Which power inverter do I need.. 400 watt or 200

I'll be going on a trip in about a week to Florida and so I needed something for my car so I can keep my laptop charged and running good. Well I was looking at these Power inverters at the walmart Website...

(400-watt) http://www.walmart.com/catalog/product.do?product_id=4891079

(200-watt) http://www.walmart.com/catalog/product.do?product_id=4965458

Well, I'll be using it for my E1705 Laptop, and playing games and stuff, but I'm not sure how much power I'll need. Would the 200-watt be fine? There is only a 5 dollar difference, but is the extra power necessary or can I just stick with the 200-watt power inverter, please Help. I'm not someone who knows all the information about this kind of stuff, and I was hoping I could get some help please, thanks.

 

Yes, I think the 200W is good...I'm fairly certain that the E1705 uses an AC adapter that is rated for no more than 135W (probably). Check the fine print on the bottom sticker of the AC adapter and find that wattage...that's the absolute max +/-10% that the laptop will ever pull.

EDIT: I just found the AC Adapter on Dell's site; you (should) have a 90W adapter so 200W is easily overkill.

 

Is it bad to get the 200W then or will it not hurt it. Because for 4 dollars more, I'll pay to get double watts because we might have two laptops. I just want to make sure getting the 200W and using just my laptop on it won't hurt anything.

 

Two laptops: 90W + 90W = 180W...maybe you should get the 400W (not that much more) just to play it safe.

Getting a 200W inverter provides for up to 200W...if your laptop asks for only 90W that is what it'll get. You won't hurt the laptop. From the description of the inverter, it looks like they put some decent surge and high current protections in.

 

Well, I think if I'm only going to use one laptop, and if that uses 90W, then the 100w INVERTEr should be fine, correct?

Well, also, are there any side effects to the cars battery or if I were going to use it plugged in for 5 hours at a time, will it do anything to the car battery, does anyone know because my mom is worried that it'll do something and so it's basically up to my dad as to whether I can use this on the trip or not. He probably will be too cautious about it, but if there's nothing wrong with using it, then I would like to use it. So are there any problems which could occur if I were to use the inverter?

 

The only thing that could go wrong with the car's battery is if you use it while the car is off, and that would be draining it. While the car is running, the battery is being charged. Thats why leaving a light on overnight can drain the battery, causing you to need a jump.
The only thing I will warn about however would be to keep the inverter away from any cloth or yourself for that matter, as some do tend to get VERY hot after awhile.

 

Well, I tested it and I can't even use it when the car is off, and also, the plug in where I plug the inverter in is right to the left of the cup holder in a dodge caravan, so that's literally inches away from the drivers legs.

I just hope it won't drain too much power.

 

The nice thing about getting the 400W inverter is that it will NOT tax the inverter with two laptops. You always want a fair bit of headroom when choosing electrical equipment, because it will last longer, be cooler and give you better performance when you're only asking for a small fraction of it's max capacity, rather than nearing it's limit. That's why power transformers blow almost exclusively in the winter... high demand coupled with working near it's environmental limits.

 

It is quite easy to calculate the power drain. 90W at 12V will be about 8 Amps, perhaps a bit more due to conversion inefficiency. The car battery is measured in Amp-hours (Ah). Check what this is and avoid draining more than half of the power (some inverters automatically stop when the think the battery voltage is getting low).

However, while the power adaptor is rated as 90W, this is the maximum capacity based on the computer running some intensive work and also recharging the battery at the same time. The battery recharge power is unlikely to exceed about 40W. You can check this using MobileMeter http://www.geocities.co.jp/SiliconValley-Oakland/8259/.

If you are using the computer outside of the car, and then recharging it, it is easy to calculate the power requirement. If the computer's battery is 80WHr, it will probably need about 100WHr to recharge. This is equivalent to about 9 Amp Hrs drain on the car battery.

I would expect that a 400W (and maybe 200W) inverter will need to be connected directly to the car battery. 400W is a lot of Amps at 12V and the power socket / wiring isn't designed to take that load. But if the power socket doesn't work when the engine is off then this is no big problem.

Hope this helps,

John

 

I would vote for the 200 watt. It won't stick out like the 100W, and will run cooler when loaded with 1-90W laptop adapter. You have the option of running two laptops IF your 12VDC outlet is rated for 20amps, which is doutfull, check owners manual. You can connect, fused, to the battery direct. $24!

Let us know how it works out.

 

Were you posting on SA as well by any chance?

Go for the 400 watt, and don't risk overloading the smaller 200watt model. Heat buildup on the really cheap models is a big concern, and over your road trip you might fry the little cheap inverter.