Sunday, 12 January 2014

FIA Kill Switch

I'd been meaning to fit a battery isolator for a while.  Partly as a safety feature for when the car is stored in the garage and partly in preparation for possibly taking part in formal motorsport events, e.g. sprints.

There are simple isolators available that just cut the positive connection to the battery.  They achieve the goal of isolating the battery, but if turned off whilst the engine is running, will very likely kill the circuit in the alternator, as the load has nowhere to go.  Also, if the ignition coil/ECU is not isolated from the alternator, it is possible for the engine to continue running even after isolating the battery.

The solution to both of these issue is to use the more advanced model of isolator switch.  As can be seen below, this not only breaks the supply to the coil/ECU, but also dumps the alternator load to a resistor for the short period after the isolation switch is activated and before the engine ceases to rotate.

The main challenges to fitting the switch to an Avon with the bodywork fitted was finding a suitable location for the switch as well as routing the wiring.  I had some bespoke cables made up by a seller on eBay.  These were 170 amp rated and had the appropriately sized ring connectors fitted on each end.

I decided to locate the kill switch in a hole that was used for a side mirror before I fitted the cage.  The one on the other side of the car still has as blanking bung.  This location for the switch should also comply with the MSA regulations, i.e. it can be activated by the driver whilst strapped in to the car, as well as a marshal from the outside of the car.

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