SAW Engine Performance & Tuning 2 — Questions and Answers
Question 1: In a SAW power source with an engine-driven generator, what does a drooping volt-ampere characteristic primarily protect against?
- Electrode burnback
- Electrode stubbing and arc instability under varying load (Correct answer)
- Flux hopper bridging
- Contact tip overheating
Correct answer: Electrode stubbing and arc instability under varying load
A drooping (constant-current) characteristic limits current surges when the arc length shortens, preventing electrode stubbing and maintaining arc stability.
Question 2: When tuning a diesel engine driving a SAW generator for cold-weather starts, which adjustment is most important?
- Increasing injector timing advance
- Enriching the air-fuel mixture at idle
- Verifying glow plug function and fuel viscosity rating (Correct answer)
- Reducing governor sensitivity
Correct answer: Verifying glow plug function and fuel viscosity rating
Cold diesel starts rely on adequate glow plug heat and low-viscosity fuel to ensure proper atomization and ignition at low temperatures.
Question 3: A SAW tractor's engine-driven wire feeder loses consistent wire feed speed as engine RPM fluctuates. The most likely cause is:
- Worn flux coating on the electrode
- An unstable governor on the engine (Correct answer)
- Incorrect polarity selection
- Excessive contact tip wear
Correct answer: An unstable governor on the engine
Wire feed speed in engine-driven SAW systems is often tied to engine RPM; governor instability causes RPM swings that directly translate to inconsistent wire feed.
Question 4: During SAW, the open-circuit voltage (OCV) of an engine-driven power source is measured at 75V. What does this indicate about engine performance?
- The engine is running below rated RPM
- The engine is running at or near rated RPM producing full excitation (Correct answer)
- The flux burden is too low
- The welding current is too high
Correct answer: The engine is running at or near rated RPM producing full excitation
OCV at or above specified levels confirms the engine is spinning the generator at rated speed, ensuring full magnetic excitation and voltage output.
Question 5: An engine-driven SAW unit shows excessive black smoke under welding load. The most appropriate corrective action is:
- Increase the flux depth
- Reduce travel speed
- Service the fuel injection system and air filter (Correct answer)
- Switch to reverse polarity
Correct answer: Service the fuel injection system and air filter
Black smoke indicates rich combustion caused by insufficient air or poor fuel atomization; servicing the air filter and injectors restores proper air-fuel ratio.
Question 6: What is the purpose of the isochronous governor in an engine driving a SAW welding generator?
- To control flux feed rate automatically
- To maintain constant engine RPM regardless of electrical load changes (Correct answer)
- To limit maximum welding current output
- To regulate cooling water temperature
Correct answer: To maintain constant engine RPM regardless of electrical load changes
An isochronous governor holds engine speed constant across load variations, ensuring stable welding output voltage and consistent arc performance.
Question 7: In SAW equipment, what effect does running the engine at below-rated RPM have on welding arc performance?
- It increases deposition rate
- It reduces heat input automatically
- It lowers OCV and may cause arc instability or failure to strike (Correct answer)
- It improves penetration by increasing current
Correct answer: It lowers OCV and may cause arc instability or failure to strike
Below-rated RPM reduces generator output, lowering OCV and available current, which makes arc starting difficult and causes unstable arc behavior.
SAW Engine Performance & Tuning 2
In a SAW power source with an engine-driven generator, what does a drooping volt-ampere characteristic primarily protect against?