175TS with 125S engine project

[George]

After nine months restoration had first ride up and down my road. Pleased so far. Will put some more miles in soon weather permitting

[Duccout]

That's really lovely George. I wish that I could get out, but the roads are really filthy.

Colin

[ranton_rambler]

I was wondering whether you’d been out yet. Hope you enjoy it!
Roads are filthy round here but no salt yet....

[George]

Seasons greetings, lets hope next year will be better than this year

I have searched this forum looking for information to understand charging system and have ended up more confused. Bear with me if my questions have been answered but I could not find answers.
Engine is early 1960s Mototrans 125TS. When I got the bike wiring had been bodged and I started again using Italian wiring diagram, image below.
My stator, image below, had three wires 2 yellow and one red.
Diagram shows stator wires:
yellow connected to yellow on rectifier,
white to A on headlight connector to main switch
Red to V1 on headlight connector to main switch
Question 1
How do I know which yellow goes to rectifier and which yellow goes to A on connector or does it not matter.
Question 2
How can I check if three wire plus earth rectifier is working with multimeter. I think that battery may have been gassing off as I noticed fluid on battery tray and had attacked silencer chrome. Are new 6 volt rectifiers available to suit my Ducati engine
Question 3
Recommended AH rating 6 volt battery.
I would prefer to keep 6 volt system for cost reasons as I have spent a lot and funds are low plus I rarely ride at night. Would like to save replacing horn, coil, lamps and indicator LED lamps
As I have it wired up The following applies with engine stopped:
Ignition on, Headlight switch off, brake light and horn operates. Ignition on headlight switch on, brake light and horn operates, headlight and rear light operates. Indicates direct feed from battery.
With ignition on red light on headlight shell is always on.
When I am sure of stator connections and with a fully charged battery I can then use multimeter to check voltage across battery terminals with bike running to confirm if charging.
Thanks in advance for any help.

[Jordan]

These work on motorbikes.

https://www.ebay.co.uk/itm/KBPC5006-Pow ... SwhglTxpgd

[veloduke]

George

I have a 63 125TS which I too wired up to the Italian diagram.

1)Firstly, either yellow wire is good, it does not matter.

2) For the rectifier, do you have a diode setting on your multimeter?
If so, isolate the rectifier and measure from each AC input to the +ve terminal. (When I say 'from', use the red meter lead. 'To', use the black lead).
This should give a reading of about 0.8. Reverse the leads and try again - now there should be no connection.
Now measure from the -ve rectifier terminal to each of the AC inputs. Again, a reading of about 0.8. Reverse the leads and measure again. Now there should be no connection.
Finally, you could measure from the -ve rectifier connection to the +ve. I would expect about 1.6.
The rectifier mentioned in the link is an ideal replacement if yours does not work. Does your current rectifier have big cooling fins on? Mine did (was original) but was broken. I used a rectifier as per link.

3) Your system operates exactly as mine does. Red light does not go out.
I used a Motobatt battery inside a dummy case. Pretty sure it was an MTB6N6, but check dimensions first, especially if using a dummy case.
I have had no problems with the battery running flat during the day, and like you rarely ride it at night.
I do know that with all the lights on, the alternator cannot provide enough juice to charge the battery. This is normal, it's mentioned in the Ducati manuals.

Hope this helps

[George]

Thanks for reply max. My rectifier is the original with large cooling fins with 1 yellow 1 green 1 brown plus earth through rectifier body. There are no markings to denote positive negative or ac input. Green wire goes to R+ on headlight shell connector, brown wire goes to R- on headlight shell connector block, would these be +ve and -ve terminals? You say to each of the AC terminals, this makes 4 terminals I have three wires on rectifier I am still confused.
Sorry to be slow understanding your answer trying to understand something I have not had to test before and would like to know which wire goes where for if I have to fit new rectifier, at that price I am tempted to replace to remove old 58 year rectifier.

[George]

Hello Max. I have ordered new rectifier as recommended. I would be obliged if you could give me an idiots guide to wiring just to make sure I get it right
Thanks in advance

[veloduke]

Actually, just checking, are you sure you have two yellows (and red) from the alternator, and not one yellow and one white (and red)?
That would make a difference according to the electrical diagram of the alternator for the 125. Of course, someone may have changed it at some point.
I'll have to check mine to be sure. Two yellows and a red come out of other alternators that I have (not 125).

The three connections that you can see are for +ve output and AC, I think AC will be the outside two. The one in the middle will be the +ve output. The -ve output is the mounting stud. The relplacement rectifier on ebay has four terminals.
I'll try to get some pics together, but it's Christmas so I'll be busy for a bit.

I will say that your original rectifier is made from Selenium rather than Silicon, and is a bit less efficient. The original may be broken anyway (mine was), but we can establish that with the meter.

It sounds to me that your wiring is correct aside from checking the alternator wire colours.

[Jordan]

Selenium diodes have less forward voltage drop than silicon diodes, but are not as durable.

Correction: It is not the case regarding voltage drops, it's the other way around!