Transfer switch
Wednesday, September 24th, 2008
Aloha Jeff,
I’m looking to be near off-grid in the next 5 years. I presently have solar attic fans, and am pumping house water from catchment tank using a 3 gal per minute/50 psi – 12 volt RV flowjet pump (soon to be powered with solar panel and battery backup).
My question – I have a 4000 watt generator and am looking for a transfer switch for the grid/gen scenario which will eventually be solar/gen scenario. Any guidance on acquiring a single, inexpensive transfer switch which will work in both situations?
Thank you very much in advance for your attention to this question.
Frank Pustka
Frank:
Of course the best transfer switches are those you can buy as an option with the larger size generators. They are expensive but well made. Most smaller capacity generators can get buy using an industrial relay having at least 30 amp capacity ( 30 amp X 240 volt = 7200 watts ). However, before trying to build your own transfer switch be sure to use a relay having a DC coil, and use an AC to DC rectifier bridge. This is because when a generator starts to wind down when turned off, it is still generating power, but as the voltage drops an AC relay will “chatter” while a DC coil will remain closed until it completely opens. This is much easier on your electrical loads downstream as you want a “clean” transfer from generator power to grid power, or inverter to generator. When the relay does not “snap” from one position to the other, the relay will not provide a clean transfer of power and will cause major voltage spikes or voltage sags to the loads downstream.
If you have no idea what I just said but still want a very-low cost transfer switch for a smaller size generator that avoids the problems I described, check out the following link:
http://www.iotaengineering.com/its50r.htm
Good luck,
Jeff Yago
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