Industrial Engineer · phase 8 of 16 · noun
Precharge Circuit
Resistor and bypass circuit that limits inrush current while the DC bus capacitors charge at power-up.
The Explain card
- Plain English
- The precharge circuit limits the surge of current into the empty bus capacitors when the drive is first powered. A resistor is in the path at power up and a contactor or thyristor bypasses it once the bus is charged.
- Example
- Power is applied and the bus climbs over a second or so through the precharge resistor. A click from the bypass contactor says the capacitors are full and the drive is ready.
- Why it matters
- Cycling power to a drive repeatedly heats that resistor and wears the bypass contact, which is why manuals limit power ups per hour. A drive that shows precharge faults is usually telling you about a stuck bypass or a bus that will not come up.
- Hook
- Filling the reservoir slowly so the dam holds.
Word knowledge
How the word is built, where it came from, and what it sits beside in memory.
In a sentence
During VFD startup, the precharge circuit keeps the bypass contactor open until the DC bus reaches the controller's enable threshold.
Why these words
- precharge English pre- plus charge identifies charging performed before normal operation
- circuit Latin circuitus, a going around, through French names the electrical arrangement that performs the action
Where it came from
- Origin
- English technical compound formed from precharge and circuit
- Entered the language
- 20th century
- What changed
- Precharge broadened from charging beforehand to naming a preparatory electrical stage, then combined with circuit for the associated hardware arrangement.
How it is spelled
- Pattern
- The prefix pre- joins charge without a hyphen.
- Pattern
- The phrase is written as two words, with precharge modifying circuit.
Spelled like
- preheat
- preload
- pretest
- charging circuit
Broken into chunks
-
pre
- preheat
- preload
- preset
-
charge
- charger
- discharge
- recharge
-
circuit
- circuitry
- circuitous
What it sits beside
Same subject
- DC bus
- bypass contactor
- rectifier
- DC bus capacitor
- variable frequency drive
Same shape
- precharge resistor
- precharge contactor
- precharge relay
VFD power-up components
- precharge resistor
- bypass contactor
- DC bus capacitor
preparatory electrical operations
- precharge
- preheat
- preset
Where it sits in the deck
Phase 8: VFD Drive Hardware and Power Path
Inside the drive: rectifier, DC bus and inverter, the three stages every variable frequency drive uses to rebuild the waveform a motor sees.
