Ciggy lighter

Depends how long you're stood idle & what you're doing. From experience, don't try comissioning Mac esterior lanterns that way as the battery life drops from 2 hours to 15 minutes with the supplied USB device & software. Which seems bizarre & may mean I need a new battery, but the Scorpio suffered the same fate.

Given the price of inverters & the price of laptops & given mine eats

I can't see why I need to bother with that. I've been successfully running a 150W inverter from lighter sockets regularly for about 6 years in multiple vehicles.

John

A Scorpio I'd guess has a 70 amp/hour battery or thereabouts. To flatten it in ten minutes means theoretically drawing about 400 amps, but in practice anyway far more than a cigar lighter and wiring could do without burning out.

Because large current draw items should not be run through temporary connections - there can be problems with heat generation from bad electrical contacts, wear an tear etc. Not a problem on a low-draw appliance as it will not cause a fire if shorted or poorly contacted. A higher draw appliance may cause excessive heating even way before the fuse blows. I've actually had a set of fog lights wired through a 15A fuse set fire to the front of my car when the temporary connector arc'd

- fuse never blew but the heat generated was enough to ignite the paint on the bumper, cable seemed fine.

Thing is its *probably* fine but to be safest you'd want it properly wired in. The whole point of the OPs question was why dont they provide high-draw sockets as standard - its because high draw appliances are safest when run through their own fused and properly switched live. Adding that to a car could cost upward of =A32 per car. =A32 on a car that sells 1 million is =A32million. We all know the story of the guy for ford who saved them something stupid like 2p per car and got a massive bonux. The guy who suggests a =A32 expense would be fired :-)

But a 150w inverter is not a high draw appliance IMO.

Assuming it was new & fully charged you'd be right. But given the age & the usage it wasn't, & to be fair it lasted just over an hour. The bit I don't understand is how the usb port can guzzle that much power. Fortunately the genny in the boot solved the problem.

Ok if the engine isn't running, but I wouldn't like to directly expose an expensive laptop to the noisy environment of a running car's electrical system ;)

Lee