| jazzbass |
04-19-2004 07:21 PM |
Quote:
Originally posted by Early_S_Man
Uh ... Chris, the diode in the red relays, and the resistor or diode in standard DIN relays ... is across the coil, not the contacts!!! Suppression diodes, as they are commonly referred to, have nothing to do with contact arcing ... they are to suppress the high-Voltage inductive spike that would normally be introduced to the +12 Volt power bus and cause havok to semiconductor devices spread thoughout the electrical system, such as CDI units, factory alarm control boxes, etc!
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Uh... you're right! I checked my red relay and the diode is across 85 and 86 - the coil. When I heard the relays had a supression diode, I just assumed the diode was across the contacts - thinking they were used like the flywheel diodes we used to put across the drain-source junctions of motor control MOSFETs in our control systems. I guess they're flywheeling the back EMF from the coil, not the load. Interesting, because theoretically, the electrical system would benefit from all the relays having flywheel diodes. Also, it means the coil is polarized - don't connect 86 to gound and 85 to +12 unless you like melted realys.
See how your EE skills atrophy when you start writing software for a living?
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