Can you run a lap top from a car battery?

[batema (Mark)]

Hi,

Wondering if someone could advise me how to run a lap top from a 12 V car battery. I would love to be able to drive to a dark site and set up for photography however the battery on my lap top only last for about an hour and a half.

Mark

[PeterM]

There are several ways. A 12 volt to 240 volt power inverter from say Jaycar/Dick Smith. Generally the cheaper ones are not modified to deliver "clean" power so it is wise to pay the extra $ for one of these, I think a modified 150 watt inverter will cost about $200??. You can look in say Repco or your local Harvey Norman computer type stores as some carry a cig lighter adapter that have a voltage selector switch and interchangeable "heads" for the power supply lead that goes into your laptop, theseare generally around $50-$100. Of course it is very important to set the correct voltage for your laptop and get the polarity of the "head" correct. Just make sure whatever you use it has a fuse between the battery and laptop as I think you will find the above do. Some laptops draw a bit of power so if you are using your cars main battery be aware of this so you don't get caught at that dark sky site with a flat battery.
PeterM

[erick (Eric)]

I bought the really cheap inverter from Jaycar (CAT. NO. MI5121) when it was on special for under $40, as I recall. An oscilloscope shows a square wave output. The power brick makes a funny buzz, but it drives the laptop. Pulls a couple of amps of the 12V dc input, as I recall, so I don't think I'd want to run it from the car battery for more that 4 or 5 hours. Have wondered if that will drop if I pull out the laptop battery. Yet to test. Still I haven't had that opportunity yet to trial it for some hours in the dark cold night!

[sheeny (Al)]

Do a search for a 12V air travel adapter for your lappy. I just bought a replacement one for my lappy for $32. It has a 12V plug to fit a cigarette lighter socket and steps the voltage up to whatever your lappy needs. Just make sure the one you buy is the right one for your lappy.

Al.

[h0ughy (David)]

they will suck between 3-6amps - so you wont get a long time with the car battery. deep cycle battery 110 ah will give you about 8 hours before the voltage drops to an unacceptable level and needs a recharge. I had two 110 ah batteries to run the lappy dew heaters and the 3.5ah required for my cooled camera. the laptop was being run directly through a purpose built converter -12 -19v and sucks 5 amps - so be well aware - you will suck the life out of anything in a short while (can go all night though)

[Omaroo (Chris Malikoff)]

As h0ughy says, it's good advice to go with a deep cycle. I have an 110 amp/hour unit that I use to power the G11 mount, 8 heaters, SBIG camera and 2 small laptops, and this lasts me for a very long (into the morning) session, and maybe even two evenings until 2:00am or so. A charge using a 10 amp charger refreshes it in one day. Deep cycle batteries must not be run flat - just like a cranking battery must not either. The difference between the two types is that deep cycle batteries are designed to be taken down to the threshold many times wheras cranking (car) batteries are not. They need to be constantly charged and are only designed to provide high level of current (400 amps or more) for very short periods.

Don't use you cars' battery unless you like walking home.

[AndrewJ]

I use a Switchmode DC-DC Jaycar Lappie supply that has variable output.

I also use an HP lappie and found an interesting quirk with it
It comes with a std AC-DC 18.5V @ 3.5A supply
( and 18.5V is what the manual specifies )
But they also sell a DC - DC adapter as well. This has 2 output voltages.
If you use a 14V supply ( IIRC ), the lappie will still run happily,
but it disconnects the internal battery charging circuit
which gives a much lower current draw.

Thus running the converter from battery to +14V will give better life to the supply battery, vs going up to 19V or so.

Andrew

[erick (Eric)]

Walked through Jaycar this morning. 150W "Car Laptop Power Supply" - 12V in through ciggie plug, output 15, 16, 18, 19, 20, 22, 24V @6A (!!) - 8 different plug adapters. Marked down from $64.95 to $57.95.

