Does constantly energizing a relay shorten its life?

[kansas_ray]

Hi all,

If so, by how much? Can anyone point me to any info on the subject or pass
on any personal experience?

We can re-layout a board to use an OMRON G5V-2-H-24VDC relay in a normally
de-energized position but I wonder if it's worth the effort.

Regards,
Ray

 

[Spehro Pefhany]

Hi all,

If so, by how much? Can anyone point me to any info on the subject or pass
on any personal experience?

It makes the coil run hotter, but as long as you're well below the
maximum it should not appreciably affect life. AC relays run a lot
hotter than DC ones of the same type.

We can re-layout a board to use an OMRON G5V-2-H-24VDC relay in a normally
de-energized position but I wonder if it's worth the effort.

What is that, a 150mW coil or something? It's not worth any effort at
all unless you're operating very near the high temperature extreme
and/or are going to be putting overvoltage on the coil.

If you're switching significant current compared to the ratings, note
that the NC contacts are generally not as good as the NO for
electrical life.

Best regards,
Spehro Pefhany

 

[kansas_ray]

It makes the coil run hotter, but as long as you're well below the
maximum it should not appreciably affect life. AC relays run a lot
hotter than DC ones of the same type.


What is that, a 150mW coil or something? It's not worth any effort at
all unless you're operating very near the high temperature extreme
and/or are going to be putting overvoltage on the coil.

If you're switching significant current compared to the ratings, note
that the NC contacts are generally not as good as the NO for
electrical life.

Best regards,
Spehro Pefhany

Thanks for the response. That's a load off my mind (and a cost savings for
my company).

Best regards in your direction,
Ray

 

[Walter Harley]

Hi all,

If so, by how much? Can anyone point me to any info on the subject or pass
on any personal experience?

If you're interested in further detail on the topic, there was a recent
thread on sci.electronics.design on exactly this question.

But, Spehro's answer summarizes it.

 

[kansas_ray]

If you're interested in further detail on the topic, there was a recent
thread on sci.electronics.design on exactly this question.

But, Spehro's answer summarizes it.

I was diligent in that I googled "constantly" "energized" "relay" in groups
and got no decent hits. I would be interested in more detail if you could
provide a link or appropriate google key words.

Regards,
Ray

 

[YD]

Hi all,

If so, by how much? Can anyone point me to any info on the subject or pass
on any personal experience?

We can re-layout a board to use an OMRON G5V-2-H-24VDC relay in a normally
de-energized position but I wonder if it's worth the effort.

Regards,
Ray

It should be okay unless the ambient is very hot or you run it at more
than 10% overvoltage. Vibration can be more of an issue, I've seen the
wire break at the solder joint.

- YD.

 

[Mac]

I was diligent in that I googled "constantly" "energized" "relay" in groups
and got no decent hits. I would be interested in more detail if you could
provide a link or appropriate google key words.

Regards,
Ray

It looks like the first message was dec 27, 2003. The subject was: "Do
relay coils wear out if used continuously?"

The original poster was "Michael," with email
"[email protected]."

Here is the full text of his post:

Hi - I'm working on a new design that incorporate a DPDT relay. The coil
will be "on" about half of the time, 24/7/365. Will that present a
problem for some relays? It won't switch positions very often - probably
10 times a day at most. But the coil will be on for hours, days, even
weeks at a time. Is this something to be worried about? If it matters -
it will be switching some 120VAC lines. Oh, and are there any
characteristics I should look for in a relay for this application?
Current will be fairly low - only maybe 10 or so outdoor lights (maybe
50W or so each?) will be connected to it, and it will be operating off
of 5V DC. Thanks!

Michael

You should be able to find the thread now. ;-)

Mac

 

[DJ]

Hi all,

If so, by how much? Can anyone point me to any info on the subject or pass
on any personal experience?

We can re-layout a board to use an OMRON G5V-2-H-24VDC relay in a normally
de-energized position but I wonder if it's worth the effort.

