I am literally pulling my hair out.

A week ago I decided I needed to control two circuits of 120vac low amperage
(less than 500ma) with a single pushbutton. I have a tactile type button beneath a plastic membrane (like your cell phone) that I can use to relay these circuits from bothon/bothoff. Suffice it to say that I have no options at the user control point. I cannot use a dpdt pushbutton on the panel. I have to use a single momentary to toggle power dpdt style.

I saw immediately that a dpdt relay would be necessary, with a low enough voltage/amperage on the coil to operate it with the pushbutton. Ok so far. Then I went to Digikey to get a relay that would alternate, and latch, using the pushbutton..... the same pushbutton. Push on... push off.

Within a few hours I was seeing stars. I'm told by many experts that this cannot be done without microprocessing. The only other options are expensive and extremely bulky industrial relays rated from 30 to 100 amps.

But I can actually accomplish this myself with a little 12vdc push solenoid and a dpdt latching pushbutton! I hate like hell to have to cobble something this ugly together. I'm F L A B B E R G A S T E D that this is such an impossible feat to accomplish. I sit with a pencil and paper and try to get three dpdt dual coil latching relays to do this by bouncing off of one another and all i get is a headache and bad memories of the logic section of the LSAT! Why can't I buy this? Waaaaaaah. I'm going to cry like a child pretty soon.

I've found flip flop pcb units that almost do what I need. They are too complex and, more importantly, lose their status upon deenergizing (requiring another layer of complexity with diodes and batteries to keep 'memory' on the circuit).

As well as losing the last 'condition' of the relay if I use cmos, 555 timers, et al, I really need a purely electromechanical solution since this is going to be used in a welding project that will be exposed to extreme HF at times. That does funky stuff to homemade circuits.

I've actually talked with no less than half a dozen engineers at the major relay manufacturers and they've all seemed pretty stumped as to why I'd want to do this. I feel like I landed on another planet. The web is chock full of posts from people trying to accomplish this with rube goldbergian spagetti messes of relays, connectors, diodes, transistors, etc, etc.


So picture a small barrel type solenoid acuator.... 12vdc coil..... depressing a dpdt latching microswitch.... and this inside of a little plastic cube that is pcb mountable. Does anyone manufacture this thing??? A volkswagen headlight relay does it. It's 12vdc. But it's bulky, way overrated contacts for my needs, and only spdt. I'd have to add another relay to it yet. Another messy solution.

Please, dear god, help me. If you guys can lead me to the light you will be superheros and will have stumped all the "experts" on top of it.

Thank you. I'll calm down now and take a few steps back. I'll have a beer. I'll be back tomorrow on tenter hooks...

 

It's never to late to learn about microcontrollers.

__________________
Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com

 

What you need is what's called a single coil magnetic latch relay. Ever see those score boards that have discs that flip over to spell/show numbers etc? They have a magnetic pole piece that will hold in place until pulsed again.

Few companies make these things, but you can get them. Machinery controls used to have them, to reduce power consumption/heat in a large control system. Aslo it would avoid mechanical riots if parts of a system went down.

Magnecraft still sell some, check this link to get an idea:

Item # 755XBXC-24A, 755 Magnetic Latching Octal Relay / DPDT, 16 Amp Rating on Magnecraft

There are some really tiny ones that use the same mechnical linkage as a push on-push off switch on the actuator. They respond like a retractable pen.


Here is another maker, willow

PCB POWER

 

Google got me this page
Latching relay controlled by single pushbutton
using the search phrase "Single push button latching relay"

The one about using a flip flop seems promising. Mind you I definitely agree with blueroom, it's never too late and will solve about a billion headaches to learn the basics of using a cheap micro controller, and the HF a welding rig can put out will have to be filtered no matter what. Once you have one though feature creap becomes a problem, because they're so useful for so many different things that they eventually embed themselves in your way of thinking. Keep in mind, the cheapest AVR I have only costs 50 cents. To drive relays or 'real' loads you only need a few transistors, and the device suddenly becomes 'intelligent'.

