Turn on relay by default, turn off when push button press

Reloadron

Joined Jan 15, 2015
5,916
Thanks, Ron, this indeed is the circuitI was describing., even drawn with standard symbols. And all of your comments are exactly on target. Doing this with an arduino would be a whole lot more complex, more expensive, and much less reliable.
Yeah, it can be done using a uP (Micro-Processor) and any of a few dozen of them. I just figure micro-controllers have their place but something like this is a few buttons and a relay. Most of us saw and placed a thousand of them in our career.
Simple, basic crude and reliable.

Ron
 

MisterBill2

Joined Jan 23, 2018
8,481
View attachment 198597

You know more than I.
You know this will work.
Maybe you should help.
OK, when the start button is pressed there will be a DC voltage impressed across the SSR control to engage it. So yes, 12 hours later I see that it could work. It was an error on my part to say that it would not work. It was also 4:30 AM when I made that evaluation. It does add a fair amount of power dissipation in that added resistor.
I understand that there is an effort to avoid adding a second relay that would only serge to support the latching function. But what is wrong with adding one more low powered and inexpensive part? The other benefit is that it allows all of the controls circuitry to be done in complete isolation from the mains power.
 

danadak

Joined Mar 10, 2018
4,057
Relay logic does not need contact debouncing. Why junkify a well proven very reliable arrangement with a toy processor?
IN ADDITION, the TS mentioned in their fourth sentence that they did NOT want to use an arduino. That alone is a good reason to not consider it.
A nice 32 bit RISC processor with some analog to boot, my feelings are hurt :) There is, as I am sure you know, a ton of people using these
in non toy applications, youtube, web, full of some interesting stuff done with them. Its not my first processor of choice, but ATTINY85 is a great
hobbyist foray into the dark world of processors

"IN ADDITION, the TS mentioned in their fourth sentence that they did NOT want to use an arduino."

And my curiosity led me to asking the question, but why ? Maybe a bad habit I have, but I am a proponent of
using processors since 1972. I see at AAC a lot of timer use, really old timer use, discrete logic, and always thinking
crappy accuracy over T & V, lousy flexibility, more interconnect (less reliability), more components to do a given job,
power up transients, thats not exactly a path of enlightenment. When I ask "WHY" I have had some interesting
diverse answers, from "I do not understand" to "I had a bad experience" to " I hate them and don't know why"..........

But I also believe once shown don't shove, if a person wants to stay in RTL and DTL logic world thats a legit choice,
just leave the seeds of progress behind to hatch another day and support the path they have chosen. Thats all any
of us can ask for when seeking help.

You stated ladder logic has no bounce issues, I am not experienced in it, what handles mechanical switch
bounce in the logic fabric input vectors ?

Regards, Dana.
 

MisterBill2

Joined Jan 23, 2018
8,481
Mechanical relays with their inertia and 25 to 50 millisecond operation times tend to completely ignore the millisecond contact bounce periods. And even better, they handle over voltage spikes and excess current surges repeatedly with no problems at all. In addition, a relay always starts up in a known state without any special,initializing system. So for a simple power on/off control just a simple relay is the way to go. Also, they are totally insensitive to static electricity, except for real lightning strikes. One more benefit is that products from almost a hundred suppliers are available to fit the application.
 

MisterBill2

Joined Jan 23, 2018
8,481
Years ago I used some of those in a project, they are pretty cool little devices.

Ron
Indeed the Ledex device is handy but it has the problem that when the power goes off and everything forgets, it is still in it's last state when the power returns. A single sealed on relay has no such problem, nor does it need to boot up.
 

danadak

Joined Mar 10, 2018
4,057
Mechanical relays with their inertia and 25 to 50 millisecond operation times tend to completely ignore the millisecond contact bounce periods. And even better, they handle over voltage spikes and excess current surges repeatedly with no problems at all. In addition, a relay always starts up in a known state without any special,initializing system. So for a simple power on/off control just a simple relay is the way to go. Also, they are totally insensitive to static electricity, except for real lightning strikes. One more benefit is that products from almost a hundred suppliers are available to fit the application.
In general thats a safe bet but I recenly had P-B's exhibiting > 100 mS in bounce. The
application was mis-behaving so I setup on scope and did measurements. Surprising
to say the least. I did not dissect the switch (probably should have), and started using
in routines 200 mS as min closure / release time in debounce code. Not exactly an elegant
rigorous solution. And lag is human interface noticeable. I did not like that as a result but
was in a hurry.

100 mS had been my goto debounce time. Web searches find people using everything from
10 mS to 100 mS. That tells us we do not have a good handle on this problem, and "get away"
with marginal designs. Reminds me of the issue associated with DRAM bit errors long ago,
and error correction arguments as to how much to detect/correct. That all went away when
BERs finally got real low from manufacturers. (Or did it.....:))

UGLY to say the least.

