?


I have a 3 wire/phase alternator and all 3 are feeding my battery. My bike is a scrambler and my rides consist of about 30 minutes of stomping around open fields. So far no dead or smoking over charged battery.

In your case, one stator lead might be enough or might not. Why not run all 3 into the rectifier and then into the battery? Just measure the AC output voltage around 5k rpm. I doubt it would go over 7.4v but a multimeter will tell for sure. I might do the same test today if I can get some free time.

ducwiz
Posts: 604
Joined: Tue May 22, 2012 12:52 pm
Location: near Frankfurt, Germany

Re: Regulator/Rectifier

Postby ducwiz » Tue May 05, 2020 6:15 pm

Seems that there are still misconceptions about the Ducati w/c alternators. Yes, they have 3 wires, but - no, they do not have 3 phases ! They have only two.
What is a 3phase alternator:
Image
taken from https://electrical-engineering-portal.com/few-words-about-three-phase-alternator

Here we can see, that it can have 3 or 4 wires, in both possible winding configurations. If the center or neutral wire is left out for the wye connection, we also see only 3.
What is a 2phase alternator:
Image
taken from the Ducati Pantah manual.
The upper figure shows a 2phase alternator, like those in our w/c singles. See - ist also has 3 wires ! The lower one is a single phase version, never used in the singles.

The first basic difference is:
in a 3phase system you measure the same AC voltage between every possible pair of the output wires/branches, and a different buit also identical AC voltage between each branch and the neutral.
But in a 2phase system we measure the same AC voltage between each phase/branch and the neutral/center wire, but twice that voltage between the two phases!
The second difference:
The phase angle in a 3phase system is always 120° between two branch/phase voltages, but 180° between the two phases/branchs of the 2phase system.

Again: having 3 wires coming from an alternator does not necessarily mean it's a 3phase system !

"tobydmv", how would you connect those 3 wires to a rectifier bridge, which has 2 AC input terminals and 2 DC outputs (+ and -)?

Hans

tobydmv
Posts: 88
Joined: Wed Apr 16, 2014 4:59 am

Re: Regulator/Rectifier

Postby tobydmv » Tue May 05, 2020 8:44 pm

ducwiz wrote:"tobydmv", how would you connect those 3 wires to a rectifier bridge, which has 2 AC input terminals and 2 DC outputs (+ and -)?

Hans


Well you kinda take two wires, twist them together, and crimp on a terminal, then connect the male and female bits together like its Saturday night :lol:

Jordan
Posts: 1380
Joined: Fri Dec 24, 2010 11:29 am

Re: Regulator/Rectifier

Postby Jordan » Wed May 06, 2020 1:23 am

ducwiz wrote:
But in a 2phase system we measure the same AC voltage between each phase/branch and the neutral/center wire, but twice that voltage between the two phases!
The second difference:
The phase angle in a 3phase system is always 120° between two branch/phase voltages, but 180° between the two phases/branchs of the 2phase system.

Hans


I have trouble with this definition of two phase.
Assuming centre tap is not connected and diodes not included, if the phases are 180 degrees apart, would not the AC voltages in the two branches cancel each other, resulting in zero volts output?
I might be wrong, but think that they are in phase, so that is why they can provide increase voltage when used together?

However, half wave rectified DC voltages could be 180 degrees apart.
This is the situation in a single phase, centre tapped, full-wave type alternator.

ducwiz
Posts: 604
Joined: Tue May 22, 2012 12:52 pm
Location: near Frankfurt, Germany

Re: Regulator/Rectifier

Postby ducwiz » Wed May 06, 2020 7:14 am

tobydmv wrote:
ducwiz wrote:"tobydmv", how would you connect those 3 wires to a rectifier bridge, which has 2 AC input terminals and 2 DC outputs (+ and -)?

Hans


Well you kinda take two wires, twist them together, and crimp on a terminal, then connect the male and female bits together like its Saturday night :lol:


You don't tell us which 2 of three wires you recommend to twist together. So, I presume you would take the two yellow ones.

Imho that's not a good idea. The voltages of the two yellow wires are in 180° phase angle, referred to the red center wire/tap. This means: while one side has positive polarity, the other is negative. We all learned: connecting two opposite polarities results in a short circuit, and in 0 Volt measured across the red and the two now twisted yellow wire ends. Inside the stator winding, the max. possible AC current will circulate in useless manner. This can be checked i. e. by a current clamp meter or an ammeter with very low inner resistance. It would be nice if you make this experiment with yor bike at home and report the results here.
If I'm wrong, I promise to send you a bottle of good wine.

