3000W Chinese Gensets Info.

professor95 wrote:
Yes, there is a cheap, simple and dirty solution. I pondered on making such a circuit, but decided it was not really that necessary. If you are determined to do it...

If AC out on the genset should rise so will the DC voltage out of the adapter and the voltage to the base of the transistor. When the voltage on the base of the transistor hits +.7 VDC or higher, the transistor conducts and supply voltage flows from the collector to emitter. This keys the relay which grounds the line going to the low oil shutdown switch.

I'm not sure that would protect anything electronic from an AVR failure that caused high voltage? The reason is the generator has considerable rotating inertia and takes a while to shut down from when the spark is shut off (i.e. the low oil switch) on the engine. The too-high voltage would be around long enough to do damage before the generator slowed enough to reduce it.

Instead, I would suggest a circuit that opens a high powered relay instantly disconnecting the load (which also could be used to for starting the generator unloaded and unloading it for shutdown) if the voltage exceeds a certain value. The trick is not having it trip on brief transients. If people are interested in such a circuit, let me know (I'm an Electrical Engineer by education and profession)?

A much easier option for the average Joe might be to use a couple of high-end powerstrips that have advanced surge protection? Panamax and others make power strips that will disconnect the load during overvoltage conditions. Most any computer UPS also does this. So any sensitive loads could be plugged into such a device that is, in turn, plugged into the generator.

This could all get a bit tricky, however, as I've found that generator powered circuits are much more prone to nasty voltage spikes than regular home power. This is because the national power grid has a VERY low impedance. So anything that dumps a brief spike of current back into your home power wiring tends to largely get "absorbed" by the huge power grid (i.e. all of your loads, your neighbor's loads, etc.).

But when you're running your own little tiny "grid" from a generator, and something dumps a spike of current (like turning off an inductive load such as a motor) there isn't anywhere near as much load to absorb the spike. So high quality surge suppressors are a good idea anyway for anything sensitive when you're running on generator power.

There have been posts about, for example, the digital controls on microwave ovens freaking out on generator power, and these spikes are one explanation why. I've had a few things fail on generator power. Using my Fluke isolated Scope I've observed voltage spikes over 400 volts when the refrigerator compressor turns off while on generator power. While on line power it's just a little blip--more like 140 volts.

Light bulbs, motors, heating appliances, and those sorts of loads are unlikely to be bothered by brief spikes or overvoltage conditions. But anything electronic could be either temporarily glitched or even permanently damaged by big spikes or an AVR failure or other overvoltage condition.

It IS a good idea to start and shut down a generator with the load disconnected. It's even better to give the generator a few minutes to warm up before putting much of a load on it--especially if it's in cold weather.

Engine clearances--including the bearings, piston, rings, etc.--are made to fit right at operating temperature. When the engine is cold, the clearances are typically very "sloppy" and hence the engine is much more prone to wear and damage. Plus, the splash lubrication system doesn't likely have much of the thick cold oil in all the places it needs to be in a just-started cold engine. So it's best to give it some time before dumping a big load on it--especially motor loads with high starting currents like refrigerators, AC units, etc.

I'm not sure about AVR damage, but shutting the generator down loaded may possibly damage or "glitch" some digital devices with the gradually falling voltage. So it's also best to disconnect the load before shutting down. You want it disconnected before starting it again anyway, so why not do it before shutting down? If everything is connected through a single 30 amp twistlock plug, it's fairly easy to just use the plug as the disconnect (assuming you're not using a remote start/stop panel).

Once it's fully broken in, I'll be doing some load tests, voltage regulation tests and more on my Champion. I'll let others here know what I find out. I have lots of lab-grade instrumentation to measure the voltage, current, watts, power factor, harmonic distortion (waveform quality), output impedance, engine and generator head temperatures, etc.