Regards, Dana.
 
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MisterBill2

Joined Jan 23, 2018
8,481
In general thats a safe bet but I recenly had P-B's exhibiting > 100 mS in bounce. The
application was mis-behaving so I setup on scope and did measurements. Surprising
to say the least. I did not dissect the switch (probably should have), and started using
in routines 200 mS as min closure / release time in debounce code. Not exactly an elegant
rigorous solution. And lag is human interface noticeable. I did not like that as a result but
was in a hurry.

100 mS had been my goto debounce time. Web searches find people using everything from
10 mS to 100 mS. That tells us we do not have a good handle on this problem, and "get away"
with marginal designs. Reminds me of the issue associated with DRAM bit errors long ago,
and error correction arguments as to how much to detect/correct. That all went away when
BERs finally got real low from manufacturers. (Or did it.....:))

UGLY to say the least.

Regards, Dana.
No place in the TS remarks do we see anything describing what would be powered. So there is no way to know if any contact bounce affecting that 40 amp SSR would matter one bit. AND, if the bounce is in the pushbutton then that may not have any effect on the load that is on the output side of the relay. Even better, if the TS uses a small mechanical relay so as to have good isolation and low voltage on the control circuit, button bounce is not in the discussion even.
 

danadak

Joined Mar 10, 2018
4,057
I guess we are both making assumptions, best to wait for TS to confirm -

1) What is load ?
2) Intermittent pulse on/off of load, would that be an issue for TS
3) SSR datasheet
4) Current schematic (if there is anything to start with)

Regards, Dana.
 

MisterBill2

Joined Jan 23, 2018
8,481
I guess we are both making assumptions, best to wait for TS to confirm -

1) What is load ?
2) Intermittent pulse on/off of load, would that be an issue for TS
3) SSR datasheet
4) Current schematic (if there is anything to start with)

Regards, Dana.
The TS asked for one button to switch on the relay and a second button to switch it off, and also asked to NOT USE an arduino. The classic circuit has been around for many years and has delivered satisfactory performance for all of that time. It has the added benefit of switching off and not making an automatic restart after a power failure, which can be a life-saving benefit. An additional benefit is that because of the response time of mechanical relays contact bounce is not an issue.
And certainly, seeing the SSR data sheet will clarify a number of questions.
 

panic mode

Joined Oct 10, 2011
1,881
industrial controls such as buttons are rated for AC voltage and currents and this is used all the time.
AC or DC does not matter. if you want isolation, get a small relay and transformer or wallwart style power supply, 1NO and 1NC buttons. and use this to drive SSR. nice thing about SSR is that it is quiet. contactors can be very loud.
using small relay will make it still audible if not enclosed but much more pleasant than loud "CLACK" from power relay or contactor.
1581303114465.png
 

MisterBill2

Joined Jan 23, 2018
8,481
industrial controls such as buttons are rated for AC voltage and currents and this is used all the time.
AC or DC does not matter. if you want isolation, get a small relay and transformer or wallwart style power supply, 1NO and 1NC buttons. and use this to drive SSR. nice thing about SSR is that it is quiet. contactors can be very loud.
using small relay will make it still audible if not enclosed but much more pleasant than loud "CLACK" from power relay or contactor.
View attachment 198720
This is the sort of circuit that I have been talking about. Notice that there is a complete lack of fragile programmable logic devices that require a precisely regulated power source as well as protective mounting arrangements.
 

ci139

Joined Jul 11, 2016
1,696
i speculate that although Mr. sforsandeep says that he has a 40A SSR - the load would be less than 9.6kW
https://www.galco.com/techdoc/elmc/rm1a60d50_crdmh2.pdf shows the thermal considerations involved however

i personally have used tested only a small power http://www.vishay.com/docs/83838/lh1546at.pdf for 12V switch . . .
Typical R
ON = 22Ω makes it a poor alternative for mechanical 12V controlled 5A @ 240Vrms ~AC, 8A @ 30V –DC https://datasheet.octopart.com/G5LC-1-DC12-Omron-datasheet-20900.pdf
 
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MisterBill2

Joined Jan 23, 2018
8,481

danadak

Joined Mar 10, 2018
4,057
This is the sort of circuit that I have been talking about. Notice that there is a complete lack of fragile programmable logic devices that require a precisely regulated power source as well as protective mounting arrangements.
Actually a 10-20% ZENER or a 3 term regulator (generally non precise) adequate in many designs to power a processor.

Will be instructive to see what his load looks like. Maybe then we can also recommend SSR transient protection
solutions if needed. And of course fault conditions have not been broached with TS, in case thats of import,
easily achieved with those "fragile programmable logic devices".

Regards, Dana.
 
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