[EE] Miniature relay

[Isaac M. Bavaresco]

Dear All,

I need a miniature PCB relay to operate a lock. The contact may be
SPST-NO or SPDT-NO. The application may use a variety of different locks
with voltages in the range of 6 V to 24 V AC or DC and the current up to
2 A.

For some applications I already use miniature telecom relays, but their
current capability is at most 1 A or 2 A.

Does anybody know of some very small PCB relays with current capability
of at least 4 A? SMD preferably but PTH acceptable, coil voltage of 5 V
or 12 V.

Best regards,

Isaac


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[Allen Mulvey]

I am currently using Schrack RTE24005 DPDT relays. They are rated 8A @ 250VAC. They are bigger than the 1 and 2 amp micro-relays I sometimes use but they seem to handle almost anything I need.

https://www.mouser.com/productdetail/te-connectivity-schrack/rte24005?qs=CUfic%2FGsH5CuQV4J3ppyPg%3D%3D

Allen

-----Original Message-----
From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf Of Isaac M. Bavaresco
Sent: Wednesday, October 17, 2018 9:19 AM
To: ***@mit.edu
Subject: [EE] Miniature relay

Dear All,

I need a miniature PCB relay to operate a lock. The contact may be
SPST-NO or SPDT-NO. The application may use a variety of different locks
with voltages in the range of 6 V to 24 V AC or DC and the current up to
2 A.

For some applications I already use miniature telecom relays, but their
current capability is at most 1 A or 2 A.

Does anybody know of some very small PCB relays with current capability
of at least 4 A? SMD preferably but PTH acceptable, coil voltage of 5 V
or 12 V.

Best regards,

Isaac


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[David Van Horn]

How are you handling the voltage spike on switchoff?

-----Original Message-----
From: piclist-***@mit.edu <piclist-***@mit.edu> On Behalf Of Allen Mulvey
Sent: Wednesday, October 17, 2018 7:50 AM
To: 'Microcontroller discussion list - Public.' <***@mit.edu>
Subject: RE: [EE] Miniature relay

I am currently using Schrack RTE24005 DPDT relays. They are rated 8A @ 250VAC. They are bigger than the 1 and 2 amp micro-relays I sometimes use but they seem to handle almost anything I need.

https://www.mouser.com/productdetail/te-connectivity-schrack/rte24005?qs=CUfic%2FGsH5CuQV4J3ppyPg%3D%3D

Allen

-----Original Message-----
From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf Of Isaac M. Bavaresco
Sent: Wednesday, October 17, 2018 9:19 AM
To: ***@mit.edu
Subject: [EE] Miniature relay

Dear All,

I need a miniature PCB relay to operate a lock. The contact may be SPST-NO or SPDT-NO. The application may use a variety of different locks with voltages in the range of 6 V to 24 V AC or DC and the current up to
2 A.

For some applications I already use miniature telecom relays, but their current capability is at most 1 A or 2 A.

Does anybody know of some very small PCB relays with current capability of at least 4 A? SMD preferably but PTH acceptable, coil voltage of 5 V or 12 V.

Best regards,

Isaac


---
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[Allen Mulvey]

I use the usual diode in parallel with the coil.

Allen

-----Original Message-----
From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf Of David Van Horn
Sent: Wednesday, October 17, 2018 10:50 AM
To: Microcontroller discussion list - Public.
Subject: RE: [EE] Miniature relay

How are you handling the voltage spike on switchoff?

-----Original Message-----
From: piclist-***@mit.edu <piclist-***@mit.edu> On Behalf Of Allen Mulvey
Sent: Wednesday, October 17, 2018 7:50 AM
To: 'Microcontroller discussion list - Public.' <***@mit.edu>
Subject: RE: [EE] Miniature relay

I am currently using Schrack RTE24005 DPDT relays. They are rated 8A @ 250VAC. They are bigger than the 1 and 2 amp micro-relays I sometimes use but they seem to handle almost anything I need.

https://www.mouser.com/productdetail/te-connectivity-schrack/rte24005?qs=CUfic%2FGsH5CuQV4J3ppyPg%3D%3D

Allen

-----Original Message-----
From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf Of Isaac M. Bavaresco
Sent: Wednesday, October 17, 2018 9:19 AM
To: ***@mit.edu
Subject: [EE] Miniature relay

Dear All,

I need a miniature PCB relay to operate a lock. The contact may be SPST-NO or SPDT-NO. The application may use a variety of different locks with voltages in the range of 6 V to 24 V AC or DC and the current up to
2 A.

