3000W Chinese Gensets Info.

Dan86300zxt wrote:
Hey Professor...
Got a technical question.
*Is it possible to utilize two items to feed house power at the same time?
^^^I have been reading alot on home grid tie type stuff...seamless power switching is possible, I just don't know what would be the most cost effective unit to buy to suit my needs. I am unsure if merely utilizing an automatic transfer switch would do the job...)

-The reason I ask, is because, my generator(I have the AP2k digital inverter all custom fitted into my dedicated compartment)...will not make enough power to kick on the compressor to my rooftop a/c unit.(It'll run the fan, but not the heat portion, nor the cooling, generator revs up, but goes into overload and nothing, no 120v output until I turn off rooftop for the generator to "reset"...)

*On shore power, I have measured the rooftop unit to pull a continous 1580watts/13.45 amps while cooling, and noticed that while heating on low heat, pulling a continous 1820 watts/15.3 amps. I do not know what the start up wattage is or amperage.(My meter quit working...I accidentally overloaded it checking combinations of things....)

*I wish there was a way to utilize an appropiate sized modified sine wave inverter to start up and run the rooftop a/c temporarily.....and then start up the generator to let the generator take over completely by switching the inverter to off..

**I have a very good feeling that if the rooftop a/c was running already, that the generator would be able to handle the whole load of it...it's the start up power needs that my generator isn't happy with. (I don't even get a growl or grrr or nothing from the rooftop compressor...because the generator determines the load too high and goes into overload protection mode)

Ideas please...
thnx,
Dan

Yes, it is possible. But, with limitations.

The first limitation is the appliance must be what is know as AC/DC. This would include appliances that are purely resistive like electric heaters, incandescent light bulbs, hot plates or some brush type electric motors as in power tools. With these devices you can usually supply power without regard to frequency or synchronization of the AC wave. But, be aware that if two un-synchronized generators or a generator and inverter are connected in parallel one power source can work as a brake on the other.

The second limitation involves synchronization of the sine wave from the two power sources.

Most AC appliances using electric motors are designed around the principle of the changing polarity of a rotating magnetic field. They are "brushless" and depend upon a clocked line frequency to provide a specific speed and core temperature. When AC power is combined without synchronization there is a very high likelyhood that the forces of the needed magnetic field will counteract each other causing the device to loose power or even come to a complete stop. If motion is maintained, heating and meltdown are inevitable.

Inductive devices such as transformers and solenoids designed for single phase, 60 Hz AC will quickly heat and possibly self destruct when powered from multi-phase power sources. The list of problems goes on - these are merely examples.

That said, it IS POSSIBLE to do something such as you suggest if extremely fast switching is employed. For example, let's say you did manage to start an AC motor from a DC to AC inverter and it was running satisfactorily. Then, power from the inverter was switched off and power from the generator was applied. The switching would ideally need to occur within the time frame of one AC cycle. The electric motor might stumble slightly as the frequency is changed during a particular cycle, but the momentum would allow it to continue even if the second power source were not synchronized upon transfer.

But, alas, we can encounter problems with this simple system depending upon how the appliance is controlled. Many modern air conditioner compressors employ "control boards" that rely upon a totally uninterrupted sync signal from the AC power source. The loss or interruption of the signal causes immediate disconnect from the power source. Another problem is simple inductive (electromagnetic) relays often used to control ATS circuits are much too slow to allow seamless transfer. ATS units that incorporate SCR, Triac or transistor switching have a much better chance of changing at the needed speed. But, unless technology has recently changed you will only find this type of transfer circuity in rather expensive high current UPS switching systems used in commercial service.

Your best chance of success might be a simple break before make manual transfer switch with an extremely fast hand on the handle.

I hope this helps. Perhaps some others on the thread have different ideas or another approach you might use.