I bought a MotoMaster Eliminator Mobile Power Outlet Digital Power Inverter rated for 400 W.

It has thoses specs:

AC output voltage: 115 V
Max Continuous AC power: 320 W
AC Output frequency: 60 ±1 Hz
AC Output waveform wave: Modified Sine Wave

I can plug my little iPhone adapter in the inverter AC outlet and it charges.

When I plug my MacBook's adapter, I hear little ticks from the adapter, and nothing happens. I unplug it from the inverter, plug it in the wall outlet, and nothing happens. I have to unplug it from the wall, wait a minute or two, re-plug it to the wall and my MacBook is charging again.

What's happening? I bought this specially to charge my laptop when doing camping. Is there something I can do?

1 Answer 1


The problem lies in one little word: Modified sine wave. Which typically has a rather tenuous connection with an actual sine wave. Rather, its voltage is a periodic step function with rather few steps (though I can't say for sure about the specific model you mention). You need an inverter that provides the latter. They exist, but tend to be more expensive. I use one made by Mascot, and it charges my macbooks just fine. My previous inverter, with its modified sine wave, did not.

  • Seems to be logical! How can we know if an adapter needs an Actual Sine wave to work properly?
    – vIceBerg
    Jul 21, 2012 at 20:22
  • By trial and error? Seriously, power adapters are designed to work with sine wave input, and if they happen to work with anything else, consider yourself lucky. Few if any producers of such will announce the fact if they do work; they just open themselves up to customer complaints if they don't work for some particular variant of “modified sine wave”. I have also heard stories of phone chargers destroyed by inverters. The behaviour you see with powerbook adapters may well be some protective circuit kicking in in response to unexpected input. Jul 21, 2012 at 20:30
  • Thank you so much. I'll return the product and look for an actual sine wave device for better compatibilité
    – vIceBerg
    Jul 21, 2012 at 20:32

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