If you’ve travelling via bike, you’ll know there’s a certain advantage to packing light. But what if you need to take your beefy desktop-replacement laptop with you on one of these trips? These power hungry machines can’t go far without their chargers (or a place to plug them in), which generally makes them poor traveling companions.
Luckily, [transistor-man] came up with a solution to this particular problem by reusing his e-bike’s battery pack as a mobile power source for his Lenovo laptop. The energy demands of this particular computer are too high for USB-C Power Delivery, and as such, he had to hack up a way to feed it 20 volts DC via its proprietary square power connector. His bike’s battery puts out between 30 and 42 VDC depending on charge, so at least on paper, it should work out fine.
With a bit of experimentation, [transistor-man] determined that the peak current during his laptop’s charge cycle was 8 amps, or 160 watts. He reasoned there was no way it could continuously operate at such high current, so he estimated the could get away with a DC-DC converter that would accept the voltage range of his battery and output a constant voltage with around 150 watts of power. As it so happens, these are fairly common on the second hand market, and he picked one up to be the heart of his new gadget.
The trick here was the converter he bought only outputs 24 V. He didn’t want to add another regulator onto the system, so he decided to drop the output by four volts the old-school way — with a resistor. He then designed 3D printable caps for either side of his converter, one to cover the terminals, and another to hold a handy wattmeter from Adafruit. Now that the core components are settled, there’s no reason [transistor-man] couldn’t adapt his creation for other devices that need some extended runtime.
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