Generators and computers

[David Paul]

May very well be a dumb question rlitman, but will an older microwave cause damage to a new inverter style generator? I just updated my generator from a 5000 watt to a 6500 watt inverter style generator. The microwave made all kinds of noise and did not work with the old generator (non inverter) but seems to work with the new one.

 

[rlitman]

May very well be a dumb question rlitman, but will an older microwave cause damage to a new inverter style generator? I just updated my generator from a 5000 watt to a 6500 watt inverter style generator. The microwave made all kinds of noise and did not work with the old generator (non inverter) but seems to work with the new one.

Not a dumb question, but I don't have a good answer for you. I don't think I'd be comfortable running a microwave on any home sized generators but if you're willing to risk it and it works, who am I to be a buzz kill.

 

[AA/FC]

Microwaves are run all day, every day in RV/Motorhomes/Camper trailers on generator power without much issue. If the generator (inverter, or non-inverter) has enough power to run the microwave then I don't think there's much else to worry about.
Just my $0.02

 

[wyliesdiesels]

Not a dumb question, but I don't have a good answer for you. I don't think I'd be comfortable running a microwave on any home sized generators but if you're willing to risk it and it works, who am I to be a buzz kill.

why? are the gennys in RVs different in that they can run microwaves somehow?

 

[rlitman]

why? are the gennys in RVs different in that they can run microwaves somehow?

Fair point. I'm sure some of it is my paranoia talking. Also, don't RVs also usually have smaller (size and power) appliances and very often have soft start kits on the ACs, etc? That being said, google is loaded with people complaining about RV microwave power while on generator, and most RVs are designed to work best on "shore" power. In years past, better RV generators were 1800 RPM 2-cylinder synchronous, and were way under-rated (or to be more fair, most "emergency" generators are way over-rated), with lots more "starting" capacity (i.e. subtransient reactance), since they were designed for continuous use.

Anyway, I'm not saying it won't work. All I'm saying is, microwaves push the envelope more than most other appliances when it comes to small generators. In terms of failure to work, as well as causing damage to themselves, the generators and anything else that may be sensitive and plugged in at the wrong time. It's a risk I'd rather live without.

Now at work, on a megawatt generator, I don't have any concerns about the microwave. But even so, half a dozen failed capacitors in the wrong place will make more than enough noise to re-create the OP's UPS running on battery issue. BTDT, and chasing them down was lots of fun. To be fair, we're talking about caps the size of shaving cream cans (maybe twice the size of a central air compressor cap), but for 600VAC caps, that's still not a lot of capacitance.

 

[Jack Ryan]

The pictures explain the modified sine wave versus our sine wave. The scope pictures shows the output wave forms that the device deals with. Computers, even the industrial grades are power sensitive.

The image on the left is suffering from AC coupling issues. That is not a typical modified sine wave.

Jack

 

[David Paul]

Thanks guys for the replies. Gives me some points to consider. If needed I think I’ll keep it to just reheating coffee.

 

[Max]

The image on the left is suffering from AC coupling issues. That is not a typical modified sine wave.

Jack

I agree that the left one looks like an improperly scope probe. Here is another example:

 

[RPH]

Most likely switching noise from the transistors being turned on and off. This is a shot of a power quality meter. Nice clean sine wave until the mosfets start switching. This was heat treating a pinion gear. There is plenty of noise to be dealt with in high power applications. Plenty of engineering time spent mitigating this noise. This noise is contributing to the shoot through problems that come with transistors.
Clean sine wave.


Mosfet noise during heating cycle.

 

[Jack Ryan]

Most likely switching noise from the transistors being turned on and off. This is a shot of a power quality meter. Nice clean sine wave until the mosfets start switching. This was heat treating a pinion gear. There is plenty of noise to be dealt with in high power applications. Plenty of engineering time spent mitigating this noise. This noise is contributing to the shoot through problems that come with transistors.
Clean sine wave.

Mosfet noise during heating cycle.

I have no idea what type of inverter that is but the switching happens all the lime. Here, it looks like all hell broke loose when the load was applied. I think it is possible that noise was created by the load.

Again, without knowing the full context, it is hard to say. If it is a single level of PWM (not sinusoidal PWM), it is difficult to imagine how switching could generate that noise.

Jack

 

[MushCreek]

I tried running our water heater on our generator. It worked, but it didn't like it. The generator kept bogging down until it sounded like it was going to stall, then it would rev back up again. After 1/2 hour of that, I decided it wasn't worth possibly damaging the generator. The water heater elements are 4500 watts, well within the generator's capacity, but I think it's 4500 watts on one leg, judging by the way it's wired. One element is on one 120V leg, the other element is on the other.

 

[rlitman]

I tried running our water heater on our generator. It worked, but it didn't like it. The generator kept bogging down until it sounded like it was going to stall, then it would rev back up again. After 1/2 hour of that, I decided it wasn't worth possibly damaging the generator. The water heater elements are 4500 watts, well within the generator's capacity, but I think it's 4500 watts on one leg, judging by the way it's wired. One element is on one 120V leg, the other element is on the other.

That doesn't seem right to me. You would need a breaker twice the size (40A) for it to work that way. More likely each leg is switched separately, so one leg on each element remains hot when the thermostat is off.

