power conditioning

[[email protected]]

This is probably an old question, but here it goes again.

I have recently bought a generator for emergency use. I want to
occasionally use it to power the tv and/or computer equipment. I have
read numerous posts that state some generators operate electronic
equipment ok and many that say it fried the electronics. So here's the
question: What type of power conditioning is best for interfacing the
generator power to electronics? UPS? Inverter? Other?

Enuf

 

[Mike Berger]

The best way to run your electronics on backup power is with DC,
using the generator to charge the batteries. High-reliability
Telco and network equipment is powered by 48 volt inverters.

Most smaller UPS's don't work well on power from small generators.
The voltage and frequency will both be too unstable. They'll keep
switching back and forth between line voltage and inverter.

So if you're running anything besides lights and motors from the
generator, you're taking a chance with out-of-spec noisy power.

 

[[email protected]]

The best way to run your electronics on backup power is with DC,
using the generator to charge the batteries. High-reliability
Telco and network equipment is powered by 48 volt inverters.

Most smaller UPS's don't work well on power from small generators.
The voltage and frequency will both be too unstable. They'll keep
switching back and forth between line voltage and inverter.

So if you're running anything besides lights and motors from the
generator, you're taking a chance with out-of-spec noisy power.

OK, inverters come with outputs in true sine wave and modified sine
wave, with the modified wave units being more common and cheaper. Will
tv's & computers work ok with modified sine wave inverters?

Enuf

 

[[email protected]]

OK, inverters come with outputs in true sine wave and modified sine
wave, with the modified wave units being more common and cheaper.

Actually, the cheapest and the most common inverters have
square-wave-output.

Will
tv's & computers work ok with modified sine wave inverters?

Yes.

 

[Mike Berger]

For the most part, yes.

 

[Bennett Price]

I wonder about the initial assumption that a small generator is unsafe
for TV/PC. Isn't the generator's output pretty close to a perfect sine
wave - better than what comes out of a UPS? The frequency may go up and
down a bit - I don't think this is a big problem unless you are using a
turntable. Voltage will waiver but if you don't overload the generator
this might not be too bad.

If you wish to use a UPS w. the generator, be sure to buy one that has a
sensitivity switch to ignore generator variations.

 

[Mike Berger]

They're unsafe in that the voltage and frequency can fluctuate wildly
especially as the load changes. I'm sure some consumer electronics
devices will handle it fine, but most of it isn't designed with wide
operating margins these days.

 

[Mike Berger]

In your experience which ones work ok with generators? None of my
APC SMART-UPS or Matrix UPS controllers do, even at lowest sensitivity.
The very high end Lieberts work, but they're extremely expensive.

 

[Michael A. Terrell]

I wonder about the initial assumption that a small generator is unsafe
for TV/PC. Isn't the generator's output pretty close to a perfect sine
wave - better than what comes out of a UPS? The frequency may go up and
down a bit - I don't think this is a big problem unless you are using a
turntable. Voltage will waiver but if you don't overload the generator
this might not be too bad.

If you wish to use a UPS w. the generator, be sure to buy one that has a
sensitivity switch to ignore generator variations.

No. Take a look at the output with a scope and you'll see.

 

[Bud--]

No. Take a look at the output with a scope and you'll see.

Any idea why it isn't a sine wave?

bud--

 

[Michael A. Terrell]

Any idea why it isn't a sine wave?

bud--

It would take way too much typing. Find a college EE book on power
generation and distribution, then prepare for some heavy reading.

In layman's terms, its the transformers and motors that help clean up
the power on the grid and you don't have all that to help filter the
output on a single small generator.

 

[Mike Berger]

Not to mention the serious phase shift.

 

[Bennett Price]

I stand corrected about suitability of small generator for TV/PC.
I found the following APC FAQ's very helpful. Also addresses waveform
of small generators (with non-linear loads).