The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Stu55Flash on 19.08. 2010 00:22

Title: Jury Rigging
Post by: Stu55Flash on 19.08. 2010 00:22
Has anyone tried to "jury rig" their ignition to improve it using an AC coil as: 170523598139. I did this on my Fanny B. The biggest problem with high tension coils is that they breakdown with age and do not generate a high enough voltage. You simply connect the HT lead to the input of the coil and it generates a higher voltage at the plug - a good hot blue spark instead of yellow one. The mag is still used to generate the spark at the correct time. On my Fanny B I hid the coil under the tank. I had loads of starting problems before using this idea and non afterwards.

Title: Re: Jury Rigging
Post by: wilko on 19.08. 2010 09:40
I'm confused? We talking about  maggy's?
Title: Re: Jury Rigging
Post by: lawnmowerman on 19.08. 2010 10:39
Interesting concept. We are looking to use the coil as a step up transformer. May work in theory but not sure about the insulation resistance of the coil's primary winding which is only designed for 6 or 12v - it may leak to earth losing some of the mag's voltage and dissipating some power as heat in the coil. Also, increasing the voltage proportionately decreases the current - not sure what effect this may have on the spark but there is only a finite amount of power (voltage x current) available from the mag.
IMHO, at the end of the day you would probably be masking a mag problem and adding more components and potential for problems.
If you try it I would be interested to know the result.

Title: Re: Jury Rigging
Post by: chaterlea25 on 20.08. 2010 22:49
Hi All,
I googled the number Stu gave and it comes up as a coil for pazon or similar types of electronic ignition
(not 6 0r 12 volt) in these systems a pulse is thrown at the LT side of the coil and is transformed into a high voltage for the plug!!
IF you connect a lead from your mag to earth via the coil windings you do not get a high voltage into the LT it is simply converted (shorted) into a current pulse (very small)
I have never heard of doing this before?????
30 or so years ago I converted a couple of mags to work with a remote coil, (energy transfer) it works well if you use an AC coil from a scooter or honda 50,
The slipring and brush have to be kept clean and free from oil, as they now have to crry a current pulse from the LT winding.
I even got a V twin BSA running well on this setup using 2 coils
Back then mag rebuilds were as about as expensive as they are now??? so I think in real terms a lot cheaper now???
Or maybe I can afford it nowadays??????

Recently I was at a Steam Fair  and had a wander through the stationary engine exhibits
One engine was running away happily with a flourescent light choke acting as a kind of coil ???? ???? ????
I couldnt find the owner to ask how it worked, maybe it was a booster for the LT magneto some of these engines had
John O R
Title: Re: Jury Rigging
Post by: lawnmowerman on 21.08. 2010 20:52
Good point John. I thought there must be a reason why it would not work or everybody would be doing it and the mag rebuilders would go bust.
I have just remembered the way a coil works - the voltage via the closed points is applied to the primary through to earth while the points are closed (dwell). This allows a considerable build up of flux in the coil primary and it is only when the points open that a back emf is produced, instantly releasing all the stored energy in the coil primary. It is then magnified by the many more turns on the secondary winding to produce a short duration spark at the plug. Although many thousand volts - very little current and short duration.
A similar high voltage short duration low energy voltage pulse is produced by the mag and would not be enough to fully flux a coil primary.
Sorry if I have repeated what you said but I am just trying to get it right in my head. It is many years since I studied telecommunications principles as an apprentice and the theory is very similar to electromagnetic relays and switches.
Quite interesting to hear about the remote coil set up - I guess that this replaces the "coil" in the mag to step up the voltage to spark levels, but as you say, means that the slipring and brushes have to carry more current.

Title: Re: Jury Rigging
Post by: chaterlea25 on 22.08. 2010 00:26
HI Jim and All,
I'm not saying it doesn't work, just that I have not heard of it or tried it!!!
I know that many mag windings lose resistance as they age and the insulation breaks down between the adjacent windings, this makes them lose voltage for the spark, the voltage will only rise enough to jump the gap in the plug
the bigger the gap you make the spark jump the bigger the voltage needed,
This is bad news for the poor windings as the "stress " on them is increased considerably
It is bad practice to spin over your bikes mag without the leads grounded or connected to the plugs
Modern coils used in transistorised ignition or CDI are a different animal,!!!
They are fired by a voltage pulse (spike) As the Pazon boys state the wattage needed to fire the coil is minimal
This has set me thinking ???? ???? ????
On the mag remote coil conversions the current is generated by the LT windings in the mag, this is in parallel with the second coil primary, when the points open the mag coil discharges its current into the second coil, this change is enough to generate the spark in the secondary coil

John O R
Title: Re: Jury Rigging
Post by: Stu55Flash on 22.08. 2010 00:39
The system works fine on the Fanny B in this case its a single cylinder. First a tried a new HT coil, these fit inside the flywheel and therefore get hot. When hot, the spark is was not hot enough to ignite the fuel - oil mix. OK when running not good enough to restart. I gave up with this and stripped the HT windings off the old coil - which were green and shorted. I then connected this to the input of an AC coil which is what I think the Pazon coil is but for a twin. These are different to the DC coils. In effect instead of generating a pulse electronically you are generating it mechanically. The system works even if you don't remove the knacker ed HT windings as these are shorted out and therefore won't transform up to the required voltage.  The mag output is effectively the output of the HT coil on the villiers engined Fanny B. I am hoping my mag works ok, if it doesn't I will give it a try. Just wondered if anyone had tried.
Title: Re: Jury Rigging magneto
Post by: Guy Wilson on 20.03. 2021 15:02
I appreciate this post is 10 years old now... I was running a magneto powered Bantam D7 with mag removed and connected  points directly to a condenser and coil with a battery providing the power ( a total loss system) and it ran fine while the battery had enough juice.. Could a mag with dead windings or winding removed be used in the same way? On a single cylinder could the low tension wire come from the cut out on the mag to the condenser and coil? On a twin, would it be possible to run the low tension leads from the slip ring output to separate coils? Am I just thinking out load and this is a ridiculous idea?
Title: Re: Jury Rigging
Post by: chaterlea25 on 21.03. 2021 01:01
Hi Guy,
Yes it is possible to do it, as I wrote way back then, I did several conversions back in the day, If the LT is brought out to the twin cylinder slip ring  it can work as  did with a BSA V twin (where one spark is compromised anyway)
There were several magazine articles posted about it in the 80's
The principal is energy transfer ignition, as used on early Honda 50's and lots of other lightweights

Title: Re: Jury Rigging
Post by: Guy Wilson on 21.03. 2021 07:09
Thanks John, Its good to know in theory that it would work and I was thinking of it as more get me home solution on the A10 as coils and car batteries etc  are easier to find off the shelf in Kenya than mags. In addition, I have a number of singles B33, B31 and Matchless that it would be financially viable to run that way - I can't justify spending four or five mag refurbishes..
I'll post some results once I and if it works!
Thank you,