control a latching relay with one switch?

Caveman

Joined Apr 15, 2008
471
There is a way, but I've got to try to remember, it basically involves passing the current back and forth through a capacitor. I'll try to get back to you within the day to let you know if I remember.
 

beenthere

Joined Apr 20, 2004
15,819
Single coil is the only one that will work with one switch. How much of a load are you switching? I've been using a P & B 12 volt latching relay to run a set of lights in my basement for 8 years. From 5 locations, at that (all the pushbutton switches are in parallel).
 

beenthere

Joined Apr 20, 2004
15,819
Check the Potter & Brumfield S89R11DAC1-12 impulse latching relay. It changes state with each application of voltage - no polarity reversal needed. It's goo for 15 maps @ 120 VAC. A momentary pushbutton switch is all it needs, along with the coil voltage.

I see your problem now. These are way too big for your application. You may need to use KMoffett's trick.

Another thought - if this is a weenie DIP relay, you might think about using a flip-flop that is toggled by the switch. Each debounced press of the switch toggles the flip-flop to the next state, supplying of cutting off current to the relay coil.
 
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SgtWookie

Joined Jul 17, 2007
22,230
Hello Anne,
Have you considered push-on, push-off switches to control the relay's coil?


Since the length of the button's exposed shaft changes, you really wouldn't need a lit indicator - unless you wanted to be able to observe it while wearing a welder's mask. A small LED with a suitable current limiting resistor would serve in that regard.
Ebay auction:
http://cgi.ebay.com/10-Miniature-DP...oryZ4660QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

You could use this switch to control the coil of a low-voltage relay. This one is DPDT; each contact rated 100mA @ 30v
 
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SgtWookie

Joined Jul 17, 2007
22,230
Here's a likely candidate...
http://www.hosfelt.com/en-us/dept_111.html
Third item from the top. At this price I can experiment to my hearts' content. I'll order half a dozen of 'em.
Quite a bargain!

I went a searching for 'flip-flop' circuits. Is this beyond beginner level?
The problem with using flip-flops is that they would "forget" their logic state when the power was turned off.
An example of a Dual-D Flip Flop would be a CMOS 4000-series 4013, or CD4013B (many different manufacturer part numbers), a J-K Flip Flop would be a 4027 (CD4027B) etc. But, unless you kept them supplied with voltage, they'd "forget".

I guess my 'problem' is that I have sufficient imagination to find use for all the little 'black boxes" in the catalogs. When I need to open them up I get in trouble.
Everyone's been there at least several times. If they deny, they lie. ;)
 

beenthere

Joined Apr 20, 2004
15,819
The short answer is no. The contacts will burn with too much current, and they may not separate enough to stop arcing with 120 VAC applied. You may have to consider a solid state relay to keep package size down. You could use a pushbutton switch, but it would have to be alternate action (maintained contact).
 

SgtWookie

Joined Jul 17, 2007
22,230
The type of switch I posted is in common use on items like test equipment (oscilloscopes, frequency counters, etc.) No, it would not be suitable for 120v switching, but would be for 24v, 12v, 6v, 5v, etc. I do know that Skycraft Surplus has (or had) in stock some VERY small 120v to 6.3v or 7.5v transformers, which might be used to supply current to this switch, to power a relay's coil. I do not recommend running a component at it's maximum ratings, as it's lifespan will be considerably diminished.

You seem to have your mind set on a switch-controlled relay. Would it be possible for you to consider something like a micro SPST, DPST, or DPDT toggle switch? Sometimes the simplest route is the best.

I don't know if this is the same project you were working on before, but I suspect that your space constraints are rather tight. Cost is always a factor.

Those tiny latching relays you found seem rather promising. Price is right, too.
 
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