Relay - SS vs Mechanical

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Hi all,

Is there any good reason why a Solid State Relay can't be used in
place of a mechanical one for switching regular appliances on
240VAC/10A with a DC signal.

I'm thinking of using one in the Silicon Chip Energy meter and I have
a suitable 20A device in the parts box but no mechanical equivalent.

Thanks in advance,

Rob.

 

[Phil Allison]

Is there any good reason why a Solid State Relay can't be used in
place of a mechanical one for switching regular appliances on
240VAC/10A with a DC signal.

I'm thinking of using one in the Silicon Chip Energy meter and I have
a suitable 20A device in the parts box but no mechanical equivalent.

Thanks in advance,

** A 20Amp SSR uses a large triac to do the actual AC switching -
these have minimum current ratings as well as maximum ones. Make sure the
appliance does not have a low current standby mode that derives its power
via a small iron core transformer ( eg a microwave oven) . The triac in
the SSR may not operate this tranny - or worse burn it out by only
operating during one half cycle so feeding it with a large DC component and
a small AC one.




................ Phil

 

[Bill Bailley]

Hi all,

Is there any good reason why a Solid State Relay can't be used in
place of a mechanical one for switching regular appliances on
240VAC/10A with a DC signal.

I'm thinking of using one in the Silicon Chip Energy meter and I have
a suitable 20A device in the parts box but no mechanical equivalent.

Thanks in advance,

Rob.

I don't know anything about the Silicon Chip project, but I have used solid
state relays to extend the life of some of my older air conditioning units.
A big problem with the older units is that the thermostat contacts switch
the compressor directly without benefit of a relay. The thermostat contacts
last a year or so and then the thermostat has to be replaced. The
thermostats now just switch a 5 volt DC supply to the SS relay control
input, and the thermostats appear (after 4 years) to have a much extended
life. Radio Parts Group has a useful range of SS relays.

One gotcha. There is always a small leakage current through SS relays. This
can give the unwary a severe bite, or possibly worse.

Bill.

 

[Jason James]

Hi all,

Is there any good reason why a Solid State Relay can't be used in
place of a mechanical one for switching regular appliances on
240VAC/10A with a DC signal.

Reliability. The SSRs used in control cubicles to switch a bunch of taxiway
and r/way lighting transformer primaries, used to fail from time to time.
Then again I'm not sure if there was any inductive-load protection.

Personaly, in high power situations, a mech relay gives me much more
confidence.


Jason

 

[Phil Allison]

"Jason James"

Reliability. The SSRs used in control cubicles to switch a bunch of
taxiway
and r/way lighting transformer primaries, used to fail from time to time.
Then again I'm not sure if there was any inductive-load protection.

** You are not real sure of anything.

Personaly, in high power situations, a mech relay gives me much more
confidence.

** What a fool.




................ Phil

 

[Jason James]

"Jason James"



** You are not real sure of anything.

Well Phil,..I didn't have to work on the things, so it was an observation
ie, they used to fail,..

** What a fool.

Oh, really, try telling that to the designers of activation cctry for soft
start HT supplies in transmitters. They all used relays and were virtually
100% reliable.


Jason

 

[Phil Allison]

"Jason James"

"Phil Allison"

Well Phil,..I didn't have to work on the things, so it was an observation
ie, they used to fail,..

** Proves nothing about all the other SSRs that did not.

Oh, really, try telling that to the designers of activation cctry for soft
start HT supplies in transmitters. They all used relays and were virtually
100% reliable.

** Which, even if true, has no connection with the OP's question, my
comment or reality.

Relays are mechanical and so wear out.

SSRs are not mechanical and so do not.





............. Phil

 

[Jason James]

"Jason James"


** Proves nothing about all the other SSRs that did not.



** Which, even if true, has no connection with the OP's question, my
comment or reality.

Suuuure Phil.

Relays are mechanical and so wear out.

Relay failure generally is an extremely rare event IME. Heavier contactors
have been known to fail but fall well short of any rate worthy of mention.

SSRs in the context of my experience have failed at a rate which was
significant,..and that is how my answer to his question was framed.

Jason

 

[Phil Allison]

"Jason James"

"Phil Allison"

Suuuure Phil.



Relay failure generally is an extremely rare event IME.

** All relays *wear out* - contacts have a limited switching life.

You have trouble with reading as well as thinking.

SSRs in the context of my experience have failed at a rate which was
significant,..and that is how my answer to his question was framed.

** Your "experience" is non existant.




............. Phil

 

[MC]

"Jason James"




** Proves nothing about all the other SSRs that did not.





** Which, even if true, has no connection with the OP's question, my
comment or reality.

Relays are mechanical and so wear out.

SSRs are not mechanical and so do not.

True.., but relays (in aggregate), tend to fail in a more
predictable state, ie. they usually fail to operate when required.

 

[Phil Allison]

"MC"

"Jason James"

Relay failure generally is an extremely rare event IME.

True.., but relays (in aggregate), tend to fail in a more
predictable state, ie. they usually fail to operate when required.

** That is bullshit - relays often fail on ( ie contacts welded) or
else fail to make ( contacts burned) - or- become intermittent (
tarnished contacts) -or- develop excess contact resistance and
erheat -or- just plain fail to move when energised due to mechanical
friction, wear or breakage.

Vibrate or a relay hard or subject it to a sudden shock and the contacts
will open in sympathy.

