Halvledare för höga strömmar i fordon
Mechanical relays are more and more being replaced with semiconductortechnology. In this thesis it is investigated if and how the larger loads couldbe controlled by transistors. The main part of this work aims to create andverify a solution that can control the starter motor, as well as protect it incase of any failure. The different malfunctions that the solution protectsagainst is high current, too high peak current, low current, maximum cranktime and minimum cool off time. The timers also protect indirectly againstoverheating of the starter engine.The transistors used are BTS555, from Infineon. Typical rated current of thetransistor is 158 A and it has integrated functions such as temperatureprotection, short circuit protection and current sensing. The functions wastested and evaluated. The temperature protection and current sensor wasfound to satisfy the specification. The short circuit protection did notprotect against all kinds of short circuit failures thus an external over currentprotection has been added.To control the starter motor, twelve transistors were connected in parallel, toallow for a total of initial start current 2 000 A and a continuous maximumcurrent of 1 150 A. A series of tests were performed on the transistors, theexternal protections and the starter motor, until everything worked togetheras planned. The control circuits is designed with simple gate logic incombination with other active and passive components.The transistors are the largest expense. The used solution has an estimatedprice of 400 SEK, assembling excluded. The assembling is estimated to takeone hour.Conclusions made from measurements and tests shows that it is possible tocontrol the starter motor by using semiconductor technology. Since thesolenoid in the current starter relay will not be excluded, the solution mightbe hard to motivate in an economic aspect. The advantages with asemiconductor solution are the protective functions and that the startermotor will be disconnected from the batteries when not being used.To control the smaller loads, such as the preheater, the semi conductor relayis a competitive alternative since the mechanical relay and the fuse can bereplaced.