CONSUMPTION OF POWER.

Auckland Star, Volume LX, Issue 124, 28 May 1929, Page 19

CONSUMPTION OF POWER.

INTERESTING TESTS. When the owner-driver presses the 1 starter button again and again on a cold morning in an endeavour to coax a reluctant engine to fire, he is probably I quite unaware of the fact that a literally enormous current, which may easily amount to more than 200 amperes, is 1 being caused to flow from the longsuffering batteries. For those whose knowledge of electricity is small it may be explained that the total current consumption, say, of a private house with n dozen lamps burning, is only about four amperes, so that a starter motor is taking electricity at 50 times this rate. Another way of looking at it is that on a 12-volt system 200 amperes represents a power 0f'2400 watts, which is actually more than three horse-power—a greater power than that employed for broadcast- ( ing in many cases. These aiid many ' other interesting points are made clear by a series of oscillograph teste on i starter motors of various types recently carried out at the National Physical Laboratory (England). The oscillograph ; is a device which makes a continuous i record of current consumption and/or 1 voltage, so enabling the investigators to ascertain just what is happening from the instant at which the starter switch .is operated until the point at which it ! is released. Typical graphs cf this kind were first obtained from a well-known four-cylinder car of about 12 h.p. Jittid with it chain-driven dynamotor and 12-volt lighting equipment. When a graph was taken with the engine cold the mixture commenced to fire after three-quarters of a second, the starter switch being released abouthalf a second later; incidentally, the dynamotor was turning the engine at about 150 r.p.m. When the is witch was first operated a current of 130 amperes flowed from the batteries. The second experiment makes an interesting comparison, as it was carried out under identical conditions but for the fact that the engine was hot, the radiator tei>"pcrature being about 190 degrees F. The total current consumption was very much less, owing to the fact that tho engine fired in a quarter of a second as against three-quarters of a second, and the engine was turned by the starter at about 240 r.p.m. Tests were als"> made upon another car of much the same size which was fitted with the ordinary starter motor and Bendix drive in of a dynamotor. Two typical graphs were obtained from this car, one with the engine cold, the other when the engine was hot. In the first case, with a cold engine, the ignition switch Was left "off" in order to correspond with the conditions imposed by an inexpericncod driver trying to start with incorrect carburetter settings. Closing the switch produced a current flow of 154 amperes, and then as the pinion slid into mesh with the teeth on the flywheel, there was a sudden increase of current to 228' amperes and a drop of voltage to l).l. Thereafter the current fluctuated above and below a figure of about 100 amperes according to the compressions in the cylinders. In tho second case, when the engine was hot and the ignition ■switch on, approximately the same' initial flow of current was given, but (as before) the total consumption was found to be very much less than with a cold engine.