question for auto electrician about brit bike alternators

Hi, I am a mere mechanic so auto electrical is not my forte, but I understand the basics.

Most Commandos are positive earth. Will a 3 phase [ 3 wire ] alternator work on positive earth like the earlier single phase [ 2 wire ] alternators.

Dereck

Re: question for auto electrician about brit bike alternator

Yes.
You would need a 3-phase rectifier or reg/rec.

Re: question for auto electrician about brit bike alternator

kerinorton said:

Hi, I am a mere mechanic so auto electrical is not my forte, but I understand the basics.

Most Commandos are positive earth. Will a 3 phase [ 3 wire ] alternator work on positive earth like the earlier single phase [ 2 wire ] alternators.

Dereck

Click to expand...

The RM24 Lucas alternator is three phase , three wire and was used in some models of Nortons



http://www.ebay.com/itm/LUCAS-12VOLT-3- ... 7d&vxp=mtr

Re: question for auto electrician about brit bike alternator

jimbo said:

The RM24 Lucas alternator is three phase , three wire and was used in some models of Nortons

Click to expand...

The high output alternator fitted to the 850 Mk3 (and JPN) Commandos was the single-phase two-wire 180W RM23, not three-phase (RM24).

Re: question for auto electrician about brit bike alternator

Shit . That was quick. I didn't think it mattered what system you had so long as you had the right regulator/rectifier pack to suit the polarity you wanted.
Many thanks. Dereck.

Re: question for auto electrician about brit bike alternator

I had better as another question. Its all about a mates 750 triumph. It is an early frame with a later engine. He had removed the battery and forgotten which way round it was supposed to be in the bike. Naturally, because of it age, i presumed it was positive earth. I helped him set up the boyer on the bike some time ago after we did up the carbs. It ran for a brief period then it stopped. It kept doing that, so then we started looking for other reasons. I had made the earlier mistake of presuming it was positive earth, so had wired up the boyer accordingly. Looks like it was a bad mistake. Hope the boyer is ok. Surprised it went in the first place. Every time we go back to it, we start the bike but it runs for only about thirty seconds or so then dies. We have had problems sorting out a fuel leak near the feed to the rh carb as well and have come to the conclusion that the hoses need renewing. Bloody hard to tell where that slight leak was coming from. I have been trying to find out if it is negative earth or positive. It has been discovered that it is a 3s rectifier, which is supposed to be negative earth. It was just about impossible to read the numbers but finally we did. DUH. In the mean time he had bought a fairly new triumph triple so had not done anything to the other bike.

Dereck

Re: question for auto electrician about brit bike alternator

kerinorton said:

Its all about a mates 750 triumph. It is an early frame with a later engine. I had been trying to find out if it is negative earth or positive.

Click to expand...

Which side of the battery is normally connected to the "earth"/"ground" side, positive or negative?

If an attempt was made to connect the battery 'the wrong way' then with the reg/rec (or Zener and rectifier) connected, the main fuse should blow immediately (assuming it has one and it's the correct rating)? The fact that it runs at all with a Boyer suggests the Boyer is correctly wired for the polarity as it is.

Actual polarity can be a matter of choice so all you (or he) basically needs to do is decide on a polarity, and then check the various polarity sensitive items such as electronic ignition, regulator/rectifier, LEDs (if any) and finally the battery are connected according to the chosen polarity.

Re: question for auto electrician about brit bike alternator

thanks LAB. I thought as well that if it was wired the wrong way round, it wouldn't go. ????????????????????? Hmm work to be done tomorrow.

Re: question for auto electrician about brit bike alternator

Is there a simple way to test what zener diode it has. I have looked on the web to see if there is information about part numbers etc but not been sure what I am reading as various different suppliers use different numbers and often refer back to different lucas numbers. If say i fitted a light bulb in circuit with the zener, would it light the bulb one way only. I would presume it would act like a regular diode. Trouble is, he lives quite a way from me and I never seem to have my test gear with me when i ride my commando to his place and then have a play with his bike. Or it gets too bloody hot to think properly.
Thanks for your help LAB. Given me something to think about when i work on it tomorrow. Hope the Boyer is ok.
Thinking about it, there was one blown fuse on the bench. When we reversed the battery back to positive earth, I am sure that fuse didn't blow. Getting somewhere me thinks.
Dereck

Re: question for auto electrician about brit bike alternator

Zener Diode behaviour is on reverse voltage.

A normal diode conducts in one direction only. (with .5 V drop)

A Zener does that plus also conducts in reverse , once the threshold voltage is exceeded.

Assuimg a 14.4V Zener, then rig up an AA or simllar 1.5V battery, test leads and light. The light should work in one direction only, this is the forward voltage.

Connection in Zener usage would be the other way round.

Clear as mud no doubt but I'm not great at explaining things.

Re: question for auto electrician about brit bike alternator

My kid's '79 Bonneville is negative ground with a three phase alternator and Lucas RITA ignition. I believe it's the first year that Triumph switched to negative ground (earth).

Re: question for auto electrician about brit bike alternator

Thanks Rob and Jim. Dereck