Relay back emf protection

Gareth Magennis

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Oct 22, 2014, 2:52:30 PM10/22/14

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Following on from the Automotive Relay thread;

What are the reasons behind the apparent fact that relays last longest in
this order of coil protection:

1. No protection at all
2. Zener diode
3. Resistor (6 x coil resistance)
4. Diode

(No protection being the relay lasts longest, the standard diode being the
worst thing for the relay - forget the circuit protection issues just now)

From this data - scroll to the bottom for a chart:

http://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=Automotive_Relay_Applications&DocType=CS&DocLang=EN

Cheers,

Gareth.

amdx

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Oct 22, 2014, 5:24:10 PM10/22/14

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On 10/22/2014 1:52 PM, Gareth Magennis wrote:
> Following on from the Automotive Relay thread;
>

> What are the reasons behind the apparent fact that relays last longest
> in this order of coil protection:

Arcing on opening.

> 1. No protection at all

Fastest opening. Less damage to contacts.

> 2. Zener diode

If indeed your order is correct,
Slow opening.

> 3. Resistor (6 x coil resistance)

Slower Opening.

> 4. Diode

Slowest Opening.
Most damage to contacts.

>
>
> (No protection being the relay lasts longest, the standard diode being
> the worst thing for the relay - forget the circuit protection issues
> just now)
>
>
> From this data - scroll to the bottom for a chart:
>
> http://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=Automotive_Relay_Applications&DocType=CS&DocLang=EN
>
>
>
>
> Cheers,
>
>
> Gareth.

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bud--

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Oct 23, 2014, 2:54:10 PM10/23/14

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On 10/22/2014 3:23 PM, amdx wrote:
> On 10/22/2014 1:52 PM, Gareth Magennis wrote:
>> Following on from the Automotive Relay thread;
>>
>
>
>> What are the reasons behind the apparent fact that relays last longest
>> in this order of coil protection:
>
>
> Arcing on opening.
>
>
>
>> 1. No protection at all
>
> Fastest opening. Less damage to contacts.
>
>> 2. Zener diode
>
> If indeed your order is correct,
> Slow opening.
>
>> 3. Resistor (6 x coil resistance)
>
> Slower Opening.
>
>> 4. Diode
>
> Slowest Opening.
> Most damage to contacts.

http://web.archive.org/web/20110104003731/http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3264.pdf

John Robertson

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Oct 23, 2014, 8:01:22 PM10/23/14

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This is very interesting, it raises points I had never considered such
as the momentary current flow through the diode and coil, and how that
can stress other parts. The two articles are good reading!

It explains why (in my field of pinball repair) manufacturers stopped
putting suppression diodes on the coils and instead put them in place to
protect the driver devices (transistors/Mosfets, etc.).

Thanks for bringing this topic up!

Do note that both articles say you HAVE to protect the driver device
from the back EMF!!

John :-#)#

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Gareth Magennis

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Oct 24, 2014, 2:02:25 PM10/24/14

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"bud--" wrote in message
news:54494ed0$0$44150$c3e8da3$3a1a...@news.astraweb.com...

Thanks for that link. Interesting indeed.

Gareth.