Solid state SIMPLE anti-restart circuit wanted. Has Anybody done that already.

Thread Starter

MisterBill2

Joined Jan 23, 2018
13,128
I am seeking a simple but reliable solid state equivalent for the simple start/stop sealed relay contacts scheme that we all know and love.
A mains power scheme that will switch on with an "ON" button and stay on except if the power fails, at which time it must switch off and not switch back on until the "ON" button is pressed again. The load in this case will be less than 5 amps, but needs to stay energized for years, unless the power fails. Then it must not switch back on until the button is pressed. The load can live with a few volts drop across the control system.
 

LowQCab

Joined Nov 6, 2012
2,506
Is that 5-Amps DC or 5-Amps AC ?
At what Voltage ?
Is this a remotely located Start-Button, or self-contained all in one box ?
What Voltages are readily available for Control-Power ?
.
.
.
 

nsaspook

Joined Aug 27, 2009
10,416
Is this a safety-critical self-holding device?

https://www.ia.omron.com/product/cautions/18/safety_precautions.html
Self-holding Circuits

Self-holding circuits must use mechanical relays. SSRs cannot be used to design self-holding circuits because of the following reasons.

1Parasitic capacitance exists between the terminals of the SSR output semiconductor elements (transistors and MOS FETs), and the charging current flows to the parasitic capacitance. When the power supply is turned on and an excessive rising voltage is generated, the charging current flows to the input side as well, which may cause a malfunction.

2Because OMRON SSRs cannot be used at less than the minimum load current, the self-holding input current may not flow correctly.
 

Thread Starter

MisterBill2

Joined Jan 23, 2018
13,128
No, this is not a safety critical device. It is an appliance sort that needs to be recalibrated when the power has gone off, or it iver-runs and grinds the gears.
The power, as stated in post #1, is mains, 120 volts, nominal. And the current is mains power level, less than 5 amps at 120V/60H.
And the reason for wanting solid state is to reduce the holding power needed.
I have included the relay circuit in over a hundred machines and that would be the choice except that it gets warmwith therelay staying on for weeks at a time. The control buttons will be local to the package, no wireless needed or wanted. Fast response, less than a second is required. And the arrangement can have a bit of voltage drop between input source and the load. 120 in and 110 out will be OK. The buttons might even be AB 800T series if I can find them.
 

nsaspook

Joined Aug 27, 2009
10,416
The relay holding power levels are minimal (~2.0VA) for a properly sized old school octal relay for that load range. IMO, little reason to change a proven design.
 

crutschow

Joined Mar 14, 2008
30,791
I would think you could use an SSR with the control voltage (typically 3-32Vdc) provided by a common small 5Vdc output wallwort.
Modern switching type wallworts are very efficient, but you still may not save much power over a 10A power relay with an AC coil.
The wallwort would be powered from the SSR AC output, so you would then have to close a switch to initially power the wallwort from the unswitched 120Vac.

Below is a block diagram of my proposed configuration:
I show a double-throw switch so the load current doesn't go through the switch upon start-up.
If you use a single-pole switch then that current will go through the switch when pressed.

1661568579887.png
 

Thread Starter

MisterBill2

Joined Jan 23, 2018
13,128
Indeed that could work. The challenge will be in packaging a wall wart in a reliable manner. Functionally it is close, except that it takes a three terminal switch (SPDT) because the SSR has only one pole. I will need to revisit mechanical relays. But still there should be a simple solid state scheme.
I am hoping that somebody has created one.
 

crutschow

Joined Mar 14, 2008
30,791
The challenge will be in packaging a wall wart in a reliable manner.
How about hard wiring to the main's AC source for the SSR with an extension cord socket?
. Functionally it is close, except that it takes a three terminal switch (SPDT) because the SSR has only one pole.
You can use a SPST switch.
It just means the switch will initially have to carry the load current when it is momentarily closed to activate the relay (below).
You can add R1 if you need to reduce that current.

1661583843038.png
 
Last edited:

eetech00

Joined Jun 8, 2013
3,418
How about hard wiring to the main's AC source for the SSR with an extension cord socket?
You can use a SPST switch.
It just means the switch will initially have to carry the load current when it is momentarily closed to activate the relay (below).
You can add R1 if you need to reduce that current.

View attachment 274822
Hmmm....but how will this "anti-restart" if switch must be in same position to start or run?
 

Thread Starter

MisterBill2

Joined Jan 23, 2018
13,128
Problem solved, issue resolved and a mechanical relay will work after all.
The secret starts with a high resistance coil with lots of turns. But the secret is that when it operates there is no air gap once the relay pulls in, and so the inductance increases and the current drops. How is THAT for a sneaky way to reduce holding current. So I built the box using that relay that has a 120 volt coil, so no power wasted in a small hot transformer. It has been energized 5 days and does not feel warm yet.
Thanks everybody for some interesting suggestions.!
 
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