On 10/24/2014 2:02 PM, Ian Field wrote:


"DaveC" wrote in message
...
I have a 12V SPST cube relay in my junque box. The diagram molded into
the
relay¹s housing includes a component connected in parallel with the coil
which looks suspiciously like a resistor.

It¹s not a back-emf diode: I connected the relay coil using both
polarities
(using a current-limited power supply) and the same current draw is
measured.


What is the purpose of this resistor?

There are such things as bidirectional transient suppressor diodes.

Although I've never seen it on a car relay - a resistor isn't
impossible, it could act as a "Q-spoiler" to damp inductive ringing.

Or a bit more likely - a VDR.

Think of it as an RC snubber without the C. The capacitance will be
whatever the coil and wiring supply.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net