Bill,
DC coil polarity is an issue because polarized relays generally contain a
reverse-biased snubbing diode across the relay coil to: (1) protect a
solid-state driving circuit from damage resulting from the rapid coil flux
collapse; and (2) to decrease the relay . Measure the coil resistance with
a DVM or VOM, then reverse the test leads and measure again. This may give
you an indication if the snubbing diode is already part of the relay. Equal
readings generally signifies a non-polarized relay coil.
Most DC relays without indication of "+/-" polarity are non-polarized. For
QSK operation, it may be best to add your own snubbing diodes to all relays,
including the vacuum relays. It may also be helpful to review the following
discussion concerning the use of relay snubbing diodes:
http://www.cliftonlaboratories.com/diode_turn-on_time.htm
Paul, W9AC
> There is no +/- indication anywhere on the relay body -- and according to
> Allen Bond of MGS, polarity on this particular relay probably doesn't
> matter. He said that in his experience, all polarity-sensitive reed relays
> are clearly marked with +/-. However, there is a schematic diagram of the
> relay printed on the body, and in this diagram, one terminal of the
> solenoid coil is represented by an unfilled circle, while the other
> terminal is represented by a filled circle. I'm wondering whether this
> might be indicative of coil polarity.
>
> Does anyone on this list know if this is true for this particular
> MGS-supplied relay?
>
> Bill W5WVO
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