SIMPLE
Page 47
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Coil ignition, 3
ast article (April 11) it was that a condense had to be I to a coil ignition to prevent arcing at the : breaker points. Although .nser" is the name gener,en to this component by s in the motor trade, the al engineer calls it a cepa'id this is the right term. btain the high voltage in ondary winding, and ultiat the sparking plug, a ollapse of the magnetic the coil is necessary. To .3 this the current must )1Iapse rapidly when the open.
out a condenser, the curies to flow across the after they have opened, due to a self-inductance effect. This slows down the collapse of the magnetic field and also causes arcing across the points causing them to burn out.
When the contact breaker points open and a condenser is connected across the points, the current, instead of causing arcing, flows into the condenser." When the points close again, the condenser discharges and the electricity released helps to build up the primary current more rapidly than otherwise would be the case.
The condenser consists of two sheets of foil or metallised paper which are separated and insulated from each other by waxed paper. The modern condenser has wound strips of paper upon which a thin metal film has been deposited, so as to give a continuous metal surface.
The advantage of this method of construction is that the condenser is self-sealing; if a hole is made in the paper, the metal film around the hole is evaporated. The wound strips of metal and paper is contained in a metal container.
One of the sheets of foil is connected to earth and the other to the insulated side of the contact breaker.
Condensers give very little trouble, but if defects occur they can be of two kinds. If the insulation breaks down and a "short" circuit occurs the contact breaker points cannot break the primary circuit and no high tension current is produced. If the condenser has an "open" circuit, arcing will occur at the points and the spark produced will be weak and erratic.
The unit of electrical capacity,' by which condensers are measured, is the farad. This unit is much too large'for practical purposes so another unit the microfarad — one millionth of a farad, has been adopted. The capacitance of ignition condensers is generally about 0.20 micro-farads.
Although there are instruments designed for testing condensers, these are not general available to mechanics in the smaller workshops and defective condensers are usually diagnosed by a process of substitution (a new condenser is fitted, if the engine then performs satisfactorily, the old condenser was obviously faulty). Badly burned contact breaker points will, of course, give an indication as to where the trouble lies.