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RV Electrical: Using DC Power is More Efficient
Photographer and cyclist and Mac expert and software engineer Lloyd Chambers is available for consulting on general Sprinter considerations at his usual consulting rates via phone, or in person in the Palo Alto, CA area. Save yourself hours and mistakes by discussing issues up-front. More about Lloyd....
Get your batteries and alternator and regulator (the whole kit!) from NationsStarterAlternator.com.
Field report to come with usage once installed and built up.
A power inverter converts 12V DC current from the batteries into 120 volt AC household power. This generally wastes at least 10% of the available battery power during the conversion process. Worse, most devices actually convert that AC power back into DC power for a DC-AC-DC loop, wasting still more energy. That is why calculating a realistic power drain load must take into account conversion losses—battery that appears to be adequate might in fact have 10% to 15% less available power than it seems when AC is the main draw.
Accordingly, when feasible and conveneient it is preferable to power devices off DC power, because even the best most efficient inverters are no more than 90% efficient, which by my math means a very significant factor: 111 watts of DC power net out at 100 watts of AC power (111 watts X 0.90 = 99.9 watts)—and that’s often a best case.
Given the guaranteed losses in using DC power inverted to AC power (and perhaps back to DC power), using DC power directly is a smart move. How efficient DC-DC adapters are is seemingly dependent on many factors. One hopes that DC-DC is more efficient than the DC-AC or DC-AC-DC loop, but it is not a given and should be measured.
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DC power chargers and appliances:
Devices that use 12V DC directly should be nearly 100% efficient. Devices that convert 12/13/14 volt DC into some other voltage could waste power also. It all depends.
- Many 12 volt appliances are available for RV usage that use 12V DC.
- Newer laptop computers use the 90 watt capability of USB-C such as the BatPower CPD 110W PD USB-C Car Charger for MacBook Pro.
- For 2012-2012 MacBook Pro, the BatPower CCA 110W Laptop Car Charger for Macbook Pro, MacBook Air and MacBook (2006-2015 Mac laptops) looks to be a good option.
- Similarly, USB-A ports charge some cameras like the Sony A7 series, and some Leica cameras have direct DC charging for the battery charger.