Good day all,

Any one with idea on how to achieve this Changeover I would like to make.

I want to manually switch my Refrigerator to Inverter AC power using a simple Switch + 12v DPDT Relay on NO. But when Grid power is restored, the Relay should automatically be switched back to Grid on NC so the Refrigerator continues on Grid power but when the Grid goes off, theRefrigerator goes off. So to use the Refrigerator on Inverter, I need to use the switch again.

I hope the explanation does it.

Thanks

 

Couldn't come up with a way to do it with only one relay, but you could configure two relays, with one in a latching configuration with push-button control.
When power goes out, the first AC relay, powered by the grid, drops out and its NC contacts sends 12V power to the PB controlled relay
You then push the button to latch the relay and connect the inverter.
When power comes back on, it energizes the first relay which releases the second relay and connects the fridge back to the Grid.
Then you would have to press the button again after the next outage.
If you also want a manual stop of the inverter, you could add a second PB.

Sound feasible for you?

 

Couldn't come up with a way to do it with only one relay, but you could configure two relays, with one in a latching configuration with push-button control.
When power goes out, the first AC relay, powered by the grid, drops out and its NC contacts sends 12V power to the PB controlled relay
You then push the button to latch the relay and connect the inverter.
When power comes back on, it energizes the first relay which releases the second relay and connects the fridge back to the Grid.
Then you would have to press the button again after the next outage.
If you also want a manual stop of the inverter, you could add a second PB.

Sound feasible for you?

Thank you @crutschow
I also thought of it not working with one relay which is fine.

Could you please illustrate your idea?

Another thing I thought is, the Relay for switching to inverter needs a momentary button switch which would require a latch circuit.

 

Could you please illustrate your idea?

Below:

Do you want a second PB for manual off?

 

Below:
View attachment 360879
Do you want a second PB for manual off?

Thank you @crutschow but this circuit isn't what I wanted to design.

I'll sketch out my design on my next reply.

Again, thank you for always popping up for me.

 

@crutschow

Here's a quick one I drew on Proto. Thats a DPDT Relay with my Fridge on the COM, Grid power on the NC and Inverter power on the NO.

So, by default, if Grid is available, the fridge works. When Grid isn't available, the inverter is always on as it's used power my everyday home appliances except when I chose to run the fridge on it.

Whenever I choose to run the fridge with the Inverter, I push the Latch button on the circuit powered by a steadily available 12VDC, and the fridge runs on the inverter power.

Because my battery bank isn't much, I want to only run the fridge on inverter for a limited time, to turn off the fridge, I push the Latch button again and the Relay returns to its NC position.

THE DESIGN I ACTUALLY WANT
During when the Fridge is running on the inverter, if the Grid power is restored, without pushing a button or been present, the relay should be de-energized (Like another separate circuit taking off power from the relay) so the fridge continues work on the Grid which is now available on the NC. If the Grid is then taken off again, the Fridge goes off until I wish the continue the fridge on the inverter.

 

Is it necessary that you can power the fridge from the inverter if the grid is on?
If so, that tends to complicate the circuit.

Could you build a small circuit on a perf-board to help with that, if needed?

 

Is it necessary that you can power the fridge from the inverter if the grid is on?
If so, that tends to complicate the circuit.

Could you build a small circuit on a perf-board to help with that, if needed?

No, I wouldn't run the fridge on Inverter if Grid is available.

Yes, I can build circuit on a perf-board.

 

No, I wouldn't run the fridge on Inverter if Grid is available.

Then you can use the circuit in Post #4, but the 12V connection to U1 is not needed, and U1 will need to be a 4PDT relay to switch both sides of the fridge connection along with the switch connection shown.

If you want only one PB, then a small amount of added electronics would be needed, and that would only require a DPDT relay for U1.

 

You’ll need a delay on timer to prevent switching to grid during brown outs.

 

You’ll need a delay on timer to prevent switching to grid during brown outs.

Thank you @eetech00

I thought of this but if grid is restored during the on-time of the timer, It continues consuming the battery even when grid is available.

 

Then you can use the circuit in Post #4, but the 12V connection to U1 is not needed, and U1 will need to be a 4PDT relay to switch both sides of the fridge connection along with the switch connection shown.

