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I'm using a 1200W pure sine wave inverter and a series of extension cords to power devices in a mobile home. When charging my laptop, I noticed it was charging slowly. According to my battery monitor when the laptop is plugged in it consumes roughly 0.8A or 10W. I then plugged directly into the inverter instead of the extension cord and it consumed roughly 2.78A or 34W for charging the laptop. Great. Must be a faulty extension cord, or just low quality. I then tried a tiny 250W space heater and did the same: it drew the same 250-270W it is rated for both when plugged into the extension cord and when directly into the inverter. So why does the laptop power draw drop significantly and not the heater?

By standard, the laptop charger converts 100-240V AC at 1.2A to 19V DC at 2.37A, for 45W charging. The battery monitor is wired into the 12V DC current before the inverter and reads the total load of the inverter. If the laptop charger pulls 1.2A at 110-120V, wouldn't that mean the current drawn from the 12V system is somewhere around 12A then?

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    \$\begingroup\$ Or the laptop was not charging the battery to begin with. Sometimes they manage the battery so that even when mains is plugged in, the laptop runs on AC power and does not charge battery, if it is already full enough. \$\endgroup\$
    – Justme
    Commented Jan 9, 2021 at 15:19
  • \$\begingroup\$ Moving the mouse turned the screen on and increased power consumption? \$\endgroup\$
    – user16324
    Commented Jan 9, 2021 at 15:27

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Cheap inverters switch DC to AC and as such rely on low inductance. A suitable metal film cap might improve this. Do the math on Q , ESR and conjugate impedance matching or consult supplier.

An extension cord is about 1.5 uH/m.

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