Snubber Selection

** 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

someone posted this app note a few days ago

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.

"

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.

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.

y d

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!

tky

old

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"

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 "

** 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

You're just afraid they would stop pushing you down the stairs, because they would be busy pushing him.

--

If you have broadband, your ISP may have a NNTP news server included in your account:

Sporadic E is the Earth's aluminum foil beanie for the 'global warming' sheep.

Nice to see that you visited my web sight. I hope you learned something you little insignificant ant!

I've squashed more than you can count boy!, every time I step on one, Phil and a few others come to mind!

"For you PHIL!!!!!!!!!!!!"

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.

"

Not exactly true; the numbers VERY MUCH matter here. A lightning-strike surge can overheat the MOV and damage it, but an ounce of relay-magnetic-core can only possibly store (at saturation) about 0.01 watt-second of energy. An MOV rated at 1 joule (i.e. 1 watt-second) won't get hot enough to change at all. It'll cool before a second switching event occurs, and will last your lifetime.

That maybe true in your view.

Mov's were intended to absorb over voltage when over voltage is there how ever, when used like they're suppose to be, no over voltage will appear on a normal use. And it is true that MOV's do break down over time with even minor suppression activities even if you don't want to hear it..

Have you ever done a temp check on a wheeling diode after it has suppressed a few collapses from a coil in a short time ?

You may change your view of things. Internal heating of MOV's even small. causes their make up to break down.

In all the years of my experience doing this (many), I have never seen MOV's being used to suppress the collapsation of a field . They are only used in areas where the voltage isn't expected to be in a dangerous level on normal operation.

The original idea of a MOV was that in most cases it could clamp on an over voltage and possibly short in the process how ever, this would take out the fused link that is suppose to be in the circuit along with it.

I have replaced a good many MOV's in home electronics that just broke down over time from constant minor transients on the service and they just take out the fuse. You replace the MOV and the fuse.

Most of these repairs were not related to mother nature. Those that were, normally left some ash behind.

Also while we're on the subject, you really want to use a diode on the coil to suppress as much of the wheeling voltage as possible with the diode being connected close to the coil. The will help keep the voltage down at a low level so that that minimum RFI is generated.

You then have this problem of reverse polarity voltage being in the circuit where it may not be so welcomed when using a MOV because they aren't polarized! so what do you do to absorb the wheeling voltage on the damaging side? Use a diode in series? what a hack!.

I think at this point it should be obvious that a MOV is the last thing you want to put on a relay coil for wheeling voltage suppression.

Even with diodes, there is a noise issue in the R.F. world. Using a R+C snubber does wonders for that.

Bye.

"

" Maynard A. Philbrook = wacky code scribbler, aka Jamie "

** Huh ? Maynard is off with the faries.

** Huh ? Maynard is off with the faries. ** Huh ? Maynard is off with the faries.

** Huh ? Maynard is off with the fairies. ** Huh ? Maynard is off with the fairies. ** Maynard is a software writer and a radio ham - he has no real electronics experience.

As one can easily tell by reading any of his posts.

** Horse manure.

** Maynard is still crapping on about lightning bolts.

Must be a big worry for radio hams.

** Maynard is still crapping on about lightning bolts. ** Maynard is still crapping on about lightning bolts. ** Huh ? Maynard is off with the fairies.

BTW: Relay makers actually advise AGAINST using diode suppression cos it slows down the release and prolongs contact arcing.

** Huh ??? Maynard is completely off with the fairies. ** Funny how relay makers suggest using them - ain't it ?

Bet they never thought of seeking the opinions of a code scribbling radio ham.

** Huh ? Maynard is off with the fairies. ** Drop dead - you PITA f*****ad.

...... Phil