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Old December 6th, 2017, 05:27 PM   #16
Bering C Sparky
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Interested and following for any reply's to Highland Controls Comment.

(I googled PIV of a diode but came up with formulas to calculate PV for a diode....and I don't have time to go through all that at the moment.)
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Old December 6th, 2017, 05:29 PM   #17
GaryS
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I have always used 600 or 1000 V PIV 1A rating get them by the 100 pack cheep that way.
The lowest rating should be 2 X coil voltage.
I standardized on the 600 or 1000 V there cheep and readily available
the ratings foe the one shown in 600V 1A
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Old December 6th, 2017, 05:47 PM   #18
Bering C Sparky
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Quote:
Originally Posted by GaryS View Post
I have always used 600 or 1000 V PIV 1A rating get them by the 100 pack cheep that way.
The lowest rating should be 2 X coil voltage.
I standardized on the 600 or 1000 V there cheep and readily available
the ratings foe the one shown in 600V 1A

Thanks
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Old December 6th, 2017, 09:14 PM   #19
Gene Bond
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Quote:
Originally Posted by Highland Controls View Post
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.
It's fine. As long as the PIV is ~2x the operating voltage life is good. Higher voltage rating just means they cost more... just like wire ratings.
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Old December 6th, 2017, 09:18 PM   #20
Gene Bond
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Quote:
Originally Posted by GaryS View Post
<snip>
Using a diode with a cap or RC network will never work, something is going to blow.
Curious what you see happening?

The Cap will discharge through the resistor and coil. The diode will snub the reverse voltage (due to the field collapsing and the cap discharging)... It all should wash out. I'm lost?
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Old December 6th, 2017, 09:57 PM   #21
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Quote:
Originally Posted by Bering C Sparky View Post
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
Those contactors have built in suppression. You can see the module if you look at the side of the contactor.
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Old December 6th, 2017, 11:21 PM   #22
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Gene
Have you ever connected a diode across a power supply in the forward direction.
The first time the ac cycle on the supply forward biases the diode it will conduct and short out the supply blowing out the diode (if you are lucky that all you will do) but it could short out the output devise, short out the power supply, start a fire in the panel. Basically a large number of bad things.
Do you want to explain to your customer why the pane just went up in flames
As I said the RC snubbers are only for AC powered coils, diodes are only for DC coils and MOV's can be used on either. With anything correct sizing is important.
on a Dc relay the diode will be blocking when the power is on and the relay is energized when the power is off the relay is deenergized the diode will conduct and short the collapsing field current. In an AC supply the polarity is always reversing and the diode will conduct for 50% of the time but on the first 1/2 cycle forward biased it will be shorted out>
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Old December 7th, 2017, 12:55 AM   #23
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Quote:
Originally Posted by Bering C Sparky View Post
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
I feel your pain. We have similar idiotic setups. I just buy a lot of "widgets" from my local electrical wholesaler. The price is always $1. The actual quantity just varies....

No one in procurement has queried me about how many widgets we've used this year so far...
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Old December 7th, 2017, 01:29 AM   #24
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1) Flyback name. In TV electronics, the Damper or Flyback diode conducted during the time when the transformer was off, causing the beam to "fly back" to the beginning of the next scan line.
From repairfaq.org:
"The term 'flyback' probably originated because the high voltage pulse that charges the CRT capacitance is generated by the collapse of the magnetic field in the core of the transformer during the short retrace period - when the electron beam in the CRT 'flies back' to the start of a new scan line. The flux in the core changes slowly during scan and is abruptly switched in polarity by the HOT turning off during the flyback or retrace period." Link.

2) MOVs can have a finite life. I agree that in this application, they should last forever if properly sized. Any line spikes that could cause damage would be absorbed by the coil. MOV degradation is a known problem. Documented here.

3) Peak reverse should be at least 10 times supply voltage. For 24V, the spike can reach 300 volts.
4) Relays have delayed dropout with diodes. Yes, the voltage across the diode will be under one volt, because all of the energy is being sent back to the coil, delaying the collapse of the magnetic field.
From Wiki:
" In an ideal flyback diode selection, one would seek a diode which has very large peak forward current capacity (to handle voltage transients without burning out the diode), low forward voltage drop, and a reverse breakdown voltage suited to the inductor's power supply. Depending on the application and equipment involved, some voltage surges can be upwards of 10 times the voltage of the power source, so it is critical not to underestimate the energy contained within an energized inductor. When used with a DC coil relay, a flyback diode can cause delayed drop-out of the contacts when power is removed, due to the continued circulation of current in the relay coil and diode. When rapid opening of the contacts is important, a low-value resistor can be placed in series with the diode to help dissipate the coil energy faster, at the expense of higher voltage at the switch." Link.

Again, 1N4937 is fine. 1 Amp at 600 volts. The Wiki starts confusing the issue by mentioning faster switching Schottky's, but this is related to power supply design, not snubber diodes.

