Protecting PC from Voltage Surges While Running Without UPS

[Manojit Ghosh]

Hi,

What precautions should be taken when running a pc without ups to protect it from voltage surges?

 

[RoasterMen]

Use an AVR.

 

[Megahertz07]

Any surge arrest with more than 2.000 J and with a switch is good.
SurgeArrest - Newegg.com

I would buy this BELKIN BE112230-08 8 Feet 12 Outlets 3780 Joules Surge Protector with Telephone and Coaxial Protection - Newegg.com

 

[TechnoMage2016]

Newegg? They pulled a Bait n Switch on me and really ticked me off, so I shredded my card, closed my account and will do NO business with them...EVER AGAIN.

Ok, back on topic:
There are two types of surge protection. One is passive protection where some solid state device like a "Transorb"* shunts the surge (voltage spike) to ground. Think of it as being a 5000Watt Zener Diode.
The transorb or even a Varistor, is usually NOT destroyed in the shunting process.
Here is a better explanation.
Transient-voltage-suppression diode - Wikipedia

I worked with Transorbs a lot when I was doing Spike Suppression work at CAT, years ago.

Then there are the type of surge suppression used in most Telephone Line surge suppressors.
That is usually a small in-line fuse. It takes time to blow out a fuse and in that time enough of the surge can pass through to damage delicate electronic components, like we find in a Telephone Modem.
In most cases, when one of those Surge Suppressors stops a surge by blowing out the fuse, the Surge Suppressor has to be replaced, because the fuse is soldered in, and is not easily replaced. I've done a few of those, but it's a real PITA, even to just find replacement fuses.

What many PC users don't fully understand, is the amount of Surge Suppression already built into the PSU in the (desktop) PC. That's pretty extensive in the better quality PSU's.

In most places in the US, the local power company will supply a Surge Protector where the Line Power enters the house (home or business). I have one of those, where the Power Line enters the Electric Meter.
Then at the wall outlet where my PC is connected, I have a "TeleMax 2" surge protector with a very high
Joule rating.* Then there is the APC UPS, also with a Surge Suppression Circuit with a high Joule rating.
* The retail $ on that TeleMax 2, was more than I spent on my latest UPS.

So by the time the PSU output reaches my PC's circuits, it's already been through 3 very good Surge Suppressors.
Add to that, the other four UPS's and several surge suppressed power strips in my house and the additive Surge Suppression is up in the Millions of Joules.

So my personal recommendation, as a Computer tech, is to always have your PC or other sensitive electronics, plugged into a UPS of adaquate wattage capability.
I also recommend the APC Brand of UPS. Over the past 25 years, I've always gotten the best results with the APC brand of UPS. You can even replace the little Gel-Cell battery in the UPS, with a much larger Lead Acid battery, like a car or tractor battery. I have three UPS's, that use such external batteries for their reserve power.
http://i63.tinypic.com/29kywyp.jpg Click link to view picture. This battery only cost me $19.95 at Walmart.

On my first test run of this UPS, it ran my desktop PC system for three hours, before it ever gave out with the first beep.
I once tried a hookup like this with a Cyber Power UPS, and it absolutely would not work.

Cheers Mates, and Happy Computing,
TechnoMage

 

[mrjimphelps]

I've always felt that a UPS or other battery system will give good protection against surges and spikes, because the computer is running off of the battery, not the A/C current. The battery absorbs the surges and spikes, because it is connected directly to the A/C current.

Technomage, do you agree with that statement? And if so, how long could you safely continue with surges and spikes happening on the A/C line? The point of my question is, if you are running your computer off of a standard gasoline generator, and using a UPS as a buffer for the fluctuations in power from the generator, how long could you safely operate your computer in that situation? Seems to me you could go for a long time.

 

[TechnoMage2016]

Well, your premise that the UPS runs the inverter constantly is somewhat flawed.
Granted, there are some very expensive UPS's that do that, but the cheaper home variety DO NOT (run the inverter constantly).

Under normal AC input, the UPS directs the power right through to the output jacks. (inverter is shut off and the battery charging circuit is running, to keep the battery fully charged). And when there is a line power failure, only then do relays close directing the battery power through the inverter (square wave output) to the output jacks.

Then when the line power returns, relays transfer again, directing the Line Power to the output jacks and the inverter is turned off, and the battery charger circuit begins to recharge the battery.

Years ago, I designed and built similar systems. And in later years, I worked as a technician in a shop where we repaired APC UPS's, under contract with APC. So I have a Working knowledge of those devices.

Also, in VERY Expensive UPS's you can get one that does put out a sinusoidal Sine Wave, when under battery power. (60 cps, crystal controlled) Most electronics today, like TV's, PC's, and other home electronics, do not require a Sine Wave input, but are perfectly happy with the square wave output of the common UPS.

Generally speaking, only motors that incorporate a start capacitor require a Sine Wave input. Brush type motors like most vac. cleaners, hand tools and kitchen appliances, just don't care, whether the AC they get is Sine Wave or Square wave, as long as the voltage and frequency are correct.
My electric toaster runs great on 120 volts, 60 cycle square wave, but it hums like a Bi***!
My Microwave oven works too, but with a little extra Hummmmmm!

Ok, that's more than was asked, but I do go on and on sometimes. It's an Auld Fahrt thing!

Y'all have a great day now, Y'hear?
TechnoMage

 

[mrjimphelps]

I have read that it is bad for a computer to run it off of a gasoline generator, because of the fluctuations in power. Is this true? And if so, what is the best, or maybe the most practical, way of making it safe to run a computer off of a gasoline generator?

