Quiescent Current
This is the standby current drawn by the system while the vehicle is switched off, and it determines how much the battery will discharge while parked. Even a current of a few milliamps creates a meaningful loss over weeks of standing. Whether the standby current is negligible is decided by looking at parking time and battery capacity together.
The calculation can be done directly: standby current (A) × parking time (hours) gives the amp-hours consumed. For example, a 30 mA standby current consumes roughly 21.6 Ah in 30 days; that is a significant part of the usable capacity of a medium-sized battery.
- Measurement: an ammeter is connected in series with the battery negative cable; it is read with the vehicle switched off and all systems in sleep.
- Reduction: moving devices that draw standby current onto the ignition supply, or fitting an isolator switch on the line, is the most practical solution.
- Winter standstill: on a tractor that will not be used for a long time, disconnecting the battery terminal or connecting the battery to a charger should also be considered.
Kits such as the LFT20, which contain no board, processor or sensor, are not in circuit as a consumer while the switch is not pressed. On systems with control electronics you need to know the product's standby behaviour; a standby current value not declared by the manufacturer is not written down by guessing, it is determined by measurement.
The context in which this term is used: Converting a tractor hydraulic lever to electronic control