Anyone know of a good cheap relay for 120VAC needing low coil power

[[email protected]]

I'm trying to use my little AVR to control up to 12 120VAC loads, up to 5
amps.  Does anyone know of a cheap (< $5 US) relay (SPST-NO) that only
needs 40 mA or less to activate?  My Tyco T77 relays need 90 mA at 5VDC to
pull in the contacts, it turns out, so the processor dies. The lowest I've
found on-line is 60 mA. I don't have a harsh environment, or rapid
switching requirements, just need a simple on-off relay.  I'm switching
banks of lights, should look cool if I can get it to work.  Thanks for any
advice.

Mike Ross

--

 

[CheapscateDave]

I would get a 1.5 amp wall wort to power the relays and use some NPN
transistors as relay drivers. There are even IC circuits if you don't
want to use transistors. This may be cheaper than buying new relays.
Dave

 

[CheapscateDave]

http://www.google.com/search?hl=en&q=ULM2003&btnG=Google+Search

 

[[email protected]]

I'm trying to use my little AVR to control up to 12 120VAC loads, up to 5
amps. Does anyone know of a cheap (< $5 US) relay (SPST-NO) that only
needs 40 mA or less to activate? My Tyco T77 relays need 90 mA at 5VDC to
pull in the contacts, it turns out, so the processor dies. The lowest I've
found on-line is 60 mA. I don't have a harsh environment, or rapid
switching requirements, just need a simple on-off relay. I'm switching
banks of lights, should look cool if I can get it to work. Thanks for any
advice.

Mike Ross

--

Hi, Mike. In order to get that kind of current rating, you need some
distance between the contacts, thus more power to pull them in. I
don't believe the beastie you're looking for exists.

The best solution might be to go with some solid state relays. They'll
require only a few mA to drive the internal opto-triac LED, and many
can be driven directly from the AVR pin.

If you gotta have relays for some reason, and you've got some AVR pins
to spare, you might want to look into magnetically latching relays.
The magnetically latching relay has two coils -- one to set, and one to
reset. Although they'll require more current than you can afford, each
coil only has to be pulsed (100ms. or so) to change the relay state.
You can use a resistor to slowly charge a local cap, which can be used
for the coil power to turn on or off the relay, like this (view in
fixed font or M$ Notepad):
|
|VCC
| +
| | ___ More relays
| '-|___|-o------o--o-----o--o----->
| R | | |RY1A | |RY1B
| +| - C| - C|
| C --- ^ C| ^ C|
| --- | C| | C|
| | | | | |
| | '--o '--o
| === | |
| GND |/ |/
| -| -|
| | |> | |>
| .-. | .-. |
| | | | | | |
| | | === | | ===
| From AVR '-' GND '-' GND
| | |
| >-------------' |
| >----------------------'
|
(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

Latching relays are sensitive to vibration, and obviously don't turn
off by themselves at power down, but your description indicates that
might not be too much of a problem.

But still, SSRs seem to be your best bet.

Good luck
Chris

 

[Phil Allison]

<[email protected]

I'm trying to use my little AVR to control up to 12 120VAC loads, up to 5
amps. Does anyone know of a cheap (< $5 US) relay (SPST-NO) that only
needs 40 mA or less to activate? My Tyco T77 relays need 90 mA at 5VDC to
pull in the contacts, it turns out, so the processor dies. The lowest I've
found on-line is 60 mA. I don't have a harsh environment, or rapid
switching requirements, just need a simple on-off relay. I'm switching
banks of lights, should look cool if I can get it to work. Thanks for any
advice.

** For heaven's sake - add a darn relay driver IC !




........ Phil

 

[Sal Brisindi]

I'm trying to use my little AVR to control up to 12 120VAC loads, up to 5
amps. Does anyone know of a cheap (< $5 US) relay (SPST-NO) that only
needs 40 mA or less to activate? My Tyco T77 relays need 90 mA at 5VDC to
pull in the contacts, it turns out, so the processor dies. The lowest I've
found on-line is 60 mA. I don't have a harsh environment, or rapid
switching requirements, just need a simple on-off relay. I'm switching
banks of lights, should look cool if I can get it to work. Thanks for any
advice.