For some applications I already use miniature telecom relays, but their current capability is at most 1 A or 2 A.

Does anybody know of some very small PCB relays with current capability of at least 4 A? SMD preferably but PTH acceptable, coil voltage of 5 V or 12 V.

Best regards,

Isaac


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[Isaac M. Bavaresco]

For DC coils I use a freewheeling diode.

Some clients use AC locks. Those are supplied with R/C snubbers to be
installed in parallel with the coil.

Cheers,

Isaac

Post by David Van Horn
How are you handling the voltage spike on switchoff?
-----Original Message-----
Sent: Wednesday, October 17, 2018 7:50 AM
Subject: RE: [EE] Miniature relay
https://www.mouser.com/productdetail/te-connectivity-schrack/rte24005?qs=CUfic%2FGsH5CuQV4J3ppyPg%3D%3D
Allen
-----Original Message-----
Sent: Wednesday, October 17, 2018 9:19 AM
Subject: [EE] Miniature relay
Dear All,
I need a miniature PCB relay to operate a lock. The contact may be SPST-NO or SPDT-NO. The application may use a variety of different locks with voltages in the range of 6 V to 24 V AC or DC and the current up to
2 A.
For some applications I already use miniature telecom relays, but their current capability is at most 1 A or 2 A.
Does anybody know of some very small PCB relays with current capability of at least 4 A? SMD preferably but PTH acceptable, coil voltage of 5 V or 12 V.
Best regards,
Isaac
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[Isaac M. Bavaresco]

Hi Allen,

This one has good specs but it is much bigger than the telecom ones, yet
much smaller than the ones that I have found so far.

If I cannot find a smaller one, it seems that this is the way to go.

Thanks,

Isaac

Post by Allen Mulvey
https://www.mouser.com/productdetail/te-connectivity-schrack/rte24005?qs=CUfic%2FGsH5CuQV4J3ppyPg%3D%3D
Allen
-----Original Message-----
Sent: Wednesday, October 17, 2018 9:19 AM
Subject: [EE] Miniature relay
Dear All,
I need a miniature PCB relay to operate a lock. The contact may be
SPST-NO or SPDT-NO. The application may use a variety of different locks
with voltages in the range of 6 V to 24 V AC or DC and the current up to
2 A.
For some applications I already use miniature telecom relays, but their
current capability is at most 1 A or 2 A.
Does anybody know of some very small PCB relays with current capability
of at least 4 A? SMD preferably but PTH acceptable, coil voltage of 5 V
or 12 V.
Best regards,
Isaac
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[Timmothy Relerford]

Just use a FET.

Regards,

Jim

-------- Original Message --------
Subject: [EE] Miniature relay
Date: Wed, October 17, 2018 8:19 am
Dear All,
I need a miniature PCB relay to operate a lock. The contact may be
SPST-NO or SPDT-NO. The application may use a variety of different locks
with voltages in the range of 6 V to 24 V AC or DC and the current up to
2 A.
For some applications I already use miniature telecom relays, but their
current capability is at most 1 A or 2 A.
Does anybody know of some very small PCB relays with current capability
of at least 4 A? SMD preferably but PTH acceptable, coil voltage of 5 V
or 12 V.
Best regards,
Isaac
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[Isaac M. Bavaresco]

I need galvanic isolation.

Thanks.

