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Sci.Electronics.Basics -> sizing a freewheeling diode for a coil
There are 39 messages in this thread.
You are currently looking at messages 20 to 39.
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Author: JamieDate: 16:04 02-06-07
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Tony Williams wrote:
> In article <87sl9a4opm.fsf@cordelia.devereux.me.uk>,
> John Devereux <jdREMOVE@THISdevereux.me.uk> wrote:
>
>
>>> I've had it. 1N4148s gone to a short circuit.
>>> Never found out why.
>
>
>>ESD? Were the contacts connected to "external" signals?
>
>
> They were multiplexing resistor values to simulate
> a thermistor, into a unit that was about 3ft away.
>
> The relay coils were 24V/1k. I still don't see
> any reason why 3 1N4148s in a bank of 8 should
> all go s/c, but they did. The only reasonable
> explanation was possibly a bad batch of diodes.
>
That's possible, I've had that happen before where
the leads pulled out enough to loss connection.
it was a batch of diodes with bad bonding
on the leads
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
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Author: JamieDate: 16:48 02-06-07
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JackShephard wrote:
>>
>>
> JackShephard looks in the mirror.
>
> "You fucking retard"
How many times have I told you to stop talking to your
self? I'm glad you're finally coming to terms of what you are.
Are you now ready to join the human race?
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
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Author: JackShephardDate: 17:25 02-06-07
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Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in
news:Mxk8i.295$8A7.40@newsfe06.lga:
> JackShephard wrote:
>
>>>
>>>
>> JackShephard looks in the mirror.
>>
>> "You fucking retard"
> How many times have I told you to stop talking to your
> self? I'm glad you're finally coming to terms of what you are.
>
> Are you now ready to join the human race?
>
>
You're mother is a retard.
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Author: Spehro PefhanyDate: 18:00 02-06-07
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On Sat, 02 Jun 2007 12:15:19 -0400, the renowned Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:
>Tony Williams wrote:
>
>> In article <ns-dnQFpFNJUbf3bnZ2dnUVZ_hudnZ2d@comcast.com>,
>> John Popelish <jpopelish@rica.net> wrote:
>>
>>>Eeyore wrote:
>>
>>
>>>>I've known quite small relays to 'take out' 1N4148s, 914s etc.
>>
>>
>>>I hear people say this, but I have never seen a case of it.
>>>I have used 1N4148 diodes for 200 mA coils for years.
>>
>>
>> I've had it. 1N4148s gone to a short circuit.
>> Never found out why.
>>
>maybe you should be using faster switching diodes?
1N4148s have a maximum reverse recovery time of 4ns. 1N400x diodes are
around 1,000 times longer.
> also, I do know if the relay chatters it can heat up
>diodes.
Do tell.. how would that work?
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the
reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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Author: MattDate: 18:07 02-06-07
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ian field wrote:
> "John Devereux" <jdREMOVE@THISdevereux.me.uk> wrote in message
> news:87odjy4ohq.fsf@cordelia.devereux.me.uk...
>> whit3rd <whit3rd@gmail.com> writes:
>>
>>> On Jun 1, 9:24 pm, John Popelish <jpopel...@rica.net> wrote:
>>>> Eeyore wrote:
>>>>> I've known quite small relays to 'take out' 1N4148s, 914s etc.
>>>> I hear people say this, but I have never seen a case of it.
>>>> I have used 1N4148 diodes for 200 mA coils for years.
>>> It's the energy storage, proportional to inductance and square of
>>> the current, that matters. A 200 mA coil on a reed switch
>>> has much lower stored energy than a 50 mA coil on a frame
>>> relay. When you're using more current than the (average)
>>> rating on your diode, it only succeeds if the temperature
>>> spike doesn't melt anything.
>> But the diode will still only see the 50mA current, even if the stored
>> energy is *enormous*. It will just take a bit longer for that current
>> to decay when the driver is switched off (and this will be independent
>> of the diode rating).
