I Charged a Supercap to 4V With My Counter-Rotating Device (Bridge Rectifier)

Hook

I just watched the meter climb to 4.07 volts on a 5.5 volt 20 farad supercap bank using nothing but proximity pickup through a bridge rectifier on my counter-rotating device. The hum is real but the charging still happens.

Watch this experiment

I hook three 12-volt batteries to the trifilar 28-gauge strand wired in series, run it through the bridge rectifier, and dump the output into two parallel supercaps. You hear the resonance build, see the voltage creep, then I kill the power before it hits the cap limit.

What you'll learn

How a bridge rectifier turns the induced pulses into usable DC on a counter-rotating device, why one drive circuit hums while the others stay quiet, and how I threw together a latching relay safety cutoff in about ten minutes.

From the bench

Started at 3.72 V on the parallel 20 F bank. After a short run I stopped at 4.07 V. The caps are rated 5.5 V so we still had headroom. I pulled the clips off, killed the battery feed, and let it coast. No fancy scope shots—just my handheld meter and what I could catch on camera.

How it works / what we changed

The 28-gauge trifilar strand sits near the spinning magnets and feeds straight into the bridge rectifier. From there the DC goes into the parallel supercaps. When the cap bank is connected the whole thing hums but still charges. Without the caps the red and black drives run clean while the green one resonates and does not pull much useful work.

Counter-rotating device

My counter-rotating device uses a solid shaft with opposing magnet arrays so one side spins one way and the other spins opposite. The pickup coils sit in the middle and collect through proximity. The shaft feels balanced—only a tiny natural resonant rumble on the little wooden test stand, almost nothing on the big bench.

Pulse motor resonance

You can hear the hum get stronger each time I cycle the circuit. It steps up. With the supercaps connected the resonance is there but the voltage still climbs. When I run the drives separately the green circuit is the one that likes to hum and does not perform as well. Red and black stay smooth and quiet.

Safety relay upgrade

I grabbed a 12-volt latching relay, an infrared receiver, a MOSFET, and a scrap PCB. Soldered it up quick so I have a hard power cut if anything gets out of hand. The infrared sensor will let me trigger it remotely. I want this safety relay upgrade in place before I push the counter-rotating device any faster.

Supercap charging

The parallel 20-farad supercaps fill faster with all three batteries on. I watched it go from 3.72 V up to 4.07 V in a short run. That is a decent chunk of DC from a small coil set. The bridge rectifier cleans it up so the caps see straight DC instead of raw pulses.

Trifilar coil

Right now the pickup is a 28-gauge trifilar strand in series. The front drive coils are 26, 28, and 32 gauge trifilar and I want to change them to 20 gauge. I do not have fresh 20-gauge wire so I will cannibalize some old coils. Thicker wire should give stronger drive with less heat.

Pulse motor troubleshooting

I ran each drive circuit on its own. Red was nice and smooth. Black ran even better—super quiet. Green is the one that resonates and does not pull its weight. The light on the back bounces if anything wobbles, so you get instant visual feedback. The shaft feels solid; the little rumble is just natural resonant vibration, not a wobble.

Latching relay

The 12-volt latching relay is the heart of the new safety circuit. Once it flips it stays off until I reset it. Paired with the infrared receiver I can kill power from across the bench without touching anything. Simple, cheap, and it gives me peace of mind when I am about to let the device spin fast.

Infrared sensor

I am using a basic infrared receiver so the latching relay can be triggered by a remote or a simple beam break. Nothing fancy—just enough to cut power if the counter-rotating device starts acting up. I still need to finish mounting it but the PCB is already populated.

Builder checklist

• 28-gauge trifilar pickup in series to bridge rectifier
• Parallel 5.5 V 20 F supercaps for storage
• Three 12 V batteries for drive saturation
• Red and black circuits for clean running, green for resonance test
• 12 V latching relay + infrared receiver + MOSFET on PCB for safety
• Check shaft balance before every speed run
• Have a kill switch you can hit fast

Troubleshooting

If one drive hums and will not pull, try running the circuits separately like I did. Resonance can step up each power cycle—disconnect the cap bank to see clean drive behavior. Voltage creeps slowly near the top of the supercap rating; stop early so you do not overvolt. Little rumble on a wooden stand is normal; move to a heavier table if it bothers you.

Safety

Always have a fast way to kill power. That is why I built the safety relay upgrade. Watch your supercap voltage—5.5 V max on these. The bridge rectifier gets warm with three batteries; keep an eye on it. Wear eye protection if you are spinning heavy magnet rotors. Do not leave the bench while the device is running.

FAQ

Why does the green circuit hum? It resonates more than the red or black. Still works but not as clean.

Does the resonance stop the charging? No—the supercaps still climb even while it hums.

Can I skip the bridge rectifier? You can, but then the caps see raw AC-style pulses instead of clean DC.

How fast do the supercaps fill? Faster with all three batteries and the cap bank connected. I hit 4.07 V pretty quick.

Is the shaft balanced? Yes—almost zero visible wobble. Just a tiny natural resonant vibration on the small stand.

Related on this site

• How to Build a Pulse Motor: Complete Beginner's Guide
• Best Wire Gauge for Pulse Motor Coils (AWG Guide)
• Pulse Motor Rotor Design: Magnets, Materials and Balance
• Pulse Motor Battery Charging

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