So... who knows the answer...

Submitted: Wednesday, Jun 08, 2005 at 18:24
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... and it's NOT 42!!!

For those of you that take laptops out and about with you, and use them frequently whilst stationary, what sort of run time are you getting whilst the unit is plugged into an external 12 volt battery? I am not particularly interested in those that use a 240 volt inverter.... but those that use the likes of the kerio, etc.

I am under the impression, that my apple iBook, should be drawing around 1 a/h, whilst under normal use, like word processing, and up to 2 if I'm watching a DVD.

Anyone got any clues?

Cheers

Wolfie
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Reply By: Utemad - Wednesday, Jun 08, 2005 at 18:53

Wednesday, Jun 08, 2005 at 18:53
Well I have never flattened a 12v battery whilst using my laptop so I don't know. However on the bottom of my HP laptop it says it _Affordable_Storage_Drawers.aspx 3.95 amps at 19v. I would assume this to be maximum.

However back to your situation. If you draw a max of 2amps then I would guess you won't have to worry about flattening your battery unless you plan on running your laptop for about 2 days straight.
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Follow Up By: Lone Wolf - Wednesday, Jun 08, 2005 at 18:57

Wednesday, Jun 08, 2005 at 18:57
Thank you. Tell me, if it _Affordable_Storage_Drawers.aspx 3.95@19 volts, would that then be like 6.25 @ 12 volts?

Cheers

Wolfie
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Follow Up By: Utemad - Wednesday, Jun 08, 2005 at 19:09

Wednesday, Jun 08, 2005 at 19:09
Well on my 12v power pack it says that it is 6 amp max output and 11.5 amp max input. So you are probably right in saying that it is 6.25 amps input

This is mine
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Follow Up By: Mike Harding - Thursday, Jun 09, 2005 at 08:49

Thursday, Jun 09, 2005 at 08:49
To find the current at 12V convert 19.5V and 3.95A to watts by multiplying them = 75W now to convert to current at 12V divide 75 by 12 = 6.25A.

75W is the very, very, very :) maximum power your computer will ever draw and only when _everything is working ie. the DVD drive is working, the hard disk is writing, the sound is playing at maximum volume, the microprocessor is running at maximum speed, the internal battery is flat and being charged at maximum rate, the USB ports are both in use and supplying maximum current to external devices, the mouse is moving, the display is updating at maximum frame rate etc.

In reality it's average power consumption will probably be of the order of 25W or less (2A at 12V) or less. Keep in mind that if the computer is running from _any_ external power source it thinks it's running from the mains and probably turns off all it's power saving features it would use when running from internal it's battery. Many notebooks allow you to turn power saving on when an external supply is in use - so you may wish to do that too and that will reduce average power consumption even more.

Mike Harding
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Follow Up By: Bonz (Vic) - Saturday, Jun 11, 2005 at 18:12

Saturday, Jun 11, 2005 at 18:12
"the DVD drive is working, the hard disk is writing, the sound is playing at maximum volume, the microprocessor is running at maximum speed, the internal battery is flat and being charged at maximum rate, the USB ports are both in use and supplying maximum current to external devices, the mouse is moving, the display is updating at maximum frame rate etc. "

Sounds exactly like Wolfie would be doing, meltdown here we come :)
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Reply By: KiwiAngler - Wednesday, Jun 08, 2005 at 19:38

Wednesday, Jun 08, 2005 at 19:38
I find if the puter is basically 'just sitting there' then I get a few hours out of the on board battery. Which is a 14.8v 4400 mAH lithium ion battery.
If I am running explorer and using realtime mapping I get about 2 hours out of it.
I usually get about 1 1/2 DVDs.

If I connect to a power pack (12v Waeco 24Ah) I find it drains it very quickly.

I use one of these when driving and it keeps the puter battery fully charged no matter what the puter is running

http://www.vanson.com.hk/details/p3050.html

No electrician or puter geek...what I have written is what it is
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Follow Up By: Lone Wolf - Wednesday, Jun 08, 2005 at 19:54

Wednesday, Jun 08, 2005 at 19:54
Now... we are getting somewhere...

I have ascertained that my battery is a 14.4 @ 4000 mah... which, allowing for the rported 6 hrs. general use, makes for a consumption figure of around 0.8 A/h @ 12 volts.

Now, it is interesting that you say the Outback, which I also have, drains quickly. So, it doesn't run the system for 24 hrs.

Bugger!

The best I can come up with, is a trickle charge 20 watt panel, which will maybe not keep up.......

Bugger!

I shall now look towards plan "B".......

Oh, by the way, it's for data logging in the bush, tied in with my Canon Camera.

Cheers

Wolfie

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Follow Up By: KiwiAngler - Wednesday, Jun 08, 2005 at 20:07

Wednesday, Jun 08, 2005 at 20:07
I have never managed to get 6 hrs out of my puter on board battery even though 'mathematically' it should.

Get the notebook power pack that I use

http://www.vanson.com.hk/details/p3050.htm
it just saves all the hassles

I am guessing you also use Ozi with PhotoTool and merge the data with the photos?

Have you seen this?
http://homepages.tig.com.au/~robk/datalogger.html
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Follow Up By: BenSpoon - Thursday, Jun 09, 2005 at 11:18

Thursday, Jun 09, 2005 at 11:18
Lone Wolf-
As Mike H mentined, when external power cuts out the lappys generally have features to cut down on their power usage... it may pay to invest in a timer relay that cycles on and off the power from the external batt pack- that way you still charge the batts, but use the power saving stuff in between. Generally when on battery the CPU slows itself a few cycles and panel brightness goes down. Also look at turning off any unused ports to save a little extra.
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Reply By: Russel & Mary - Wednesday, Jun 08, 2005 at 22:05

Wednesday, Jun 08, 2005 at 22:05
Ford Prefect said it was 42.
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Follow Up By: Member - Blue (VIC) - Wednesday, Jun 08, 2005 at 22:35

Wednesday, Jun 08, 2005 at 22:35
But he used to be a white guy with very blue eyes...
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Follow Up By: Bonz (Vic) - Saturday, Jun 11, 2005 at 18:15

Saturday, Jun 11, 2005 at 18:15
No No No Deep Thought said it was 42. Thats why they built the earth to ascertain the answer, and also to placate Majikthise and the other visionary.
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Reply By: geocacher (djcache) - Wednesday, Jun 08, 2005 at 23:17

Wednesday, Jun 08, 2005 at 23:17
Hi Wolfie,

The problem is that many if not all laptops run at quite high currents at a voltage higher than 12v.

Therefore you need a thing called a DC-DC converter to step the voltage up. This is the Kerio or similar device (mine was from Jaycar and cost $89 and works just fine) which plugs into the cigarette lighter. The problem is that this conversion is not a particularly efficient process and an item that _Affordable_Storage_Drawers.aspx say 1 amp at 15 volts will require much more current at 12 volts to generate the lower current at a higher voltage.

My Toshiba power supply has an output of 5Amps at 15 volts and I would expect that my Jaycar DC-DC converter is using all of its stated 6 amp draw to generate that sort of current at that voltage. I can run some tests if you like.

AnswerID: 114983

Reply By: Kiwi Ray - Thursday, Jun 09, 2005 at 05:52

Thursday, Jun 09, 2005 at 05:52
Hi Wolfie
If you wish to run your lap top for long periods there is special adaptors to fit either 24 12 vdc i.e. cars and trucks you just need to find one that matches the voltage for your lap-top. Places like Dick Smith have them use the ones with the voltage stabilizer. my truck has them wired in for work.
just an idea for you
Ray
AnswerID: 114994

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