How to build a remotely controlled dpdt "impulse" switch?

[willlllbur]

"that's a relay" you say?

I've been trying to find this relay for two weeks without success. Turns out it's just not produced.

I need an electromechanical (no ICs or pcbs) dpdt 'impulse' relay, sometimes called a flip-flop. The 'impulse' label is used pretty freely with relays, but there is really only one exact type that it fits, it is a special form of latching relay. A signal/current of one polarity is used to switch the relay status and the relay remains latched even when the current is removed. A second signal/current of the same polarity, from the SAME switch/source brings changes the relay status back and it latches. One momentary switch press to latch on, same momentary switch, press again, latch off.

I cannot use microcontrols for some rather complicated reasons.
This isn't a homework assignment. I've been asked that before. I'm adding a process to a tig welder that uses extremely powerful HF in the arc and I'd like to avoid IC timers and microcontrol as much as possible. I also need this switch to remain in last chose state when power is taken away. A microcontroller will not do that unless backed up with a battery - another headache to avoid using a purely mechanical solution.

There are a few industrial controls that accomplish this with internal changeover/latching cams. I can't seem to find one that is 'ice cube' sized or pcb mountable. I only need to switch half an amp 120vac. The coil rating needs to be low enough to make use of a tiny 'tact' spst membrane switch.

Unless I can get any better suggestions, (ideally, an actual relay from a manufacterer) I'm going to have to get a 12vdc push solenoid and hack it together with a little dpdt latching pushbutton. Ugly.. but essentially what I'm needing.

Any ideas?

[chipmonk]

Hi willlllbur
is it something like this http://www.factorymation.com/s.nl/it.A/id.5812/.f?category=16336

pete

[Zlatko]

willlllbur,

Another thought... how about a push on/ push off switch mechanically linked to a small solenoid that is activated by a momentary switch?
You can probably even modify a normal relay by adding a push on / push off switch to be driven by the relay/ solenoid arm... ( dremel and some elbow grease mandatory )
since you only need 0.5A max ...

Chears

[willlllbur]

chipmonk,

That's precisely the function I'm looking for. As they describe it themselves..

The 711 Impulse Sequencing relay is an alternating relay used for load sharing or toggling ON/OFF of the load. Unidirectional momentary pulses cause the contacts to transfer from one side to the other. There is no need to redirect the polarity of the input in order to change and maintain states.

Problem is, this relay is about three inches tall and two inches wide. I just don't have that volume inside this project. And I also have a hunch that the coil on this monster will draw more amperage than a little microminiature 'tact' switch is rated for. I'd have to add yet another relay to manage the Magnecraft.

Zlatko,

Thank you for that, you arrived there quicker than I did when I had begun this quest. I did, however get there eventually, and described pretty much the same in the last line of my post above. The effort is very much appreciated however.

The answer to this is probably going to be applying a borrowed ratchet (your second suggestion), perhaps something like a click on/off ball point pen mechanism, to the arm of a standard dpdt relay.

Just a damn shame I can't buy one of these, that's all.

[Zlatko]

willlllbur,

I don't know where you live, but did you look at www.digikey.com ?
I've had stuff shipped from them to Australia cheaper and faster than some of the Australian distributors could do. Plus, they have an immense range of products.

search for " latching relay " then select " signal up to 2 A .... "

click on "in stock", apply filters, click on "DPDT" and apply filters again.
click on "viev page" ... they are rated at up to 30V DC ... but I think they will be fine for 0.5A at 120V AC ... ?

For instance PN 255-1005-5-ND is $3.16 and 1A @ 30VDC 0.5A@125VAC 1.5g ( 0.053 oz ) dim ... 14mm x 9mm x 5mm PCB mount ? Good?

Cheers

[willlllbur]

Zlatko,

You're beginning to see why this is so maddening. All of these latching relays require separate switches to control them. I'm trying to accomplish this with one momentary. If you look into the data sheets you'll find that it is necessary to change polarity (separate switch) to change the state of a single coil, or apply current to another set of pins (separate switch) to change the state of a dual coil.

I have not found a signal (not power) latching relay at digikey, mouser, maplin, newark, et al, that is this type of 'impulse' relay. It just does not exist unfortunately... until someone proves me wrong.. hopefully.

[Zlatko]

willlllbur,

Sorry, I didn't look close enough at the datasheets ... :(

I was just thinking , perhaps you could use one with 4 DPDTs and use one pair to reverse the polarity to the coil ... but ... that would just turn it into a vibrator ... :(
Also .. I think these types of relays would be affected by the magnetic fields.

I like the ball point pen idea .. can you get it small enough?

Cheers