Design with two triacs

Hi. I need a UPS to supply a refrigerator. It works with 220V AC. I have an inverter to supply it when the electricity interrupted.
First, i used two contactors. Then, i changed my design to two triacs. Block diagram of my design is below.
When there is electricity, T1 will be triggered and T2 is cutted off. Then, if there is no electricity T2 will be triggered and T1 is cutted off.
T1 and T2 wont be triggered at the same time.

Do you see any problem in this circuit?

**broken link removed**

It should work provided the two controls are never allowed to activate at the same time. Please remember that sudden changes in voltage across a triac will also trigger it so it would be wise to fit snubber or filter networks around both devices to ensure interference or even spikes from the compressor motor cannot turn the other triac on. This is particularly important if your inverter does not produce a sine wave output.

A suggestion: instead of two control signals to the triacs, use one 'enable' signal and one signal to operate a small changeover relay. The enable signal goes to the common contact of the relay and each of the other poles goes to a triac. This still uses two control signals but ensures it is impossible to turn both triacs on simultaneously.

Brian.

In order to have a quick switch over you must syncronize the inverter to the grid so there is not a disruption of AC phase to motor.

If you have an independent, random phase, inverter suddenly take over power to refridgerator you may do damage to refridgerator compressor. The flip over phase may be 180 degs out of phase, or any other random relationship.

If you don't syncronize the inverter you should let the refridg stay off until compressor head pressure subsides (several minutes) before applying inverter.

Thank you for your comments.

If the electricity cutted off, i will wait for 10 seconds and then i will supply the refrigerator with inverter. I will control triacs with pic microcontroller. For this reason they won't be triggered at the same time. I will try this circuit in 2 days. If i see a problem i will try to connect 4 triacs. Additional triacs will be connect to Mp's.
Best regards

otuzsubat said:

For this reason they won't be triggered at the same time.

Click to expand...

'Never say never'. Put a fuse in the line.

otuzsubat said:

Thank you for your comments.

If the electricity cutted off, i will wait for 10 seconds and then i will supply the refrigerator with inverter. I will control triacs with pic microcontroller. For this reason they won't be triggered at the same time. I will try this circuit in 2 days. If i see a problem i will try to connect 4 triacs. Additional triacs will be connect to Mp's.
Best regards

Click to expand...

What if microcontroller goes faulty?

Better add an circuit which deactivates main while UPS is functioning and vice versa

The UPS will be having an in built relay which swicthes the output from mains and to inverter in an event of power failure. The 2 triac just complicate the simple design. The single output of the UPS which is swicthed to and fro will do what you are supposed to do with your said setup. Just use a 2-3 minute dealy circuit which will protect the compressor. 10 seconds delay whay you have mentioned, is too low. Cheers