__________________

 

Hi wsemajd,

all you need is a so called ELTACO, a relay used in home electric appliances such as lamps to be controlled from different locations. (They are also called current pulse latching relays.)

You won't need any microcontroller for that simple task. (Bill, shame on you!)

Those ELTACOs work with mains power and can be used like a normal switch. You can connect any number of pushbuttons in parallel to operate the circuit.

This is not an electronic issue, but an electric one.

Try to find one at your local electric shop. I'm sure they have those latching relays on stock. Here are three sample numbers (ABB): ABB-E251-110 (single closing contact 110VAC operation), ABB-252-110 (dual closing contact 110VAC operation) and ABB-262-110 (one NO and one NC contact 110VAC operation) Also check out ABB before consulting the electric shop. (ABB = Asia Brown Boveri)

The function is very simple: Push once - light on, push the second time from any other location (or the same) - light off.

WARNING: As soon as your kids have found out how the pushbuttons work they will not stop playing with them.

Regards

Hans

 

Here's another one by Tyco, goes for about $1.50 at places like Digikey

RT424A05 Product Details - Tyco Electronics

 

This relay is DC operated and requires reverse connection to switch off! (Reverse connection with the same button?) The ABB relay is AC operated from mains power and requires just a second current pulse to switch off. Addionally that relay can handle loads up to 16A.

Boncuk

 

Thank you all so much for the responses. I'm afraid I'm not really any closer.

I do not want to use a microcontroller for this. I've already had problems filtering HF in circuits around this rig and it's troublesome. I agree completely that pcb microcontrol would be a highly useful skill to learn. I'm sure I will find dozens of uses for it in future projects... I'll look into it soon. It's just too steep a learning curve for what I want to accomplish right now. An electromechanical latching pushbutton dpdt. I'm just a welder who enjoys tinkering with gadgets.

Boncuk, that is exactly the idea. Unfortunately I came across those already (altho it took me a couple of days). The ABB relays were among others I've already come across and was referring to as "expensive and extremely bulky industrial relays rated from 30 to 100 amps" (I should have said 15 to 100 amps) These are all way too large in any case to even fit onto the board of this project. And overrated by anything exceeding 500ma.


zevon8, You mentioned another relay of this same style and then went on to say...

"There are some really tiny ones that use the same mechnical linkage as a push on-push off switch on the actuator. They respond like a retractable pen."

This is EXACTLY what I'm searching for. Did you actually come across any examples of this?

 

The link to the products by Willow are available in AC coils, so polarity is not an issue. It will likely be very hard to find something much smaller than the ones they offer. For DC coils, yes the polarity is often required to be reversed, I forgot to check the one I linked to above.

 

boncuk, I give in...

Magnecraft - 711XBXCL-12D - Allied Electronics

It's fifty bucks cheaper than other versions I've seen. Throwing in the fact that I anticipated using led status lights on my panel, and this thing already has them there for me to just extend there, cinched it for me. I imagine if I take the plastic cover off I can reduce the size enought to shoehorn it somewhere into this project.

Minimum coil demand for switching is 100ma @5vdc. I can actually use 8vdc that I have available in the machine. 12vdc would be easier. Will the momentary power switch that I'm cannibalizing from my old toshiba laptop handle this ok?

Thanks for sending me back to reconsider these things.

 

Hi wsemajb,

glad to hear you found something suiting your needs.

If that relay has an operating voltage of 5V I would consider to apply a current limiting resistor for two reasons: The coil might fry at a steady high voltage and last not least the current consumption will encrease considerably.

The ABB relays I suggested are normally to be mounted in a distributor cabinet, and of course they have to be bulky because of the high switching current.

If you just want to operate at low DC I suggest to have a look at Finder Home Page

They offer a small size latching relay available for 6/12/24V DC operation and capable of 16A/250VAC load current. Check for relay type 40.61

This type of relay requires a very short DC pulse (reversed) to disengage.

Regards

Hans