>>
>> --
>>
>> John Devereux
>
> An application note from a relay manufacturer that I read a while ago
> suggests a small signal diode in series with a zener.
>
> Apparently if just a diode is used, the emf due to collapsing field can pass
> enough current round the diode/coil circuit to cause faltering contact
> separation and contact burn. There are other serious issues but I'd have to
> search out the appnote to remind me what they are.
>
> The zener should be wired so it would forward conduct with the transistor on
> and the small signal diode in series pointing the other way to prevent that
> happening, a guesstimate of Vz might be about 60% of the transistor's
> breakdown voltage.
I think you mean this one:
http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3311.pdf
> The application of relay coil suppression with DC relays
>
> This application note has been written in response to the numerous
> application problems resulting from improper relay coil suppression. The
> typical symptom is random "tack" welding of the normally-open contacts
> when switching an inductive load or a lamp load with high inrush current.
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Author: Paul Hovnanian P.E.Date: 19:39 02-06-07
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Author: James ArthurDate: 20:15 02-06-07
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On Jun 2, 3:22 am, Tony Williams <t...@ledelec.demon.co.uk> wrote:
> In article <87sl9a4opm....@cordelia.devereux.me.uk>,
> John Devereux <jdREM...@THISdevereux.me.uk> wrote:
>
> > > I've had it. 1N4148s gone to a short circuit.
> > > Never found out why.
> > ESD? Were the contacts connected to "external" signals?
>
> They were multiplexing resistor values to simulate
> a thermistor, into a unit that was about 3ft away.
>
> The relay coils were 24V/1k. I still don't see
> any reason why 3 1N4148s in a bank of 8 should
> all go s/c, but they did. The only reasonable
> explanation was possibly a bad batch of diodes.
>
> --
> Tony Williams.
I've seen 1n4148s fail across small relays, the 'off hook' relay in
a modem. The cause? Surges in the switched circuit. Big ones. The
loop area of the relays' contacts and connections--as laid out on the
PCB--was sufficient to couple said surges into their coils & pop
1n4148s. A transformer, it was.
This modem was in my PC. After losing several diodes in succession,
I fixed the problem by 'improving' the layout to reduce the loop area
& proximity to the coil.
Designing industrial stuff, we picked relays wired such that the one-
turn switched loop wouldn't couple back to the coil, and laid out
traces carefully on both sides exactly to avoid this problem.
Otherwise, lightning-induced surges can make quite a mess of things as
they propagate backward from the relays and onto your board.
Cheers,
James Arthur
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Author: Robert AdsettDate: 20:17 02-06-07
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Author: JasenDate: 20:49 02-06-07
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On 2007-06-02, whit3rd <whit3rd@gmail.com> wrote:
> On Jun 1, 9:24 pm, John Popelish <jpopel...@rica.net> wrote:
>> Eeyore wrote:
>> > I've known quite small relays to 'take out' 1N4148s, 914s etc.
>>
>> I hear people say this, but I have never seen a case of it.
>> I have used 1N4148 diodes for 200 mA coils for years.
>
> It's the energy storage, proportional to inductance and square of
> the current, that matters. A 200 mA coil on a reed switch
> has much lower stored energy than a 50 mA coil on a frame
> relay. When you're using more current than the (average)
> rating on your diode, it only succeeds if the temperature
> spike doesn't melt anything.
last I checked 1N4148 was rated for 200 mA continuous.
Bye.
Jasen
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Author: MarraDate: 20:57 02-06-07
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On 2 Jun, 23:00, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat>
wrote:
> On Sat, 02 Jun 2007 12:15:19 -0400, the renowned Jamie
>
>
>
> <jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
> >Tony Williams wrote:
>
> >> In article <ns-dnQFpFNJUbf3bnZ2dnUVZ_hudn...@comcast.com>,
> >> John Popelish <jpopel...@rica.net> wrote:
>
> >>>Eeyore wrote:
>
> >>>>I've known quite small relays to 'take out' 1N4148s, 914s etc.
>
> >>>I hear people say this, but I have never seen a case of it.