If you want only one PB, then a small amount of added electronics would be needed, and that would only require a DPDT relay for U1.

I don't understand the diagram in Post #4 pls, where does the Fridge connects to?

 

where does the Fridge connects to?

U1 connects the Fridge to either the Grid or the Inverter (in place of the inverter connection I show).
U1 needs to be a 4PDT relay as I stated in Post #9 so you use two poles for the Fridge and one pole for the switch.

Or you could use one small 12V SPDT relay for the switch, and one larger 12V DPDT relay for the Fridge.
The two relay coils would be connected in parallel, of course.

 

U1 connects the Fridge to either the Grid or the Inverter (in place of the inverter connection I show).
U1 needs to be a 4PDT relay as I stated in Post #9 so you use two poles for the Fridge and one pole for the switch.

Or you could use one small 12V SPDT relay for the switch, and one larger 12V DPDT relay for the Fridge.
The two relay coils would be connected in parallel, of course.

Does the circuit in Post #4 use a flip switch or momentary latch PB?

 

Does the circuit in Post #4 use a flip switch or momentary latch PB?

It uses a momentary, normally-open (not latch) push-button.

 

Thank you @eetech00

I thought of this but if grid is restored during the on-time of the timer, It continues consuming the battery even when grid is available.

No. Start the timer when the AC grid is restored but don't apply the AC load. After a set time, say 30 seconds, the load is then connected to the grid.

 

It uses a momentary, normally-open (not latch) push-button.

Thank you @crutschow

A momentary button only closes when button is pushed rigth? What about when the button is released?

I have looked at the circuit at Post #4 any it doesn't work. I'll draw a sketch on my next post to explain better.

 

This seems kind of difficult to accomplish without the use of microcontroller.

This is basically what I look to achieve.
A 2PDT relay with the fridge been powered with either Grid or Inverter.

(Image1)
The grid controls the relay, so when the grid goes out, the fridge is returned to been powered from the inverter.


But the fridge isn't going to be powered at all times even though the inverter would always be on, so a switch is needed to turn the fridge ON/OFF.
While the grid isn't available, the inverter can be turned on, allowed to work till preferred time and then turned off (using the switch).

But, in times when no one is available, if the grid is restored and goes out again, the fridge shouldn't continue on the inverter. If I still wish to continue using the fridge on the inverter, then I have to go push the switch again. This means, the switch has to be a single-push ON/OFF button (Latch switch)

All I can think for this to work is this - An extra relay should give a 12v power to the Latch switch circuit on NC so that when grid becomes available,it energizes the relay and takes power off the Latch circuit. When the grid later goes out, the Latch circuit gets is power but would be reset to its OFF state and needs another button press to close the circuit.



And then, there needs another Relay which the Latch Switch controls. This relay is going between the Fridge and the 2PDT Relay.

This, I don't know where to place it.

 

A momentary button only closes when button is pushed rigth? What about when the button is released?

When the button is released the contacts open.
What else could they do?

As I explained in Post #13 you can use one 4PDT relay for both the push-button latch function and switching the Fridge, or one SPDT relay for the latch circuit and one DPDT relay for the Fridge with the two relay coils in parallel (so the latch circuit controls both relays).

What about that don't you understand?

 

When the button is released the contacts open.
What else could they do?

As I explained in Post #13 you can use one 4PDT relay for both the push-button latch function and switching the Fridge, or one SPDT relay for the latch circuit and one DPDT relay for the Fridge with the two relay coils in parallel (so the latch circuit controls both relays).

What about that don't you understand?

Yes @crutschow , Like I explained in my last post, Having a SPDT and DPDT Relay coils in parallel seems like a good idea but the problem is this.

Both relay coils would be triggered by the grid when it becomes available, but what does the Latch circuit control? The SPDT relay only gives power to the circuit.

With both relays in NC positions (Grid unavailable) - The Latch circuit gets 12v to operate via the SPDT while the fridge connected to the Inverter via the DPDT. What happens when I use the PB on the latch circuit? What does it latch ON?

With relays now in NO position (Grid available) - The fridge connects to grid while the latch circuit goes off which would make it reset its state when next it gets 12v.




This is a simple Relay controlled Latch circuit I grabbed online so to explain my above concern.