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Can a 1N4007 Be an Effective Relay Snubber?

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Jack Smith-6

Can a 1N4007 Be an Effective Relay Snubber?

To answer, I hope definitively, the question "is a 1N4007 power diode
too slow to be used as a relay coil snubber," I've updated my December
2007 diode turn-on time measurements with data taken this morning
showing the effectiveness of (a) no snubber; (b) 1N4148 snubber and (c)
1N4007 snubber with a typical small relay switched by a 2N7000 MOSFET
transistor. I've also looked at the how much the relay release time
lengthens when a snubber is added. (Of course, the specifics are
dependent upon the particular relay but the concepts are similar.)

The details are at http://www.cliftonlaboratories.com/diode_turn-on_time.htm

The "Cliff's Notes" version is that the turn-on (note I said turn-on,
not turn-off) time of a 1N4007 diode is sufficiently fast to be a very
effective relay snubber. The data also shows that a diode or MOV or
other technique should be used to control inductive field decay voltages.

Jack K8ZOA
www.cliftonlaboratories.com

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w5tvw

Re: Can a 1N4007 Be an Effective Relay Snubber?

I have used 1N4007 diodes for this purpose and had no trouble! The last
relay I took care of was the keying relays in the old Navy "TCS-12"
transmitter I have. If you get across the key contacts when you are
sending, the collapsing relay coil fields will give you quite a belt! Diode
installed and no more problems!

73,

Sandy W5TVW

----- Original Message -----
From: "Jack Smith" <[hidden email]>
To: "'Elecraft'" <[hidden email]>
Sent: Wednesday, April 08, 2009 1:22 PM
Subject: [Elecraft] Can a 1N4007 Be an Effective Relay Snubber?

> To answer, I hope definitively, the question "is a 1N4007 power diode
> too slow to be used as a relay coil snubber," I've updated my December
> 2007 diode turn-on time measurements with data taken this morning
> showing the effectiveness of (a) no snubber; (b) 1N4148 snubber and (c)
> 1N4007 snubber with a typical small relay switched by a 2N7000 MOSFET
> transistor. I've also looked at the how much the relay release time
> lengthens when a snubber is added. (Of course, the specifics are
> dependent upon the particular relay but the concepts are similar.)
>
> The details are at
> http://www.cliftonlaboratories.com/diode_turn-on_time.htm
>
> The "Cliff's Notes" version is that the turn-on (note I said turn-on,
> not turn-off) time of a 1N4007 diode is sufficiently fast to be a very
> effective relay snubber. The data also shows that a diode or MOV or
> other technique should be used to control inductive field decay voltages.
>
> Jack K8ZOA
> www.cliftonlaboratories.com
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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P.B. Christensen

Re: Can a 1N4007 Be an Effective Relay Snubber?

>> To answer, I hope definitively, the question "is a 1N4007 power diode
>> too slow to be used as a relay coil snubber,"

Just curious -- over the years, I've seen references to the main purpose of
the snubber diode being used; (1) to decrease the action time of the relay,
since the decaying flux of the relay coil tends to keep the contacts engaged
(NO), or disengaged (NC) longer than necessary after voltage is removed from
the coil; and (2) to primarily protect a solid-state switching device (e.g.,
an open NPN collector) from damage, also being caused by the snap of the
decaying flux of the relay coil. I realize both uses of the diode are
valid, but it seems that unless there's an extremely high flux developed by
coil, the primary purpose of the diode is for relay speed, rather than
switching device protection.

Paul, W9AC

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Jack Smith-6

Re: Can a 1N4007 Be an Effective Relay Snubber?

The quick test I did today used a common 2N7000 MOSFET to switch a
physically small relay typical of those used in ham gear. I think this
is a reasonably common arrangement and I've used it in the past myself.

The turn-off voltage exceeds the 2N7000's maximum permitted source-drain
voltage of 60 volts. What happens is that the 2N7000 breaks down at
70-75 volts and acts like a Zener diode.

I'll leave it to the designer to decide whether it's a good thing or a
bad thing to have the 2N7000 break down with every diode switch cycle. I
don't recall seeing a caution in the 2N7000 data sheet recommending that
the device not be operated in a mode that causes it to break down but it
seems to me that it isn't a good idea for a reliable design. The relay
coil resistance will limit the peak current through the 2N7000 when in
break down mode, but it still leaves me uncomfortable.

