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  1. #1
    rkk1986 Guest

    Default Can a car handle this?

    Can a car (Camry 2000) drive at 70 mph, with the air conditioner blasting, and a laptop eating 300W (using the power inverter)? Is there anyway I can figure this out?

  2. #2
    Join Date
    Jan 1998
    Location
    Las Vegas, Nevada
    Posts
    10,059

    Default Are you totally serious?

    Can a car (Camry 2000) drive at 70 mph, with the air conditioner blasting, and a laptop eating 300W (using the power inverter)? Is there anyway I can figure this out?
    I don't know where to start... What kind of a laptop do you have that could possibly "eat" 300 watts? Laptops work off of batteries and the most that they could "pull" would be a mere fraction of that. I would think a 2000 Camry could deal with that load all day and all night (until it ran out of gas).

    M

  3. #3

    Default

    The short answer is yes. We have done this on a number of trips. As long as the battery & alternator are in good shape you shouldn't have a problem. If your laptop really draws 300w (most draw less than that) you might want to connect the inverter directly to the battery since the 25+ amp draw is pushing an auxillary power outlet.

  4. Default

    Easily, and more.

    My car is drawing somewhere between 600-700 watts on stock alternator, no signs of struggling or lights dimming. I think once you start going over 700-800 watts, then you have to start worrying about upgrading alternators or batteries.

    Laptops should not consume anything near 300W, that's about what a full desktop uses, but maybe you're talking about a 300W inverter used to power it? I think most laptops use about 20 watts of power, some more, some less. We were running a laptop off a 140 watt inverter with no problem.

    If you really are going to use a full 300 watts, you might want to follow the advice about connecting it straight to the battery, the cigarettle plugs are normally fused at 10-20 amps.

  5. #5
    rkk1986 Guest

    Default Quite serious indeed.

    My laptop is an HP Pavilion ze5500. The connector on the laptop (where you plug in the AC power) says 90 W. But this is the input to the laptop or, said another way, the output of the AC adapter the laptop comes with. If I calculate the power input for my ac adapter, it comes to about 250 Watts (110V * the 2.25 Amps specified on the adapter = 248 W.) (And yes, I'll be using a 300 W off the shelf inverter.) I'm assuming that because it is an off the shelf inverter, that I will be abe to plug it in directly to the cig lighter - but it does seem likely that it will be drawing close to 20 Amps. How would I go about connecting it directly to the battery? I am assuming I can not drive while I have my laptop connected (I was planning on using it for like GPS and stuff.)

  6. #6
    Join Date
    Jan 1998
    Location
    Las Vegas, Nevada
    Posts
    10,059

    Default 300 Watt Inverter

    I still think you are making this way too complicated. With a 300 hundred watt inverter you would be able to run a portable refrigerator, 1-2 GPS modules and a laptop all at the same time.

    I wouldn't suggest hooking anything as delicate as a new laptop to your battery even with the anti-surge/bad RF noise prevention possibilites afforded by an inverter.

    Mark
    Last edited by Mark Sedenquist; 05-17-2005 at 05:20 PM.

  7. #7

    Default

    I have run a laptop with a 150W (or was it 140W?) inverter plugged into the cigarette lighter with no problems.

  8. Default

    If your laptop really is drawing 250 watts, either you're carrying around a huge car battery to power it, or you're getting about 10 minutes of use out of each charge on a normal battery. 250 watts is LOT of energy for any battery operated device, that's getting into the range of a motorized scooters and heavy duty power tools. Here's a quick calculation you can use to check, if you're laptop consumes 250 watts, then to power it for 2 hours @ 12 V you'd need a 40 Amp hour battery (or 40,000 mA hour). a 40 amp hour battery weighs about 30 lbs, and is roughly the size of a small car battery. Or to do it backwards, look at the rating on your battery (in Amp hours), divide that by the normal runtime you get with that battery (in hours), then multiply by the battery voltage. that will give you your power requirement. I'm betting is somewhere around 20 watts.

    And when connecting it to the battery, I mean connecting the inverter to the battery, not the laptop. You can connect the laptop directly to the battery using special DC power cord though, if you're worried about efficiency. But if you already have an inverter, don't bother.

  9. #9

    Default

    Quote Originally Posted by rkk1986
    My laptop is an HP Pavilion ze5500. The connector on the laptop (where you plug in the AC power) says 90 W. But this is the input to the laptop or, said another way, the output of the AC adapter the laptop comes with. If I calculate the power input for my ac adapter, it comes to about 250 Watts (110V * the 2.25 Amps specified on the adapter = 248 W.) (And yes, I'll be using a 300 W off the shelf inverter.) I'm assuming that because it is an off the shelf inverter, that I will be abe to plug it in directly to the cig lighter - but it does seem likely that it will be drawing close to 20 Amps. How would I go about connecting it directly to the battery? I am assuming I can not drive while I have my laptop connected (I was planning on using it for like GPS and stuff.)
    I think you are a bit confused in how watts are determined. Watts for a computer are the same on either 120v AC or 12V DC. The current draw is determined by dividing the watts by the voltage. In the case of your 90w laptop, running on 120V AC it will draw about 3/4 of an amp. If plugged into a inverter (or a 12v laptop power supply such as this) it will draw about 7.5 amps from your auto battery. Actually it will be a bit more, because the inverter or power supply will have some losses, but those losses are typically under 10%.

    There is no reason you can't keep your laptop, GPS, and other stuff working while you are driving (other than keeping your eyes on the road). Again, we have done this on many trips, from a couple of miles to our last 10,000+ cross country trip. If you use the inverter, the only thing I would watch is the load on the 12v side. Most inverters over 200 - 250 watts either have a set of alligator clamps or suggest cutting off power accessory connector & wiring the inverter directly to the battery (include the appropriate fuse). I really don't think you need to do this - even the 90 watts listed is only a peak; the average will be far less.

  10. #10
    Join Date
    Jan 1998
    Location
    Las Vegas, Nevada
    Posts
    10,059

    Default A welcome voice of reason

    Jon,

    Thanks for that quick calculation -- I knew I wasn't being clear about the consumed watts arthimetic. Yeah, the draw on a laptop is almost negligible when attached to a 300-watt inverter.

    Mark

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