Maplin auto electronics projects
Auto electronics projects Stator windings in which current is generated Diodes convert alternating current to d.c. Rotar turns inside stator assembly Figure 1.17 Alternator and control circuitry Both systems have a built-in ignition warning light with one side connected to the battery +12 V terminal, the other to the dynamo or alternator output. If the genera- tor is not working, when the engine is switched off for 22 Car electrical systems instance, or when the fan-belt is slipping or broken, the 12 V bulb has 12 volts across it and it lights. Normally the lamp has 12 volts on either side and it goes out. Lighting Little needs to be said about the normal lighting circuits except to say that the headlamp bulbs can consume sev- eral amperes each and so cable of the correct size must be used to prevent heating (or melting) of the wiring. Many bulbs, as in Figure 1.18, have two filaments for compactness. Quartz halogen bulbs, with a gas surround- ing the tungsten filaments, give off greater brightness. Figure 1.18 Dual filament bulbs 23 Auto electronics projects As the headlamps between them consume several am- peres, the headlamp (or flasher) switch has to be heavy duty and high current wires must be sent to the dash- board. Consequently a relay is often positioned near the headlamps, as in Figure 1.19, this being activated via a (preferred) low current switch and wiring. Operating the switch activates the relay which connects the headlamps directly to the battery terminal. One final lighting device in common use is the spring steel flasher unit (see Figure 1.20) which turns the indi- cator lamps on and off. Figure 1.19 Headlamp relay 24 Car electrical systems While cold, the contacts are held together by the dia- phragm. When current passes through the contacts, by indicating to turn left or right, the resistance metal heats up, expands and pushes the contacts apart. They then cool again, close and the sequence repeats 60 to 120 times a minute. Emergency light units are similar except that heavy duty contacts are used. Current from A I Current to indicator switch | φ indicator lamps Indicator lamps on' Indicator lamps off Figure 1.20 Flasher unit Starter motor and other accessories In a similar way to the headlights being operated via a remote control relay, a starter solenoid is used as in Fig- ure 1.21 to switch the 400 amps to the starter motor. This wiring is the thickest to be seen under the bonnet and every step is taken to minimise any heat generated 25 Auto electronics projects despite the costs of the thick copper wire. The starter motor engages with the engine via the flywheel to start the engine, as seen in Figure 1.22. If the ignition circuit is working well, a few turns of the engine should cause the engine to fire and continue under its own steam. The starter motor is then disconnected from the engine. Figure 1.21 Starter solenoid Two methods are used, a pre-engaged motor whose pin- ion is always linked to the flywheel, a solenoid operating a plunger to engage the starter motor with its pinion (like a small clutch), and the inertia type whose pinion slides along the shaft to engage with the flywheel as soon as the starter motor operates. These are shown in Figure 1.23. Figures 1.24 to 1.28 illustrate a number of other elec- trical accessories which are essential, and some legally required, in the modern motor car. 26 Car electrical systems Figure 1.22 Flywheel Petrol pumps operate either via a mechanical rocker assembly coupled to the engine forming a small mechani- cal pump (Figure 1.24), or an electrical diaphragm pump, rather like a vibrator, which pumps the petrol from the tank to the engine, as in Figure 1.25. The petrol gauge operates using a small float coupled to a variable resist- ance unit. As the petrol level rises or falls, the current to the gauge rises or falls accordingly. This unit, similar to a WC ball-cock, is sealed for fire reasons, see Figure 1.26. 