You should be fine with anything, the inverter will trip before the fuse blows, they are 15A fuses. Most laptop chargers are less than 4A.

 

I once blew the fuse with an older inverter and needed to get it fixed so it's definitely possible!

 

You probably had a very cheaply made inverter. Also if the fuse blows, get another one from the spares in your engine bay and replace it yourself. Costs nothing and takes a minute.

 

Might cost a little more if you can find one, but sometimes you can find a power adapter that actually plugs right into the 12v outlet in the car and then outputs to a plug that goes into the laptop. They have a built in in-line transformer that steps the voltage up to the voltage the laptop needs to operate and charge (19v usually) so there's less current draw since there's no access wasted power converting from 12v to 110v then back down to 19v. It basically looks like an original wall charger/adapter for the laptop, only instead of a 110v plug on the end it has a 12v socket plug on it.

I have one for my Dell Mini that also works on my wife's larger full size Dell and it works fantastically well, and it's passively cooled unlike most inverters so there's no fan noise whizzing away while it's in use.

 

Either I'm not reading you post correctly, or some of these people responding didn't read your post at ALL!?!?!


Let me see what I can clear up for you

The size of inverter you will need will depend on how many Watts your laptop adapter takes +10%
So if you look at your laptop power adapter and it says 120VAC 240 watts then you know you need an inverter that's 240 Watts +10% or more.
If it lists AMPS instead of Watts (IE: 120VAC 2.0 Amps) then convert the amps to Watts via calculation below...
The power P in watts (W) is equal to the current I in amps (A), times the voltage V in volts (V):
P(W) = I(A)× V(V)

NOW you can convert that wattage into amperage on your DC side so you know how many AMPS it will pull at 12Volts (The adapter in my example lists 120Volts @ 2 amps)
Since you trade volts for amps and vice versa as we decrease the voltage with the same wattage the amperage MUST increase.
So 240+Watts at 12 volts is 20AMPS!!!

The wiring in this 8th gen through the cig lighter is about 4 amps and 6-8 MAX (And honestly looking for trouble much past that.
Even though you may have a 15amp fuse, the wire in this car is REALLY small at the cig lighter.
So if you have a super tiny super efficient laptop then you MIGHT be able to get that down low enough to run off the Cig lighter but to be on the safe side I would run power directly from that battery to be safe.


Hope that made some sense, let me know if you have questions..

 

I assumed his laptop wouldn't use anything much past the limit. True, the wiring can't support 15A however with everything else running + the startup voltage spike, the fuse is sure to blow before it melts.

OP, your laptop charger will say the wattage. You're most likely pulling 65w, under 100w max. Now if you have an extremely powerful gaming laptop, you might be pulling more than 100w however that's still unlikely.
Most ultrabooks - 45w
Most newer laptops - 65w
Most older/gaming laptops - 100w
+ if you want to charge your phone too add 30w max (assuming you're running Quickcharge 3.0)

 

No need to get overly theoretical - You can get one of those little 150 watt Bestek inverters for about $25 on Amazon. That shoujld do it.

 

Eliminating discussion of the inefficiency of the inverter itself (that is, assuming it is 100% efficient): An inverter that takes 12V, and converts it to 120V and puts out 150VA with a power factor of 1 means that it's putting out 120V at 1.25A. Therefore, its input at 12V is 12.5A. Many cigar lighter circuits now have a 10A limits. If you replace the fuse with a 15A fuse, you're underprotecting the circuit and could potentially have an electrical fire.

However, inverters are more in the range of 85 to 90% efficient.

Another thing to consider is these inverters deliver a stepped approximation to sine, which is fine for lightbulbs and light power tools but not good for your electronics. You'll either damage the laptop's own power cord transformer (for some devices with power factor correcting power supplies), or the inverter will fail early-- or both.

If you want a decent 120V power supply in your car, you're going to need a pretty expensive direct wire inverter that delivers a sine wave. The advantage is that it'll power just LOTS of stuff if you want, and it's not going to damage your electronic goods.

 

If you're going to be running expensive electronics direct like a home sound system when out camping or something, yes you should get a pure sine wave inverter because home electronics may not be okay with a square wave or even stepped square wave input. However, the first thing the AC runs into on a laptop charger is a transformer which smooths out a lot of "spikyness". I've run a few laptop chargers on those little plug in inverters and haven't had a failure yet. Even running a 75 watt plug in will charge your laptop if it's off. You have to keep air circulation around the inverter though, because they trip when they overheat and the more power you're running through them the more they heat up -

To put it simply though, it is power that is constant - volts times amps is watts. Volts times amps in equals volts times amp out, discounting inefficiency. Volts are push (potential), amps are flow (current). Watts are power.

:smile:

 

If you're going to be running expensive electronics direct like a home sound system when out camping or something, yes you should get a pure sine wave inverter because home electronics may not be okay with a square wave or even stepped square wave input. However, the first thing the AC runs into on a laptop charger is a transformer which smooths out a lot of "spikyness".

Almost every electronic device like TVs, home stereos, and desktop computers, have a transformer that's "the first thing the AC runs into". With laptops, the transformer is merely external to the device. Sure, the transformer might "take it", but it'll run warmer and can make the inverter's job more difficult (and depending on the power factor, exceed the inverter's capacity).

And typically any power supply that does power factor correction will refuse to start if it's not on a sine wave. An architectural firm thought they were being smart by getting UPSes for each of their workstations (they'd have done better to ensure the building itself had better power), and discovered that the workstations would not switch on when plugged in to the inverter.

And, finally, don't conflate VA (apparent power) with W (real power), for non-resistive loads the power factor is usually less than 1, and harmonics introduced by multiple transformers (for example, if you run two different transformer loads, you can run into a distortion power factor issue.). If your laptop power supply has a power factor of .8, and is rated for a 150W input, it's going to be a 187.5VA load, exceeding the capacity of the 150VA inverter (which is fine in bursts but if you're running the laptop all maxed out that's a recipe for trouble).

And, often: You don't get what you don't pay for. I've chewed through enough cheap auto inverters that I'm saving up for a nice "off-grid" quality inverter.

 

One idea I do have is to take one of my older small APC UPSes, disable the alarm 'chirper' and hardwire it to the the battery of my Previa. It's still not a sine wave but at least it'll be durable enough to run tools lights and stuff so I don't have to use shore power for those things.

 

Wow. This thread was super fascinating. Thanks guys. The bestek is ordered and on its way!