Effects of a Volt-ampere Curve On a Welding Arc Flashcards
What happens to the volts and amps when you have a short arc vs a long arc?
Short arc= low arc voltages and high welding currents
Long arc= high arc voltage and low welding currents
What are 2 classifications for welding power sources and which one is better for SMAW?
Constant current (CC) and constant voltage (CV). Constant current is standard for SMAW
What is an open circuit called? (OCV) what is the OCV range?
Open circuit voltage (OCV) 50 to 100 v normally around 70V
What is the middle of the volt-amp curve called? And what is its normal range?
The normal voltage levels during welding also known as the “arc voltage”. Its normal range is 18v to 36v
Explain the difference between CC and CV
CC has a “drooping” (or sloping”) electrical characteristic. This drop indicates that the current of the arc will remain fairly stable across a wide range of voltage changes
Constant voltage power sources have a fairly flat volt-amp curve. Power sources of this type produce a very stable voltage regardless of the amount of current.
What happens to the volt-amp curve when you have a higher open circuit voltage (OCV) vs a lower (OCV)?
Low range is better for?
High range is better for?
Higher OCV slope is steeper and Lower OCV slope is flatter.
With a flat volt-amp curve, and change in arc length will be noticeably change the current level. With a steep volt-amp curve, any change in arc length will only cause minor current change
Low range is better for out of position welding
High range is better for flat and high-production welding
What control on a welding power source gives you some controls over the volt-amp curve?
Arc dig, crisp and soft or arc force control
Ac transformers used as welding power sources are also called _________. Line voltages for single phase and 3 phase are? The transformer converts these line voltages into open circuit welding voltages in the range of?
Step-down transformers
115v or 220v for single phase and 115v, 208v, 480v or 575v for 3 phase
Open circuit line voltages in the range of 60v to 80v with amps as high as 1500A
Explain a transformer/rectifier
The transformer part transforms the AC line current down into usable AC current and the rectifier converts it to DC. This can be used with either single phase (with a capacitor to get consistent currents) or 3 phase
Explain AC/DC transformer/rectifier
Works just like a transformer/rectifier but have a switch to bypass the rectifier circuit to produce AC currents
What part of an engine driven power source reduces and increases the engine speed when you’re welding?
The governor
What are the dials on an engine driven welding power source that let’s you control the volt-amp curve?
“Dual control welding power sources” also known as “job select dials”
Tapped type, the stepped type or continuous control type. The tapped and stepped type offer a range of prescribed settings. The continuous control type allows for infinite settings adjustment
Describe the steps an inverter takes
What is the efficiency of a transformer vs an inverter
- Takes in ACine power
- rectify it to DC
- Converts it to electronically to high-frequency (3 to 50 kilohertz) AC
- Transforms it to welding voltages
- Converts it back to AC
Conventional transformer at 60 Hertz would weigh 19.5 kg (42 Ib). It would have an efficiency of 90% and produce a heat loss of 10%
An equivalent inverter operating at 200 000 hertz would weigh 1.5kg (3 1/3 Ib). It would operate at 98% efficiency and produce only 2% heat loss
A standard transformer/rectifier can lose how much of its incoming power vs the energy loss of an inverter
55% and as low as 15%
What does NEMA and ASME stand for?
National Electrical Manufacturers Association
American society of mechanical engineers