Jack

Paul Christensen wrote:

>>> To answer, I hope definitively, the question "is a 1N4007 power diode
>>> too slow to be used as a relay coil snubber,"
>>>
>
> Just curious -- over the years, I've seen references to the main purpose of
> the snubber diode being used; (1) to decrease the action time of the relay,
> since the decaying flux of the relay coil tends to keep the contacts engaged
> (NO), or disengaged (NC) longer than necessary after voltage is removed from
> the coil; and (2) to primarily protect a solid-state switching device (e.g.,
> an open NPN collector) from damage, also being caused by the snap of the
> decaying flux of the relay coil. I realize both uses of the diode are
> valid, but it seems that unless there's an extremely high flux developed by
> coil, the primary purpose of the diode is for relay speed, rather than
> switching device protection.
>
> Paul, W9AC
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>

Mel

Re: Can a 1N4007 Be an Effective Relay Snubber?

In reply to this post by Jack Smith-6

Hi, I have used the diode snubber in all designs of relay control from small reed to large contactors. I usually check the series resistance of the relay and the non solid state device activation and measure the voltage "kick". I then use ohms law to determine the peak current that would occur against the relay resistance and size the diode accordingly. Most of the time the 1N4000 series are well suited for small relay applications. When in doubt, measure the relay parameters..

Mel, K6KBE

--- On Wed, 4/8/09, Jack Smith <[hidden email]> wrote:

From: Jack Smith <[hidden email]>
Subject: Re: [Elecraft] Can a 1N4007 Be an Effective Relay Snubber?
To: "Paul Christensen" <[hidden email]>
Cc: "'Elecraft'" <[hidden email]>
Date: Wednesday, April 8, 2009, 2:43 PM

The quick test I did today used a common 2N7000 MOSFET to switch a
physically small relay typical of those used in ham gear. I think this
is a reasonably common arrangement and I've used it in the past myself.

The turn-off voltage exceeds the 2N7000's maximum permitted source-drain
voltage of 60 volts. What happens is that the 2N7000 breaks down at
70-75 volts and acts like a Zener diode.

I'll leave it to the designer to decide whether it's a good thing or a
bad thing to have the 2N7000 break down with every diode switch cycle. I
don't recall seeing a caution in the 2N7000 data sheet recommending that
the device not be operated in a mode that causes it to break down but it
seems to me that it isn't a good idea for a reliable design. The relay
coil resistance will limit the peak current through the 2N7000 when in
break down mode, but it still leaves me uncomfortable.

Jack

Paul Christensen wrote:

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w5tvw

Re: Can a 1N4007 Be an Effective Relay Snubber?

In reply to this post by P.B. Christensen

The flux can be very considerable! As the flux collapses it can induce a
very high voltage transient across the coil far exceeding the voltage
produced to energize the relay. There is a certain amount of energy stored
there in many instances. The 'back EMF" pulse can wreak havoc with solid
state gear and shock the hell out of someone who happens to be across the
circuit when the field collapses! Seems like I was havinga discussion of
neon tubes (NE-2?) across relay coils in the old ARC-27 UHF aircraft
transceiver (a true boat anchor piece of gear!). These were probably
primarily to limit the pulse to whatever the ionization potential of the
NE-2 is. (probably around 60-65 volts?) Silicon diodes didn't exist in
those days or they probably would have been used instead.

73,

Sandy W5TVW

----- Original Message -----
From: "Paul Christensen" <[hidden email]>
To: "'Elecraft'" <[hidden email]>
Sent: Wednesday, April 08, 2009 4:11 PM
Subject: Re: [Elecraft] Can a 1N4007 Be an Effective Relay Snubber?

>>> To answer, I hope definitively, the question "is a 1N4007 power diode
>>> too slow to be used as a relay coil snubber,"
>
> Just curious -- over the years, I've seen references to the main purpose
> of
> the snubber diode being used; (1) to decrease the action time of the
> relay,
> since the decaying flux of the relay coil tends to keep the contacts
> engaged
> (NO), or disengaged (NC) longer than necessary after voltage is removed
> from
> the coil; and (2) to primarily protect a solid-state switching device
> (e.g.,
> an open NPN collector) from damage, also being caused by the snap of the
> decaying flux of the relay coil. I realize both uses of the diode are
> valid, but it seems that unless there's an extremely high flux developed
> by
> coil, the primary purpose of the diode is for relay speed, rather than
> switching device protection.
>
> Paul, W9AC
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

Eric Swartz - WA6HHQ

Re: Can a 1N4007 Be an Effective Relay Snubber? [END of Thread]

Administrator

Let's end this thread for now. I think we've pretty much beaten it to
death. ;-)

73, Eric WA6HHQ
Elecraft List Moderator

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Bill Coleman-2

Re: Can a 1N4007 Be an Effective Relay Snubber?