> >>>I have used 1N4148 diodes for 200 mA coils for years.
>
> >> I've had it. 1N4148s gone to a short circuit.
> >> Never found out why.
>
> >maybe you should be using faster switching diodes?
>
> 1N4148s have a maximum reverse recovery time of 4ns. 1N400x diodes are
> around 1,000 times longer.
>
> > also, I do know if the relay chatters it can heat up
> >diodes.
>
> Do tell.. how would that work?
>
> Best regards,
> Spehro Pefhany
> --
> "it's the network..." "The Journey is the
reward"
> s...@interlog.com Info for manufacturers:http://www.trexon.com
> Embedded software/hardware/analog Info for designers: http://www.speff.com
you get contact bounce on the relay.
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Author: JamieDate: 21:24 02-06-07
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Spehro Pefhany wrote:
> On Sat, 02 Jun 2007 12:15:19 -0400, the renowned Jamie
> <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:
>
>
>>Tony Williams wrote:
>>
>>
>>>In article <ns-dnQFpFNJUbf3bnZ2dnUVZ_hudnZ2d@comcast.com>,
>>> John Popelish <jpopelish@rica.net> wrote:
>>>
>>>
>>>>Eeyore wrote:
>>>
>>>
>>>>>I've known quite small relays to 'take out' 1N4148s, 914s etc.
>>>
>>>
>>>>I hear people say this, but I have never seen a case of it.
>>>>I have used 1N4148 diodes for 200 mA coils for years.
>>>
>>>
>>> I've had it. 1N4148s gone to a short circuit.
>>> Never found out why.
>>>
>>
>>maybe you should be using faster switching diodes?
>
>
> 1N4148s have a maximum reverse recovery time of 4ns. 1N400x diodes are
> around 1,000 times longer.
>
>
>> also, I do know if the relay chatters it can heat up
>>diodes.
>
>
> Do tell.. how would that work?
>
>
> Best regards,
> Spehro Pefhany
Was that suppose to be a joke?
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
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Author: Spehro PefhanyDate: 22:45 02-06-07
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On Sat, 02 Jun 2007 21:24:59 -0400, the renowned Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:
>Spehro Pefhany wrote:
>
>> On Sat, 02 Jun 2007 12:15:19 -0400, the renowned Jamie
>> <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:
>>
>>
>>>Tony Williams wrote:
>>>
>>>
>>>>In article <ns-dnQFpFNJUbf3bnZ2dnUVZ_hudnZ2d@comcast.com>,
>>>> John Popelish <jpopelish@rica.net> wrote:
>>>>
>>>>
>>>>>Eeyore wrote:
>>>>
>>>>
>>>>>>I've known quite small relays to 'take out' 1N4148s, 914s etc.
>>>>
>>>>
>>>>>I hear people say this, but I have never seen a case of it.
>>>>>I have used 1N4148 diodes for 200 mA coils for years.
>>>>
>>>>
>>>> I've had it. 1N4148s gone to a short circuit.
>>>> Never found out why.
>>>>
>>>
>>>maybe you should be using faster switching diodes?
>>
>>
>> 1N4148s have a maximum reverse recovery time of 4ns. 1N400x diodes are
>> around 1,000 times longer.
>>
>>
>>> also, I do know if the relay chatters it can heat up
>>>diodes.
>>
>>
>> Do tell.. how would that work?
>>
>>
>> Best regards,
>> Spehro Pefhany
> Was that suppose to be a joke?
Not really, I really have no idea what s/he is talking about in terms
of potentially harmful heating. Do you?
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the
reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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Author: Robert AdsettDate: 00:19 03-06-07
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In article <1180832279.630438.322230@o5g2000hsb.googlegroups.com>, Marra
says...
> On 2 Jun, 23:00, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat>
> wrote:
> > On Sat, 02 Jun 2007 12:15:19 -0400, the renowned Jamie
> >
> >
> >
> > <jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
> > >Tony Williams wrote:
> >
> > >> In article <ns-dnQFpFNJUbf3bnZ2dnUVZ_hudn...@comcast.com>,
> > >> John Popelish <jpopel...@rica.net> wrote:
> >
> > >>>Eeyore wrote:
> >
> > >>>>I've known quite small relays to 'take out' 1N4148s, 914s etc.