 

[wyliesdiesels]

I tried running our water heater on our generator. It worked, but it didn't like it. The generator kept bogging down until it sounded like it was going to stall, then it would rev back up again. After 1/2 hour of that, I decided it wasn't worth possibly damaging the generator. The water heater elements are 4500 watts, well within the generator's capacity, but I think it's 4500 watts on one leg, judging by the way it's wired. One element is on one 120V leg, the other element is on the other.

That doesnt make sense for a 240v water heater.

It would mean the other end of the elements are wired to neutral. It also means you would get a quarter of their rated heat output.

More than likely, the thermostat is setup to have the lower element on until water gets to set temp point, then upper element is switched on (lower element is off). Both are wired 240v

 

[fitter30]

Use a cheap champion gen with tablets wifi and flat screen tv have no problems.

 

[Lucid Moments]

Use a cheap champion gen with tablets wifi and flat screen tv have no problems.

The funny thing is that the only thing that seems to have an issue with the power from my generator is the UPS. I have two other PCs that are not on UPSs and with the generator on they had no issues.

 

[The Cobbler]

More than likely, the thermostat is setup to have the lower element on until water gets to set temp point, then upper element is switched on (lower element is off). Both are wired 240v

I am pretty certain typically the top element comes on first to heat the of of that tank, then it switches off & the bottom heater comes on to heat the lower portion and bring the top up to full temp.

 

[rlitman]

The funny thing is that the only thing that seems to have an issue with the power from my generator is the UPS. I have two other PCs that are not on UPSs and with the generator on they had no issues.

The UPS is designed to make a decision. When the incoming power seems fine, go with it. Otherwise, switch to battery. Computers don't have that option. They just take what they're plugged into and either work or not.

But keep in mind that modern electronics are designed to work around the globe, where they could see anything in between 100 and 250 volts, and frequencies around from 50 to as high as 400 hz. Which means your 21st century computer will be happy with just about anything, but your UPS is still designed around the needs of 1970's computers (and yes, that means that "true sinewave" UPS isn't really all that important).

 

[dcg9381]

Also, don't RVs also usually have smaller (size and power) appliances and very often have soft start kits on the ACs, etc?

Some RVs come with soft starts. In my experience, not many. They are usually installed after.
Appliances (microwave) is smaller than residential (typically), but the AC is usually a bigger load than the RV microwave.

That being said, google is loaded with people complaining about RV microwave power while on generator, and most RVs are designed to work best on "shore" power. In years past, better RV generators were 1800 RPM 2-cylinder synchronous, and were way under-rated (or to be more fair, most "emergency" generators are way over-rated), with lots more "starting" capacity (i.e. subtransient reactance), since they were designed for continuous use.

People don't understand power management. They don't realize that they're running a fairly substantial draw by keeping their ammonia refrigerator on "electric" and they often leave the water heater on. Then they want to know why they can't start their AC with a 3000 watt generator.

You should be able to run a microwave off any RV generator capable of powering an AC (typically 2000 watts with soft start or above wattage). People just need to be aware of what else is "on" at the time... Or step up to generators in the 5000+ watt range.

My truck camper gets by on a 2000 watt inverter generator or 2500 watt Onan generator just fine. But you can do one major appliance at a time.... You have to manage the power. Shore power is 3600 watts for a "30A" RV.

 

[wyliesdiesels]

but your UPS is still designed around the needs of 1970's computers (and yes, that means that "true sinewave" UPS isn't really all that important).

thats highly dependent on the UPS model. I can adjust all the transfer parameters on my UPSs. but I use Eaton UPSs which are higher quality than your "engineered grade" consumer UPSs

 

[dcg9381]

I tried running our water heater on our generator. It worked, but it didn't like it. The generator kept bogging down until it sounded like it was going to stall, then it would rev back up again. After 1/2 hour of that, I decided it wasn't worth possibly damaging the generator. The water heater elements are 4500 watts, well within the generator's capacity, but I think it's 4500 watts on one leg, judging by the way it's wired. One element is on one 120V leg, the other element is on the other.

This is an excellent example of "need to test your generator"...
Can you easily disable the upper element? That's how I'd handle it.

 

[Jack Ryan]

Use a cheap champion gen with tablets wifi and flat screen tv have no problems.

Those devices have a switch mode power supply. The first action is to rectify the mains voltage which removed any issues with mains frequency and wave shape. A DC/DC converter then produces the (clean) DC voltage required by the device.

Things change a bit when high current is needed but consumer devices like these are not really "sensitive electronics".

The funny thing is that the only thing that seems to have an issue with the power from my generator is the UPS. I have two other PCs that are not on UPSs and with the generator on they had no issues.

As was mentioned, the UPS is designed to detect "dirty power" and transfer to battery operation. It assumes that whatever is connected to it does contain "sensitive electronics".

Jack

 

[RPH]

This is a board level print for a switch mode power supply. As one can see there is quite a bit more than most realize. SMPS units tend to operate at a high frequency to reduce component size and footprint. This helps with noise immunity. After filtering, then it is chopped back into the required dc output.

 

[Jack Ryan]

This is a board level print for a switch mode power supply. As one can see there is quite a bit more than most realize. SMPS units tend to operate at a high frequency to reduce component size and footprint. This helps with noise immunity. After filtering, then it is chopped back into the required dc output.

On the other hand, there is a lot more there than there is in a basic power supply.

The addition of soft start with its associated control logic, filtering to help stop switching noise being reflected back into the mains and multiple positive and negative DC outputs add to the complexity.

Jack