14-10-2012, 04:10 PM
The general-purpose airframe-mounted relays with a 28v DC coil, used on many modern aircraft for all sorts of switching applications, normally as standard have a diode built-in across the coil to protect whatever switch contacts are operating the relay coil. The relay coil is then polarity-sensitive - it must be connected so the diode is reverse-biassed when the coil is energised. When the controlling switch opens the diode becomes forward-biassed and dissipates the energy stored in the relay coil.
It's probably worth following this practice, add a diode across the contactor coil rather than the switch contacts - and make sure its the right way round!
The back-emf can be a surprisingly high voltage, so don't skimp on the diode ratings.
Andy
It's probably worth following this practice, add a diode across the contactor coil rather than the switch contacts - and make sure its the right way round!
The back-emf can be a surprisingly high voltage, so don't skimp on the diode ratings.
Andy