Mike Ross

Hi Mike,
Why don't you use a optoisolator and a triac. Much cheaper than a relay
and will use hardly any current to switch them on/off.

Regards,
Sal Brisindi
http://www.tuberadios.com

 

[[email protected]]

Mike, at first I believed you were out of luck, but tonight in my
Newark Electronics catalog I ran across this interesting little number:

Siemens RY610005, Coil current 44.0 ma., coil resistance 113-ohms,
contact rating 8A at 250VAC, Price in quantities from 1-99 is $3.15.
Seems perfect for a 5V power relay..

This is likely a 1999 price (Catalog 117), but you can likely check it
out on www.newark.com.(Damn, if this thing existed years back, think of
the lives all all of the 2N2270 relay drives whose lives could have
been saved!

Good luck.

Harry C.

 

[Sal Brisindi]

I'm trying to use my little AVR to control up to 12 120VAC loads, up to 5
amps. Does anyone know of a cheap (< $5 US) relay (SPST-NO) that only
needs 40 mA or less to activate? My Tyco T77 relays need 90 mA at 5VDC to
pull in the contacts, it turns out, so the processor dies. The lowest I've
found on-line is 60 mA. I don't have a harsh environment, or rapid
switching requirements, just need a simple on-off relay. I'm switching
banks of lights, should look cool if I can get it to work. Thanks for any
advice.

Mike Ross

Mike,
To get an idea how to connect the optoisolator take a look at this link.

http://users.tkk.fi/~jalapaav/elektroniikka/triac/triac2s.gif

Regards,
Sal

 

[Spehro Pefhany]

On Wed, 31 May 2006 00:08:23 GMT, the renowned

I'm trying to use my little AVR to control up to 12 120VAC loads, up to 5
amps.  Does anyone know of a cheap (< $5 US) relay (SPST-NO) that only
needs 40 mA or less to activate?  My Tyco T77 relays need 90 mA at 5VDC to
pull in the contacts, it turns out, so the processor dies. The lowest I've
found on-line is 60 mA. I don't have a harsh environment, or rapid
switching requirements, just need a simple on-off relay.  I'm switching
banks of lights, should look cool if I can get it to work.  Thanks for any
advice.

Mike Ross

Use a higher voltage relay coil, such as 12V, and get one rated for *a
tungsten load* *at the current you need to operate at*. You will
probably need 1W at least per coil to meet your stated requirements.

Using a low coil current relay on a tungsten load at a rating anywhere
close to the resistive rating is just asking for very short life at
best, and welded contacts at worst.

A typical cheap-ass '30A' (resistive) relay such as the T90 might be
derated to 5A with a tungsten load.

You can easily use triacs, but the disadvantages are severe-- the heat
loss at 10A will be quite large (so big heat sinks to keep the triacs
from failing), and lamps of any size will kill the triac when they
burn out unless you significantly overrate the triac and use a good
fuse.

The only relatively inexpensive one with sufficient ratings that comes
to mind atm is the T92, which has a coil power of around 1.7W for DC
coil units, and costs around $5 US in moderate quantity. Check that
the life is sufficient for your application. Data sheet values for
this item are umm.. 'not necessarily pessimistic'.

Small definite purpose contactors will have longer life, but they are
noisy (acoustically and electrically) and are generally nasty beasts.

 

[K `Sleep]

I do know of really cheap, inexpensive switching transistors that can
drive practically any small relay you will find... called a 2N2222 or
2N3904.

 

[Phil Allison]

<[email protected]

I'm trying to use my little AVR to control up to 12 120VAC loads, up to 5
amps. Does anyone know of a cheap (< $5 US) relay (SPST-NO) that only
needs 40 mA or less to activate? My Tyco T77 relays need 90 mA at 5VDC to
pull in the contacts, it turns out, so the processor dies. The lowest I've
found on-line is 60 mA. I don't have a harsh environment, or rapid
switching requirements, just need a simple on-off relay. I'm switching
banks of lights, should look cool if I can get it to work. Thanks for any
advice.

