Zener Diode on Brums

[charlie weeks]

Can anyone tell me where the Zener diode and it’s heat sink were fitted on late Brums ? What shape was the heat sink ? Was it a Triumph semi hemispherical shape or the flat triangular type fitted to BSA’s or something completely different and unique to Brums ?

Thanks

Charlie

[BigKev]

Hello Charlie. Not sure if this is original, but its a good spot to hang it. I purchased a Triumph heat sink and diode to suit. KP

[James]

I don’t think they ever had one as they were all 6 volts without diodes, but I’m not sure on that. But the photo in the above post seems to look right if they did, and is a good way and a good spot to put one.

[Adriangv]

Hi,
I have a 1969 Brum Scott. It did not have a Zenner diode fitted. Just an unregulated 6 volt system.
Adrian

[Barrie]

@Adriangv wrote:

Hi,
I have a 1969 Brum Scott. It did not have a Zenner diode fitted. Just an unregulated 6 volt system.
Adrian

Your machine should be running a 12v system driven by an alternator off the L/H side of the crank , the drawing I have shows no voltage regulation device of any kind, strange but true !
If your running a 6v system using a dynamo, which is not standard for your year, then you will have a regulator box fitted to the machine
If you can clarify which charging system you have fitted I will help you sort out your query .

Barrie
https://www.scotttechnicalities.com.au/technicalities/Chapter%205/5.1%20Wiring%20Diagrams.pdf

[James]

@Barrie wrote:

@Adriangv wrote:

Hi,
I have a 1969 Brum Scott. It did not have a Zenner diode fitted. Just an unregulated 6 volt system.
Adrian

Your machine should be running a 12v system driven by an alternator off the L/H side of the crank , the drawing I have shows no voltage regulation device of any kind, strange but true !
If your running a 6v system using a dynamo, which is not standard for your year, then you will have a regulator box fitted to the machine
If you can clarify which charging system you have fitted I will help you sort out your query .

Barrie
https://www.scotttechnicalities.com.au/technicalities/Chapter%205/5.1%20Wiring%20Diagrams.pdf

where does it mention anything about 12 volts in the attached instructions? 😯 The voltage reg is in the switch and the operator, as stated in the text.

[Barrie]

For the year it should be a 12 volts ac charging system, in which case the zener and the heat sink should be in the air flow below the Headlight

On The 6volt ac system the system is unregulated, Normal daytime running uses only half the alternator,The switch brings in the other two coils of the alternator when you turn on the lights.
Regulator in the switch ?……Rubbish!

[James]

@Barrie wrote:

For the year it should be a 12 volts ac charging system, in which case the zener and the heat sink should be in the air flow below the Headlight

On The 6volt ac system the system is unregulated, Normal daytime running uses only half the alternator,The switch brings in the other two coils of the alternator when you turn on the lights.
Regulator in the switch ?……Rubbish!

Sorry, well its kind of “in the switch” as the switch is made and is wired to make the correct connections in the different modes, that’s what I meant. I have not seen any documents, manuals, or tech articles that mention a Holder installed 12v regulated system, are there any?

[Barrie]

Holder installed 12v regulated system, are there any
What do you mean ?

[charlie weeks]

Gentlemen

Thank you for your replies. I intend to convert my Brum to 12V and I am certain that I remember someone saying that they had a late Zener equipped Brum. The trouble with the Scott is the radiator is right where every other manufacture fitted their Zeners and as well as taking up the obvious place it’s not a good idea to site one near a tank of hot water !

On first glance at Kev’s photos I thought he had attached it to the fork yokes but it looks more like the top centre radiator fixing bolt. Is this correct Kev ? I also intend to use the Triumph heat sink and a small Lucas rectifier also as I think that this would give a semblance of originality but perhaps a modern regulator with the alternator on full output is a better idea.

Charlie

[dave bushell]

My friend owns the penultimate Birmingham Scott first registered in 1972 and that has a 6v system. Also, advertising literature for the Brum states that it is equipped With a 6v system. I know many owners have gone down the 12v route but I have found that the 6v system can produce very good lights providing you have a good earthing system and use heavy duty wiring for the main runs.
Dave

[James]

@dave bushell wrote:

My friend owns the penultimate Birmingham Scott first registered in 1972 and that has a 6v system. Also, advertising literature for the Brum states that it is equipped With a 6v system. I know many owners have gone down the 12v route but I have found that the 6v system can produce very good lights providing you have a good earthing system and use heavy duty wiring for the main runs.
Dave

I have the original type 6v system with new wiring and it does very well, however it will pop light bulbs if I’m not careful. Pos earth 6volt diodes are kind of hard to find 😯
Probably should have gone with 12v regulated,but I wanted the bike work as it was intended with all the quirks and the correct 6 position Miller switch ,I guess.

[scott596]

I don`t know of any standard Birmingham Scotts with 12volt systems only those modified by their owners, in my opinion the standard 6volt system gives a perfectly good headlight and charges the battery OK why change it? Alan Noakes. scottworkshop@hotmail.co.uk

[charlie weeks]

Alan

If 6v is so good car manufacturers would have stayed with it. Why wouldn’t someone have brighter lights if they could ? Isn’t engineering about continuous improvement ?

Charlie

[dave bushell]

Material cost is cheaper when using 12v as compared with 6v as current flow is half that of the 6v system and this means there is less voltage drop over a given length of cable arriving at it’s destination, I.e. the headlamp bulb. On a 6v system, this voltage drop can be reduced by using a heavier (and more expensive) cable. Thus when you’re manufacturing thousands/millions of vehicles, there’s quite a material cost savings with 12v
Dave

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