A system to enable the automatic turn on of electric generator in case of power failure and turn off when power is restored. In case of power failure, the system will enable choke, start ignition and switch the house power supply over to the generator. When mains power is restored, the house will be switched over to it and the generator will be turned off.
a. Problem Statement and history:
Lengthy power failures are a part of life in Pakistan and are expected to remain so for the short- to mid-term future. To cope with this problem, those who can afford to, buy either a UPS (Uninterruptible Power Supply) or a (diesel) or (petrol and/or gas) electric generator. An average household minimum requirement can be fulfilled by a generator supplying 300 to 3,000 Watts of electric power. Generators in this power range almost never come with an in-built ATS (Automatic Transfer Switch). So owners of these have to manually start the generator and switch the household power supply from mains to generator and do the reverse when mains power is back. Our project will automate these tasks reliably and safely.
b. Existing solutions and their shortcomings:
This is not the first time this problem is being tackled. Some generators come with built-in ATS. But those are either the higher power varieties (usually >10 kW) or are significantly more expensive than their non-ATS counterparts (usually approx. at least Rs. 10,000 more expensive.) another currently available solution is ready-made off-the-shelf ATS but they are quite expensive, some of which can be more expensive than the generator itself!
c. Our solution and its advantages relative to other solutions:
Our solution is based on simplicity, reliability, safety, and affordability. We have used minimum moving parts and a micro-controller for the logic to ensure reliability. The electric transfer switch is a completely sealed 20A relay and the printed circuit board itself is enclosed in a box to ensure safety. The number and choice of components, the circuit design, the mechanical design, are all made to ensure simplicity and affordability.
d. Alternatives considered before arriving at and deciding on this solution:
We considered using solid-state relays (for both sub-component control and power supply switching) but settled on electromechanical ones as the cost difference was quite large while performance improvement was insignificant in our case.
e. Off-the-shelf components used:
- 20-pin 89C2051 – the “brains” of this system
- 78LS245 – buffer IC to enable the microcontroller to run many loads
- 12V 10A electromechanical relays x 4
- Optocouplers (4N25) to detect mains or generator power
- 12.00000 MHz timer to synchronize circuit logic operations
- LM 393 voltage comparators
- 22A electromechanical relay for physical connection of house electricity to mains or generator
f. Estimated and actual budget:
- Initial estimated budget: ~ Rs. 2,000.
- Actual budget: ~ Rs. 3,000
g. Timeline of project:
22 Feb 2010 – Start of semester
20 Apr 2010 – Project proposal submitted
22 Apr 2010 – Work started
26 Apr 2010 – Initial hardware and circuit completed and demonstrated
12 May 2010 – Partial system installed on the generator for robustness testing
01 Jun 2010 – Major work completed
08 Jun 2010 – Final testing
09 Jun 2010 – Project demonstrated and this report submitted.
h. Field testing:
The part of the system which was to be fixed on the generator was first completed and installed to test the effects of vibration on the effectiveness and lifetime of the product. The result after about a month was a success. At the same time, the work on the electronic part was being completed and that was also subjected to much troubleshooting. Then the complete system was assembled and tested successfully.