> >
> > >>>I hear people say this, but I have never seen a case of it.
> > >>>I have used 1N4148 diodes for 200 mA coils for years.
> >
> > >> I've had it. 1N4148s gone to a short circuit.
> > >> Never found out why.
> >
> > >maybe you should be using faster switching diodes?
> >
> > 1N4148s have a maximum reverse recovery time of 4ns. 1N400x diodes are
> > around 1,000 times longer.
> >
> > > also, I do know if the relay chatters it can heat up
> > >diodes.
> >
> > Do tell.. how would that work?
> >
>
> you get contact bounce on the relay.
And?
Robert
--
Posted via a free Usenet account from http://www.teranews.com
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Author: JackShephardDate: 14:32 03-06-07
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On Sat, 02 Jun 2007 16:48:58 -0400, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:
>JackShephard wrote:
>
>>>
>>>
>> JackShephard looks in the mirror.
>>
>> "You fucking retard"
> How many times have I told you to stop talking to your
>self? I'm glad you're finally coming to terms of what you are.
>
> Are you now ready to join the human race?
The person you need to blame this on is "Lamey The Cable Guy" or
whatever fucking stupid nym he is going by now.
The posts is a forgery/clone or whatever you want to call it. I did not
write it. That goes for the next one you read as well. I was never in
this thread.
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Author: ian fieldDate: 09:10 04-06-07
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"Matt" <themattfella@xxyyyzzzz.com> wrote in message
news:ySl8i.9649$ya1.4156@news02.roc.ny...
> ian field wrote:
>> "John Devereux" <jdREMOVE@THISdevereux.me.uk> wrote in message
>> news:87odjy4ohq.fsf@cordelia.devereux.me.uk...
>>> whit3rd <whit3rd@gmail.com> writes:
>>>
>>>> On Jun 1, 9:24 pm, John Popelish <jpopel...@rica.net> wrote:
>>>>> Eeyore wrote:
>>>>>> I've known quite small relays to 'take out' 1N4148s, 914s etc.
>>>>> I hear people say this, but I have never seen a case of it.
>>>>> I have used 1N4148 diodes for 200 mA coils for years.
>>>> It's the energy storage, proportional to inductance and square of
>>>> the current, that matters. A 200 mA coil on a reed switch
>>>> has much lower stored energy than a 50 mA coil on a frame
>>>> relay. When you're using more current than the (average)
>>>> rating on your diode, it only succeeds if the temperature
>>>> spike doesn't melt anything.
>>> But the diode will still only see the 50mA current, even if the stored
>>> energy is *enormous*. It will just take a bit longer for that current
>>> to decay when the driver is switched off (and this will be independent
>>> of the diode rating).
>>>
>>> --
>>>
>>> John Devereux
>>
>> An application note from a relay manufacturer that I read a while ago
>> suggests a small signal diode in series with a zener.
>>
>> Apparently if just a diode is used, the emf due to collapsing field can
>> pass enough current round the diode/coil circuit to cause faltering
>> contact separation and contact burn. There are other serious issues but
>> I'd have to search out the appnote to remind me what they are.
>>
>> The zener should be wired so it would forward conduct with the transistor
>> on and the small signal diode in series pointing the other way to prevent
>> that happening, a guesstimate of Vz might be about 60% of the
>> transistor's breakdown voltage.
>
> I think you mean this one:
>
> http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3311.pdf
>> The application of relay coil suppression with DC relays
>>
>> This application note has been written in response to the numerous
>> application problems resulting from improper relay coil suppression. The
>> typical symptom is random "tack" welding of the normally-open
contacts
>> when switching an inductive load or a lamp load with high inrush current.
>
Backspacing the URL to "appnotes/" presents a selection of pdf's.
