DC Conversion and Amp Hours for CPAP
I had a 12v plug installed in our bedroom and now I need to try and figure out how much my CPAP machine uses. I bought a Kill A Watt device and measured 8 hours of sleep last night. The device onl...
Forum Discussion
If we assume the DC-DC converter in the cable is equally as efficient as the AC power supply for the CPAP machine (which seems as reasonable a guess as any), then you can divide the 360 watt-hours by 12V to get 30 Ah for the night, or 3.75A average current draw from the 12V battery.
The 3.75A rating on the 24V output is irrelevant to this calculation; that's just the maximum rated output for the DC-DC converter in that cord. If the CPAP machine were to use the full 3.75A at 24V that the cord can supply, you'd have somewhere around 8A input on the 12V side as the converter can't create energy out of nothing (and indeed consumes/wastes a little itself in the voltage conversion process).
The 3.75A rating on the 24V output is irrelevant to this calculation; that's just the maximum rated output for the DC-DC converter in that cord. If the CPAP machine were to use the full 3.75A at 24V that the cord can supply, you'd have somewhere around 8A input on the 12V side as the converter can't create energy out of nothing (and indeed consumes/wastes a little itself in the voltage conversion process).
