THAT STARTING STRAIN.

Putaruru Press, Volume V, Issue 212, 24 November 1927, Page 7

THAT STARTING STRAIN.

FACTS ABOUT BATTERIES. We have received letters from new car owners expressing surprise that the discharge from their batteries on' starting up may reach as much as 150 or more amperes, and this appears to alarm them somewhat. There is no need for anxiety, for it is important to understand that such a high discharge is only momentary. The explanation, simply stated, is that when the starter switch is closed and current flows through the starter windings, the armature has to develop a very powerful turning effort to overcome the strong resistance offered by the engine. For an instant the armature can only rotate very slowly, but simultaneously there is a maximum flow or rush of current which enables the armature to exert its greatest turning effort and overcome the resistance offered. Immediately this is effected the armature is able to increase its speed very rapidly. It might be thought that the great initial rush of current ,vould continue until the s tartar switch was released, bu actually the current strength is automatically reduced when the armature “ jumps ” up to its maximum speed. This -s brought about by a certain electrical effect known as the generation of a “ back electromotive ” force in the armature; this means that an independent current is generated in the armature which opposes the main inflowing current and brings it down to quite a small amount. If it be imagined that the starter can run quite free without having to engage the flywheel, the result of switching on the current would be instantly to run it up to an enormous speed; but if there were an ammeter in the circuit, it would only show a very few amperes passing. The fact to laeep in mind is that the heavy discharge required by a starter can only last for an instant if the starting conditions are normal. If the engine is very stiff and it fails to fire at once, it would mean that the discharge current would not fall off to its minimum value, but even so it would be nothing like so heavy as the initial discharge. It might mean that 30 or 40 amperes would be passing, but even this would lagt for a few seconds only.