A note on diode construction. The limit is about 400-600 volts. To make a 1000 volt diode, they put 2 in series. That's why the forward conduction jumps from 1V to 1.7V for the 1000 volt (for 1N and UF 400x series)

To revise my earlier statement about first choice, it's UF4004. UF4007 is a 1000V device.






Last edited by keithkyll; December 7th, 2017 at 01:54 AM. Reason: More info
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Old December 7th, 2017, 05:21 AM   #25
Gene Bond
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Quote:
Originally Posted by GaryS View Post
Gene
Have you ever connected a diode across a power supply in the forward direction.
The first time the ac cycle on the supply forward biases the diode it will conduct and short out the supply blowing out the diode (if you are lucky that all you will do) but it could short out the output devise, short out the power supply, start a fire in the panel. Basically a large number of bad things.
Do you want to explain to your customer why the pane just went up in flames
As I said the RC snubbers are only for AC powered coils, diodes are only for DC coils and MOV's can be used on either. With anything correct sizing is important.
on a Dc relay the diode will be blocking when the power is on and the relay is energized when the power is off the relay is deenergized the diode will conduct and short the collapsing field current. In an AC supply the polarity is always reversing and the diode will conduct for 50% of the time but on the first 1/2 cycle forward biased it will be shorted out>
OK, I was talking about DC, and you were talking about AC... Never Mind
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Old December 7th, 2017, 09:48 AM   #26
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Originally Posted by keithkyll View Post
3) Peak reverse should be at least 10 times supply voltage. For 24V, the spike can reach 300 volts.
Ask a former boss of mine about that.
I connected the coil of a 24VDC relay through the relay's NC contact to function as a buzzer.
He did NOT believe that it would generate a high voltage.
Until he touched the coil wire.
The next day, I was still employed.
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Old December 7th, 2017, 11:09 AM   #27
Bering C Sparky
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Quote:
Originally Posted by justblaze View Post
Those contactors have built in suppression. You can see the module if you look at the side of the contactor.
Would you happen to know if they are using a Diode or a MOV as suppression in these?

BCS
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Old December 7th, 2017, 01:14 PM   #28
keithkyll
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From Schneider datasheet for LC1D09BD. BD is the code for a 24DC coil.
"Coil technology - Built-in bidirectional peak limiting diode suppressor"

Link
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Old December 7th, 2017, 01:23 PM   #29
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Quote:
Originally Posted by keithkyll View Post
1) Flyback name. In TV electronics, the Damper or Flyback diode conducted during the time when the transformer was off, causing the beam to "fly back" to the beginning of the next scan line.
From repairfaq.org:
"The term 'flyback' probably originated because the high voltage pulse that charges the CRT capacitance is generated by the collapse of the magnetic field in the core of the transformer during the short retrace period - when the electron beam in the CRT 'flies back' to the start of a new scan line. The flux in the core changes slowly during scan and is abruptly switched in polarity by the HOT turning off during the flyback or retrace period." Link.

2) MOVs can have a finite life. I agree that in this application, they should last forever if properly sized. Any line spikes that could cause damage would be absorbed by the coil. MOV degradation is a known problem. Documented here.

3) Peak reverse should be at least 10 times supply voltage. For 24V, the spike can reach 300 volts.
4) Relays have delayed dropout with diodes. Yes, the voltage across the diode will be under one volt, because all of the energy is being sent back to the coil, delaying the collapse of the magnetic field.
From Wiki:
" In an ideal flyback diode selection, one would seek a diode which has very large peak forward current capacity (to handle voltage transients without burning out the diode), low forward voltage drop, and a reverse breakdown voltage suited to the inductor's power supply. Depending on the application and equipment involved, some voltage surges can be upwards of 10 times the voltage of the power source, so it is critical not to underestimate the energy contained within an energized inductor. When used with a DC coil relay, a flyback diode can cause delayed drop-out of the contacts when power is removed, due to the continued circulation of current in the relay coil and diode. When rapid opening of the contacts is important, a low-value resistor can be placed in series with the diode to help dissipate the coil energy faster, at the expense of higher voltage at the switch." Link.

Again, 1N4937 is fine. 1 Amp at 600 volts. The Wiki starts confusing the issue by mentioning faster switching Schottky's, but this is related to power supply design, not snubber diodes.

A note on diode construction. The limit is about 400-600 volts. To make a 1000 volt diode, they put 2 in series. That's why the forward conduction jumps from 1V to 1.7V for the 1000 volt (for 1N and UF 400x series)

To revise my earlier statement about first choice, it's UF4004. UF4007 is a 1000V device.





Looks like the 4004 costs the same or more than the 4007 on digikey- in that case is the 4007 a better choice?
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Old December 7th, 2017, 01:36 PM   #30
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No. Forward conduction voltage is higher for the 4007.
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