** For heaven's sake - add a darn relay driver IC !


AND DO NOT RESTRICT REPLIES LIKE YOU HAVE !!!!


ARRRRRRRRRGGGGGGGGHHHHHHH !!!!





........ Phil

 

[ehsjr]

I'm trying to use my little AVR to control up to 12 120VAC loads, up to 5
amps. Does anyone know of a cheap (< $5 US) relay (SPST-NO) that only
needs 40 mA or less to activate? My Tyco T77 relays need 90 mA at 5VDC to
pull in the contacts, it turns out, so the processor dies. The lowest I've
found on-line is 60 mA. I don't have a harsh environment, or rapid
switching requirements, just need a simple on-off relay. I'm switching
banks of lights, should look cool if I can get it to work. Thanks for any
advice.

Mike Ross

You didn't mention the voltage. An Omron G6RN-1A-12 will carry
up to 8 amps resistive at 250 VAC and needs only 18.3 mA at 12
volts. The 5 volt version of that relay takes 44 mA.
Mouser part # 653-G6B-1114P-DC5 is an Omron 5 V coil, 40 mA
SPST that will carry 5 amps resistive at 250 VAC

Is there a reason you can't use a driver transistor with your
Tyco relays? That's the cheapest solution.
Ed

 

[Jasen Betts]

I'm trying to use my little AVR to control up to 12 120VAC loads, up to 5
amps.  Does anyone know of a cheap (< $5 US) relay (SPST-NO) that only
needs 40 mA or less to activate?

a solid-state relay.

 My Tyco T77 relays need 90 mA at 5VDC to
pull in the contacts, it turns out, so the processor dies. The lowest I've
found on-line is 60 mA. I don't have a harsh environment, or rapid
switching requirements, just need a simple on-off relay.  I'm switching
banks of lights, should look cool if I can get it to work.  Thanks for any
advice.

For switching lights an optocoupled triac is probably the way to go (cheeper
than SSR), look at the MOC3010 data sheet.

 

[Pooh Bear]

a solid-state relay.


For switching lights an optocoupled triac is probably the way to go (cheeper
than SSR), look at the MOC3010 data sheet.

Don't forget to derate the current rating for lamp loads.

Graham

 

[[email protected]]

Hi Mike,
Why don't you use a optoisolator and a triac. Much cheaper than a relay
and will use hardly any current to switch them on/off.

Regards,
Sal Brisindi
http://www.tuberadios.com

Wow, lots of good replies, thanks for all the fine advice. With help from
this group, I found a part at DigiKey, an Omron 10A contactor needing only
40 mA to pull on. This was the easiest solution to implement, not
necessarily the best way to go, but I think it will work. I'm hoping that
derating by half will be sufficient to drive 5A of HPS lighting without
trouble. Thanks to all.

Mike Ross


--

 

[[email protected]]

Mike, Siemens as a line of PC board mounted relays that draw 44 ma at 5
Volts, and can switch 8 Amps @120V. They're priced in the $3.00 range.
(I found them in the Newark Electronics catalog.

If you would like the model numbers and more specifics, post a
followup.

Harry C.

 

[Tim Auton]

I'm trying to use my little AVR to control up to 12 120VAC loads, up to 5
amps.  Does anyone know of a cheap (< $5 US) relay (SPST-NO) that only
needs 40 mA or less to activate?  My Tyco T77 relays need 90 mA at 5VDC to
pull in the contacts, it turns out, so the processor dies. The lowest I've
found on-line is 60 mA. I don't have a harsh environment, or rapid
switching requirements, just need a simple on-off relay.  I'm switching
banks of lights, should look cool if I can get it to work.  Thanks for any
advice.

