What capacitor to use to reduce voltage spikes on 6v system

[Littlewood]

Hi, Im new here and know very little about electronics, my problem/questions is:

I have a 1944 HD WLA Motorcycle that runs on a 6v system. The generator is switched by a simple mechanical relay, no voltage regulator, the generator at idle puts out 6.4 - 6.8v as per manual, the problem start when rpm is increased, the voltage spikes to 8.1v, needles to say I go through a few 6v bulbs (35w). See attached extracts from the original manual on amps. On the wiring diagram you will see a condenser on the generator, this acts as a radio suppressor, I would like to replace this with a modern capacitor to smooth out the spikes in voltage.

Will this work and how do I calculate the size of Capacitor required?

Many thanks
James

 

[MikeMl]

The capacitor is there for RFI suppression; it will do nothing for your voltage regulation problem. Get rid of the POS electromechanical regulator, and put a real voltage regulator on it...

 

[crutschow]

Some of the old motorcycles used a brute-force method of having a shunt zener regulator to sink away the excess current and keep the voltage below the desired maximum (perhaps about 7V). The regulator would likely have to dissipate perhaps up to 50W so it would need a good heatsink. If a large wattage zener is difficult to find, you could use a small 6.2V zener is series with a resistor and the base of an NPN power transistor.

 

[claudinemann]

I agree with Mike Ml. You are supposed to use a real voltage regulator. It's effective and guaranteed, rather than experimenting. Moreover, when you push through with this, it will add to your knowledge and experience. So it will really benefit you.

 

[Mr RB]

You can buy 6v voltage regulators to suit your old Harley from many places. Somewhere like custom chrome or JP cycles should sell a number of products to suit.

 

[debe]

The relay is not a regulator, its to disconect the generator from the battery when the generator is not puting out a voltage. In the 4th image it shows how to adjust the voltage of the generator, by shifting the 3rd brush. This is a realy old style generator using 3rd brush feed to the field winding to regulate the voltage.