Batteryless alternator

[Jordan Princic.]

Those with 3 wire alternators may be interested to know that it's possible to run your bike without a battery. In fact, it's possible to do so with a 2 wire, but using lights, etc tends to make the engine cut out. The 3 wire can be used with some added components to get reliable running without a battery.
The cost of the components is offset by saving on battery. It's a 12 volt system. See: http://www.geocities.com/magdyno/index.html

[gsneyd]

A couple of comments on your circuit. The problem with a solid state alternator is that whenever its in circuit it pumps out current al the time. Any current not used will have to absorbed by the Zener(s) (12v ?, you didn't state). Hence it will get hot (very hot). Suggest that for the lighting circuit you put a switch before the zener, hence when no lights are on it will not have to absorb current, when the lights are on, they (hopefully) will absorb the current.

With the ignition circuit which need to be in all the time, then that circuit will absorb the current.

Overall it’s the same principle as on my 1963 G12 which switches in more alternator windings dependant on the positions of ignition and lighting switches, but without the benefits of the zeners and Boyer Branson kit. But money will cure that.

I like your thinking for a cheaper solution though.

What current did you allow for in the size of the rectifier. in the next article (Alternator wiring) Kierain Enright says 108 watts = 9 amps with a surge to 15a. do you agree?

Graham

[Jordan Princic.]

Good idea to switch out the lighting coils if you want to run without lights - no point in making power just for heating the zener. I have lights on all the time.
The 2nd capacitor may not be needed - I thought the DC horn might be happier with it though.
It's a 12V system, but 6V would work too, if you could get appropriate zeners. I used commonly available Lucas ones.
Bridge rectifiers are overkill at 35Amps - these are the easiest to find in the electronics shops, cheap and have 1/4 inch blade terminals.
It doesn't matter whether Boyer or points ignition is used. The alternator makes 9V at kickover speeds, Boyer operates from 8V, so I just thought I'd mention that.
This circuit differs from your G12 in that it is really split into 2 - doesn't just switch in extra coils with the lights. This is what makes it possible for the bike to run without a battery, without being upset by turning on the lights.

[Kieran Enright.]

Dear Graham,

ref. your question about current ratings for the rectifier etc, bear in mind I was talking about a system with a battery in circuit. This acts as a voltage regulator in that, like a Zener diode, if the output voltage from the alternator starts to rise, the battery absorbs more current, and damps it down. Take the battery away, and unless you replace it with something which can absorb excess power, the output voltage can go a lot higher than most people realise. The proof of that is if the connection between a battery and a frame goes open circuit, the bulbs are very bright even at a tickover. As soon as the revs rise, the bulb filaments burn out.
The nominal 12V output from an alternator is about 14 - 14.5 volts at cruising revs, and THAT is only the D.C equivalent; the PEAK voltage is 1.414 times as much, so can easily top 20V.
Take the battery out of circuit, and unless you replace it with a load which can absorb a lot of power, such as a Zener diode or a hefty capacitor, you might double that figure at high revs. So the voltage rating of the rectifier is just as important as the current rating. I think even using a 50V rectifier is pushing your luck; I wouldn't use less than 100V PIV. The other thing to bear in mind when replacing Lucas components with parts meant for use in radios, etc, is that a motor vehicle environment is incredibly harsh on electronics, and Lucas knew that. So their quoted ratings for their parts are VERY conservative, and really do allow for 'worst case' scenarios.

Hope this helps,

Kes Enright
black.five@cwcom.net

[Jordan Princic.]

Rectifier is rated 35A, 400 volts.
No worries!

[Colin F]

Why are you trying to re invent the wheel?
Lucas literature from the 1960's gave instructions on how to convert from 6volts to 12 volts, and how using a 2MC capacator (supplied by lucas) the bike can be run without a battery.
My 350 has been run on this system for several years now, starts with a totally flat battery, even without one, in one or two kicks.
I also have an off road tiger cub that has always run on zener / capacitor system, only has a battery fitted for MOT's so that the horn can be heard over the engine noise .
Any one who needs help/advise/parts contact me, adress etc in Jampot.