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Old 09-07-2008, 21:23   #16
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Bit of info here on power usage of computers that a few other sites refer back to as a source.

How much electricity does my computer use?

Dave
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Old 10-07-2008, 11:48   #17
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I'm confused by all these opinions on efficiencies of DC vs AC power for computers. Can anyone cite some empirical tests?
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Old 10-07-2008, 12:26   #18
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"Whatever, the claim that the car type adapters are DC only devices is entirely incorrect - they go 12v DC in -> AC -> DC out."
Midland, that's not quite right. The "DC to DC" adapters really do NOT USE AC at any point. They may used pulsed DC--but that's still not AC. AC power supplies typically use transformers (as in wall warts) and transformers are always terribly less efficient than "switching" power supplies, which are all solid-state and DC all the way. The switched DC pulses they use, are still not AC power even if they are similar to it.

Regardless of that, I've never heard anyone say they are more efficient because they don't use AC. They are simply "twice" as efficient because they are doing ONE CONVERSION, instead of converting once up to 110VAC and then A SECOND CONVERSION back down to the lower DC level the laptop needs. The savings is from one conversion instead of two--and it really doesn't matter what flavor (AC, DC, PWM, PDC) the internal electricity is.

That's where the big gain is.

Sandy-
Since computers (especially laptops) internally DO NOT USE AC FOR ANYTHING, there is no reason to waste power in making or supplying AC to computers. Computers run internally on 3.3 volts, 5 volts, and 12 volts, depending on which parts you are talking about. Now, if all you need is 5.5 DC volts (today's laptops) why on earth would you waste your time and money making 120 volts of AC? That would be like sweeping your floor before you vacuum it: You're just doing the same job twice and wasting fully half your effort.
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Old 10-07-2008, 12:42   #19
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Many thanks!

Thanks so much for all your replys, I'm still trying to digest it all..

The boat I'm looking at does have an inboard engine, with a 12v system. It seems good news to me, that I don't have to bother with an ac set up at all.. and that I can run the laptop off the system already there.. could I just plug it in to the 12v and see if it works?!

I still have to consider the best way to charge the batteries, but i'm getting there, I think..

Warm regards,
Mark.
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Old 10-07-2008, 16:23   #20
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Mark, very few laptops will just plug into 12VDC. If you have a dc-to-dc power adapter for it, yes, that should plug in directly. Usually sold as a "car and airplane" adpater under names like "Airporte" and Igo's "Dual Power" line, that uses the same brick for 12VDC and 120VAC, with two different power cords.
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Old 10-07-2008, 16:43   #21
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Quote:
Originally Posted by hellosailor View Post
"
Computers run internally on 3.3 volts, 5 volts, and 12 volts, depending on which parts you are talking about..
So as I have the space onboard, there is probably no reason why I cant use the computer I'm banging away on now is there?

I too was told everything was 12 v or less, even the large lcd monitor, portable hard drives and printer seem to use 12v or less.

Dave
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Old 10-07-2008, 16:47   #22
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Originally Posted by hellosailor View Post
Midland, that's not quite right. The "DC to DC" adapters really do NOT USE AC at any point. They may used pulsed DC--but that's still not AC. AC power supplies typically use transformers (as in wall warts) and transformers are always terribly less efficient than "switching" power supplies, which are all solid-state and DC all the way. The switched DC pulses they use, are still not AC power even if they are similar to it.
A simple explanation of buck and boost converters, using simplified circuit diagrams is at DC-DC Converter Basics. There are plenty of other sources on the internet including Wiki. People will see that they do work as I say and that the mode of chopping DC up to AC is similar to an inverter.

Sandy - I don't know of any empirical comparison of efficiency between going the inverter way or the step up converter (boost converter) way but as I said I suspect that as long as a small inverter is used the difference is small, or if one looks at it from the point of view of energy lost it is of little consequence.

The following is as I see it -

Putting it in context typical laptops draw around 2 Amps or so if not charging their battery (a friend and I tested a number of HP/Compaq 1GHz to 2GHz ones, but undoubtedly some use more and others less) - and people seem to forget that if the laptop is drawing a couple of amps more while charging its battery this, apart from the conversion loss, is not lost energy. So as long as the powering arrangement used is scaled towards powering the notebook or other small appliances of similar draw, rather than 1kW appliances it takes a large inefficiency to result in much actual loss in Ah.

