Didier Stevens

Monday 2 November 2020

Quickpost: Portable Power

Filed under: Hardware,Quickpost — Didier Stevens @ 0:00

I did some tests to generate electricity (230V AC) with a portable 12V battery (well, it’s 10 Kg).

I have a 12V VRLA battery with a capacity of 35,000 mAh. That’s 12V times 35 Ah = 420 Wh. Or equivalent to a 116,667 mAh (420,000 mWh / 3.6 V) USB powerbank.

Charging this 12V battery with a 12V battery charger connected to a 230V power outlet takes almost 7 hours (6:57) and requires 0.49 kWh. That is measured with a plug-in electricity meter with a .00 kWh precision. And I’m working under the assumption that the power requirement of the electricity meter is so small that it can be neglected.

Then I use this fully charged battery to power a 230V 150W halogen lamp via a 12V DC to 230V AC power inverter (modified sine wave).

It runs for 2 hours (2 tests: 2:01 and 2:03) and consumes 0.30 kWh.

Of the 0.49 kWh energy I put into my system, I get 0.30 kWh out of the system. That’s 61%, or a bit better than half of the energy I put into the system.

The main phases where I expect the energy losses are occurring, is in 230V AC to 12V DC conversion and electrical to chemical energy conversion (charging); and chemical to electrical conversion and 12V DC to 230V AC conversion (discharging). I believe the highest energy loss to occur in the power inverter.

And with energy loss, I mean energy that is converted into forms that are not directly useful to me, like heat.

Remark that the halogen lamp test stopped after 2 hours, because the power inverter stopped converting. The battery voltage was 11.5 V then, and I could still draw 1 A at 11.5 V for an hour (I stopped that test after 1 hour).

Next I’m going to try out a 12V to 5V adapter and power some USB devices.

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