The post explains a simple configuration which can be used as a automatic changeover circuit for switching AC grid mains to generator mains, during power failures or outages.
The explained circuit will effectively switch the connected appliances to the generator mains during power failure however it won't be able to switch start the generator automatically, this will need to be done manually, because most generators involve a difficult mechanical actuation procedure.
How the Circuit Works
Referring to the given diagram we can see a simple circuit comprising of a TP relay (triple pole relay) and an transformerless power supply circuit.
The input of the transformerless power supply circuit is connected to the mains 220V or 120V input.
When mains power is present, the connected relay activates with this power and switches ON the load or the appliances via its N/O contacts.
Conversely when mains power fails, the relay deactivates and connects with the N/C contacts which may be wired up with the generator mains.
Now as soon as the generator is pulled started, the mains finds its way through the connected N/O contacts of the relay to the appliances.
The third set of contacts is used for enabling and disabling of the CDI unit of the generator so that when mains is restored, the generator is automatically halted.
Simple yet effective.....
Circuit Schematic
Bakare Emmanuel says
i would want to request and upgrade to this system, to include a buzzer (using ic 555 timer set at 1minute ), two led indicator (one for main one for generator) The system will do two main function, switch from main to generator when power fails and switch back to main when power is restored . It will sound an alarm that will automatically go off after a period of time , say 1 minutes.
It will have some fail safe features, like , circuit breaker (when main is having low current and one needs to use the generator) and fuse ( for over current protection).
thanks.
looking forward to your quick response..
Swag says
I already have many such upgraded circuits, you can type “ATS” in the search box and find them, you may also search by typing “generator changeover” in the search box for the same.
Bakare Emmanuel says
sorry to disturb you . none of the ”ATS”, has anything like i requested. being a newbie and yet to be fully capable of design but undergoing training, this idea came to mind and i will want to build it ..
please help.
Swag says
Only the LED indicators are not included in my other similar articles, which can be simply done by adding an LED parallel with the existing relay coil. LED must include a 1K series resistor
alarm can be made using a small ready made buzzer and wiring it again in parallel with the relay coil. however one of the wires of the buzzer must have a series 100uF capacitor, and a 220K resistor in parallel with this capacitor.
gbenga comrade says
hi sir what kind of relay that can be used for this particular change over or i can make use of 3phase contactor to do it
Swagatam says
Gbenga, due to low current contactor cannot be used in this circuit, you must use ordinary 400 ohm type relay here….you can probably use the contacts of this relay to operate the contactor and wire the contactor contacts for the overcharge actions
Swagatam says
….it's not "overcharge", it should be "changeover" actions…
Nnaka Stanley says
Sir, great work on the circuit. But please I need a changeover circuit, this time with three different power sources; generator, AC mains and an inverter supply. So far, what I've come up with is a manual changeover using a bypass, I need one which is automatic. Thanks
Swagatam says
Hi NNaka, I already have this design in my website, please search it in the following link
https://homemade-circuits.com/search/label/Relay%20Changeovers
priti says
sir, please tell me about power losses by this changeover circuit.
Swagatam says
power consumption will be as per the rating of the relay coil, could be around 50mA, which will be consumed from the AC mains
priti says
if this circuit is used for changeover relay, then how much power losses will take place by the circuit.
VINCENT MWENDE says
great work Swagatam,have learned a lot in the past 6 months.
Swagatam says
It's my pleasure Vincent!
Unknown says
If not then what I have to change in this circuit
Unknown says
Hi Sir can I use this above circuit for 40 amp and 63 amp single phase/3phase
Swagatam says
yes it can be used but the upper DPDT relay will need to be selected appropriately to handle the large amp.
also for such huge relay, the activation will need to be done through a AC/DC adapter, a capacitive power supply may not be strong enough….
FredoRicko says
What is the maximum load that a 30A 250VAC can accommodate if used in the circuit above?? Can it power a house with all the basic appliances?? Thanks
Swagatam says
yes this much power is more than enough for powering a house with basic appliances.
The relay will need to be appropriately selected for handling 30A, and also the 474 capacitor which also may need to be upgraded
EKEH EMMANUEL CHIJIOKE says
how many pole contactor is the one used above? can i use the above changeover system for heavy amperage as in to be used for an entire flat that has up to 3 deep freezers and two ac units with other appliances? put me through please
Swagatam says
yes you can use the above circuit for any desired high current application, you just need to change the relays as per the ampere rating of the load, and instead of a capacitive power supply you may have to use a 12V AC/DC adapter for powering the relay coils
EKEH EMMANUEL CHIJIOKE says
thanx for the reply and assistance rendered so far. a have a contactor of LC1D09, it has L1 to L3, T1 to T3 and A1 and A2 two NO n NC that are in the opposite sides of the contactor. i dont know how to use it as a changeover for that your circuit. pls how do i go about it. pls i really need your expectrics. pls come to my rescure
Swagatam says
the shown diagram uses it's own recommended relays, it's not meant to be used with a contactor.
I a sorry I won't be able to interpret the details of your contactor.
If you are interested to build the above circuit then you may have to incorporate separate relays as per the power specs of the connected load.
Norie Coquilla says
Mr. EKE. I have a design of ATS using two Contactors. I'll be glad to share it with if you wish.
EKEH EMMANUEL CHIJIOKE says
I will be glad if you would share yours with me. I really appreciate your time and support in rendering assistance to me. Thanks alot.
EKEH EMMANUEL CHIJIOKE says
please i really need your assistance to build and automatic changeover switch of 90amps 220 volts single phase and it should have the ability to switch off the generator set once there is power from the grid
Swagatam says
you can use the circuit that's shown in the above article, it exactly matches your requirement.
RAHUL V C IFS says
What is the wattage of 1 megaohm resistance
Swagatam says
1/4 watt
RAHUL V C IFS says
Thanks
Henry Ndukwe says
Hi swagatam can a 373j/400v go in place of the 474/400v in the circuit
thanks
Swagatam says
Hi Henry, if your relay is able to trigger comfortably with this cap then it would be fine
Adegbite Abdul Lateef says
Thanks. How do you connect your CDI GND and cdi gnd with relay.
Alfred Emasoga says
Sir, can one use three SPDT relay connected in parallel, in place of a 3P (three pole) relay? Or would series connection of the three individual coils be a better option?
Swagatam says
Alfred, it may be done with a parallel connection, series connection would require three times the coil voltage as the input.
preston jose says
If I need it to connect it to an inverter for mains and when the current goes, the inverter would handle
What will be the modifications ti do?
Swagatam says
You will just need a single DPDT relay, the generator AC will get replaced with inverter AC and the lower CDI section will not be required.
Muhammad Junaid says
Dear Admin, I require the modified functionality of this circuit, I need to design an ATS (Automatic Transfer Switch) for current of 10A at 220V, would you please help regarding this..?
Thanks
Swagatam says
I'll see if I can do it.
Anonymous says
Hi Swagatam,
what is the voltage of the relay?
Ragards,
Swagatam says
it should be a 12V/400 ohms spdt, with 220V/7amp contacts
Anonymous says
Hello sir. can i use this circuit for my inverter with some modification?
What is the changeover time? if i connect to my computer may i able to run my pc with out rebooting it?
Swagatam says
It can be tried, the changeover time may differ from relay to relay, normally it would be around 3ms approximately.
Qaisar Hussain says
can you tell how it is possible to overcome changeover time.
Swagatam says
use a heavy duty relay with low coil resistance, an decrease the value of the input cap to 2.2uF/400V