[batema (Mark)]

Thankyou all for your responses. I was thinking of buying a battery rather than hooking it to the car but you've given me great guidance. Thanks

Mark

[kinetic (Steve)]

As stated by Eric earlier, cheap 12v inverters put out a horrible
square wave AC. This is not ideal for plugpack type step up or
step down converters. First sign you notice, they hum badly.
If the spike suppression/smoothing is not ideal, (read cheap or non
existent), then your $50 inverter could potentially kill your very
expensive laptop.
Having said that, Laptop supplies usually have good suppression of
nasties that emerge from badly inverted or dirty AC.

In the fine print of most cheapies there is sometimes the mention
'not suitable for notebooks/ laptops etc....

regards,
Steve B.

[MrB (Simon)]

You don't need a 12 to 240v inverter, as Eric has posted there's a 150W 12v to lappie DC-DC converter. There's also an 80W one if you're lappy is not one of the power hungry types. MP-3463 $37.95

[Gargoyle_Steve (Steve)]

I use a large capacity deep cycle battery with a proper 12v power supply for my laptop. Invertors have another serious 'defect' in this regards apart from waveform output - they are quite wasteful of power, ie inefficient when conveting 12vDC to 240v AC - power losses often 10-25% !! Then of course with your original laptop power supply/cord you're stepping that back down to 14-19V - too many conversions for my liking.

Regardless of whether you have anything plugged into it or not the invertor is STILL using power as long as it connected to a battery too, unless it has it's own switch, which many don't. All in all that's a lot of wasted power when you're trying to get every bit you can to run your laptop, etc.

Mark I notice that you're only 12km's from me - drop me a message if you'd be interested in catching up for some observing, I can show you my battery box / laptop / solar charging setup sometime too.

[Davekyn (David)]

Have to go along with Andrew on this one, & am actually suprised to see so many using inverters...unless ofcourse you already had such a set up. DC-DC by far cheaper and more practicle. I to use a measly 18amp hour that keeps me going all night in power saving modes. I also use 2x10watt solar panels off eBay and the system keeps me going night after night
Better still...if your just observing, grab an iPhone & download starmap....will keep you going forever.
Ofcourse depending on how much processing you will be doing; just be mindful that can efect the rate at which you will drain your battery.

[Kal (Andrew)]

I went to ebay and bought an aftermarket "oversize" battery for my laptop. Instead of two hours off the standard battery I now get 5 hours of continous use from the larger battery. Depends on the laptop design and what is available but it's another simple alternative to the common problem of longer field life of the lappy.

[Newtownian]

A point I havent seen noted here is that netbooks are nominally much more efficient than laptops. I recently obtained one of the Acer Aspire One units which nominally requires about 10 W or possibly less - nominally this means for a 13 AmpH 12 V deep cycle lead battery (4.3 kg) I could get 15 hours viewing depending on losses. The alternative battery size noted by comparison of 110 AmpH weighs if not a tonne at least something that looks like it.

A point to note about netbooks - some have small electronic 'hard disks' and some that look very similar. Mine has a full blown hard drive - 120 GB operating a windows XP system and can be plugged into a full 1900X1200 monitor. They are the size of a book instead of a brick and are the real ideal control unit conceptually at least. The only thing missing is a CD read write system which can be an extra.

This said the points made by other contributors though of course must be recognised especially:
- the inefficiencies involved in converting up and then down.
- the fact that a deep cycle lead cell should not go below 70% discharge.
- if you discharge batteries quickly the resistance goes up and the nominal output goes down.

So what needs answering is just how efficient these things are in reality. There seem to be other netbook discussions around which may help to.

[Glenhuon (Bill)]

I bought one of the DC-DC converters on Ebay, cost around $40 inc. postage. Not used it in the field yet but does a good job of recharging the lappy while travelling. If you have one of the older Dells with the square 3 pin plug most of the converters don't seem to include one but this did. I needed one as I run 2 lappies for imaging and guiding.

Cheers
Bill