27 Auto electronics projects 28 c* «— Ο Ο ε <σ CO <ν> α> »_ β> Car electrical systems 29 Figure 1.23 Continued Auto electronics projects Figure 1.24 Mechanical fuel pump Horns come in all shapes and sizes. Figure 1.27 shows a simple type, working like a vibrator whose diaphragm output is mechanically amplified to warn pedestrians to get out of the way. Ammeters can be fitted in any car: a simple means of installation necessitating a minor change to the wiring 30 Car electrical systems Figure 1.25 Electric fuel pump 31 [...]... it, it originally r e p l a c e d a m e t h o d s o a r c h a i c as to b e u n b e l i e v a b l e Automotive ignition — a brief history E a r l i e s t m o t o r c a r s , or in fact anything using t h e newfangled gas e n g i n e ( m a n y of w h i c h w e r e a l s o u s e d for 35 Auto electronics projects powering agricultural m a c h i n e r y ) , of slightly o v e r a cent u r y ago had to make... warns t h e driver of impending t r o u b l e ( s e e Figure 1.29) T h e day of t h e J a m e s B o n d s u p e r c a r or t h e Night R i d e r ' s Kit l o o m s n e a r e r e v e r y d a y 33 Auto electronics projects Figure 1.29 34 Computerised dashboard 2 The Electronic ignition e l e c t r o - m e c h a n i c a l ignition s y s t e m t h a t h a s b e e n u s e d t o fire t h e fuel/air m i x t.. .Auto electronics projects Figure 1 2 6 Fuel gauge and float as shown in Figure 1.28 B y this m e a n s t h e a m m e t e r d o e s not r e c o r d t h e s t a r t e r m o t o r c u r r e n t , but all o t h e... ) In E u r o p e t h e r e was great res i s t a n c e to coil ignition, e s p e c i a l l y among t h e B r i t i s h , who t h o u g h t it too gimmicky C u s t o m e r s wouldn't buy a 37 Auto electronics projects c a r if it had coil ignition — m a n u f a c t u r e r s had to r e v e r t to t h e m a g n e t o in o r d e r t o b e a b l e t o maintain s a l e s Would you b e l i e v e that s... h a n i c a l s y s t e m at rest With s w i t c h S I open, nothing is happening When S I c l o s e s in Figure 2 1 ( b ) , c u r r e n t flows in t h e p r i m a r y winding LI of T l , 39 Auto electronics projects t h e ignition coil T l has a laminated s t e e l c o r e and a fin i t e t i m e is t a k e n for t h i s c o r e t o r e a c h magnetic s a t u r a t i o n , by which time t h e primary... e s t leads and a b a t t e r y So this is w h e r e t h e o t h e r c l e v e r bit c o m e s in, t h e third c o m p o n e n t in t h e set-up, C I T o this day it is still c a l l e d 41 Auto electronics projects a condenser, a v e r y old-fashioned name for a c a p a c i t o r Its function is to m o m e n t a r i l y take o v e r from t h e s w i t c h As S I o p e n s , c u r r e n t flow... Figure 2 3 Laminated core as a bundle of steel strips HT Ίΐνβ* connects to this, and is passed via the coil spring at the top to HT socket Internal construction of a typical ignition coil 43 Auto electronics projects Advantages of electronic ignition T h e first two p r o b l e m s a r e p r a c t i c a l l y s o l v e d by e l e c t r o n i c switching, t h e third b y using t h e coil in a different... a c t u r e d t o c o p e C o n s e q u e n t l y e l e c t r o n i c ignition was e x p e n s i v e and usually only found a t t a c h e d t o similarly unaffordable s p o r t s c a r s 45 Auto electronics projects Timing sensors In t h e 1970s, solid s t a t e ignition with t h r e e v e r s i o n s of timing s e n s o r proliferated T h e simplest was the s o called transistor assisted ignition, . 1 .26 . 27 Auto electronics projects 28 c* «— Ο Ο ε <σ CO <ν> α> »_ β> Car electrical systems 29 Figure 1 .23 Continued Auto electronics projects Figure 1 .24 . generated 25 Auto electronics projects despite the costs of the thick copper wire. The starter motor engages with the engine via the flywheel to start the engine, as seen in Figure 1 .22 . If the. 30 Car electrical systems Figure 1 .25 Electric fuel pump 31 Auto electronics projects Figure 1 .26 Fuel gauge and float as shown in Figure 1 .28 . By this means the ammeter does not