Hans

ducwiz
Posts: 604
Joined: Tue May 22, 2012 12:52 pm
Location: near Frankfurt, Germany

Re: Regulator/Rectifier

Postby ducwiz » Wed May 06, 2020 7:41 am

Jordan wrote:
ducwiz wrote:
But in a 2phase system we measure the same AC voltage between each phase/branch and the neutral/center wire, but twice that voltage between the two phases!
The second difference:
The phase angle in a 3phase system is always 120° between two branch/phase voltages, but 180° between the two phases/branchs of the 2phase system.

Hans


I have trouble with this definition of two phase.
Assuming centre tap is not connected and diodes not included, if the phases are 180 degrees apart, would not the AC voltages in the two branches cancel each other, resulting in zero volts output?
I might be wrong, but think that they are in phase, so that is why they can provide increase voltage when used together?

However, half wave rectified DC voltages could be 180 degrees apart.
This is the situation in a single phase, centre tapped, full-wave type alternator.


Jordan,

here comes a little "enlightment" ;) :
Basically, if you do not connect the center tap anywhere, the alternator consists of two identical windings, connected in series. This means, their voltages sum up, not cancel themselves out. This would happen in case of paralleling them (see my last post).
Experiment: ground red/center tap and the observe the phase angle of the voltages on a 2channel osciloscope. You will realize 180° phase difference.

Btw., even the older n/c 60W alternator is also a 2phase version, but here the center tap is locally grounded and the stator plate. This results in only 2 wires coming out from the motor. The reference/neutral/center tap or however else one likes to name it is the chassis of the bike itself!

So, for me, a single phase, centre tapped, full-wave type alternator as you name it, does not exist. A single phase alternator always has only two terminals/wires only, no tap. It can be floating from ground an rectified by a bridge, or grounded on one side, so only a half-wave rectifier is possible.
Again: The expression "2phase" is only justified if a reference (i.e. center tap) terminal/connection is present, against which the two "phases" have a non-zero phase angle.

Btw, the 12Volt conversion of w/c alternators is based on omitting/disconnecting the red wire/center tap and feeding a bridge rectifier from the two yellow wires. The result is a doubled AC input voltage, and in turn a 12V DC system. OK, a new R-R for 12V is needed. Today, people use cheap chinese scooter regulators based on the shunt regulation principle. This was discussed and shown in earlier threads. Many years ago, I converted the original Ducati R-R (series regulation) by adding 2 power diodes to form a bridge, and a small electronic circuit connected between the "marrone" terminal and battery+. This little device subtracts 7 Volt from the battery voltage. My conversion thread can also be found somewhere.

cheers Hans

Jordan
Posts: 1380
Joined: Fri Dec 24, 2010 11:29 am

Re: Regulator/Rectifier

Postby Jordan » Wed May 06, 2020 8:05 am

Thanks Hans.
Now, I will have to get out my old CRO and see for myself.
I am preparing myself for a serving of humble pie. :)
It must be said though, there are many textbook descriptions of centre-tapped, full wave, single phase alternators.

ducwiz
Posts: 604
Joined: Tue May 22, 2012 12:52 pm
Location: near Frankfurt, Germany

Re: Regulator/Rectifier

Postby ducwiz » Wed May 06, 2020 9:56 am

Jordan,

CRO - which motorcyclist has such an instrument at hand, and is moreover able to operate it? Seems we both are those lucky guys. I must confess I have 2 .. a Tektronix 465 2Ch analog and an HP 54602A 2ch mixed analog/digital storage. Both from the late 80ies.

As the english is not my native language, I sometimes do not understand quite well, sorry for that. So, "a serving of humble pie" sounds like an idiom, or a kind of saying. The only Humble Pie I know is the former british beat / rock band ...

Hans

Jordan
Posts: 1380
Joined: Fri Dec 24, 2010 11:29 am

Re: Regulator/Rectifier

Postby Jordan » Wed May 06, 2020 10:54 am

It means to be humble and admit mistake.
I like tools.
My CRO is second hand, cheaply bought and I can operate it like a novice.
It does have dual trace, so will be suitable for the alternator test I think.

A Cathode Ray Oscilloscope is a type of voltmeter, that can instantaneously display levels as they change, showing waveforms.
These days they no longer make them with cathode ray tubes (like in old TVs), and are usually called Digital Storage Oscilloscopes - DSO.
It's easier to say "crow".


Return to “Ducati Singles Main Discussions (& How to Join)”

Who is online

Users browsing this forum: No registered users and 55 guests