Five free practice questions on charging systems: content area C of the ASE T6 Electrical/Electronic Systems test, 7 of its 50 scored questions (14%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.
01The questions
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A truck's alternator has an adjustable regulator and a remote sense lead to the battery positive posts. Any of these could cause charging voltage at the batteries above specification EXCEPT:
- a regulator that has failed with the field held fully on.
- an open phase winding in the stator.
- corrosion in the sense lead's connection at the batteries.
- a regulator setpoint adjusted above the specification.
Show the answer
B. Correct. An open stator winding takes part of the alternator's output away, so it can only lower what the alternator delivers; it cannot push battery voltage above the setpoint. The other three make the regulator hold a higher voltage or lose control of the field.
Why not the others
A. A regulator stuck with the field on lets output rise with speed and ignore the sensed voltage, so it can overcharge. This is one of the common overcharge causes.
C. The sense input draws a small current, so resistance in its lead makes the regulator see less than the true battery voltage and raise output to make up for it. The batteries then end up above specification.
D. The regulator holds whatever voltage it is set to at the sense point, so a setting above specification overcharges the batteries. The adjustment is reset to the manufacturer's figure.
ID T6-C-009 · Task T6-C-2 (ASE task list)
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A truck's alternator grounds through its mounting to the engine, and its regulator senses voltage at the alternator's own output terminal. Its adjusting-bracket bolt is found loose. Any of these could result EXCEPT:
- a rise in battery voltage above specification.
- a cracked mounting ear from vibration.
- a high voltage drop in the alternator's ground path.
- a belt that squeals and wears on its edges.
Show the answer
A. Correct. A slipping belt cuts output, and ground-path resistance drops voltage before it reaches the batteries, so every effect of a loose mounting lowers battery voltage. Nothing about the bracket can push the batteries above what the regulator holds at its terminal.
Why not the others
B. With the bolt loose, the alternator vibrates against its bracket, and the cast mounting ears can crack. Mounts are inspected for cracks whenever a loose bolt is found.
C. This alternator returns its current through its mounting, so a loose joint adds resistance to the ground path. A ground-side voltage drop test with the alternator loaded would show it.
D. A loose adjusting bolt lets the alternator shift, slackening the belt so it slips and squeals and pulling the pulley out of line so the belt edges wear. Retighten to the manufacturer's torque and check alignment.
ID T6-C-012 · Task T6-C-3 (ASE task list)
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A technician puts a transformer-type current clamp, made for AC current only, around a truck's alternator output cable, and it reads near zero while the alternator is charging hard. Why?
- The clamp must go around the ground cable instead
- The rectifier's ripple cancels the reading in its jaws
- Alternator output is too high for its jaws to read
- It senses only a changing magnetic field
Show the answer
D. Correct. A transformer-type clamp works by induction, so only a changing current induces a signal in it; the alternator's DC output makes a steady field it cannot sense, and the clamp shows only the small ripple. DC output is measured with a Hall-effect (DC) clamp or a shunt.
Why not the others
A. The ground cable carries the same DC current, so the clamp would read near zero there too. A DC-capable clamp is needed, placed around the output cable.
B. Ripple is the small AC part riding on the DC, and it is about all this clamp can see; it does not cancel anything. The DC itself makes a steady field that an induction clamp cannot detect.
C. A current above the clamp's range would show as over-range, not as near zero. The clamp reads nothing because steady DC does not induce a signal in a transformer-type clamp.
ID T6-C-015 · Task T6-C-4 (ASE task list)
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A new ring terminal is being crimped onto a truck's alternator output cable. Besides fitting the cable's gauge, why must the ring's hole match the size of the alternator's output stud?
- A larger hole lets the ring carry more current
- The hole size sets how tightly the barrel grips the strands
- An oversized ring seats on less area under the nut
- The stud size, not the gauge, sets the cable's current rating
Show the answer
C. Correct. Charging current crosses the joint through the ring's flat faces clamped by the nut, and a ring with a hole too large for the stud sits off center with less of its face clamped. The smaller contact area heats under load and can loosen with vibration, raising the voltage drop at the stud.