Post by Timmothy Relerford
Just use a FET.
Regards,
Jim

-------- Original Message --------
Subject: [EE] Miniature relay
Date: Wed, October 17, 2018 8:19 am
Dear All,
I need a miniature PCB relay to operate a lock. The contact may be
SPST-NO or SPDT-NO. The application may use a variety of different locks
with voltages in the range of 6 V to 24 V AC or DC and the current up to
2 A.
For some applications I already use miniature telecom relays, but their
current capability is at most 1 A or 2 A.
Does anybody know of some very small PCB relays with current capability
of at least 4 A? SMD preferably but PTH acceptable, coil voltage of 5 V
or 12 V.
Best regards,
Isaac
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[Brent Brown]

For a "medium-small" sized relay I'm currently using the Hongfa HFD41A, nominal
3A (max 5A) SPDT contacts...

https://nz.apexelex.com/specs/relays/HFD41_HFD41A.pdf

For smaller, quieter, and more expensive option you might try a Solid State Relay
(optocoupler). Some fairly impressive new Toshiba parts at DigiKey...

https://www.digikey.co.nz/products/en/relays/14?k=TLP35&newproducts=1

Problem of course is that, if used directly, they are not as tolerant to brief over
current events as relay contacts are.

Brent.

Post by Isaac M. Bavaresco
Dear All,
I need a miniature PCB relay to operate a lock. The contact may be
SPST-NO or SPDT-NO. The application may use a variety of different locks
with voltages in the range of 6 V to 24 V AC or DC and the current up to
2 A.
For some applications I already use miniature telecom relays, but their
current capability is at most 1 A or 2 A.
Does anybody know of some very small PCB relays with current
capability
of at least 4 A? SMD preferably but PTH acceptable, coil voltage of 5 V
or 12 V.
Best regards,
Isaac
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[RussellMc]

Post by Isaac M. Bavaresco
Dear All,
I need a miniature PCB relay to operate a lock. The contact may be
SPST-NO or SPDT-NO. The application may use a variety of different locks
with voltages in the range of 6 V to 24 V AC or DC and the current up to
2 A.

Be absolutely certain that the contacts are rated to handle the maximum AC
voltage that will be encountered.

The AC load spec is almost always far more stringent than the DC load spec
and failure to note this can cause relay failure at well below apparent
rated (DC) value.



Russell
.

[Martin McCormick]

Post by RussellMc
Be absolutely certain that the contacts are rated to handle the maximum AC
voltage that will be encountered.
The AC load spec is almost always far more stringent than the DC load spec
and failure to note this can cause relay failure at well below apparent
rated (DC) value.
Russell

Now, I am curious. Why would the AC load spec be more
stringent? It would seem to me that DC conditions would be worse
since the flow of current is always at it's peak unless one is
closing the contacts on an inductive load at which point it would
be less current while the field was building in the inductor. When
the contacts opened, there could be a nasty arc if the inductor
had built up enough magnetic field.

In AC, you sort of roll the dice and the contacts could
sometimes open or close right at a 0 crossing and nothing much
would happen as far as sparks or spikes. The peak voltage,
assuming a sine wave, would be roughly 1.4 times the RMS voltage.

What am I missing?

Martin McCormick WB5AGZ

[Harold Hallikainen]

Post by Martin McCormick

Post by RussellMc
Be absolutely certain that the contacts are rated to handle the maximum AC
voltage that will be encountered.
The AC load spec is almost always far more stringent than the DC load spec
and failure to note this can cause relay failure at well below apparent
rated (DC) value.
Russell

Now, I am curious. Why would the AC load spec be more
stringent? It would seem to me that DC conditions would be worse
since the flow of current is always at it's peak unless one is
closing the contacts on an inductive load at which point it would
be less current while the field was building in the inductor. When
the contacts opened, there could be a nasty arc if the inductor
had built up enough magnetic field.
In AC, you sort of roll the dice and the contacts could
sometimes open or close right at a 0 crossing and nothing much
would happen as far as sparks or spikes. The peak voltage,
assuming a sine wave, would be roughly 1.4 times the RMS voltage.
What am I missing?
Martin McCormick WB5AGZ

Also with an AC load, you get an arc quench every half cycle that you
don't get with DC. Choosing a random relay from Mouser:

https://www.mouser.com/datasheet/2/307/en-g5le-1131193.pdf

Rated load
Resistive: 10 A at 120 VAC; 8 A at 30 VDC
Inductive: 5 A at 120 VAC; 4 A at 30 VDC

Harold

[RussellMc]

Post by Martin McCormick

Post by RussellMc
Be absolutely certain that the contacts are rated to handle the maximum

AC

Post by RussellMc
voltage that will be encountered.
The AC load spec is almost always far more stringent than the DC load

spec

Post by RussellMc
and failure to note this can cause relay failure at well below apparent
rated (DC) value.
Russell

Now, I am curious. Why would the AC load spec be more
stringent?

