run a laptop from a petrol generator?

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stevetc
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run a laptop from a petrol generator?

Post: # 220156Post stevetc »

This time of year, the solar panel doesn't quite provide enough for the laptop on top of everything else, so i have occasionally been running it off a 4-stroke 1k petrol gennie. Thing is, i've been told i should never do this if i value the laptop (i do!) but no-one's seemed to know of anything i can do that'll make it okay. I've been variously told that it's because the gennie can produce power-spikes, and told that it's because the generator produces square waves, not a proper sine. (I don't have access to an oscilloscope).

Is there some gubbins i can buy which will sort this problem out? I know a bit about electrics, but don't wanna make an expensive mistake here. I've had a bit of search round google, and not much to be found. Does the box on the power cable of the laptop solve this anyway by producing regulated dc current? I can charge a battery and then run it from an inverter later but this seems like an inefficient use of petrol. Any suggestions would be valued.

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gregorach
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Re: run a laptop from a petrol generator?

Post: # 220159Post gregorach »

This may answer your question.
Cheers

Dunc

stevetc
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Re: run a laptop from a petrol generator?

Post: # 220186Post stevetc »

Thanks for that! It's quite reassuring, but there're a few different opinions there, which is the problem i've found - some people say NEVER do it, others that it's okay. It does help by suggesting that i need a surge-protector . . . Will try and find one. I've spoken to people in maplins and they don't know what i'm talking about. Haven't looked at web-sellers yet cos wanted to be sure it was the right thing. . .

Thanks for the help tho, i'll keep asking around . . .

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Re: run a laptop from a petrol generator?

Post: # 220187Post Green Aura »

Maggie

Never doubt that you can change history. You already have. Marge Piercy

Life shrinks or expands in proportion to one's courage. Anais Nin

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KathyLauren
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Re: run a laptop from a petrol generator?

Post: # 220228Post KathyLauren »

I do it all the time. In fact, I specifically got a laptop in order to be able to run it off the generator. I don't need the portability.

The rule about *never* running a computer off a generator applies to ordinary desktop and tower computers, not to laptops.

The problem is the generator's response to a sudden load. When a large load, such as a freezer, kicks in, the generator's throttle is still providing power for the previous, lower load level. As a result, the generator's speed drops, making both the voltage and the frequency drop as well. Within a fraction of a second, the governor senses the drop in speed and opens the throttle to compensate, and the generator resumes its normal speed. You see the momentary drop in speed as a flicker of the lights.

A computer that draws its power directly from the line will be adversely affected not so much by the drop in voltage, but by the drop in frequency.

A laptop does not operate directly from the power line. It draws its power from a battery. The power line is just there to keep the battery topped up. A battery charger is not significantly affected by minor changes in power line frequency, so there is no problem running a laptop off a generator. In effect, all laptops has built-in online UPS systems, which is exactly what they recommend for running electronics off a generator.

stevetc
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Re: run a laptop from a petrol generator?

Post: # 220230Post stevetc »

Thanks GreenAura . . . I don't know why the guy in maplins didn't know what I was talking about – that looks like the sorta thing they should have. . .

KeithBC – you have really reassured me! I've found quite a bit of advice on google, but all contradictory, and it didn't seem to be from people who actually did this. You've been running your laptop from a generator for a while, then? And it's okay? I've got mates who run a soundsystem from a big generator and they didn't seem to understand what I was worrying about.

I've been doing it anyway, for 3 or 4 weeks now, and the laptop seems fine . . . I had a think about power-spikes and sine-waves, and decided it would be cool. . . but then there's been times in the past when I've said “It'll be fine. . . “ (And you know how that1 ends. . .)

If you're telling me that I can keep doing it and I don't have to buy anything electronic & expensive, then that's the ideal result!

Do you mind my askin what size gennie you're using? Does it make a difference that mine is a baby 1k? And does other load make a difference, as long as it's constant?

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Re: run a laptop from a petrol generator?

Post: # 220236Post KathyLauren »

I don't make a habit of running it off the genny. I just needed the capability if I'm working when the power goes out. I do contract system maintenance over the Internet, and I have to be available to work even if we're in the middle of a storm. I've done it quite a bit, with no adverse effects.

I use a 6kW generator, because it also powers the fridge, freezer, and the well pump. The well pump is a biggie - about a 2 or 3kW momentary load when it kicks in. A bigger generator is better, because it will lose less speed when a new load comes on line. Minimizing the fluctuations is prudent even with equipment that is fault-tolerant.

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Re: run a laptop from a petrol generator?

Post: # 220237Post KathyLauren »

As for sizing the generator to the load(s), you have to consider both the steady load and the momentary loads. For steady loads (lights, motors that are already running), you don't want to draw more than 50% of the steady-state capacity of the generator. You can, in theory, draw up to 100% of its capacity, but that's not a good practice. A 100% safety margin is considered standard practice in most electrical designs.

For anything with a motor, you also have to consider the starting load. Electric motors draw a huge excess current when they are starting. A 1 horsepower motor (1HP is about 750 Watts) will draw 750 watts when it is running, but might draw 2000 watts or more for a second while it is starting. If you run it on a 1kW generator, it will stall the engine even though the running power 750W is less than the generator's rating.

Most modern generators are rated for a surge load in addition to their running load. Mine, for example is rated at 6kW running and 8kW surge. Applying the 100% safety factor rule (i.e. don''t use more than 50% of its capacity) that means I shouldn't use it to run any combination of motors that will draw more than 4000W starting, or any combination of loads that will add up to more than 3000W running.

You should plan for multiple loads starting simultaneously. This is not uncommon, for instance if you close a main breaker while several appliances are waiting for power. So my 4000W maximum surge load needs to be enough to cover the well pump, fridge and freezer all starting at the same time.

stevetc
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Re: run a laptop from a petrol generator?

Post: # 220301Post stevetc »

Wow, 6k . . . mine's only a 1.1, which is fine for me. We do also have a community 4k . . . but from what you say, it sounds as though I'm better off sticking to my own little one where I know what loads are running. . . I only use it with a phone charger, laptop, battery charger . . . and it seems to be okay. With the community one, I won't know when other peoples' loads are going on an off. . . I'll go and get a surge protector, tho. . . thanks!

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