Why not the others
A. Current crosses the joint through the flat faces clamped under the nut, not through the hole, so a larger hole only removes contact metal. An oversized ring seats on less area and can shift on the stud.
B. The barrel and the crimp die set the grip on the strands; the hole size has nothing to do with it. The hole must match the stud so the ring seats fully under the nut.
D. The cable's gauge and length set its resistance and current capacity; the stud size only decides which ring fits. The ring must match both the cable and the stud.
ID T6-C-021 · Task T6-C-6 (ASE task list)
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After a start, a truck's self-exciting (one-wire) alternator does not begin charging at idle until the engine is raised briefly to a higher speed; after that it charges normally, even at idle. Why?
- Its residual magnetism needs speed to excite the field
- Its brushes must warm up to make good contact
- Its belt slips until it warms and grips the pulley
- Its regulator waits for the batteries to surface-charge
Show the answer
A. Correct. With no excitation wire, the field gets its first current only from the alternator's own output, which starts from the small residual magnetism in the rotor. That needs speed to build enough voltage to turn the regulator on; once the field is energized, output sustains it at any speed.
Why not the others
B. Brushes do not need to warm up to conduct, and here charging begins as soon as the speed is raised, not after a warm-up period. The speed is needed so residual magnetism can build turn-on voltage.
C. A slipping belt would cut output at any speed and would not be cured by one brief rise in rpm. The alternator needs that speed so its residual magnetism can build enough voltage to excite the field.
D. The batteries cannot surface-charge until the alternator starts charging. The alternator starts once speed lets its residual magnetism make enough voltage to energize the field.
ID T6-C-024 · Task T6-C-7 (ASE task list)
02Answer key
| Question | Answer |
|---|---|
| Q1 | B |
| Q2 | A |
| Q3 | D |
| Q4 | C |
| Q5 | A |
03What area C covers
This content area covers truck and tractor charging systems: dash voltmeters, indicators and alternator-driven tachometers, diagnosing a truck that will not charge or overcharges, belts, gear drives, pulleys and tensioners, AC ripple and amperage output tests with the right clamp, voltage drop tests on both sides of the circuit, cable and terminal repair, and the regulator, rectifier, diode trio and remote sense lead.
The ASE test specification calls this content area “Charging System Diagnosis and Repair”. It carries 7 of the 50 scored questions, 14% of the test.
- Check dash voltmeters, indicators and R-terminal tachometer signals
- Find why a truck will not charge or overcharges
- Inspect belts, drive gears, pulleys, brackets and tensioners
- Measure alternator output current and AC ripple
- Voltage drop test both sides of the charging circuit
- Repair output cables, ring terminals and connections
- Test regulators, rectifiers, diode trios and sense leads
04What the questions turn on
Compare sensed and battery voltage
An alternator holding 14.2 volts at its own terminal while no current leaves it and the batteries sit at rest points to an open in the output path. Sensing true high voltage yet holding output up means the regulator lost field control.
Reading output the right way
An AC-only transformer clamp senses a changing field, so on a DC output cable it reads near zero and shows only ripple. Output is read with a Hall-effect DC clamp or a shunt. Hot output runs below cold output, since winding resistance rises with heat.
Drops add along the path
Charging circuit drops add from one point to the next. Splitting the reading at the starter's battery terminal, or at the ring terminal on an output stud, shows which section carries the excess resistance, and that section is repaired and retested at the same current.
Idle output has a ceiling
At idle an alternator can make only its rated idle output. With sleeper loads above that figure, the batteries make up the difference and run down. A higher regulator setting adds nothing, since below the setpoint the field is already at full current.
05The other content areas
The T6 test has five content areas. Each has its own page of free questions:
The ASE T6 Electrical/Electronic Systems practice test page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.
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