Baby Bear, I am having trouble geting Google to produce results. I cut and pasted the entire string but keep getting a "no results found" to my search query.
to the original poster:
As for the automatic transfer switch the schematics I did find all lack a critical element. They do not show the circuitry associated with the coil of the transfer switch and they do not show how the generator is actually started.
This is important. The simplest approach is to use a double throw relay or contactor with a coil rated for the mains voltage. Hwever depending on your local utility power authority, additional safety features may be required. For loads of less than 30A arc quenching may not be so difficult to achieve. But not all relays are equally suited because they lack the required snap action to quickly extinguish the arc created by load break. A motor start contactor is better suited since it is by design intended to open the on load contacts at full rated amps. In my own experience the contacts must move at least 6 mm and do so quickly in something like 16 - 20 milliscond.
If you intend to build this from scratch I suggest you include a flyback diode to prevent back EMF since part of your house loads will most likely include inductive motor loads.
If you choose to drive the relay coil direct from mains, when the mains voltage disappears, the relay or contactor drops out and this in turn connects the load to the generator. Simple and nearly fool proof. BUT, . . how to start the generator automatically is the big question. Many products advertising an Auto start feature only provide a dry contact for signalling the generator start. a seperate controller board supplied by the genset maker is required.
Many of the home type generators of less than 10 kW do not have any sophistication in the start circuit. They rely on the operator to manually toggle the start switch. Feed-back as to when to stop pressing the start switch is a matter of the operator hearing the motor actually running. If the motor has a low oil pressure switch ( safety) then a bypass circuit must be provided. Otherwisse it will never start. If a diesel engine; a glow plug timer circuit must also be included.
Secondly; a cranking limiter circuit must also be provided. Otherwise how does it know when to release the momentary start button. Failure to release the cranking circuit wil damage the starter motor. If the genset is not air cooled, you need additional bypass circuits for the various alarms assocuiated with the liquid cooling circuit. This dependent on the model of generator provided. these timer functions could get expensive. you can use either individual timer relays or a more sophisticated PLC. These are available for under $100 USD.
In off-grid applications and larger yachts I specify use a controller board designed to work with many of the brand name generators. Being a North American product I doubt it would be availabel in Pakistan. Try siemens or ABB for somethign appropriate locally. It provides the necessary bypass circuits timers and cranking limiters needed to safely start gensets automatically.
I have a chinese copy of a Yanmar engine for my own installation and am doing exactly the same thing as you are trying to do. Unfortunately the Yanmar is so basic it means a lot of extra work to set it up for automatic operation. Still tinkering.
The commercial board cost USD $560 and involves a couple of hours to install.
Since you are an electronics tech it should not be any problem to figure out something yourself using what is actually available to you locally in Pakistan. But it could get expensive. Not much point in using a schematic calling for parts that you cannot get easily or at low cost.
If cost is not an issue why not just buy a commercially made transfer switch. It certainly would be easier.
