Line conditioners are also a thing. They’ll smooth out the electricity from the generator and provide constant 120V 60Hz. They’re designed to do exactly what you want, but won’t save you much over getting a UPS.
A good UPS will also protect your computer from brown outs during regular times, and should run long enough so that you can move the UPS from the wall to the generator when the power goes out. Look for a UPS that has a good line conditioner builtin.
A normal lead acid UPS will take a long time to charge, so if your generator is providing bad power, causing the UPS to cut over to the battery, you may drain the battery quicker than you can recharge it during the good times.
I’ve had pretty good luck with the Cyberpower ones. They’re usually much cheaper than APC, and when everything is working, they’re just as good. The problem I’ve had with Cyberpower is they don’t always know when their battery is dead. They’ll claim everything is good and 25 minutes of runtime at current load, then switch to battery and die immediately. In my experience APC will just start complaining the battery is bad.
I’ve never seen a lower limit that high. Japan has a 100 V standard and essentially all modern devices are made to be compatible with that as a lower limit. Many supplies will give some extra margin and are rated down to 90 V. And all will have some engineering margin and will handle drops even below that, especially if the supply is not loaded at close to the maximum.
My PC regularly keeps running through power glitches that reset my oven clock and other devices. It has beefy smoothing capacitors that will handle glitches of a cycle or two.
In my experience with generators of that size, a UPS will often not accept the generator output due to noise and frequency variation. This is especially true if you are adding additional loads or if the existing loads are cycling on and off. UPSs are intentionally designed to switch to battery power if the input varies by X, which means many units constantly switch between commercial and battery power…which isn’t desirable.
I’ve found that a better solution is to use an auto transformer (about $100 on Amazon). Proper auto transformers isolate the output from the input and do a lot to reduce noise and transients. The switching power supplies in computers seem to appreciate this. Switching power supplies are fairly tolerant of frequency and voltage changes, as evidenced by the fact that many of them are designed for both 120V/60Hz and 240/50Hz commercial power (usually laptop bricks, but you get the idea).
Ah, now ya tells me-- I just ordered that $175 UPS I linked to above on Amazon.
Oh well, at least a UPS will prevent my PC from immediately shutting down when the power goes out. And, I think our generator supplies pretty reliable power-- as I mentioned, we’ve run other electronics like our TVs on generator power and never had a problem. I’ve even run an older PC I used to use for work, that I wasn’t as concerned about ruining, on generator power, and didn’t have any noticeable issues. Maybe I’ll test the UPC on generator to see how well it charges so I know what to expect when the power goes out again for reals.
An maybe I’ll get that auto transformer too, and set up a chain of “incoming power supply → auto transformer → UPC → computer”. Unless that would be problematic somehow…?
The point is, a UPS will handle the same tasks as a line conditioner - whatever the issues with power going in, power coming out will be OK for the computer (and also not interrupted). I suppose another issue is - what else is the generator running? Does it power a fridge or freezer, which could dip the voltage when it kicks in? A UPS is designed for such power problems.
What’s the mechanism for switching over? Do you have to manually unplug the whatever from the house and into a cord running to the generator (and then back later?) If so, UPS is doubly good. Depends how fast you can react, whether 15min is good enough to fire up the generator and switch the UPS over. It should be, I would think.
The power rating of a typical computer is designed to handle a variety of boards thrown at it. Unless your computer has an advanced graphics board or some other interesting add-ons, 330 should be fine. But when you get into graphics workstations, a Geforce GTX 3060 board for example needs an extra 150W and the higher end (3090) double that. Some computers with slots have a power supply sized to handle such extra loads, but if you aren’t putting that load in, you should be fine. Laptops, even less draw.
The 1500VA UPS units I have will switch between line voltage and battery every few seconds/minutes when I’m on a standard generator. The batteries, of course, run down and I end up getting maybe 140% of expected runtime. The whole point of a generator is to have continuous uptime, so it’s disappointing.
Auto-transformers are pretty good at filtering spikes and high-frequency noise. Might work…might not. The ones I have were used with old film projectors. They basically eliminated blown lamps due to spikes coming from the antiquated wiring in an old building. A scope shows that there’s a lot less noise when I put one on the generator output.
So you’re saying that if I could expect to get 15 minutes of computer runtime off the battery with no power at all, I might only be able to expect 25 minutes or so of battery power on the generator? That sucks.
I have two 1500VA units, one is an APC and the other is some other brand (Belkin?). The circuitry senses errors in the commercial power and switches over to internal battery in about 1/60 second to maintain the output to my computers. The problem is that a standard generator has enough noise and variation to convince the UPS that it needs to use the batteries. My units also won’t switch back to the input (now generator power) for a certain period of time. This is to make sure that input power has actually been restored and is stable.
The result is that any error at all in the generator output makes the UPS go to internal batteries for 5-10 seconds, then switch back to the generator for maybe another few seconds.