By the way, thanks for the info.

 

[TechnoMage2016]

Not since the days of the IBM AT, have PC power supplies been of the 'Series Regulated' (analog) variety.

Every power supply for PC's, TV's, VCR's, cable boxes and most other home electronics are of the "Switching Regulator" variety. The very first thing they do is rectify the line power to High Voltage DC and then regulate that down to whatever output voltage is required. So hash on the AC line is basically ignored (filtered out) at the input circuitry. PC (desktop) power supplies are loaded with surge and spike protection. Open one up and look at it sometime.
My own computer, for instance, runs just fine on my generator's output, of 124 vac. Or my UPS output of 120 v-Square Wave AC.

Once the input AC gets through the surge protection, and in-line fuse, the first device it sees is a Full Wave Bridge Rectifier, and from there on, everything in the PSU is DC.

Somewhere I read that "all men are created equal", but that is not true for Generators. I'm quite sure that some are better than others. I have what I think is a pretty good one, but without an O'scope, I can't tell if there is any 'Hash' on the output or not. I just know that it runs my deep-well pump, and fridge, and even my window AC, OK.
And for me, that's the main consideration. That guarantees that I have lights, fresh water, and cold beer.

I hope that answers your question.
TechnoMage

 

[Lady Fitzgerald]

...Generally speaking, only motors that incorporate a start capacitor require a Sine Wave input. Brush type motors like most vac. cleaners, hand tools and kitchen appliances, just don't care, whether the AC they get is Sine Wave or Square wave, as long as the voltage and frequency are correct...

Actually, more and more appliances now require sine wave AC to run properly or, in some cases, to run at all. Most Samsung refrigerators, especially the smart ones, will not run on a square wave or will not last long if they do run at all (check the RV forums for the horror tales of what happens when someone tries to run a Samsung residential fridge off a square wave inverter). This is becoming true with more and more appliances that are depending more and more on electronics to operate. More and more computer PSUs (especially the active PFC—Power Factor Correction—variety) will not run or run well on even a stepped sine wave; they have to have a sine wave. For that reason, I always recommend that people only get a sine wave UPS (better safe than sorry).

Computer PSUs regulate their output so spikes and surges in the output will not be a factor but the input has very little such protection, if any. At the very least, one should have a surge arrestor on the input.

 

[Megahertz07]

Generally speaking, only motors that incorporate a start capacitor require a Sine Wave input.

You are terribly wrong.

Generally speaking, motors that are mainly powered on the stator are pure ac motors and very dependent on frequency. The RPM is the frequency (cycles per minute) divided by the number of pair of poles). And any voltage that isn't pure sine has harmonics that only generate heat and noise.

Generally speaking, motors that are mainly powered on the rotor (brush type) are DC motors. Some of these motors are fed (field stator and rotor) by AC and they act as an electrical - mechanic rectifier. (field stator and rotor are in series).

Transformers are very dependent on frequency and only a small DC current can saturate it. Again, any voltage that isn't pure sine has harmonics that only generate heat and noise.

The only thing that will run independent of the frequency are rectifiers an resistance heaters (as a toster).

As Lady mentioned, Power Factor Correction devices are LC resonant devices. The harmonics of a non sine wave can be disastrous.

Computer power supply's work on tree phases:
Rectifier - The AC is rectified and charges a high voltage electrolytic capacitor.
Inverter - The DC voltage of the electrolytic capacitor passes thought a PWM inverter that feeds a high frequency ferrite transformer.
Rectifier - The ferrite transformer AC output is rectified and charges a low voltage electrolytic capacitor.

The output (12V, 5V) is controlled by altering the PWM of the inverter.

In my opinion, UPS doesn't protect a computer more than a good surge arrest (LC low pass filter + Varistor)

Mega,
Electrical Engineer

 

[Ranger4]

I use a surge suppressor & a UPS on my computer. I also use this combination when running the computer from my 7.5KW back up generator which is petrol powered & does not have sine wave output. In fact the voltage & frequency do vary slightly depending on the load on the generator, but this have never been a problem with the computer & it works perfectly.

I also run a 50" plasma Panasonic TV from the same generator & it works perfectly as well, so I am inclined to think that too much is being made by sine wave output generators. The fridge, kettle, toaster, all the lights & the cordless phone also work on the generator.

Most devices that incorporate intricate electronics use a transformer & rectifier to convert the AC current to DC usually about 3-12 volts. Also a lot of hand held devices use batteries that slowly drop in voltage as they are used so constant voltage on these devices is not a problem.

The most damaging things for electronic equipment are voltage spikes from electrical storms & bad power authority switching systems. A lightning strike nearby to you that hits the power line will very likely blow most of your electric equipment that is not disconnected from the power.

 

[Megahertz07]

Bligh you're right on generator voltage & frequency do vary slightly depending on the load on the generator but all mechanic generators produce sine wave outputs (single phase or 3 phase).
I also have a 2.4KW gas back up generator that I power all my house (including Air conditioners). Only the water heater (3Kw) is left out.

 

[Ranger4]

Luiz, mine is the same as yours so I can run the whole house including the Air Conditioner, stove, microwave etc., not necessarily all at once though. Of course the water heater is not included. I get a lot of electrical power outages here from storms & other failures.

Thanks for pointing out my mistake on sine wave. I was really trying to point out the variation of generator load & speed causing changes in voltage & frequency.

Just as an interesting side note my microwave has a clock that it tied to main frequency, hence it is very accurate. However, when using the generator it tends to gain slightly, indicating a slightly higher frequency than the mains.

Also we have 240 volts 50 Hertz power here.