In reply to this post by Jack Smith-6

On Apr 8, 2009, at 2:22 PM, Jack Smith wrote:

> The "Cliff's Notes" version is that the turn-on (note I said turn-on,
> not turn-off) time of a 1N4007 diode is sufficiently fast to be a very
> effective relay snubber.

Interesting! It's always true that experiment trumps theory.

Curious, though, that you would promote using a 1N4007 as a snubber
for a 12 volt relay. It would make more sense to use a 1N4001, which
has virtually identical characteristics as the 1N4007, except for the
reverse breakdown voltage. The 1N4001, with a reverse breakdown of 50
volts, it will withstand the relay energizing voltage of 12 volts.

The 1N4001 can be purchased for about a penny each in bulk. The 1N4007
is about four times more expensive. That's a three cent difference.
And, you know, hams are cheap. <grin>

Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email]
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901

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Jack Smith-6

Re: Can a 1N4007 Be an Effective Relay Snubber?

Any of the 1N400x series work well for this purpose.

I've slowly learned the lesson that as a very small kit provider that
it's often cheaper to use the same part in multiple kits even though it
may be over-rated for some applications because the increased volume
reduces the price, fewer stock keeping concerns, etc.

Hence, my "standard power diode" for designs (reverse voltage
protection, relay snubbing, etc.) is the 1N4007.

And, there's no "theory" that I'm aware of predicting a 1N4007 diode has
a slow turn-on time. What there seems to be the case is that because
these diodes have a slow turn-off time (predicted by theory and
confirmed in practice), hams have confused the two and reached the
incorrect conclusion that slow turn-off = slow turn-on. Quite different
physics are at work in these two conditions.

Jack

Bill Coleman wrote:

> On Apr 8, 2009, at 2:22 PM, Jack Smith wrote:
>
>
>> The "Cliff's Notes" version is that the turn-on (note I said turn-on,
>> not turn-off) time of a 1N4007 diode is sufficiently fast to be a very
>> effective relay snubber.
>>
>
>
> Interesting! It's always true that experiment trumps theory.
>
> Curious, though, that you would promote using a 1N4007 as a snubber
> for a 12 volt relay. It would make more sense to use a 1N4001, which
> has virtually identical characteristics as the 1N4007, except for the
> reverse breakdown voltage. The 1N4001, with a reverse breakdown of 50
> volts, it will withstand the relay energizing voltage of 12 volts.
>
> The 1N4001 can be purchased for about a penny each in bulk. The 1N4007
> is about four times more expensive. That's a three cent difference.
> And, you know, hams are cheap. <grin>
>
>
> Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email]
> Web: http://boringhamradiopart.blogspot.com
> Quote: "Not within a thousand years will man ever fly!"
> -- Wilbur Wright, 1901
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>

w5tvw

Re: Can a 1N4007 Be an Effective Relay Snubber?

In reply to this post by Bill Coleman-2

I've used nothing but 1n4007's for years now for relay snubbers. They work
just great.

I don't bother with the slightly cheaper 1n4001's and that sort. You can
get the 1N4007's cheap enough and use one type diode for everything. Some
of the manufacturers don't put any identifcation on the diodes other than
the cathode stripe which makes identifying the difference a pain in the
butt.

73,

Sandy W5TVW

----- Original Message -----
From: "Bill Coleman" <[hidden email]>
To: "Jack Smith" <[hidden email]>
Cc: "'Elecraft'" <[hidden email]>
Sent: Tuesday, May 12, 2009 9:54 PM
Subject: Re: [Elecraft] Can a 1N4007 Be an Effective Relay Snubber?

>
> On Apr 8, 2009, at 2:22 PM, Jack Smith wrote:
>
>> The "Cliff's Notes" version is that the turn-on (note I said turn-on,
>> not turn-off) time of a 1N4007 diode is sufficiently fast to be a very
>> effective relay snubber.
>
>
> Interesting! It's always true that experiment trumps theory.
>
> Curious, though, that you would promote using a 1N4007 as a snubber
> for a 12 volt relay. It would make more sense to use a 1N4001, which
> has virtually identical characteristics as the 1N4007, except for the
> reverse breakdown voltage. The 1N4001, with a reverse breakdown of 50
> volts, it will withstand the relay energizing voltage of 12 volts.
>
> The 1N4001 can be purchased for about a penny each in bulk. The 1N4007
> is about four times more expensive. That's a three cent difference.
> And, you know, hams are cheap. <grin>
>
>
> Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email]
> Web: http://boringhamradiopart.blogspot.com
> Quote: "Not within a thousand years will man ever fly!"
> -- Wilbur Wright, 1901
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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07:04:00

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