Lucas rectifier

Hi Gary,

On the earlier Commando's the rectifier had 4 diodes in a bridge and one zener to do the regulating.

On the MkIII the rectifier had only two diodes and the pair of zeners were used as the other two arms of the bridge rectifier.

It may be that a previous owner has either upgraded to a full MKIII system or he may have fitted a pair of matched zeners.

If you can post a picture of the rectifier I can probably tell you which wire goes where.

Regards

Tony

Hi Gary,

Sorry for the slow response, I am afraid the picture is too small to see what it really is.

If it looks like

http://www.classicbikepartscheshire.com/shop/article_10147/RECTIFIER_REGULATOR-Genuine-Lucas.html?sessid=qHPiYQtnI5owjCkiLy9ORVVCFW5a6LdoLe08YTqebylZaIeXu52wgCkY0xgpsuNb&shop_param=cid%3D122%26aid%3D10147%26

You have a 'real' 850MkIII rectifier. This requires two Zeners.

Can you do a better picture ?

Regards

Tony

If it looks more like:-

http://www.classicbikepartscheshire.com/shop/article_10135/RECTIFIER-Lucas.html?shop_param=cid%3D122%26aid%3D10135%26

Then from the picture you can see the word 'stud' this goes toearthso is the positive.

The leg with the blue paint on is negative and will go off to the zener (or zeners) and then to the battery

The two yellow ones go to the aternator.

Hope that helps

Regards

Tony

Hi Gary,

It is a Lucas 3DS5, this is a three phase rectifier for a 3 phase alternator. such as the RM24.

It looks like a previous owner has upgraded the charging system, the standard Norton loom will not have enough wires.

There is no reason why you should not use this setup, have a look at :-

http://www.britcycle.com/Manuals/1979%20Ignition%20&%20Charging%20Tests.pdf

As this may help.

What you should have is three wires coming from the alternator, these goes to the three middle tags on the rectifier. The stud / tag are + and go to ground, the final one is - and goes to the Zener diode (or diodes). If you have two zeners then these are simply wired in parallel. If possible try to keep the wire length from therectifierto both zeners the same length otherwise one zener will be doing all the work.

Let me know how it goes. If you want to talk direct on the phone, email me your number and I will call.

Regards

Tony

Although regulators and zeners are 'original', another way to control an alternator is with a modern 'power box'. If you have a three phase alternator then the three phase power boxes are ideal. Boyer supply one, but that is moderately expensive and mine has just recently decided to output at a slightly lower voltage and caused me some investigation to pinpoint the problem. I could have obtained all manner of power boxes from modern Japanese stuff, but I have found the 'power module' from Wylde to work perfectly. They advertise it for older Triumphs, because not many Commandos have the three phase alternator. It is very compact in size and costs around £28, which is half the price of alternatives.

I have the power box located behind the battery cover, reckoning that there should be enough free air circulating there, which makes an easy cable run to the alternator, and to the battery terminals, via a fuse.

I also recommend you fit one of Al Oz's multi-coloured diode ignition lights. It can replace the conventional charge indicator and has the massive benefit of the colour (red - orange - yellow - pale green - emerald green) relating to the voltage of the ignition supply.

Norm.

Er yes. Being the seller of the BSDM as mentioned above they do indeed fit in a 14MM hole.

Now checking through the above I am pleased to say most of it is spot on. The two Zeners as used on the original MKIII and the JPN can be any old pair of Zeners but the two used on the three phase which are in parallel must be matched. If any one wants to have zeners checked then please get in touch I can do it, but of course to match them you really need half a dozen to select from! We do have the modern regulator/rectifiers for 3 phase as well.

AL Osborn