HVAC Electrical Class - CIRCUIT MATH

Rules for Series Circuits

  1. Total Resistance = "Add 'em up"
  2. The amperage is the same throughout the circuit
  3. The sum of all voltage drops is the source voltage

Rules for Parallel Circuits

  1. Total Resistance = Use the formula
    Parallel Formula
  2. The amperage is split across all branches
  3. The voltage is the same across all branches

How To Solve a Circuit


Calculation Grid
  1. Determine what kind of circuit: series, parallel or combination
  2. Fill grid with values given
  3. Look for pairs of 2 (series or parallel)
  4. If in series, use step S1
  5. If in parallel, use step P1
  6. Keep reducing pairs until no more pairs
  7. Fill in grid as you go - look for 2 values in any row
  8. Compute rest of values in rows with 2 values
  9. Repeat steps until done
REMEMBER:
Use Series Rules on series circuits, Parallel Rules on parallel circuits
"Change out of a Dollar" method has 2 applications - series voltage and parallel amperage

Additional Observations

  1. A series circuit may be thought of as a voltage divider
  2. Combined series resistance is larger than any resistor
  3. A parallel circuit may be thought of as a current divider
  4. Combined parallel resistance is smaller than smallest resistor
  5. If both parallel values are the same, take half of one resistor (The "Cheat" Method)
  6. Keep in mind that a combo circuit has both series and parallel parts - use the correct formula as required
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CSR Motor

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CSR Motor Definition and Characteristics CSR means Capacitor Start Capacitor Run (CSCR), typically shortened to CSR High starting torque Can handle high-demand loads 1-10 HP Can be designed for lower full-load currents and higher efficiency Operates at lower temperature than other single-phase motor types of comparable horsepower Only disadvantage to a CSR motor is its higher price - mostly the result of more capacitors, plus a starting switch Able to handle applications too demanding for any other kind of single-phase motor A CSR motor uses a potential relay or start relay (see Discussion below) Discussion Potential or "voltage" starting relays are used with single-phase capacitor-start/capacitor-run motors, which need relatively high starting torque. Their main function is to assist in starting the motor. These starting relays consist of a high-resistance coil and a set of normally closed contacts. The coil is wired between terminals 2 and 5, with the con...
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Electrical Wiring Diagram Star Delta Control and Power Circuit Using Mitsubishi PLC Program

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This article is intended to diagrammatically demonstrate the concept of the wiring principle of a star delta (wye delta) motor control and power circuit when using a PLC (Programmable Logic Controller) ladder program to control the switching of a 440 volts induction motor. The electrical components comprising the hardware parts of the circuit includes: 1.) 440 volts to 220 volts step-down transformer - 1 piece 2.) 220 volts to 24 volts step-down transformer - 1 piece 3.) 24VAC to 24VDC power supply converter - 1 piece 4.) Normally-open push  button  switch -  2 pieces 5.) Mitsubishi PLC (Programmable Logic Controller) Type FX2N-16MR-ES - 1 unit 6.)  Auxiliary  relay with 24VDC coil and minimum 1 Normally-open contact - 3 pieces 7.) 3 phase 440 volts AC NFB (No-fuse Breaker) circuit breaker (ampere rating depends on motor capacity) - 1 piece 8.) 3 phase 440 volts AC magnectic contactor with 220 VAC coil (ampere rating depends on motor capaci...
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Electrical Control Circuit Schematic Diagram of Permanent Split Capacitor Motor

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Electrical Control Circuit Schematic Diagram of Permanent Split Capacitor Motor PERMANENT SPLIT  CAPACITOR  MOTOR Figure 1: A permanent-split capacitor-run motor with the capacitor mounted on the motor Figure 2: An externally reversible permanent-split capacitor motor. To reverse, interchange   leads  T5 and T8 Figure 3: A two-voltage permanent-split capacitor motor connected for 115 volt operation Figure 4: A single-value three-lead reversible permanent-split capacitor motor Figure 5: A two-speed single-value capacitor-run motor Figure 6: A  schematic diagram  of a three-speed single-voltage capacitor-run motor
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