Regards,
Ray

Most relay data sheets quote mechanical life and electrical life. Both are in
terms of switching cycles. Mechanical life is generally many times electrical
life. A typical figure might be 5 million. Electrical life is quoted at certain
load conditions e.g. 1A, 30V DC resistive load. Typical figures range from 1
million down to as a low as 20K. Some manufacturers give curves of electrical
life versus load. These curves usually don't include the load conditions you are
actually using <g> so you have to guess.

There is also a specification for coil voltage range. The maximum voltage is
limited by permissible temperature rise and coil temperature. In many relays it
is actually only 10% over nominal. The minimum voltage is "pull in voltage",
i.e. the smallest voltage at which the relay is guaranteed to pull in. This is
typically 80% or 70% of nominal. Taking those limits into account means it is
usually impossible to drive a relay off an unregulated DC power supply and
guaratee you are within allowable limits.

 

[Spehro Pefhany]

Most relay data sheets quote mechanical life and electrical life. Both are in
terms of switching cycles. Mechanical life is generally many times electrical
life. A typical figure might be 5 million. Electrical life is quoted at certain
load conditions e.g. 1A, 30V DC resistive load. Typical figures range from 1
million down to as a low as 20K. Some manufacturers give curves of electrical
life versus load. These curves usually don't include the load conditions you are
actually using <g> so you have to guess.

You may have to guess. We *test* at the desired current, even if the
manufacturer supplies curves. A million or five million operations
doesn't take long, though you have to make sure not to switch so fast
that contact heating prejudices the results. There is a WIDE variation
in the improvement one can expect from derating resistive load
current.

There is also a specification for coil voltage range. The maximum voltage is
limited by permissible temperature rise and coil temperature. In many relays it
is actually only 10% over nominal. The minimum voltage is "pull in voltage",
i.e. the smallest voltage at which the relay is guaranteed to pull in. This is
typically 80% or 70% of nominal. Taking those limits into account means it is
usually impossible to drive a relay off an unregulated DC power supply and
guaratee you are within allowable limits.

Nonsense! MOST DC relays operate from unregulated supplies! Billions
(quite literally) of them!

Best regards,
Spehro Pefhany

 

[scada]

Hi all,

If so, by how much? Can anyone point me to any info on the subject or pass
on any personal experience?

We can re-layout a board to use an OMRON G5V-2-H-24VDC relay in a normally
de-energized position but I wonder if it's worth the effort.

Regards,
Ray

I work with relays that have been in service since the 1940's. Most of them
are the originals. When we design a relay circuit, most cases we design for
the relay to be normaly de-energized. This is mainly to save on power, the
circuits are fed from batteries that are constantly charged. I can think of
relays that are normarly energized, and have been for most of their lifetime
(1940's)! Of course, these relays are industrial and hundreds of dollars.

 

[Roger Gt]

X-No-Archive: yes

I work with relays that have been in service since the 1940's. Most of them
are the originals. When we design a relay

circuit, most cases we design for

the relay to be normally de-energized. This is mainly to save on power, the
circuits are fed from batteries that are

constantly charged. I can think of

relays that are normally energized, and have

been for most of their lifetime

(1940's)! Of course, these relays are industrial and hundreds of dollars.

Consider using latching relays.... No power
except on a change of state!

 

[kansas_ray]

It looks like the first message was dec 27, 2003. The subject was: "Do
relay coils wear out if used continuously?"

The original poster was "Michael," with email
"[email protected]."

Here is the full text of his post:



You should be able to find the thread now. ;-)

Mac

Thanks for the help!
Ray

 

[Sergey Kubushin]

X-No-Archive: yes

circuit, most cases we design for
constantly charged. I can think of
been for most of their lifetime


Consider using latching relays.... No power
except on a change of state!

It won't do in some cases. An emergency halt relay for a chemical plant or
something similar MUST be powered for the plant to operate and it MUST stop
the plant if something happened. That's why all those big red buttons are
ALWAYS break the circuit when pushed - they are in series with that relay's
coil...

