Welders and Filters Flashcards
Resistors are divided into two groups,
what are they?
- Fixed Resistors
- Variable Resistors
What are the two most important ratings of a resistor?
- Power in Watts
- Resistance in Ohms
What are the three most important ratings of a capacitor?
- Capacitance in Farads
- Voltage
- Tolerance
What are the two most important ratings of a coil?
- Inductance in Henry’s
- Maximum Current Rating
What is often referred to as a choke?
An Inductor
What is a Capacitor?
- A component in an electronic circuit that has the ability to store and release electrical charge
- This is called capacitance (C) and causes opposition to a change in voltage
- The unit of measurement is the Farad (F)
Describe the construction of a Capacitor
- A capacitor is two conductive plates separated by a dielectric layer
- This dielectric layer is an insulator that allows the two plates to be brought close together without shorting out
- The better the insulator is, the closer the plates can be brought together and the greater the capacitance
What three construction characteristics affect the capacitance of a capacitor?
- The surface area of the plates
- Capacitance increases as the surface area of the plates increases
- The distance between the plates
- Capacitance decreases as the distance between the plates increases
- The dielectric constant between the plates
- Capacitance increases as the dielectric constant increases
What are some of the common types of dielectric used in capacitors?
- Paper
- Plastic Film
- Mica
- Ceramic
- Electrolytic - Polarity Sensitive
- Tantalum - Polarity Sensitive
Which types of capacitors are polarity sensitive?
- Electrolytic
- Tantalum
What does WVDC mean?
- Working Volts DC
How many time constants does it take for a capacitor to charge?
Five Time Constants
What is the equation for one time constant?
T = R x C
- T = Time in seconds
- R = Resistance in ohms
- C = Capacitance in farads
What code rule states that capacitors shall be provided with a means of draining the stored charge?
26-222
How do Inductors behave?
- An inductor opposes a change in current
- As current increases, the inductor opposes the increase and lowers the peak value
- When the current decreases, the collapsing magnetic field tries to maintain current
What affects the Inductance of a coil?
- The inductance of a coil is affected by the number of turns in the coil and the following factors in the core:
- The permeability of the core (u)
- Inductance of the coil increases as the permeability of the core increases
- cross-sectional area of the core (A)
- Inductance of the coil increases as the cross-sectional area of the core increases
- length of magnetic path (l)
- Inductance of the coil decreases as the length of the core increases
- The permeability of the core (u)
- L = (N2uA) / l
Why are inductors called “Choke Coils”?
- Because they suppress sudden rises in current
- They also oppose sudden decreases in current
What is the formula for Percent Ripple?
% Ripple = (VRMS of the Ripple / VDC AVG) x 100
What do Filters do?
- When an AC voltage is rectified, the result is pulsating DC voltage
- Filters are used on the output of rectifiers to produce smooth DC Power
How does a Capacitor Filter work?
- This is the simplest filter circuit, it consists of a capacitor connected in parallel with the output terminals of a rectifier and in parallel with the load
- The amount of ripple at the load depends on the capacitance of the capacitor and the resistance or impedance of the load
- The greater the load, the faster the capacitor dischargers, and the greater the amount of ripple
- A capacitor’s filtering effectiveness decreases as the load increases
How does a choke filter work?
- Consists of an inductor coil connected in series with the output of a rectifier and in series with the load
- The coil can have an air core or an iron core
- Inductors oppose a change in current so they produce a reduced ripple at the load
- The two factors that determine the effectiveness of a choke filter are:
- The inductance of the choke
- The amount of current
- The filtering effect of a choke coil increases as the load increases
How does a L-Section filter work?
- Consists of a capacitor and a choke filter
- The capacitor is connected across the output after the choke filter, this reduces the possibility of voltage spikes produced by the choke at the load
- Also called a choke-input filter because the choke imputs to the capacitor
- These filters are effective over a wider range of loads
