So is it the 6.57 volts you can't understand?
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I personally can't understand how some people vape at 12, 15, 20, 30 watts. That would tear my lungs out. I saw a post the other day where someone said they like vaping a 1.8 ohm coil at 24 watts. That's 6.57 volts. I could never do that.
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4 7.2 ohm coils add up to a 1.8 ohm coil.
6.57 volts on a 7.2 ohm coil isn't hard to understand