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Author: John FieldsDate: 20:40 04-06-07
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On Sat, 02 Jun 2007 04:15:05 GMT, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:
>
>
>Phil Allison wrote:
>
>> "Matt"
>>
>> > I'm not sure of the issues in specifying the diode.
>>
>> ** Long as the diode can pass the same average current need to drive the
>> coil and sustain the DC voltage across it - it should be OK.
>>
>> The cheapest possible diode are commonly used - like 1N4148s or 1N4001s.
>
>I've known quite small relays to 'take out' 1N4148s, 914s etc.
---
Really?
How about some facts?
Like which relays are you talking about?
Do you have some part numbers and some circuits or is this just some
more of your pretense at knowledge bullshit?
--
JF
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Author: MattDate: 08:52 06-06-07
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Matt wrote:
> I am controlling the coil of a relay using a switching transistor. To
> protect the transistor I intend to use a freewheeling diode in parallel
> with the coil. I'm not sure of the issues in specifying the diode.
>
> My impulse is to simply use a 1N4007
> http://www.fairchildsemi.com/pf/1N/1N4007.html
> (1000V peak repetitive reverse voltage, 1.0A average rectified forward
> current) because it is common, cheap, and seemingly the most heavy-duty
> of the 1N400x line. Would that be a good choice for about any
> PCB-mounted relay?
Thanks for all the helpful replies.
It seems that the overall reliability of the device is best served not
by a single diode, but by a transient voltage suppressor. The diode is
a little better at protecting the transistor that switches the coil, but
apparently it can cause a not-so-clean unmaking of the relay, leading to
welding or erosion of the contacts in the case of a heavily-loaded
normally-open relay. This is described in
http://relays.tycoelectronics.com/appnotes/
http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3264.pdf
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Author: Adrian TuddenhamDate: 13:06 06-06-07
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John Popelish <jpopelish@rica.net> wrote:
> Matt wrote:
> > I am controlling the coil of a relay using a switching transistor. To
> > protect the transistor I intend to use a freewheeling diode in parallel
> > with the coil. I'm not sure of the issues in specifying the diode.
> >
> > My impulse is to simply use a 1N4007
> > http://www.fairchildsemi.com/pf/1N/1N4007.html
> > (1000V peak repetitive reverse voltage, 1.0A average rectified forward
> > current) because it is common, cheap, and seemingly the most heavy-duty
> > of the 1N400x line. Would that be a good choice for about any
> > PCB-mounted relay?
>
> The absolute minimum repetitive surge current rating for the
> diode is the steady state current for the coil, under the
> highest supply voltage. If the diode is rated for a
> continuous current equal to or greater than the coil
> current, the brief inductive quench can't possibly overheat
> the die.
If the contacts operating the relay become dirty or the control
transistor begins to oscillate, then you will get repetitive surges at
quite frequent intervals. It is better not to rely upon the
single-pulse surge current rating of the diode.
A diode with a continuous rating equal to (or greater than) the maximum
coil current will give peace of mind under all possible conditions of
operation and mis-operation.
--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
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Author: John PopelishDate: 13:25 06-06-07
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Adrian Tuddenham wrote:
> John Popelish <jpopelish@rica.net> wrote:
>> The absolute minimum repetitive surge current rating for the
>> diode is the steady state current for the coil, under the
>> highest supply voltage. (snip)
> If the contacts operating the relay become dirty or the control
> transistor begins to oscillate, then you will get repetitive surges at
> quite frequent intervals. It is better not to rely upon the
> single-pulse surge current rating of the diode.
I did not mention the single pulse surge current rating, but
the repetitive surge surge current rating. But as with any
limiting case, it is a good idea to include some safety
factor. By the way, if the coil is driven by rapid pulses,
its current will not reach the full, DC, steady state value,
but will bounce between some lower limits.
> A diode with a continuous rating equal to (or greater than) the maximum
> coil current will give peace of mind under all possible conditions of
> operation and mis-operation.
Agreed. Especially if the diode is in a good thermal situation.
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