FORD VAN POINTERS.
Page 25
Page 26
If you've noticed an error in this article please click here to report it so we can fix it.
;By R. T. Nicholson (Author of "The Book of the Ford ").
IHAVE said that troubles in the low-tension ignition circuit are due either to short circuits or to interrupted circuits, because there is one point where the circuits must be regularly interrupted if you are to get results :— 535.—Some Interesting Points About Coils. Unless the coil contacts actually separate, and so interrupt the low-tension current, you do not get that make-and-break action which is necessary for the pro. duction of the spark in the high-tension system. If . the contacts are jammed together permanently, or if, onthe •other hand, they are permanently-separated, you will get no high-tension spark. It is only because of the sharp make-and-break action in the lowtension system that you get high-tension sparks at the plugs at all.
You have, in an efficient induction coil, a series of makes-and-breaks through the trembling action of the vibrators and at each break you get a plug spark. One break would be enough for one spark, and one spark should fire the mixture; but the trembling action gives us a series of sparks, and thus theoretically makes firing much more certain than it would be with a single break. You should, however, know that there are certain systems of ignition devised for use on the Ford which do away with all' trembler action, having only a single make-and-break for the firing of each cylinder. In point of fact, with the standard system, you get four sparks in each cylinder at each timer contact.
The Ford Coil. • The Ford coil is -exactly like one of the two types of coil used on -ignition systems in the early days of motoring. Such differences as there are between those early systems and the modern Ford system lie outside the coil.
The coils are provided to induce high-tension current from Tow-tension current. What this means is
that a coil-unit passes current of low pressure, and sends out current at high pressure. Do not get the mistaken ideo, that there is any connection between the low-tension system and the high-tension system : there is not: they are quite distinct and separate. And do not suppose that the coil is an ingenious contraption for manufacturing a great amount of electricity out of a very small amount of electricity if you 'could do that, you could create energy, and run a perpetual-motion machine. All you can -do is to transform energy : you can never, create it. What you do with the coil is.. to transform fat, sluggish. electricity into thin, active electricity, and You do it by induction. You want the thin, active electricity for one purpose only on the Ford—that of getting a good hot spark at the plug points. The fat? 'siuggish electricity might be used (has been used in the past) to produce the spark at the plugs, but it is really not up to the job. In other words, high-tension current, as induced by the coil, has high voltage and low amperage ; lowtension eurrerit, as passed through your coil, has low voltage and high amperage. It is because its amperage is low that your high-tension electricity, when you touch a plug with the engine running, doesn't kill you. I read of a case the other day in which aman was killed by 200 volts which got at him from an electric .light circuit; Your sparking-plugs can give you .a shock of over 8,000 volts, but you can withstand it
because the amperage behind your high-tension voltage is so slight. If it were equal to that of an electric light circuit of 200 voltage, you would die su re enough. The theoretical action of the Ford coil-unit is illustrated in Fig; 363 Low-tension current comes to the bottom binding-post from magneto or battery (as the case may be), passes to the common coil contact (C), and up the thick spiral to the post which carries the vibrator bridge, through that bridge, through the • upper contact, down to the Tower contact on 'die vibrator, through the folded brass piece supporting the vibrator, to top binding-post (A), and thence by wire to timer. This, however, does not account for the trembling action of the vibrator. You will sec that the thick coil above C rttns round a bundle of iron wires. In so doing, it turns the bundle of wires for a moment into a magnet. (This is a well-known fact in electromagnetism.) The wires attract the vibrator, and so separate the contacts. But this separation of the contacts interrupts the low-tension current, so that there is no longer any circuit through the thick spiral, and the, bundle of wires, therefore, loses its magnetism: so that the lower contact springs upwards again and touches the 'upper one, so re-establishing the circuit. -This make-and-break action goes on and on and on, and makes one tired to think of it.
The breaking of the contaeta results in sparking at those contacts. It is this sparking that in the long run pits the tungsten— hard as it is—and makes them ragged, so that the,/ no longer meet fair!, and squarely: there is then no proper, path provitlefl for passage of low-tension current through them, and the. unit concerned becomes sulky. Induction..
Close to the low-tension spiral is the high-tension the wire of which is much finer, and also much longer. It is the relative length of the two spirals-7the greater number of turns in the high-tension spiral —that causes a high tension iirreirt to spring up— by induction—in the latter, to give us sparking at the plug points. There are about 80 turns in the high-tension spiral for each one in the low-tension spiral.
This, however, would not alone account for the increased voltage of the high-tension current it is partly due also to the presence in each coil-unit of a condenser. Without it, with 6 volts coming through from the battery, we should get only SO times as many volts.in the high-tension circuit-480. The condenser builds the voltage up to about 3,800 on battery current. The magneto, however, gives us far nitre than 6 volts when the engine is running at speed ; so that we actually get about 8,000 volts in the hightension circuits in such circumstances.
How Does Induction Happen?
This is a question which it is easier to ask than to answer. I will, however, see what I can do to explain it :
We have learnt that, in the Ford coil-unit, there is a bundle of iron wires round which the low-tension spiral runs, and that the bundle LK:comes magnetized when current passes. Now, as we have previously seen, a magnet throws out a great number of lines of force, which we may regard as something like liquid rubber bands. Our magnetized bundle of wires throws out such lines of force. Those fines of force have great penetrative power they will pass through materials which will insulate electricity, Consequently, the lines of force will penetrate the electrical insulation between the low-tension spiral and the high-tension spiral which is built up around it. But the -coils of that high-tension spiral are so fine, and so numerous that the magnetic lines of force get considerably tangled up in them ; and when the low-tension current is suddenly cut off, these lines of force try to fall back 'towards the bundle of wires and get get badly mangled in the effort. There is a rush of current round the high-tension circuit—short and Sharp—till the lines have all fallen back. The induced current may thus be considered as the cud den snapping back into position of our liquid rubber bands. It is the suddenness that gives the high-ten
sion current its kick. Really, there is no more energy in the kick of the high-tension system than in the push of the low4ension system.
Condenser.
There is no purpose in describing the condenser : it thing is certain—that if the condenser gees wrong, is "out of sight," and may be left "out of mind." One the particular coil-unit concerned will be thrown out of action, and only an expert can put it right.
If there is an interruption in the condenser, you will get brilliant sparking (arcing) at the contact points, and no sparking, or only very weak sparking, at a test gap set at the lower binding-post. If there is a short circuit in the condenser, the vibrator will be simply pulled down by the magnetized bundle of wires, and will then stick.
The condenser has one job which I have not .mentioned. Without it, there would be very hot, bright sparking at your trembler contacts, and they would consume rapidly.