[The Gonz]

How much does it cost to achieve supplying half an amp of domestic AC from your car, and throw in a USB socket?
Not much!
Car Mobile Converter Inverter DC 12V/24V to AC 220V Charger Power+USB NEW | eBay

[Shambles]

Can't be used to the ironheart transformer.

[The Gonz]

 

[tw2005]

I think you should buy one, open it up and give us your engineers report. Would you trust it?

[The Gonz]

It would be interesting to see whether it's a small oscillator, amp and transformer or some lightweight switch mode circuit. With perfect (theoretical) conservation of energy, it should draw just over 5A, but the reality is the need to dissipate some heat (vents on the case are a clear suggestion, plus supplying the USB), so who knows how much it will actually draw?

Still, from the nominal 5A to, say, double that, still gives plenty of range for the fuse to cope. Now that you mention it, I'd pay that couple of dollars to do the surgery.

PS Besides, it would be my style to dispense with the case and build the power socket into a panel somewhere like the boot if I felt the need.

[Shambles]

whether it's a small oscillator, amp and transformer or some lightweight switch mode circuit

Probably along these lines:




Where the 4047 chip provides the oscillation  Review - CD4047 Astable/Monostable Multivibrator

[The Gonz]

Yes, I've used the good ol' 4047 a lot more than the better known 555, but there's nothing like cracking one of these new inverters open for the thrill of reviewing the components and reverse engineering back to such a circuit schematic.

Mmmm... circuit porn...