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Got a technical problem? Can?t understand a piece of jargon or some technical principle? Drop us a line and we'll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097 or send an email to silicon@siliconchip.com.au

Ignition for a
Velocette motorcycle

I have bought the “Ignition Coil Driver”, as featured in SILICON CHIP, March 2007. My intention is to use it between the existing points and coil on a motorcycle. The motorcycle is a 1950s British Velocette Valiant, with a 6V battery. Will the system work with 6V? (D. R., via email).

• The ignition coil driver can be used to directly fire ignition from a points trigger provided that the circuit in the April issue (p78) showing the “to invert firing sense circuit” (Fig.21) is built. A “points-wetting” resistor (eg, 33Ω 5W) should be placed between the input and 6V supply to allow current flow through the closed points.

Finally, the 100Ω 5W resistor at the collector of Q2 should be changed to 33Ω 5W for a 6V supply.

Using the zapper with the engine running

I am wondering if the 12V Battery Zapper unit (SILICON CHIP, July 2009) can be used with the vehicle’s engine running? I don’t have 240VAC available to run a charger. (S. F., via email).

• While engine control modules normally have spike voltage protection, it is probably not a good idea to run the Zapper in a car, whether the engine is running or not. In other words, the battery should be disconnected from the vehicle. We are assuming that this is a vehicle which is seldom used. If the car is used reasonably often, then you should not have a problem with sulphation.

On the other hand, if the vehicle is older, without an engine management computer, you can probably run the Battery Zapper on it with the engine running, without any risk of damage.

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