I have some devices that i'd like to power using an inverter (laptop), and devices that used in the lighter socket (revolving light, cell charger).

I own both a 300 watt and a 75 watt inverter.

I was told that the more powerful inverter should be connected straight into the lighter socket because of the amount of current that needs to be drawn.

I intend to experiment using a 4-way lighter plug splitter and use my smaller 75 watt inverter in one of the sockets. That seems like the best way to do it.

Any thoughts?

Ohms Law can be used to roughly calculate your needs.

300 Watts at 14.4V (The most that will be coming out of your lighter socket when your car is running) constitutes 21 Amps...could be more or less depending on how your inverter is rated as there are losses internal to the inverter circuitry. If it's rated at 12V, then it's going to need 25 Amps! Your manual or the label on the box may even tell you what it's maximum current draw is at peak. One other thing to consider is that if the inverter puts out that 300W steady or peak. If it will handle 400W peak and you ask it to deliver that much, then you're taxing your vehicles circuitry even more for a brief time.

21A+ is more than any lighter socket I'm aware of. The one in my Jeep is rated for 20 but I wouldn't dare put that much through it. Even running much less powerful devices through it, the socket and the wire get plenty warm.

This is why most inverters that size and larger include wires to either connect it permanently to the car direct to the battery wiring or with alligator clamps to connect directly to battery terminals.

NOW. That being said, your notebook likely doesn't draw more than 100W which means you should be fine on your lighter socket for what you need. I run my 400W one off of low power circuits (fused for 10A) all the time.

The 75 Watt one would run in any lighter socket perfectly fine but might not be enough to run your notebook power supply. Check what it's rated for (it will be printed on the brick) before you use it.

...Or buy a 12V DC-DC converter for your laptop.

I'm happy with my 5 years old investment:
http://www.intellesale.com/-item/20936/belkin-components-120w-universal.html?r161160

Never tried the Airplane end though (probably, too shy to ask where is my personal power outlet in the plane )

It had outlived all 4 of my older laptops. The original "bricks" are in dust on the far shelves.

You're asking a lot from a single lighter socket. I'm pretty sure the socket would be fuse-protected, so you shouldn't melt the wires. But you may "go dark" all of a sudden; and as you know, this always happens at the most inconvenient time.

For ongoing use, I think the safest and most reliable approach would be to have your mechanic add extra fused circuits right from the fuse block. This is not at all complicated, so if you're handy and can test for polarity, you could do it yourself. And if your big inverter is the type with a DC power cord, you might even consider wiring it into the fuse block and hard-mounting it in a convenient place.

Indeed! The worst thing about the lighter socket is that the plug falls out too easily. If you install a (fused) power feed from the battery or fuse box consider a PowerPole outlet. You'll have to modify the plug on your inverter, or get an adapter, but PowerPoles are IMHO the way to go.

I installed one of these in my dash:

http://www.powerwerx.com/product.asp?ProdID=1783&CtgID=1681

I filed down the housing a little, and snapped it into an empty switch cutout in the centre console.

A

Car lighter plugs are NOT the worlds best power sources

IF you can do a bit of wiring yourself, here is what I would do - Ham radio (and a LOT of other folks who are "in the know") have converted over to a connector called the "Anderson Powerpole" - great connector - used by RC car and airplane folks too - and they configure the connector in what folks call the ARES standard

The normal size we use can handle 30 amps, and one of the good parts is that they are not "gendered" - aka you can use the same connector to draw power, as to charge - all my bug out batteries have them - so I can either put a load (my inverter, my radios) on the battery, or plug my charger there, and charge the battery

Here is my web page on them

http://www.thegallos.com/ppole.htm

Heh - didn't see your post until AFTER I posted mine - great minds think alike. I'll agree - powerpoles are the way to go

I'm going the powerpole route myself. I've added a hald dozen of the old style automotive jacks around various places in my truck but they are big and don't work real well. So I'm going back and putting a power pole jack next to each now. I'm also converting some of my gear over since it takes less space in the bob to carry a few leads with power poles.