12 Volt Conversion

[Doom Patrol]

Rather than go the usual 12v Electronic route I have opted for a 12v points system on a scooter I am having built at the moment. Now before you ask I don't really understand electrickery, so it's no good asking me, but among the bits and bobs I need is a heatsink as used on the old Triumph and BSA motorbikes. Now I've got one of these complete with diode and my question is where and how do you mount it? I have seen a picture somewhere, but that was a long time ago. So any help in this respect would be greatly appreciated.

[firekdp]

Never seen the Triumph/BSA type fitted to a scoot, but the original Lambretta concessionaires one was fitted to the rear mudguard.

[Doom Patrol]

It looks quite funky. A tubular centre with radial fins about the size of the palm of your hand. I've not heard of them being mounted on the mudguard, but I can't imagine it would have worked all that well if this is the sort of thing they used. Prone to vibration I would imagine.

[J1MS]

There was an article in motorcycle scooter & three wheeler that used this heat sink on a Lambretta... A few scooter dealers put them on scooters back in the 60's The reason they used them was probably because they basically used a British 12 volt system that was already being used on British bikes, so probably sourced the parts they needed from BSA & Triumph dealers...

[J1MS]

Its a long time since I have seen one on a Lambretta, but the only one I did see in the flesh, was mounted on the rear mudguard
I believe the theory was the air supply was better there by the fins of the hub to cool it... they get very hot taking heat away from the Zenor, as it dumps excess voltage to earth... The one I saw had an earth wire from the mounting point on the mudguard to the back of the rear junction box.... It was fitted on a TV 200... Ive seen these heat sinks at the Stafford Show in parts boxes on old BSA Triumph stands in recent years... the ones with a radial fin...

[Doom Patrol]

Yes, that's exactly the thing. As I say my knowledge is a bit sketchy, but it is a means of dumping the excess current. They probably were used because they were easy to scavenge from bike parts at the time. You know it's just occurred to me that I have a friend who has 12v points on his TV200. I'd forgotten all about that. I'll have to have a word with him.

[bristolmod]

Check out "The Lambretta Manual of Performance Tuning and Conversions" by Ken Herlingshaw (originals and reprints available on Ebay from time to time)

Page 50 sets out how this was done back in the 1960's

Chris

[bristolmod]

there is a simpler version- the details are over on "the other side" somewhere......

Chris

[firekdp]

This conversion was done by dealers, but it was an official conversion and could be specified on ordering a new machine. Lambretta concessionaires modified the stators and sourced the parts direct from Lucas, the heatsink, I think, was specially made for the Lambretta.
The early Indian GP200s imported over here also used the same system, with the Lucas components fitted by the dealers. The zener was fitted into the air scoop under the seat, which is why Indian scoops still have a hole in the top. There it was cooled by sufficient flow of air and didn't need a finned heatsink, but it wouldn't be a good place to get a spark if you had a poor connection.
A more efficient system is now available in the form of a podtronics unit which will regulate and rectify, this has been purposely designed to replace the lucas components. The details are in the pathfinder thread on this site.
Any chance of a picture of your heatsink?

[Doom Patrol]

Here you go.



Thanks for the tip about the book Chris.