Now I am curious!
Why did I write that ? :-) :-(.
I have transposed AC and DC and cannot imagine why I did so or why I did
not notice !!!
Sent at 19:18 according to header (NZT?) so I cannot excuse by lateness of
night.
Doh!

Yes, to all the rest, sort of.

With a capacitor it is intuitively 'obvious' that maximum AC voltage point
is the worst for closing a contact.
With an inductor "this is not the case". I am not going to risk a one
sentence explanation here :-) - rushing off to do "stuff" - so others may
wish to comment on the joys of closing and opening switches in AC loads.


Russell

[Sean Breheny]

For an inductive load, the steady-state condition is for maximum current to
coincide with zero voltage and maximum voltage at zero current.

When you suddenly connect an AC voltage source to an inductor, your current
initial condition is zero amps. If this happens at maximum voltage, then
steady-state conditions are obtained right away and there is no current
transient which must die-down before steady-state is achieved.

In the worst case, where you close the switch at minimum voltage, it will
take some time for the current to transition from the initial zero to a
sinusoid which lags the voltage by 90 degrees. This can be modelled as the
sum of the steady-state current plus an exponentially-decaying transient
current. As the resistance in the circuit goes toward zero, the peak value
of this sum approaches twice the steady-state peak value.

The math involved can be seen here (no guarantee given that there are no
errors !):

https://ibb.co/bDkORL

So, a 2x transient may not seem that bad but consider what happens if your
inductive load is close to saturation in steady-state operation. Twice the
current may put it well into saturation, and then the model I gave is no
longer true, since the inductance decreases during the transient, and the
final peak current may be 10x or more times the steady-state value. This is
especially a risk with transformers because the flux in their core is
typically maximum in the unloaded state (secondary open). Their core size
is determined primarily by heating from losses and in their desire to
minimize the size, weight, and cost of the transformer, they typically have
only a slight margin below saturation in the unloaded state. Transformers
routinely experience large transient current surges when suddenly connected
to the AC mains at a random phase.

Sean

Post by RussellMc
With a capacitor it is intuitively 'obvious' that maximum AC voltage point
is the worst for closing a contact.
With an inductor "this is not the case". I am not going to risk a one
sentence explanation here :-) - rushing off to do "stuff" - so others may
wish to comment on the joys of closing and opening switches in AC loads.
Russell
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[RussellMc]

Post by RussellMc
With an inductor "this is not the case". I am not going to risk a one
sentence explanation here :-) - rushing off to do "stuff" - so others may
wish to comment on the joys of closing and opening switches in AC loads.

Sean's very nice explanation (précis below) is what I was alluding to, but
put much better than I would have done.
It is not at all intuitive* that closing a switch at the zero voltage
crossing point can be the (very bad) worst case situation for an inductor.
* (for most people)(myself included before I had met the
situation)

*WELL WORTH BEING AWARE OF*

On Mon, 22 Oct 2018 at 20:18, Sean Breheny <***@cornell.edu> wrote:

For an inductive load, the steady-state condition is for maximum current to

Post by RussellMc
coincide with zero voltage and maximum voltage at zero current.

....

Post by RussellMc
In the *worst case*, where you *close the switch at minimum voltage*, it
will
take some time for the current to transition from the initial zero to a
sinusoid which lags the voltage by 90 degrees. This can be modelled as the
sum of the steady-state current plus an exponentially-decaying transient
current. As the resistance in the circuit goes toward zero, the peak value
of this sum approaches twice the steady-state peak value.

...

Post by RussellMc
*the final peak current may be 10x or more times the steady-state value*.

This is especially a risk with transformers because the flux in their
core is

Post by RussellMc
typically maximum in the unloaded state (secondary open). Their core size
is determined primarily by heating from losses and in their desire to
minimize the size, weight, and cost of the transformer, they typically have
only a slight margin below saturation in the unloaded state. Transformers
routinely experience large transient current surges when suddenly connected
to the AC mains at a random phase.
Sean