Generators and computers

I would worry more about the monitor than the PC. A PC switcher supply has a very wide mouth when it comes to power range. Some can go from

100-250 without a burp.

.. but does that mean I can safely run either of them through the UPS?

Generators have to be oversized to run a UPS. Putting a laser printer on a UPS is a very bad idea. Laser printers, and copiers, gulp huge amounts of current for very short durations to keep their fusers hot. This kills the output voltage of the UPS since it is a relatively weak source.

Charles Perry P.E.

I agree. A (small) generator typically produces a distorted sine wave with flat tops that do not achieve the full peak value that a service supply would. In many cases the UPS will treat this as a supply problem and keep switching to battery backup. Or worse, cycling backwards and forwards as, when the UPS goes to battery, the generator voltage rises and the UPS thinks the supply has been restored. You are often better off without the UPS when running on a generator. After all, you won't have long supply lines and have very limited distribution, so the chance of them being hit by lightning or your next door neighbour starting up an arc welder on them are pretty remote.

Laser printers, especially big ones, are best avoided with (small) generators. As Charles says, their power drain is not constant and they draw lots of amps everytime their fuser heater warms up. They could easily drag the voltage down to the point where the UPS switches to battery. And then back to genny...

So, either go for a much bigger generator or leave out the UPS. Consider using an inkjet printer instead of the laser.

I have set up and used very many systems such as you describe. To keep the UPS and laser, I would probably be looking to see a ~5kW genny. Hard to tell without a list of the equipment. Or stick to the lower power genny, leave out the UPS and swap the laser for an inkjet.

Since AC mains electricity is so clean, then plug-in UPSes want AC power from the generator to be just as clean. But generators may (or may not) be clean electricity. Therefore many plug-in UPSes will disconnect completely from AC power and switch to battery power ... until the battery dies.

Furthermore, when not in battery backup mode, the generator would then connect directly to computer. So again, what does the UPS provide? Still provides nothing useful.

Meanwhile, computers and CRTs should be so robust as to make many electrical problems irrelevant. The one generator type problem that can cause electronics damage is a generator that does not control its output voltage fast enough - responds too slow. For example, if using a laser printer, the generator must power up to meet the extra load. Then when laser printer stops consuming so much power, the generator provides too much voltage - electronics now damaged.

Two ways to solve this slow response to load changes. One is to install a generator significantly larger than required. Another is to buy those more expensive generators (ie Honda) that properly adjust to changing loads.

D> .. but does that mean I can safely run either of them through the UPS?

Invest in a laptop; forget the laser, and use a UPS with a large external battery, or a generator. The laptop AC adapter will work fine from UPS delivered power. My thinkpad AC adapter has a label that shows input voltage range of

100 - 240 and input current range of 1.4 amps to .7 amps. So a 600 watt UPS could supply power without risk to itself for as long as the external battery lasted.

A UPS + external deep cycle marine battery of sufficient ampere hours - say 200 - would give you all day quiet operation in a smaller volume than a generator and the gas to keep it running, and discharge to about 50 %. (Charge it overnight.) And the laptop battery will give you another 2-3 hours should the marine battery drop too low. If you must print, use an ink jet, plugged into the UPS.

Ed