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> Is there a relay for a momentary switch ?
Biggie
Posted: August 06, 2003 03:10 am
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Hi,
Is there a relay that work with a momentary switch ?

I want to make a momentary switch act like a push on/push off switch. Can I do it ?
I was hoping there was a relay or similar that will do it.

Options ??

Hey, the only place near me to buy anything is radio shack. If they sell a relay or something else that will do the trick, can you link me please ??

Its to power a CCFL light in my computer case. 12V I believe.

(Newb here)

Thanks as always !
-B
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Nettron
Posted: August 06, 2003 03:24 am
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[quote]Is there a relay that work with a momentary switch ?[/quote]

Yes, its called a latching relay.

[quote]Hey, the only place near me to buy anything is radio shack. If they sell a relay or something else that will do the trick, can you link me please ??[/quote]

I doubt whether Rat Shack will have latching relays and if they did it would cost you about $29.99 each plus tx.

It would be far cheaper to get them from a surplus dealer such as All Electronics. Heres a link:


http://www.allelectronics.com/cgi-bin/cate...=500&type=store

I buy alot of my components there as well as from Jameco.


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Geek
Posted: August 06, 2003 06:07 am
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You can find inexpensive latching relays, perhaps surplus or removed from equipment, at an industrial electrical dealer that supplies factories or farms.


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Biggie
Posted: August 06, 2003 01:56 pm
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Thanks for the replies.
I checked that site nettron.
I only find 1 latching relay.
5 VDC LATCHING RELAY, DPDT

I need 12V, or will this also work ??
Please advise.

Thanks again,
-B

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Nettron
Posted: August 06, 2003 05:30 pm
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[quote]I need 12V, or will this also work ??
Please advise.
[/quote]

No that wont work hmmm....

Yeah seams they are sold out of 12V latching relays, I also checked Jameco and they dont have any either.

But Surplus Traders appears to have some. They have surplus Aromat latching relays. I had a pile of those very same 12 V Aromat relays awhile ago and they work great. But i later traded them for regular non-latching types for a project i was working on.

Heres the link:


http://www.73.com/a/0527.shtml

Browse their site they have lots of other cheap goodies too. wink.gif





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Biggie
Posted: August 06, 2003 06:05 pm
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Thanks nettron !
-B
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kor
Posted: August 06, 2003 09:25 pm
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You could also get a normal relay with... I forget, the ones I've used had 2 normally open and 2 normally closed contacts and make it latch yourself.
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Nettron
Posted: August 07, 2003 02:01 am
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[quote]You could also get a normal relay with... I forget, the ones I've used had 2 normally open and 2 normally closed contacts and make it latch yourself. [/quote]

Yep, good point Kor. You can make a ordinary non-latching relay behave in a latching manner by simply using the relay contacts themselves for supplying power to the relay coil, ive done this myself at times.

The only problem is that half the contacts on a DPDT relay will be used for latching. So actually it will then be a single pole latching relay.

Another option if you cant afford to use the contacts in that manner is to use a simple set-reset flip-flop circuit ,controlled by the momentary push button, to energize the relay coil.



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Biggie
Posted: August 27, 2003 09:01 pm
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Hi all,
I tried that place nettron and they will only sell 50 units.

They list 2 12v latching relays on that side.

Aromat #RS-L2D-12V small sealed dual coil latching relay. SPDT contacts rated 1 amp @ 30 VDC/ 0.3A @ 125 VAC. 2,700 ohm coils. 0.787" x 0.394" x 0.394" case. PC leads. UL, CSA

..and..

Communications Instruments Inc. #MQP12L DPDT, 1 amp contacts. 12 VDC, 1400 ohm coil. 0.35" x 0.55" x 0.2" high

I need to ask another question.
What specs do I need to look for when trying to find the latching relay I need ?
ie: other than 12v, what do I need to make sure of spec wise to make sure I get the correct item ??

I read the last 2 posts, but I do not know to do either one.
I am at the beginner stage.

Any help is appreciated !
-Big
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kor
Posted: August 28, 2003 01:36 am
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Basically, you're looking at contact voltage and current. The coil voltage and resistance simply tell you how much current you need to supply to it which helps you design the supporting circuitry.

The contact voltage and current is what can be applied to the contacts, the part that you're switching.

I covered relays in my very first electronics class, and never since.
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Nettron
Posted: August 28, 2003 02:16 am
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Looking back at your original question you wanted a momentary pushbutton circuit for a CCFL light in your computer . Whats a CCFL light ? and how much current does it draw ?
You need to know this for choosing a relay.

Relays are mainly used in high current switching circuits. Im not sure if you really need one in your case, but any way heres a schematic which shows how to convert a normal non-latching relay into a latching relay.

user posted image


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Nettron
Posted: August 28, 2003 02:20 am
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...and heres another that uses a Flip-Flop circuit :

user posted image



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Nettron
Posted: August 28, 2003 03:58 am
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Heres one that uses just one switch for on-off control.

Its not one of mine so i cant post the schematic here. I was corresponding with the author and it appears the circuit as a few problems to iron out. But certainly worth considering.



http://electronicsworld.tripod.com/designi...designckt1.html


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