Question

which of the following methods should be observed to crank a hard-to-start, truck diesel engine?! Crank for 2 minutes, rest for 15 seconds Crank for 30 seconds, rest for 2 minutes Crank for 15 seconds, rest for 2 minutes Crank until the batteries die

Answer 1

Cranking a hard-to-start diesel engine should be done by cranking for 15 seconds followed by a 2-minute rest to protect the starter and batteries. Semi tractor trucks often use a 24 V system from four 12-V batteries for starting due to its efficiency and reduced losses. The average current for starting an engine can be calculated from the charge moved in a given time.

Step-by-step explanation:

When attempting to crank a hard-to-start diesel engine in a truck, one should follow a procedure that protects both the starter motor and the batteries. Over-cranking the starter can damage it due to overheating, and can also deplete the batteries prematurely. The best practice among the options provided is to crank for 15 seconds and then let it rest for 2 minutes. This allows the starter motor to cool down and reduces the risk of overheating.

In a semi tractor truck that uses four large 12-V batteries, these can be connected in a series-parallel configuration to achieve the required voltage and current capacity. For starting the engine, which is a heavy load, a 24 V system is more effective than a 12 V system. To produce 24 V, two pairs of 12-V batteries are connected in series (each pair producing 24 V) and then the pairs are connected in parallel. Alternatively, to produce 12 V, the batteries can be connected all in parallel.

24 V is better than 12 V for starting the truck's engine because the higher voltage can provide the necessary current without requiring the cables to be excessively large, which would be impractical and costly. Moreover, 24 V systems can deliver the same power as 12 V systems while carrying only half the current, reducing losses due to resistance in the cables and connections.

Calculating the average current involved in starting a truck engine can be done using the charge and time. For example, if a battery sets in motion 720 C of charge in 4.00 s, the average current (I) can be calculated using the formula I = Q/t. Here, Q is the charge in coulombs and t is the time in seconds. Thus, I = 720 C / 4.00 s = 180 amps.