Snubber Selection

Hi,

I have a 24VDC relay, and I need a way to supress the transient caused
by it switching after you remove the load.

I understand that my best choices are an MOV, a flyback diode
(schottky, I assume?), and a transorb.

I put a scope on it, and the transient spikes at around 1200 volts.

Which of the three options is the 'best'. Which is least likely to
ever burn out? What specs should I be paying attention to when I pick
the component?

Thanks,
Dan

 

** Frightening.

** MOVs are rugged and fairly cheap.

The voltage rating depends on what ( semi?) is driving the relay coil.

At a guess, a 50 volt MOV would be a good bet and allow the relay to
de-energise very quickly.

BTW:

there is no need to use a schottky diode.



....... Phil

 

On Wed, 28 May 2008 06:23:57 -0700 (PDT), in sci.electronics.design

someone posted this app note a few days ago
http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3311.pdf


martin

 

mov's only take a wack x number of times before they short.
use a bidiretcional TVS (Transient Voltage Suppressor) diode or schottky
diode.

http://webpages.charter.net/jamie_5"

 

"Jamie the Jerk Off "

** Bollocks.

** There is no advantage here in using schottky.

You fucking ass.



...... Phil

 

The best solution depends on the problem you want to correct. The simplest
solution is to place a plain old diode like a 1N4002 back biased around the
relay coil. The max current the diode will see on ring off is the current
that was flowing when the coil was energized. And, it only flows in the
diode for a short duration on turn off. The reverse voltage on the diode is
the same as the coil, 24 Volts in this case. There is not much of a
requirement for this diode.

The energy the diode is controlling is the energy stored in the coil's
inductance. 1/2LI^2, which ain't much. That energy is dissipated in the
coil's resistance on turn off. The diode is just redirecting it back into
the coil.

 

http://en.wikipedia.org/wiki/Varistor#Varistors_compared_to_other_transient-suppressors

I assume that's just for really really really big surges. I don't
think my relay's transient is going to put 100amps through the
varistor.

 

What an ass you are, the advantage is that schottky has a
lower threshold and is easier to get.
Since this is a DC relay, either would work, it's what easier
for you to obtain.

My self, I've found integrated snubbers to work nicely. they suppress
the pulse to help reduce RFI nicely.

Using DIodes will still give you a noise generation problem but will
protect the circuit.

Have a good day Phill as always.


http://webpages.charter.net/jamie_5"

 

No, MOVs are crap. One place where I was working when they invented the
Transzorb issued ECOs to take out all of the MOVs and replace them
with Transzorbs.

If you want a fast drop-out, you want to let the spike go as high as
it can, safely. (the amplitude of the spike is determined by how fast
the field collapses.)

Hope This Helps!
Rich

 

So, it sounds like I don't want to use an MOV.

I didn't see any negative voltage, so I'm guessing I don't need a
transorb. So, by process of elimination, I'm going to go with either a
plain old diode or a schottky. As the schottkys seem to have faster
switching time, I'm goign to go with one of them.

Thanks!

 

Does anyone have any suggestions on a part or series? There's so many
to choose from... (It's for a 24VDC relay)

 

A basic 1 amp 50 v will do it.

Select what ever package fits your needs.





--
"I'd rather have a bottle in front of me than a frontal lobotomy"

"Daily Thought:

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"

 

"Jamie the Jerk Off "

** What a FUCKING ASS you are !!

There is no advantage in having a lower threshold here and schottkys are
MORE expensive by far than ordinary silicon diodes and harder to find.

Fuckwit.


....... Phil

 

<>


So, it sounds like I don't want to use an MOV.


** Yo uare being fed bollocks by complete asses.

I didn't see any negative voltage, so I'm guessing I don't need a
transorb. So, by process of elimination, I'm going to go with either a
plain old diode or a schottky. As the schottkys seem to have faster
switching time, I'm going to go with one of them.


** You must be a fucking idiot.

Ultra fast switching is irrelevant to suppressing a relay - plus using a
diode slows the relay going off .

Can cause damage to the relay contacts.



....... Phil

 

<>

Does anyone have any suggestions on a part or series? There's so many
to choose from... (It's for a 24VDC relay)


** What current rating is the coil ?

24 volt relays vary a lot.




....... Phil

 

"Jamie the FUCKWIT Jerk Off "

** Oh my god - what an utter CRETIN !!!

Where Jamie works, all the inmates have straight jackets.




....... Phil

 

Oh really, you wouldn't do well where I work son.!



http://webpages.charter.net/jamie_5"

 

yes Phill, please come back we miss you! Your bed is still
waiting for you , straps and all.



--
"I'd rather have a bottle in front of me than a frontal lobotomy"

"Daily Thought:

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"

 

"Jamie the FUCKWIT Jerk Off "


** Complete mental retard.

What else would you expect from someone whose real name is " Maynard A.
Philbrook " who works as a code scribbler and has the ham call sign
KA1LPA.

Lives in a dream world with no idea of his monumental ignorance.



...... Phil

 

This can hardly be an issue at the power levels and impedances being
discussed here.

RL