Of course, this doesn’t happen if I use my small inverter generator, which produces pure sine wave output. But my small generator is only a continuous 1600 watts…not enough to power the other things I need.
My Dell desktops seem to run fine if I put an auto transformer directly on the big generator and then use it to power the desktop. The only problem is that I have to shut down my desktop to transfer it to the generator and then again when I take it off. So, I use a UPS for the desktops, but I don’t power the UPS from the generator. Instead, I use the 15 minutes to shut down the computers and then move the power cords to the auto transformer. Once I’m convinced that commercial power has been restored and is stable, I reverse the process.
The circuitry in the UPSs is pretty sophisticated and it apparently looks for all sorts of commercial power “errors” to make sure the transition to internal batteries takes place immediately. Newer units are even more sensitive about the quality of the input power.
After two successive failed deliveries Amazon says my package may have been lost, and gave me an easy click option to cancel the order. So I took it as a sign from the universe that I should not get the UPS and canceled it.
@ZonexandScout, I want to go the auto transformer route, but I’m really not sure what to get for my particular needs. This is what I see when I input ‘auto transformer’ into Amazon. Can you help point me in the right direction?
I generally call them “auto transformers,” but they are more properly called “isolation transformers (1:1 transformers).” The auto-transformers I use are adjustable, so you can, say, reduce the input voltage from 125 VAC to 110 VAC (or any voltage you care to).
There are several of these units in the $80 to $120 range on Amazon. They usually have a big knob on top. The problem is that these newer ones may not isolate both output legs (hot and neutral) from the input legs. The neutral may be common to both the input and output and only the hot leg goes through the transformer.
True isolation transformers are like big versions of audio ground isolators you use to get rid of hum and noise in your car. Both the hot and neutral legs of the output are completely electrically isolated from the input. High frequency noise, transient spikes, and distortion have a hard time getting across the actual transformer. Affordable units are usually in the 500 to 800 watt range, but you can get really big ones for more $$$. eBay might be an alternate source for a used one. These are often used in industrial and hospital environments.
TL:DR What you want is an isolation transformer (1:1) for 120 VAC. Both legs on the output should be isolated from both legs on the input.
Well, I looked up isolation transformers, and the ones with the wattage I would need- 650w- get real pricey. And honestly, I still don’t really understand exactly what I would need.
If I’m going to be spending upwards of $500, I’d probably just get a a separate inverter generator for my computer rather than an isolation transformer. Or just give up. And just continue to call in to work and say sorry, power out, no can work.
This inverter generator is $340 and puts out 2000 watts. Still a little pricey for 4ish power outages a year, but not too bad. Would this work for my needs if I was to decide to spring for it?
That should work just fine, I would think. I’ve got a larger standard generator and a smaller inverter generator. I prefer to run the bigger one and load it up. Engine-driven generators provide true sine-wave power, it just tends to vary a bit in frequency/voltage as the load changes. Switching power supplies actually handle that pretty well. UPSs do not…if they don’t like the input voltage, they fall back to the internal batteries. This is the root of the whole problem.
I’m fortunate to have a couple isolation transformers already. The larger industrial ones ARE pretty expensive.
Two things that may not have been explicitly mentioned …
Some computers that use active PFC (power factor correction) power supplies may require pure sine wave power to operate correctly. A cheaper UPS typically will not provide pure sine wave, but a square wave approximation. This is fine for many computers, but may not be for those with active PFC.
A high-end UPS, like an APC Smart-UPS 1500 VA, will not only provide pure sine wave backup power, but will also condition “dirty” power inputs. However I have absolutely no experience with how such units might interact with generator input power.
Just my input as a non computer guy. But I worked and was trained over 50 years ago about ships and ship board power. And I worked over 40 years ashore in office buildings.
1st about power back ups. I would buy an APC. Due to a lost neutral in a 3 phase system in one building the voltage at the outlets in some offices went up to 190 volts ac. The offices with the cheaper power backups we had to purchase new computers, the high voltage fired them. The offices that had the APC power supplies, not a one of them lost a computer. But the high voltage did fry the APC power supplies.
Newer generators produce DC power which is then inverted into 60 120 VAC power. The frequency is not depended on the RPM of the motor. One way to tell the difference when put under load the motor will speed up to maintain frequency and voltage. This is done electronically.
An older generator has a synchronized generator with an DC field. The RPM of the motor will determine the frequency and a voltage regulator will vary the field to maintain the voltage. A governor if required to keep the motor running at the proper speed, usually 3600, 1800, 1200, or 900 RPM. When a load is placed on the generator the governor will increase the fuel to maintain the proper field. Depending on the quaility of the governor the cycles may vary on or two cycles according to load.
But if you plug a good backup power supply into the generator and then plug your computer into the power supply you should not have any problem.
Now about size Watts. When setting up a display or classroom we figured 2 amps (240 watts) per computer. By using this swag figure we never had any trouble with over loaded circuits.