The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Chrisf1 on 25.05. 2009 17:27

Title: 61 A10 electrickery
Post by: Chrisf1 on 25.05. 2009 17:27
Hi again everyone my dynamo has died so when I have it rebuilt I am thinking of going 12v the only problem is my newly fitted 6v altette horn is there a way round this? Thanks Chris
Title: Re: 61 A10 electrickery
Post by: Caretaker on 25.05. 2009 17:37
I came across this interesting site 'LUCAS ALTETTE ORIGINALS ONLY'

Looks like they supply parts for 12v conversion, or maybe do a swap ?

Title: Re: 61 A10 electrickery
Post by: Chrisf1 on 25.05. 2009 17:40
Unfortunately mine is not an original just exspensive repro Chris
Title: Re: 61 A10 electrickery
Post by: Triton Thrasher on 25.05. 2009 18:39
It won't matter, for all the time you have the button pressed.
Title: Re: 61 A10 electrickery
Post by: rocket man on 25.05. 2009 19:01
another idea put a 12 volt horn someware you carnt see it like under the tank
you could use the bar which goes across drill a hole in the centre  and mount your horn on it
and disconect the 6 volt horn no one will knowe were the sound is coming from
only you 
Title: Re: 61 A10 electrickery
Post by: Beezageezauk on 25.05. 2009 19:20
Hi Chris.

I was going to convert one of my 6v bikes to 12v a few years ago and the instructions I was given didn't even mention the horn.  When I enquired about it the reply was as Triton Thrasher states.  It shouldn't matter putting 12v through your 6v horn for the amount of time you will have the horn button pressed.  I would tend to agree with the statement but I am sure that some electrical wizard on the forum will be able to advise if this is true.   

I didn't carry out the conversion in the end so my bike is still running on 6v.

Title: Re: 61 A10 electrickery
Post by: dpaddock on 25.05. 2009 19:29
Place a resistor in series with the horn having the same value of resistance as the horn and a wattage value equal to 144 divided by the resistance.

Title: Re: 61 A10 electrickery
Post by: trevinoz on 25.05. 2009 22:36
David, where does the 144 come from? If you divide 144 by the horn resistance, typically 0.6 ohm, you will need a huge resistor or bank of resistors.
The horn should be happy with 12V, it may need to be adjusted but I don't know how it is done on the repros as I haven't had the pleasure of playing with one yet.
I would ensure my horn wiring was up to scratch to handle the extra current.
Title: Re: 61 A10 electrickery
Post by: BSA_54A10 on 26.05. 2009 00:25
I used a resistor from an old ignition coil as I have a box load of old car coils.
Seems to work so for but then the only time I use the horn is to get a roadworthy or at a static display for some fun.

I also know a few upgraded bikes that have the original 6V hornl sans resistor.
Seems to work OK.
Remember that you should only be using it for very short burst so as long as you don't ride like an Italian (hand perminently on the horn) it should be ok as is although the note is horrible.
Title: Re: 61 A10 electrickery
Post by: Chrisf1 on 26.05. 2009 09:37
Hello again everyone after discussing this with Tony Cooper who in my opinion is the best for electrical rebuilds (mags or dynamo's) he has convinced me to stay with 6v so I apologise for wasting your time but it has been nice talking thanks Chris
Title: Re: 61 A10 electrickery
Post by: a10gf on 26.05. 2009 10:12
Agree, with a good working system, a good battery and one of those nice halogen in front, 6v is fine. But it was an interesting discussion, always nice to read the opinions and ideas. And found this fascinating Altette specialist site in the process.
Title: Re: 61 A10 electrickery
Post by: beezalex on 26.05. 2009 17:55
As thrasher said, a 6V horn works just fine with a 12V system.
Title: Re: 61 A10 electrickery
Post by: dpaddock on 30.05. 2009 19:46
Trev, the point I was trying to make is that when you double the voltage, you increase the power dissipated by four. Chrisf1 is concerned that his new 6v horn might be damaged by going to 12 volts. I got sideways with the math but if Chris wants to protect his horn, he'll need to put an equal resistance in series with it; if it's a 0.6 ohm horn, the power rating of the resistor should also be equal and that calculates to 60 watts.
Without that resistor, the horn's going to draw 20 amps and dissipate 240 watts. I believe it's capable of that for short bursts, but "short" is a relative term.
Title: Re: 61 A10 electrickery
Post by: BrianS on 12.03. 2017 10:04
Sorry to resurrect an old thread but it's the closest I could find to my question and I hate starting unnecessary new threads  ;)

I am sure that the advice I was given was the same as stated in this thread in that occasional bursts on the original 6v horn from a 12v supply would cause no harm but I just saw Taff the Horn's website for the first time and on his main page he has this! Any thoughts?


"The most amazing stuff which can cause folks to be hurt, plus to ruin or set fire to their Machines.

In the pages by some chap Stevens & another person published from pages under voc uk it frequently advises how it is so much more efficient to use 12Volts on 6Volts Horns.

Hilarious until you imagine what they are causing, difficult to forgive those poor lads, since they are being  VERY dangerous and could ruin a lot of good machinery, expense & perhaps cause worse to LIFE.

If you follow that:- using 12 Volts supply into 6Volts horns, firstly they burn the horns out.  secondly if there were a fault in the horn button the horn wd keep sounding.

With the Warm Petrol fumes it would set fire to the machine,  when the chap on a Machine had that problem on the M25 & pulled in to hard shoulder the horn of 6 Volts supplied with 12 had become ablaze before it could be put on its stand.

The spark in the horn was still arcing melting points etc & sparking with the engine stopped when the warm PETROL fumes from carb were getting to start a huge blaze, petrol tank next = HUGE blaze.    (Rider did not burn out, but the expensive machine rapidly did!!)

INSURANCE COs wd not pay out  fully if they found riders had been so dim as as to have set their hooters up like that, the Guys writing those papers could well be sued for providing such daft guidance.  its like telling people to put 220Volts on 110V Lamps or putting 50 PSI in 25PSI Tyres.

You do not do that, so do not listen to such a dimwits' advice."