How Low-Power Can You Go?

[lasersaber] has a passion: low-power motors. In a bid to challenge himself and inspired by betavoltaic cells, he has 3D printed and built a small nuclear powered motor!

This photovoltaic battery uses fragile glass vials of tritium extracted from keychains and a small section of a solar panel to absorb the light, generating power. After experimenting with numerous designs, [lasersaber] went with a 3D printed pyramid that houses six coils and three magnets, encapsulated in a glass cloche and accompanied by a suitably ominous green glow.

Can you guess how much power and current are coursing through this thing? Guess again. Lower. Lower.

Under 200mV and 20nA!

The motor ended up being so responsive that the act of [lasersaber] holding two different metals would make it run; even a large metal ball acting as an antenna for ambient energy is sufficient to power the motor.

Last year we featured [NurdRage]’s photoltaic cell — the very same [lasersaber] based his build on. Be aware — these are properly radioactive elements so they must be treated with the caution and respect they deserve. Definitely not for building random number generators.

[Thanks for the tip, oxide!]

28 thoughts on “How Low-Power Can You Go?

    1. I’m… kinda skeptical of this now.

      It’s not just that he’s got it set to nF and claiming it’s a nA measurement. The probe leads are in the sockets for current measurement (at least they’re in the mA socket, so that’s something) but like you said, it’s in a nF setting. So… I don’t know what the hell it would be measuring.

      And, he’s also measuring the voltage at the same time, too. The DC resistance of that multimeter is 10 Mohm. Do the math: 200 mV across 10 Mohm is… (drum roll) – 20 nA. Normally I’d say that’s just a mistake and it just means the real output current is more than that, but the fact that the expected current through the multimeter for that voltage is exactly what’s being claimed makes me go “hmm.” Something’s weird.

    2. Maybe the knob simply has a little play and it’s on the next setting, for mA?

      I wonder, are those tritium sources actually emitting Beta particles into the photocells, or are they all captured by the phosphorus coating and are the photocells just getting the green light?

      1. “Maybe the knob simply has a little play and it’s on the next setting, for mA?”

        Then it’d be 20 mA, not 20 nA – which wouldn’t match with the microammmeter beside showing “zero.”

    1. Radiowaves in general. You can buid electronic kits that lets you listen to really really low radio (as low in audio output) without having a battery in the device, by just picking up the radio waves themselves.

      Can’t remember where I read it, but some dude on the internet or in some book claimed to have had his treehouse lit 24/7 as a kid, by havng a big wire mesh on top, catching the energy from a nearby TV transmitter. They eventually got caught and asked to take the net down because they apparently leeched a significant amount of RF energy for the area behind them. I don’t know if the story is pure folklore but it’s definitely possible to extract energy from radio waves…

      1. Yep, a tuned LC circuit and diode bridge to convert it to DC and you have a small steady power source suitable for sensors or reading light.
        If you live under high voltage cable you can draw some serious power:
        This would also work at a train station with overhead 25kV cables for charging your phone. There is a reason for signposts and metal structures are grounded at the train station so you don’t get shocked touching them. It should be possible to power your home if you live between HV towers and fill your garden with antennae.

      2. As I recall, Ham Radio loop antennas that are strung up in high poles, gather voltage. Art Bell of over night radio fame put one up, and whined about the high current screwing with his rig.

      3. Farmers use(d) the same mechanism to get ‘free’ power from high voltage lines. Having long fences that have another use, which just happen to be ideally placed for harvesting energy, has allowed some of them to get away with it at least for a little while.

        Others weren’t so lucky, though. Even though electromagnatic radiation permiates your property, it apparently is still owned by someone else.

        1. getting caught is all a matter of proportion.

          unmodified fence suddenly starts taking 100x or 1000x the magnetic or rf field will get noticed. a new fence might not. then again, if the new fence literally lights up without buried power cable … a chopper (already owned by the company) plus zoom will prove this and will get you caught.

          taking 1 or 2 watts for one LED fixture probably will not get you caught as there are already large losses in the lines.

          taking 100 watts every tower as it crosses your property (if possible) probably WILL get you caught though. they can tell how far down the line the losses are occuring, without even leaving their office chairs. if it starts and stops right at your property lines; automatic red flags are raised at HQ on a map showing your property lines. at least they will think there is a tree so close to the line that touching it could schock you and they will dispatch a techs with a dashcam right away.

          also depends on type of system; my above comments are for countries with smart-grid(s), back in the day it “depended less”…

  1. I saw this post only just now… I did the math and even though lasersabers design is quite impressive he cheated on his measurements. Whether he deliberately did so I don’t know. He may just be bad at it ;)
    Anyway, the lowest power I ever got was about 60nW and my rotor measurements show that it cannot go much lower.
    see it running here:

    read all about it here:

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