 

[Don Lancaster]

It won't do in some cases. An emergency halt relay for a chemical plant or
something similar MUST be powered for the plant to operate and it MUST stop
the plant if something happened. That's why all those big red buttons are
ALWAYS break the circuit when pushed - they are in series with that relay's
coil...

---
******************************************************************
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
******************************************************************

For long life, you can drop the supply voltage considerably after the
relay pulls in.
I would think the only life factor would be the operating temperature.

--
Many thanks,

Don Lancaster
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
voice: (928)428-4073 email: [email protected] fax 847-574-1462

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Robert Baer]

It won't do in some cases. An emergency halt relay for a chemical plant or
something similar MUST be powered for the plant to operate and it MUST stop
the plant if something happened. That's why all those big red buttons are
ALWAYS break the circuit when pushed - they are in series with that relay's
coil...

---
******************************************************************
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
******************************************************************

Relays are known to last well over 50 years in intermittent operation,
and well over 20 years in continuous operation - as long as the coil and
the contacts are operated within design specs.
For higher safety reliability, consider doing *all* of the following:
1) Put a (thin - 3 mils will do fine) piece of paper, mylar, or kapton
between the pole and the armature to prevent the armature from touching
the pole piece. Reason: the iron can get magentised and may prevent
drop-out.
2) Mount the relay so that gravity can pull the armature away from the
pole piece. Reason: if the spring breaks or otherwise becomes disabled,
gravity will do the work; but only if there is that gap previously
mentioned.
3) *TEST* each and every relay for 500mSec (or better if you are fussy)
dropout *without* a spring; and then make *damn* sure you put the spring
back in; someone else should double check that the springs are properly
in place! Be advised the typical dropout time of relays is 100mSec.
Reason: This verifies that the back-up gravity powered opening of the
relays is functional and reliable.

 

[Spehro Pefhany]

Relays are known to last well over 50 years in intermittent operation,
and well over 20 years in continuous operation - as long as the coil and
the contacts are operated within design specs.
For higher safety reliability, consider doing *all* of the following:
1) Put a (thin - 3 mils will do fine) piece of paper, mylar, or kapton
between the pole and the armature to prevent the armature from touching
the pole piece. Reason: the iron can get magentised and may prevent
drop-out.
2) Mount the relay so that gravity can pull the armature away from the
pole piece. Reason: if the spring breaks or otherwise becomes disabled,
gravity will do the work; but only if there is that gap previously
mentioned.
3) *TEST* each and every relay for 500mSec (or better if you are fussy)
dropout *without* a spring; and then make *damn* sure you put the spring
back in; someone else should double check that the springs are properly
in place! Be advised the typical dropout time of relays is 100mSec.
Reason: This verifies that the back-up gravity powered opening of the
relays is functional and reliable.

There are two main constructions of power relays (which does not
include shorting-bar type contactors).

1) A hinge plus spring to return the armature, flexible wires
conduct the current.

2) A current-carrying flexure acts as the spring

In addition, European-spec relays often indirectly operate the
armature with an insulating pusher to get sufficient creepage
(typically several kV coil-to-contact). Some relays (eg. of the P&B
T-70 construction) have awful breakdown ratings of something like
500V.

THe first construction is prone to rare failures from hinge sticking.
I have seen an entire batch from a major manufacturer many years ago
that had a 5% or so failure rate due to sticking- in the field. Very,
very costly, and very subtle to find. The second is prone to possible
failure from over-current, which destroys the spring characteristics
of the flexure by annealing. The European type is probably subject to
other problems from friction or contamination in the extra moving
parts, but I've not seen them (yet).

I could go on (and on) but there are a lot of things that affect relay
reliability and life (venting vs. sealing for example, a trade-off),
but the point remains that continously energizing a relay has
essentially no effect on life under normal conditions.

Best regards,
Spehro Pefhany