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Old December 6th, 2017, 01:13 PM   #1
Bering C Sparky
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Flyback Diode

Hello guys,

Looking for some quick easy answers with out having to put in any sweat equity.

1) I have some 1N9437-E3/54 1amp fast switching diodes, are these suitable to use as flyback diodes across relay and some small contactor 24vdc coils?


2) Is there any adverse effect if I add a flyback diode on a coil that already has suppression embedded in the contactor from the manufacture?

Thanks in advance if one of you guys can give me some insight on this.
BCS
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Old December 6th, 2017, 01:31 PM   #2
GaryS
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I don't see any adverse effects of adding the flyback diodes ( in the correct direction) but I question why, if the manufacture installed suppression on the contactor then I don't see any thing to gain by adding the flyback
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Old December 6th, 2017, 01:45 PM   #3
g.mccormick
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Just be sure to install in the correct direction or else they will smoke. Band to positive
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Old December 6th, 2017, 01:56 PM   #4
Bering C Sparky
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Quote:
Originally Posted by GaryS View Post
I don't see any adverse effects of adding the flyback diodes ( in the correct direction) but I question why, if the manufacture installed suppression on the contactor then I don't see any thing to gain by adding the flyback
I am just under a time crunch, not sure if the contactors have it or not so if no adverse ramifications then I am just going to add them to all the inductive loads.

Roger that on the correct direction....I got that part under control as long as pay attention to what I am doing and don't start thinking about what I am going to do after work while putting this together....LOL

As far as the part # on the diodes I have, they should be perfectly suitable for the application....Correct?

Thanks
BCS
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Old December 6th, 2017, 02:14 PM   #5
Bering C Sparky
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While we are on the subject maybe some of you guys know off the top of your head if these contactors come from manufacturer have diodes already or not.

Schneider LC1D09
Schneider LC1D32
Both have BD designation.

(I could look it up but the schneider site is like reading hieroglyphics most of the time)

Thanks,
BCS
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Old December 6th, 2017, 02:37 PM   #6
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The correct part number is 1N4937. One of my favorites. It, as well all diodes, will delay release of relay or solenoid as the excess energy is directed back into the coil. For most applications, the extra time is negligent.
It won't hurt if you add it to any existing suppression circuitry that may or may not be present, other than the time delay mentioned above.
I've found that capacitors don't reduce the arc as well as a diode, and MOV's have a finite life. Diodes are the best choice.
Note that DC PLC outputs will also have diodes across outputs. Adding diodes at the device causes the spike to be dissipated locally. If you depend on the PLC diode, then there will be some dissipation in the wiring as well. Usually not a concern with low current stuff.
I currently use UF4007's.

Last edited by keithkyll; December 6th, 2017 at 02:38 PM. Reason: Spelling
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Old December 6th, 2017, 02:56 PM   #7
Bering C Sparky
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Quote:
Originally Posted by keithkyll View Post
The correct part number is 1N4937. One of my favorites. It, as well all diodes, will delay release of relay or solenoid as the excess energy is directed back into the coil. For most applications, the extra time is negligent.
It won't hurt if you add it to any existing suppression circuitry that may or may not be present, other than the time delay mentioned above.
I've found that capacitors don't reduce the arc as well as a diode, and MOV's have a finite life. Diodes are the best choice.
Note that DC PLC outputs will also have diodes across outputs. Adding diodes at the device causes the spike to be dissipated locally. If you depend on the PLC diode, then there will be some dissipation in the wiring as well. Usually not a concern with low current stuff.
I currently use UF4007's.
I would love to use the diode you mention above but......

1) I don't have any.
2) In order for me to get some I would have to:
Create a part request form in our purchasing data base and submit to corporate.
After a couple of days they would add the part to the data base.
Then I can create a MR (Material Requisition) and submit this back to corporate.
Then they will send out RFQ's (Request for Quote) and shop price around to 3 or 4 vendors.
Once they get back all the quotes they will order from lowest bidder.
Then depending if the person that won the bid has the part in stock or not I might see the part in 2 days to 3 weeks from now. (If we are at the dock, if we are at sea it could be 6 weeks)


Big divide between needing a part and getting a part.
Adding all these office positions sure has made things better.....NOT.

I just wanted to check if the diodes I have are suitable or not.
(I hope so because I already have 15 installed. )

BCS
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Old December 6th, 2017, 03:02 PM   #8
Bering C Sparky
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Obviously electronics are not a strong suit of mine.