Looking at it another way from ones own experience and forgetting efficiency but trying to get a grip of the energy lost as heat, the mass of a little block such as the notebook's own AC power supply, a small inverter, or a step up converter is very low so it only takes a very small amount of heat to raise their temperature a lot. But in fact these things do not get very warm so the energy lost as heat in them is in magnitude terms quite small. I suspect in order of a very few watts - a comparison can be made with how hot a similar mass enclosed light fitting might get (where most energy is emitted as heat and captured if the fitting is enclosed) - even a 5 watt lamp gets orders of magnitude hotter than any small power supply of the types mentioned above.

For large inverters I would not like to comment, except that it will vary significantly with the inverter, its type and how well it handles low loads.

For myself, I use a step up converter for powering the nav notebook purely from convenience and as there does not seem to be much point buying a small inverter given we have an around 1kW inverter on board. But I do put very small loads on that, such as charging camera batteries, etc, and don't worry about losses and any effect of those is lost in the noise so not noticable against our normal daily draw.

Regarding losses with low loads, people tend to forget that if drawing 200mA, say, a 100% loss seems terrible but the actual loss of 0.2Ah per hr run is inconsequential to other than energy starved boats.

My suggestion would normally be that if one does not have an inverter on board and a small one would be useful for other duties then buying a small quality inverter and using the notebook's own power supply might be the most useful way to go. If one has an inverter on board already, then if large then a step up converter may be worthwhile from an energy saving point of view if the boat is energy poor but if the inverter is small then using the notebook's power supply on that would be a reasonable option. As far as energy loss is concerned among those options I do not see them likely to be different enough among themselves to influence the decision (except perhaps in an extremely energy starved boat, but in such a boat one would assume one would not be powering things such as notebooks?).
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Old 10-07-2008, 17:11   #23
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Regarding powering notebooks direct off 12 v it is my experience that those using 6 cell Li-ion battery packs (so most notebooks) will mostly do so.

This is plain common sense if one thinks about it as the 6 cells are arranged in two banks of 3 in parallel giving a battery voltage of around 10.8v and (apparantly ) the computer runs quite happily on that.

The higher voltage that comes from the notebook's own power supply is normally (always?) for battery charging purposes - the Li-ion battery packs have their own over charge control circuitry inside them.

But if doing so I would be wary of the quality of the boat's DC supply in so far as spikes, etc are concerned as in normal use the notebook is not subject to those off its battery and if externally powered through its own power supply or a step up converter that will have a smoothing effect on any spikes. That is, the computer from its DC input plug may not have much protection against spikes - but we use a MOSFET surge protector on our DC systems which may provide sufficient protection.

Notebooks with 8 cell packs (2 banks of 4 cells in parallel, so around magnitude 14v) I could not comment on not having tried any, and those notebooks which "talk" to their power supplies and expect to be able to do so if anything is plugged into their power in port will provide difficulties of their own.
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Old 10-07-2008, 17:53   #24
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"This is plain common sense if one thinks about it as the 6 cells are arranged in two banks of 3 in parallel giving a battery voltage of around 10.8v and "

You and I would think so. But I've seen computers using "3x2" and "3x3" packs, that should be 10.8 volt packs, shipped with 20 volt adapters. There's no way in hell that they need 20V to charge a 10.8v LiOn pack, the batteries only need 4.x volts for charging so a 15-volt supply would be more than adequate. Something different is being done internally. Me? I'm not brave enough to randomly stick a 12V or 14V power cord into a computer that's rated for 18v (common) or 20v input, and risk blowing the whole machine.

"the mode of chopping DC up to AC is similar to an inverter." That's not SIMILAR to an inverter, it is the definition of an inverter: Any device that converts low voltage DC to higher voltage AC. Now, when you do it the other way around and convert AC to lower voltage DC, the power supply may be analog (like a traditional wall wart, with transformer in it) OR DIGITAL, like the dc-dc converters. The point is--unless you know for certain which one it is, you can't presume it is either type. You cna't presume how efficient it might be, all you can presume is that using two "power adapters" to accomplish the work of one, will be wasteful.

As Arthur Clarke said, any sufficiently advanced technology is indistinguishable from magic. "Reasonable" and 'common sense' become dangerous concepts to try applying to modern electronics, which often are designed with magic for unobvious reasons.
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Old 10-07-2008, 20:02   #25
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Thanks so much for all your replys, I'm still trying to digest it all..

The boat I'm looking at does have an inboard engine, with a 12v system. It seems good news to me, that I don't have to bother with an ac set up at all.. and that I can run the laptop off the system already there.. could I just plug it in to the 12v and see if it works?!

I still have to consider the best way to charge the batteries, but i'm getting there, I think..

Warm regards,
Mark.
Mark,

hellosaior and MLO might be leaving us in the dust with their detailed discussion. It's interesting for me and I hope for you but here is a simpler answer/recommendation.