Chose the wrong relay contact material type for a particular job and it will
have a short life or even no life.

Any day you can avoid using one and use a SSR or other electronic switch is
a good day.



BTW Do not remove my words from context so that you can misrepresent
them.





.............. Phil

 

[MC]

"MC"




** That is bullshit - relays often fail on ( ie contacts welded) or
else fail to make ( contacts burned) - or- become intermittent (
tarnished contacts) -or- develop excess contact resistance and
erheat -or- just plain fail to move when energised due to mechanical
friction, wear or breakage.

Vibrate or a relay hard or subject it to a sudden shock and the contacts
will open in sympathy.

Chose the wrong relay contact material type for a particular job and it will
have a short life or even no life.

Any day you can avoid using one and use a SSR or other electronic switch is
a good day.



BTW Do not remove my words from context so that you can misrepresent
them.

ahhh.. care to tell me which words I removed out of context in my reply.

There are *many* different failure modes for mechanical relays which are
highly dependant upon how the device is actually used, but the *most
common* failure for a relay to *not* function (ie to make or break) the
contacts when requested.

 

[Phil Allison]

"MC" <

ahhh.. care to tell me which words I removed out of context in my reply.

** See the words from JJ that I put back ??? - that was the context.

Your post has a different one.

By snipping you obscured that fact.

There are *many* different failure modes for mechanical relays which are
highly dependant upon how the device is actually used, but the *most
common* failure for a relay to *not* function (ie to make or break) the
contacts when requested.

** And that is supposed to be a point is it ???????

" When a relay fails it no longer works " ??????

Piss off.





................. Phil

 

[Jason James]

"Jason James"


** All relays *wear out* - contacts have a limited switching life.

An argument like this has to be put into context. The number of relay
failures in the ground radio-nav and comm equipment I maintained over a 26
year period from '74 to 2000, was such a rare event, that the only ones I
can recall were due to design errors eg the interface circuitry for a
converted Weston VHF TXRX placed a remote PTT relay which switched supply
volts, before a large electrolytic filter cap instaed of after. This caused
frequent relay failure due to switching currents (cap charge current) being
far beyond the specs for that particular relay.

The equipment room we had for a flight-service tower, which had 5 consoles,
contained 100s of relays invarious control cards. Not one of these -50v
relays which encompassed makes such as Siemans, Heinemann and others,
failed,...not one.

Dozens of larger contactors which were in the domain of electrical
maintenance in the main (but which we had complete observation over) and our
higher powered HF t stuff including ex- US army 500 pep HF AM Txs from WWII,
were very reliable,..in fact the only PTT (contactors which had the most
duty-cycle) contactors which failed was in one of those ex army units,..and
it was (at the time) over 30 yrs old. Even then it only failed because after
10,000s of operations, its 3-phase armature screws which held the contacts
in place, came undone. It was totally repairable.

In more complex equipment such as navaids and their control and
monitoring,..I cannot recall one relay/contactor failure except in the first
DMEs which were over 20 yrs old at the time,..and even then was confined to
fault situations which placed an overload on them.

We did experience a few failures in 240v cct breakers (these were used by
the tech to turn the main supply on and off as well),..but cct-breakers are
not quite the same thing.

You have trouble with reading as well as thinking.





** Your "experience" is non existant.

LOL!

Jason

 

[MC]

"MC" <




** See the words from JJ that I put back ??? - that was the context.

Your post has a different one.

By snipping you obscured that fact.







** And that is supposed to be a point is it ???????

" When a relay fails it no longer works " ??????

Piss off.

Take a deep breath Phil.
Take another deep breath.
Check that you haven't gotten my replies confused with others.
Ease-up on the abuse.
Take another deep breath.

 

[Jason James]

In the vast majority of cases I would agree with you
however relays do still have a place in certain high
frequency applications (although less so than they
use to) and they are more tolerant to overload than
thyristors/triacs.

Mike Harding

Then SSRs have that delightful habit of going short more often than open,..

The reassuring sound of a contactor releasing when you cut the juice is
mainly pschological I guess

Jason

 

[Phil Allison]

"Jason James"

"Phil Allison"

An argument like this has to be put into context.

** It is not an "argument" you tedious fuckwit - it is a simple fact and
is quoted in the maker's specs.





............. Phil

 

[Phil Allison]

"MC" <

Phil Allison wrote:

Take a deep breath Phil.

** Piss off moron.

Take another deep breath.

** Hold yours indefinitely.

Check that you haven't gotten my replies confused with others.

** Nope.



............ Phil

 

[Phil Allison]

"Mike Harding"
"Phil Allison"

In the vast majority of cases I would agree with you
however relays do still have a place in certain high
frequency applications (although less so than they
use to) and they are more tolerant to overload than
thyristors/triacs.

** Depends on the overload - surge or continuous ??

The same inrush surge that will weld a relay permanently - an SCR or
triac will cope with hundreds of thousands of times.

Remember that relays have very weak opening forces, unlike a mechanical
switch, so a tiny weld does them in.



............ Phil

 

[Jason James]

"Jason James"



** It is not an "argument" you tedious fuckwit - it is a simple fact and
is quoted in the maker's specs.

............ Phil

The relays which operated on speech in what we called 'audio operated
relay' modules (used for a number of monitoring and Retx functions in the
past) literally operated and relaxed millions of times. They were just a
normal flat cct board unit. Their reliability was phenomonal....

Anyway Phil,...go back to the spec sheets.

Jason