[Amps] Solenoid polarity on DC reed relays

[Bill VanAlstyne W5WVO]

Thanks for the tip. The solenoid coil measures exactly the same in both 
directions (670 ohms), which is pretty close to the claimed coil resistance 
(675 ohms). Also, when using the DVM's diode/continuity test position, the 
coil reads "OPEN" in both directions, indicating that there is no diode in 
there.

So apparently this relay does not contain an internal snubber.

But now that you've brought the question up...

The circuit I've designed uses two Kilovac HC-1 (26.5V) vacuum relays and 
this small 26.5V reed relay all in series with an appropriate dropping 
resistor (and an appropriate current shunt resistor across the reed relay), 
all across 120VDC as supplied by the SB-220 and switched through a Harbach 
T-R board. What method of relay coil snubbing would be "best practice" in a 
setup like this? Is a simple reverse-biased rectifier diode across each coil 
sufficient?

Bill W5WVO


--------------------------------------------------
From: "Paul Christensen" <w9ac at arrl.net>
Sent: Wednesday, March 10, 2010 12:23 PM
To: <amps at hidden-valley.com>; <amps at contesting.com>
Subject: Re: [Amps] Solenoid polarity on DC reed relays

> 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 at hidden-valley.com>
> To: <amps at 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 at 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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