ST Generator and domesitc appliances

[Flyingpony]

In the event of a power failure, I'm thinking of getting a full-sized standby generator, namely an CS12-2 with ST-7.5kw head.

Kind of an obvious question, but, is the power generated by the ST generator head of a suitable quality that it can run your typical household appliances?

Namely, everything from water heater elements, heat pump (air conditioning) units, desktop/laptop computers, TV, DVD, those energy saving lights, fluro light tubes, etc?

I've read about flicker and how an Automatic Voltage Regulator (ARV) can fix that - right?

Have years of experience with non-sine wave Inverters which convert from 12V DC to 240V AC, but they produce a wicked hum in some appliances which makes them sound very sick in deed.  But when those same appliances are plugged into the grid, they're silent.

Does an ST generator make appliances hum?

Thanks.

[ronmar]

My 6/1-ST-5 runs everything in my house.  The AC waveform out of mine is not too bad, and I have compared it to a couple domestic generator sets now.  It is good enough, with a little filtration added to the excitation circuit, to power 3 different UPS's in my home.  The flicker will be noticeable on incandescent lights and a little on larger 4' florescents.  We use almost exclusively CFL bulbs and they don't really show the flicker(I have to look hard for it).  Setting watching TV off the sattelite in my living room with 2 lamps on, the only way I can tell that I am on generator power is I can barely feel the thump, thump thump of the engine running thru my seat.  Since it is a small genset, occasionally the UPS that powers the entertainment center will beep if the well pump starts while the freezer and reefer are running...

[jimmer]

Is anyone able to run a microwave off a ST head?

I am not. That seems to be the only thing that will not run.

Jimmer

[Doug]

There is no reason to assume you can't run any apliance off an st head IF you can keep the frequency in spec and have a clean output from the generator ( this may require a filter with some caps... ect ).

You need to try things.

The strange hums and noises you hear on square wave inverters are caused by even harmonics. In some cases this is harmless in others it causes heating of and lower performance ( in some cases derating is required ). Some electronics realy don't like square waves and won't run at all.

Doug

[t19]

yeah mine works just fine

[ronmar]

Is anyone able to run a microwave off a ST head?

I am not. That seems to be the only thing that will not run.

Jimmer

Have you tried a different microwave?  Do you know anyone with an Oscope?  Microwaves are real sensetive to pulse shape and get the majority of their power from the peak of the sine wave.  If your generator is flat topping the sinewave, that could explain poor performance of a microwave.  Mine works OK on my ST, but my ST also has a pretty good looking sine wave.  It is a large electrical load, and about half of my 3KW available power on a single 120V leg so it will set off the UPS's that are on that leg when I run it.  I bought a 240V-120V 3KW transformer that I will plug that, and the refrigerator into when on generator power to spread their load across the 240. The refrigerator is kind of the oddball.  it usually runs at a fairly light electrical load, but there is no controlling it's automatic cycles such as defrost and sometimes it's load can run quite high.  Putting it's load across the 240 will make a prolonged generator run smoother in my situation.

Ron     

[Tom]

I've run a couple of microwaves with my 6/1 st5 rig almost no problem. The microwave we have in the kitchen is 1500 watts and if we use it while carrying a heavy load battery charging, the voltage on that leg will drop enough to cause the inverters to kick in.

[oliver90owner]

Re microwaves - remember they draw much more current than the heating power rating of the magnetron - that is why they need a large fan to keep the magnetron well cooled. 

They are often electrically rated at 50% or more above the magnetron output.  Most people don't understand that an electric kettle is a more efficient way to boil water than doing it in a microwave!

A domestic 1500 watt microwave (if that is the output, not the input) must be an awsome piece of kit!

They bought a 3 kW output machine at a place I worked a long time ago to dry samples.  Unfortunately that last bit of moisture was still difficult to get out (as the sample no longer absorbed microwaves ) and the excess reflecting around easily damaged the wave guide and magnetron.
Finished up having to put in melamine shelves to absorb the excess microwave power and that  slowed the drying times unacceptably.

Regards, RAB

[xyzer]

In the event of a power failure, I'm thinking of getting a full-sized standby generator, namely an CS12-2 with ST-7.5kw head.

Thanks.

With a 12/2 you should not have the pulsing issue the 6/1 has......am I right? I don't have one to compare.

Dave

[mkdutchman]

In the event of a power failure, I'm thinking of getting a full-sized standby generator, namely an CS12-2 with ST-7.5kw head.

Thanks.

With a 12/2 you should not have the pulsing issue the 6/1 has......am I right? I don't have one to compare.

Dave

I'm thinking someone here already was there and done that and the 12/2 has the same pulsing problems that the 6/1 has, ask Jens about that.

[Stan]

RAB....get a kill o watt and hook it up to the microwave, and then the electric kettle.  I did.  the electric kettle uses waaaay more power to boil an identical amount of water.  Don't remember the numbers, didn't do the math, just read out the readings and it wasn't even close.
Stan

[ronmar]

There was just a subject on here about the twins, and that their power strokes are not opposed like you would think they should be.  Seems silly to me, but that appears to be the way it is.

RAB is right about the power usage of a microwave.  My small kitchen unit is I think 800W, but it pulls 1.4KW from the 120V electrical outlet. 

Ron

[ronmar]

Readings ALA killo-watt...

[oliver90owner]

Stan,

The microwave issue is similar to having a battery bank and losing energy with every energy transfer.  You lose energy while recharging ( battery is heated) and you lose energy while dicharging (internal resistance losses).  If you are using the current to feed an inverter there are more losses in the inverter, and so on.  Overall efficiency is probably around 60% for light loads.

With a microwave there is a very large transformer to lose some energy.  The magnetron is not highly efficient (needs that large fan to dissipate the large amounts of wasted energy). the absorption of microwaves is very efficient.  The container of water will lose energy for the whole time it is being heated, so assuming losses are similar rates in kettle and microwave container, losses will be higher with the microwave as the process takes more time to achieve the same delta T (temperature change) as a kettle is typically a resistive 2 - 3 kW load and the typical microwave is about 800W output.

The kettle may have a higher specific heat loss than the microwave water container, but that is far outweighed by the inefficiences of the energy transfers in the microwave.  I would assume here we would be comparing a modern microwave and a modern kettle - not the old Russell Hobs type kettle which had a huge surface area, thin metal case and weighed a lot with an element about a metre long if stretched out - with good insulation and low specific heat capacity.  Ie. a small jug type plastic kettle.

Evaporation losses should be comparable (similar surface areas but different times) except that if the water is allowed to come to the boil for the same period of time, boiling losses in the kettle would be far higher, as the heating rate is about three times that of the microwave.

No contest as far as I am concerned.  Microwaves are very efficient heaters of food (avoids  long time-factor for conduction of heat into food).  Kettles are better for water (only one energy transfer - electricity to thermal).

Regards, RAB

[Stan]

Just did a reading on mine to boil 1 pint of water took 4.2 min and 0.08kwhr.
Stan
btw...that's 1.3 cents.