I would like to gather info on power requirements for an electric system for a caravan, but I struggle with basic understanding.

My laptop needs to run off the 12 V battery, but the laptop charger has 19 V, 230 W output. I didn't find any DC-DC adapter for it; I suppose an inverter will be needed.

AC input for the adaptor is rated at 100 V-240 V, 3.5 A. I am not sure what 3.5 A means here, and what inverter would be sufficient to cover requirements.

Please bear with me, I am very much a newb in this area.

  • \$\begingroup\$ Are you aware you can likely buy a car adapter for your laptop so you don't need the mains inverter to power the mains voltage adapter? \$\endgroup\$
    – Justme
    Oct 21, 2022 at 0:01
  • 1
    \$\begingroup\$ Petr (a very good russian or belarusian or kazakh or mongolian name): DC to AC inverters are very common and very cheap. But you may require special wiring given the power you are discussing. (They often include those wires and connectors and fusing.) Given your admitted ignorance, I think you should seek some off-the-shelf product. Probably better if you get something that gives you the AC you need for your existing charger. Otherwise you are in custom-made (DIY) territory. \$\endgroup\$
    – jonk
    Oct 21, 2022 at 5:10
  • \$\begingroup\$ What sort of laptop needs 230W of power? I had one years ago with a 17" screen and that only needed about 75W. \$\endgroup\$
    – Finbarr
    Oct 21, 2022 at 11:22
  • \$\begingroup\$ Its gaming laptop, charger used is this: replacement-batteries.co.uk/… \$\endgroup\$ Oct 21, 2022 at 21:32
  • \$\begingroup\$ Yes there are car adapters, was first thing i came across, but e.g. manufacturer of my laptop sells strongest 19V / 6.3A, actually what will happend if i use this for laptop rated with double amps? will battery gets charged, but likely not enought and eventually will be drained, it will only last longer than without any charging? \$\endgroup\$ Oct 21, 2022 at 21:43

1 Answer 1


The rated 3.5 Amps current is likely the value at 100 V input, since the required current for a given power would be less at the 240 voltage.

From this, we can deduce the maximum power requirement to be 3.5A x 100W = 350 Watts on the AC input. This exceeds the 230W stated for the DC output.

You may try an inverter with a cigarette lighter plug in these ranges. However, please investigate the current rating for the cigarette lighter circuit, as well as maximum capacity of the plugs. I have found one with a plug rated at 500W.

The fuse for the circuit should be greater than the wattage divided by 12V.


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