I use a Viz triple-output bench supply for this kind of testing and I'm always
crossing leads by mistake when bread-boarding something. The supply has an
adjustable, electronically-switched current trip point so no matter how abusive
I am, the supply silently trips. I just press the reset button until the next
fault occurs.
Paul, W9AC
----- Original Message -----
From: Jeff Carter
To: Paul Christensen
Sent: Wednesday, March 10, 2010 2:27 PM
Subject: Re: [Amps] Solenoid polarity on DC reed relays
Makes sense. I especially like the bench supply solution!
Thanks for the quick reply!
Jeff/KD4RBG
On Wed, Mar 10, 2010 at 2:23 PM, Paul Christensen <w9ac@arrl.net> wrote:
Jeff:
That depends on the coil resistance. The resistance check may not work on
relays with low coil resistance.
Another check is to apply DC coil voltage with a current-limiting bench
supply. Reverse the coil leads and if the diode is present, the supply will
fault.
Paul, W9AC
----- Original Message ----- From: "Jeff Carter" <amps@hidden-valley.com>
To: <amps@contesting.com>
Sent: Wednesday, March 10, 2010 2:16 PM
Subject: Re: [Amps] Solenoid polarity on DC reed relays
I don't have one here to easily check, but it seems to me that a
resistance
reading would just read the coil in either direction, since that's the
path
of least resistance.
Does this actually work? If so, why?
Jeff/KD4RBG
On Wed, Mar 10, 2010 at 2:13 PM, Paul Christensen <w9ac@arrl.net> wrote:
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.
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