You have an internal engine with an alternator on it. If you are not running a fridge you would be fine with a setup as follows.

2 banks of batteries - 1 X 110ah starting and 2 X 110ah house - This is my setup. We had a 1 and 1 setup but I expanded it as we started adding goodies. Some of the club members think it's a bit too much battery but when the kids are watching terminator 3 and not bugging me about when we will arrive, I don't - LOL.

Charge with alternator from inboard diesel. Out alternator is a 60 amp one. Our house will run for a couple of weeks of weekend sailing running the autopilot, ipod + speakers, twin 9inch DVD players, fans, lights (nav and cabin), once in a while plugging in the laptop. Usually every 3 weeks an opportunity to motor for a few hours will come up and that has been keeping us topped up.

Install a couple of cigarette lighter plugs - I don't like them but they are convenient - I stuck a battery monitor in one and it tracks the voltage of the system with 3 idiot lights. When the yellow starts to flicker off it's time to motorsail.

Install a 400W marine inverter - we dont' use it a bunch but we have plugged in the laptop and a few other things. As HS and MLO point out this is not the most efficient way to get your laptop powered but if you consider an auto adapter you can later power it on the cigarette plug.

Once you get all that going and learn some more I think you will reach the conclusion that I have that that is solar is next. ~120W will fit in terms of panel size and allow us to run some systems continuously.

Good luck...
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Old 10-07-2008, 20:38   #26
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Re laptop batts:

Largest li-ion batt I've got is a 9 cell / 85wh / 11.1v. The laptop doesn't require the batt as part of the direct circuit (unlike the old days), therefore, I'd assume less draw when no batt is connected.

The Targus air (incl cigarette lighter) travel charger I've got (since 2001) has an input of 11-16v/8a output of 3-24v.
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Old 10-07-2008, 23:43   #27
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You can replace the existing power supply with a 12 volt in unit.


Quote:
So as I have the space onboard, there is probably no reason why I cant use the computer I'm banging away on now is there?


It is easy to do. Remove 120/240v unit. Plug 12v unit back in !! As long as your computer is not a very high drawing one it works fine. Some people convert pc s to run in their cars or trucks. Others (like me) their boats. It will probably draw slightly more than a lap top, but you can buy a very cheap low powered pc if you are going to run marine applications only. (which is why the eepc and xo work well too).
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Old 11-07-2008, 01:33   #28
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Re 12v pc's:


Car enthusiasts are into 12v custom pc's with low voltage motherboards, cpu's, graphic cards & hard drives (& lack of fans but use of extra heat sinks etc). Personally, by the time you build your own system (& the cost), I'd rather go with an asus eepc & a car (12v) adapter. Given their low cost, why not also take a spare (or 2).
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Old 11-07-2008, 02:12   #29
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You can replace the existing power supply with a 12 volt in unit.






It is easy to do. Remove 120/240v unit. Plug 12v unit back in !! As long as your computer is not a very high drawing one it works fine. Some people convert pc s to run in their cars or trucks. Others (like me) their boats. It will probably draw slightly more than a lap top, but you can buy a very cheap low powered pc if you are going to run marine applications only. (which is why the eepc and xo work well too).
Yeah well thats the thing, its going to be my full media suite + nav
I currently have well over a terabyte of movies, tv series, and music for when far from anything

Plus I want it running through a 37 inch lcd tv/monitor and across to a 22 inch for nav at the internal helm station.

All this stuff is getting really cheap now and I have it all now except the 37 inch lcd which is a bit over $789
Umart Online

Linking it all in with one of these SI-TEX Explorer Plus Without GPS Antenna

I reckon I'll have a great entertainment, spectacular nav with HUGE screen and an office setup for less outlay than even 1 decent dedicated chartplotter.

Dave
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Old 11-07-2008, 07:44   #30
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Mini-itx

If you are interested in low power PC's There are type of computer built on low-pwer moterboards that look promising form onboard use. They are the mini-itx, nano-itx and pico-itx formats. With Pico-ITX, you can puy a system that is about the size of a 4x5 card!!! Here is one such kit:

mini-itx.com - news - VIA launch ARTiGO Pico-ITX Builder Kit That promises to use 20w at full load.

There are some in the mini-itx format that use plenty of power, but many of these boards, and the systems created with them, aer designed from the begining to use little power. A company called Via started this form factor. You can learn alot here: mini-itx.com - news

That is a British site, not the only place to buy this stuff, but a good starting point to learn more. I have been tempted to build one of these for years, perhaps now that I have a boat, I will do so.

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