Are you sure about that 40mA spec? That's the limit per pin in the AVR
datasheets I've got to hand, but there are other limits - on total
current on Vcc and GND and for various combinations of ports. For
example, with the ATmega 128, there's total limit of 400mA in or out
(you need 480mA for 12 40mA relays), and further limits depending on
which ports you planned to use. Check the notes in the Electrical
Characteristics section of the datasheet carefully.

I'd go for an IC to drive the relays. You can get your freewheeling
diodes built-in and enough drive for whatever relays you fancy,
without stressing the AVR's outputs. No more soldering or board space
then the diodes alone and it may even pay for itself by allowing you
to choose from a wider range of relays.


Tim

 

[DaveM]

I'm trying to use my little AVR to control up to 12 120VAC loads, up to 5
amps. Does anyone know of a cheap (< $5 US) relay (SPST-NO) that only
needs 40 mA or less to activate? My Tyco T77 relays need 90 mA at 5VDC to
pull in the contacts, it turns out, so the processor dies. The lowest I've
found on-line is 60 mA. I don't have a harsh environment, or rapid
switching requirements, just need a simple on-off relay. I'm switching
banks of lights, should look cool if I can get it to work. Thanks for any
advice.

Mike Ross

I don't think you need low power relays... your money would be better spent on a
proper interface between the AVR port and the relays. A simple transistor
between the AVR output and the relay would let you use your existing relays and
would amount to a few cents per relay.
You didn't indicate whether the AVR output is high or low when the relay should
turn on, so first, I'll assume that it's low. In that case, use a PNP
transistor (such as a 2N2907). Connect it as such:

Please view in a fixed-width font such as Courier.


+----------+ +5V
| | |
| | |
| AVR | |
| | |
| | |
| | | E
| | 10K /
| | +------+ |/
| +--------+ +------| 2N2907
| | +------+ B |\
| | \
| | |C
| | |
| | |
| | +-+-+
| | | |
| | | |
| | | | Relay coil
| | | |
| | | |
| | +-+-+
| | |
| | |
| | --+--
| | ---
| | -
+----------+



In case the AVR output is high when the relay should be on,
use an NPN transistor (such as a 2N2222) like this:

+5V
|
|
+-+-+
| |
+----------+ | |
| | | | Relay coil
| | | |
| AVR | | |
| | +-+-+
| | |
| | |C
| | 10K /
| | +------+ |/
| +--------+ +------| 2N2222
| | +------+ B |\
| | \
| | |E
| | |
| | |
| | --+--
| | ---
| | -
| |
+----------+

Total cost per output: about $0.50 US

Cheers!!!!

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Some days you're the dog, some days the hydrant.

 

[Brian]

I'm trying to use my little AVR to control up to 12 120VAC loads, up to 5
amps. Does anyone know of a cheap (< $5 US) relay (SPST-NO) that only
needs 40 mA or less to activate? My Tyco T77 relays need 90 mA at 5VDC to
pull in the contacts, it turns out, so the processor dies. The lowest I've
found on-line is 60 mA. I don't have a harsh environment, or rapid
switching requirements, just need a simple on-off relay. I'm switching
banks of lights, should look cool if I can get it to work. Thanks for any
advice.

Mike Ross

You might want to use a MOSFET (like a 2N7000) to drive the relays. Or maybe
a Darlington array, something like the ULN-2803A. This would be easier on
the AVR and also make the relay selection less fussy.
Brian

 

[Brian]

I'm trying to use my little AVR to control up to 12 120VAC loads, up to 5
amps. Does anyone know of a cheap (< $5 US) relay (SPST-NO) that only
needs 40 mA or less to activate? My Tyco T77 relays need 90 mA at 5VDC to
pull in the contacts, it turns out, so the processor dies. The lowest I've
found on-line is 60 mA. I don't have a harsh environment, or rapid
switching requirements, just need a simple on-off relay. I'm switching
banks of lights, should look cool if I can get it to work. Thanks for any
advice.

Mike Ross

You might be better off using transistors, mosfets (like a 2N7000) or a
Darlington array (like a ULN-2803A) to drive the relays. It would be easier
on the AVR and it would probably be easier to find lower priced relays.
Brian