Power Inverter


My friend and I are heading on a long cross-country road trip and my friend has a 150-watt power inverter that plugs into the cigarette lighter.

First, do I need to watch how much power I’m using or does the inverter have an internal check that will stop before I suck the battery dry?

Second, if I need to watch the amount of power I use, what should I know? The last thing I want is for my battery to die on me in the middle of a road trip.

Any inverter-related advice is appreciated!


Why do you need this inverter?

I suggest using it only when ABSOLUTELY necessary, or not at all. You could easily drain your car’s battery without realizing it, and then the car won’t start.

Personally, I’d leave the inverter at home.


Many of the newer SUV’s have a 120 plug so I doubt there should be any problems using one…make sure when you turn the car off that the 120 plug also goes off or you will drain your battery.


There will be no problem at all if you use this inverter only when the engine is running, which will be most of the time. Use it as much as you like.

Even when you are stopped for the night you may still use it for low-level use for a few hours at a time. Check the wattage on your appliance to decide how long to use it.

You need only beware of heavy usage when stopped. When used with intelligence you will experience no trouble from this gadget.


You are assuming that this vehicle’s alternator is capable of 150W. If the inverter draws more power (depends on what is actually being powered) than the alternator can supply the battery will go dead even with the engine running.


Assuming an 85A alternator, using P=IxE, the alternator’s total output is a little over 1,000 watts. The inverter will likely not draw the full 150W anyway, except for brief periods of time, under maximum load. Use it with impunity, as long as your engine is running.


What exactly is being powered?
Many times these kind of things turn friends into ex-friends when a problem develops, even if it is not related to the device being used.

Bad alternator, battery, or whatever, it will be “It was fine until that was plugged in”.


It would mainly be used to re-power our cell phones, camera batteries and laptops (we’ll use it sparingly with the laptops). The car is a 1999 Nissan Altima, how can I find out if the alternator can handle 150 watts?


Virtually any modern alternator is rated at 100a, which means an output of (12v x 100a) 1200 watts. Yes, that’s twelve hundred watts. And your battery chargers will draw only 5-10 watts. Everyone else uses these power inverters with no problems. They are cool gadgets.


You could check the fuse rating for the lighter, anything over 12.5 amps should handle the full 150W.


The rated output of an alternater is relative to its RPM. At idle or low speeds the available amperage is minimum.


your alternator will be fine, but modern laptops might want more power than the cig lighter connection can deliver. You may have to only charge the laptops with the inverter, and unplug them to run them on their batteries.

Why not get car chargers for the cell phones- - the whirring of the fan in an inverter gets VERY old after awhile.


Things like cell phone battery chargers use virtually no power at all, so don’t worry about them. And there’s no reason why you can’t use a laptop while rolling down the road for as long as you want. You’d be hard-pressed to find a laptop power supply that draws more than about 100 watts (and that’s extreme) and a few amps when delivering full power to the machine (that is when fan/drive motors are spinning up and the battery is charging). All on its own, when the machine is off or in suspend mode and merely charging its battery, the power draw is minimal.

Just unplug the inverter when the car is off, don’t run more than one laptop off of it at a time, and don’t try to microwave popcorn with it, and you’ll be fine.


Most decent inverters have built in safety features that will shut them down or “alarm” if you are overdrawing either the inverter or the battery of your car. With the engine running you should not have any problems. I ran a 150watt inverter for years to power a laptop with a 90 watt power draw and never once had an electrical problem.

To all the people issuing dire warnings about inverters, get real. Unless you are running a 600 watt inverter (or larger) without the engine running it is no big deal. That is why they sell them with cigarette lighter adaptors.