I am just not sure if the "fast switching" designation on the diode description is what you would want for this application or not.

Any explanation of this you guys can give would teach me something.

Appreciate your time.
BCS
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Old December 6th, 2017, 03:08 PM   #9
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You said "1N9437". Please verify it's a 1N4937.

As I said at the beginning, one of my favorites. Many diodes will do the job, including standard switching speed ones like 1N4004 - 1N4007.
I prefer fast switching, and the highest reverse voltage. 1N4937 is perfect.

When ordering from Mouser here in the States, I have a choice, so I go for UF4007. A bit faster than the 1N4937, but it probably doesn't matter.

So yes, your diodes will be perfect.

Now, you want to discuss where the term "Flyback" originated?
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Old December 6th, 2017, 03:15 PM   #10
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Quote:
Originally Posted by Bering C Sparky View Post
... "fast switching" designation on the diode description is what you would want for this application ...BCS
When polarity reverses, it takes time for the diode to react. Once power is removed from the coil, the reverse spike presents itself to the diode. We want it to react as soon as possible.
The faster, the better.
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Old December 6th, 2017, 03:40 PM   #11
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A few things I think need to ne cleared up
Capís or RC network suppressors are only good on an AC coil, they donít work at all on DC in fact they will cause a delayed release on a dc coil when the coil is deenergized due to stored energy in the cap.

MOVís work well if properly sizes (both voltage and joules). This is what most manufactures used as surge protectors. They work equally well on both AC and DC and if properly sizes will last forever.
They are the most popular surge suppressor used. MOVís must be size for the peak supply voltage not the rms voltage. A 120ac coli will need a 200V MOV . if you use one rated for less then it will ve conducting all the time the coil is on and will soon burn out. I have seen many time when they are sized wrong and donít last . Also they only limit the surge / collapsing field voltage to just above the rating of the mov. As the voltage across them goes up (above their rate voltage the resistance goes down and the power dissipated goes up as the resistance goes down )

Flyback diodes work very well on DC coils only. In fat contrary to what has been stated here they will shorten the release time on most relays or contactors . They provide a shorter path for the current in collapsing dc field. And limit the collapsing field voltage to less than a 1 volt. Thatís far better than any other surge suppresser. I have seen contactors without them take several seconds to release after they are turned off. As for their service life I have never run into one blown unless somebody connected the power in reverse polarity.

Connecting Both MOVís and Flyback diodes on the same device will have no detrimental effects but I donít see an real advantage to it. Maybe if the power supply feeding the coils get a surge it would protect the coils but that would be a minor thing compared to the damage it would do to other devices on the power supply.
Using a diode with a cap or RC network will never work, something is going to blow.
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Old December 6th, 2017, 03:59 PM   #12
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Quote:
Originally Posted by keithkyll View Post
You said "1N9437". Please verify it's a 1N4937.

As I said at the beginning, one of my favorites. Many diodes will do the job, including standard switching speed ones like 1N4004 - 1N4007.
I prefer fast switching, and the highest reverse voltage. 1N4937 is perfect.

When ordering from Mouser here in the States, I have a choice, so I go for UF4007. A bit faster than the 1N4937, but it probably doesn't matter.

So yes, your diodes will be perfect.

Now, you want to discuss where the term "Flyback" originated?
My bad....I have been moving at quick pace today (not my usual speed) my dyslexia must have kicked in and I read the part # you originally posted incorrectly.

Thanks for the information, and yes the 1N9437 are the ones I have.

Discuss away on the flyback subject, I am always up for learning something even if its just random trivia.

BCS
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Old December 6th, 2017, 04:07 PM   #13
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Re-read this again and it seems my dyslexia is getting worse.....LOL
Let me get a magnifying glass and see if I can read the diode.
The sticker on the plastic container we keep them in says 1N9437-E3/54....but that sticker was generated on the boat and not the manufacturer.

Stand by.
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Old December 6th, 2017, 04:13 PM   #14
Bering C Sparky
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Ok as long as I am still not seeing things upside down and backwards.... LOL

Printed on the diode is 1N4937.....

So to quote Forest Gump....."That's good, one less thing to worry about"

Man I F'ed this thread up six ways to Sunday....

Sorry for the confusion and thanks for the replies.

BCS
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Old December 6th, 2017, 05:08 PM   #15
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Correct me if I am wrong, but I don't use a diode with a high PIV. I use one that is just above my coil voltage.
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