Running a laptop off solar

[paulca]

So now it's summer my tiny solar panel setup is producing more power than I can use from my USB powered devices and a bunch of other stuff.

I need to add more load.  It's pointless to consider an inverter as I only have 38Ah of battery and a 10A limit. 

I use the laptop to watch YouTube a few hours a day, so I figured it looks like a good candidate for powering off solar.

This leaves me a number of options.

1.  Use a "Car laptop charger"
2.  Use a generic 5A boost converter that will output the 19V required.

One concern is knowing how much power the laptop actually draws, so as an experiment I will see about powering it off a bench supply while I find a better solution.  The car charger gizmos seem to state 80W on a few, at 19V that's about 4A which sounds about right.  Of course it will pull about 6A on the 12V side, which is also fine.  I can either use a LiPo that goes with the Laptop or I can charge the laptop at the charge controller and run it off batteries elsewhere.

Anyone have any suggestions or gotcha's?

[The Soulman]

I'd say "car laptop charger" less hassle and the least chance of destroying your laptop.
Note that "professional" laptops such from hp and dell actually has a third connection from charger to laptop that sends some identification data,
without valid data the laptop may not charge and throttle down the cpu.

[Cyberdragon]

I'd say "car laptop charger" less hassle and the least chance of destroying your laptop.
Note that "professional" laptops such from hp and dell actually has a third connection from charger to laptop that sends some identification data,
without valid data the laptop may not charge and throttle down the cpu.

If they're like Apple chargers, then the charger info chip will be in the plug head. You'd have to cut the cord off one and see how many wires go to the actual power converter. If there is only two, then you can just use the connector from a real charger. However, note that it will think it's the original charger so you have to make sure it can supply that current otherwise it will overload and make the PC throw errors.

Some laptops will also autodetect like phones do where it increases the current until the supply shuts off then sets the limit right below. This still has to be at least the minimum charging current.

[paulca]

I went with a 90W car laptop charger off ebay.  I already had a cigarette lighter socket with an XT60 soldered to it, so I can run the laptop off a LiPo charged from solar, or the charge controller itself which has an XT60 on it's load output.

Interestingly it took two evenings watching youtube etc. to bring the 5 Ah Lipo down to 10.6V, So I could get almost 5 hours out of it.  That suggests the laptop is only pulling an average of 1 Amp / 12 Watts.  I would have expected many times more than that.