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Old 22-05-2013, 13:09   #1
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Charge laptop when low, or just keep it plugged in?

I have a very powerful gaming laptop that I use at home for....gaming. I've been messing around with OpenCPN and would like to use it on my boat, but my laptop is very power hungry. I've been considering buying a low end netbook to use for navigation, but before I drop money on that as a single purpose tool, I'd like to know if turning my settings down on my current laptop will reduce the power draw from the power supply.

I've been trying to find information on how laptops use energy when plugged in, but it's hard to separate this particular topics from things like "should I leave my laptop plugged in all the time" nonsense. So hopefully someone who uses laptops regularly on house batteries can fill me in.

Will the laptop's power supply unit always draw maximum amps, regardless of what the laptop is asking for? Or does the power supply adjust draw based on what the laptop is asking for? If I leave the laptop plugged in while I'm using it, will it just pull a trickle from the battery, or use the full amp rating on the power supply the entire time?

Thanks!
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Old 22-05-2013, 14:05   #2
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Re: Charge laptop when low, or just keep it plugged in?

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Originally Posted by silviris View Post

Will the laptop's power supply unit always draw maximum amps, regardless of what the laptop is asking for? Or does the power supply adjust draw based on what the laptop is asking for? If I leave the laptop plugged in while I'm using it, will it just pull a trickle from the battery, or use the full amp rating on the power supply the entire time?

Thanks!
Depends on how hard the laptop is working, bright screen and lost of processing going on it will pull more. Also, a 12v power supply is much better than using an inverter and a mains supply.
But in your case I would think a netbook would draw substantially less, the asus eee range seem to get good press from boaties and non alike.
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Old 22-05-2013, 14:36   #3
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Re: Charge laptop when low, or just keep it plugged in?

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Originally Posted by silviris View Post
Will the laptop's power supply unit always draw maximum amps, regardless of what the laptop is asking for?
No.

Quote:
Originally Posted by silviris View Post
Or does the power supply adjust draw based on what the laptop is asking for?
Yes.
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Old 22-05-2013, 14:39   #4
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Re: Charge laptop when low, or just keep it plugged in?

Many gaming laptops have both "built-in" graphics on the board as well as additional "dedicated" graphics hardware that you can switch on and off. This dedicated stuff is going to be the biggest power hog in your machine and if you can switch it off then you'll see much better energy performance.

If you have one of the new gaming laptops that have SLI configurations there should be a way to disable one of the cards which will help.
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Old 23-05-2013, 09:17   #5
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Re: Charge laptop when low, or just keep it plugged in?

My experience is similar to what's already been reported;
- the power supplies are fairly smart; they will deliver more or less what's required
- an AC supply running from inverter will be less efficient than a supply that runs from 12v dc, so if you do decide to use the big laptop aboard, you should get a DC supply for it.

Beyond that, you need to take some current measurements from your laptop in various states (combinations of on/off, charged/discharged, etc) and put those numbers into your energy 'budget'.

I have a refurbished ASUS netbook for boat/mobile use; it's fine for OpenCpn and my $$$ computer is safe at home.
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Old 23-05-2013, 09:48   #6
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Re: Charge laptop when low, or just keep it plugged in?

I use a gateway /asus netbook for everything. Runs opencpn fine (with external gps) as well as SDR# (software defined radio), plus weatherfax, email, internet, etc. I did upgrade to 2 gigs ram though.

It runs about 6 actual hours on a charge (spec was 8). My primary spec in choosing the netbook was amps used to run it.

I use the 120V charger with in inverter. Laptops generally have a 17-18V battery. I found the 12V netbook charger ran pretty hot and actually pulled more 12V amps then the 120V charger on inverter. but YMMV.
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Old 24-05-2013, 08:13   #7
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Re: Charge laptop when low, or just keep it plugged in?

Whichever way you do it, the actual computer will use the same amount of energy to operate. If the laptop/netbook battery is charged, and left plugged in, the power supply will supply just enough to operate the computer plus very small amount to float the battery.
If you charge, disconnect and run on battery and then charge again etc you have the additional energy required to offset the losses in charging and discharging the battery which can be significant. However, you are only using the power supply for say 1 hour in 4 in this case rather than continuously and the power supply will not be 100% efficient. My feeling is that it is swings and roundabouts and because I use my netbook for navigation, I would rather have it fully charged at all times so should the worst happen, I have 5 hours of use independent of the boat house bank available.
If the power useage is very important, then either adjust the laptop power scheme to minimise use or get a netbook or other low power consumer. Fitting a SSD instead of a hard drive will reduce power further.
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