I Finally Got My Pulse Motor Running (Electric Type)

Hook

I fired up the shop lights and spun up a couple electric type pulse motors - one using a monopole magnet trick on the rotor and the other my 369 design with mixed gauge coils. No magic, just momentum, careful coil placement, and some real measurements from the bench.

Watch this experiment

We start outside with the big 14-inch rotor. You can see the steel strips I added to yoke the south faces of the neodymium magnets. Then we head inside to the 369 build running on a 12V system with an adjustable trigger coil and a movable pickup coil. Speed changes, voltage readings, and the sound of the motor slowing under load are all in the footage.

What you'll learn

How a monopole magnet setup changes the field so north is only detectable very close, why the 369 needs an initial push, how trigger coil position affects RPM, and what happens to battery charging when you dial voltage up or down.

From the bench

The first rotor is 14 inches with 12 neodymium magnets. I yoked the south faces with steel strips so the field between them reads mostly south on the gauss meter. Move the probe in really close, about 10 mm, and you catch the north field. Out a little and it's gone again. The whole thing has been spinning for a while on momentum plus the V-gate action from the big stator magnets - pulled in, then pushed out.

It won't start on its own. You give it a flick and the momentum carries it through the pull-push cycle. That's the basic idea I was testing.

How it works / what we changed

I tried linking the south poles with magnetic steel ribbon to see if it would create a stronger monopole effect. The meter shows mostly south all the way around until you get within Hall-effect range. Once spinning, each passing magnet gets pulled then pushed by the big stator magnets in a V-gate formation. Simple, but it needs that initial momentum.

Monopole magnet setup on the rotor

I placed steel strips around the south-facing magnets on the 14-inch rotor. The gauss meter now reads stable south between them. Only when the probe is within about 10 mm do you see the north field pop up. Move it out slightly and the north disappears. This monopole magnet approach seems to extend the south field and changes how the rotor interacts with the stator magnets.

369 design explained

I call it the 369 because there are three 16-gauge coils, three 20-gauge coils, and nine magnets on the rotor. The 16ga coils have roughly 220-300 turns each on soft iron cores. The 20ga coils are two layers and produce a very strong but compact magnetic field. There's also a separate pickup coil that can be moved in or out. Everything is wired so the drive coils work together when the trigger fires.

Pulse motor coil choices and turns

The three 16-gauge coils are wired in series with about 300 turns each. The 20-gauge coils sit on soft iron and are extremely potent even though they're not huge. I noticed the rotor speeds up a lot when the trigger coil is in the sweet spot. Being able to slide the coil in and out and side to side made tuning possible. The pickup coil measured 765 ohms - half of that is around 382 ohms, which seemed relevant for the circuit.

Transistor trigger and coil timing

A 26-gauge trigger coil sits near the rotor. Every time a magnet passes it, the trigger coil sends a signal that closes the transistor and completes the circuit to the drive coils. All the 16ga coils light up together and push the rotor. I had to turn the motor off while explaining because the noise made it hard to talk, but you can see the transistor module right on the board. Small adjustments to the trigger coil position changed speed dramatically.

Pickup coil readings and placement

The pickup coil currently reads 765 ohms. I moved it closer to the rotor with a nice air gap and you can hear the motor work a bit harder. It adds drag but also lets us see charging effects on the battery. The coil is removable so I can test with or without it. When the main coils are firing, this pickup captures some of the action and feeds it back to the battery.

Battery charging observations

We started at 7 volts and the battery sat at 12.09 V. Once I turned it up to a full 12 V system the motor slowed down noticeably but the charging current increased. Dropping back to 10 V let the rotor speed up again but charging slowed. I left it running a bit so the charge would "stick" instead of immediately dropping when shut off. It's basically charging the battery while running, though I noted that short runs of 10 minutes wouldn't hold the gain.

Builder checklist

• 14-inch rotor with 12 neodymium magnets for the monopole test
• Steel strips or magnetic ribbon to yoke south poles
• Three 16ga coils (~300 turns), three 20ga coils, 26ga trigger
• Movable trigger coil that adjusts in/out and side-to-side
• Transistor switch (exact type not shown but clearly visible on board)
• Pickup coil with measured resistance around 765 ohms
• Battery monitor showing voltage and charge rate
• Ability to vary input voltage from 7-12 V

Troubleshooting

If the motor slows when voltage increases, that's what I saw - higher voltage gave more charge current but lower RPM. Trigger coil too far away or out of position kills speed; I had to slide it carefully until it hit the fast spot, then ease it back slightly. Short runs won't let the battery charge "stick" - it drops right back. The monopole rotor needs a push; it won't self-start. If the north field won't show on the meter, get the probe within 10 mm.

Safety

These neodymium magnets are strong - keep fingers clear of the spinning 14-inch rotor. The coils get energized and can get warm; I let the 369 warm up for a few seconds at 7 V before turning it up. Watch battery voltage so you don't over-discharge while testing. Transistor circuits can spike, so I kept connections tight.

FAQ

Does the monopole magnet rotor create true monopoles? Not really. The steel strips make the field read mostly south until you get very close (~10 mm) where north appears. It's more of a field-shaping trick than a true monopole.

Why does the motor slow down at 12 volts? In my test, raising voltage increased charging current to the battery but loaded the rotor more, so RPM dropped. Lowering to 10 V let it speed back up.

How critical is trigger coil position? Extremely. A small movement in or out changed speed a lot. It needs to be adjustable in two axes.

Will it charge a battery? I saw the battery voltage rise while running, especially at 12 V. Short runs lose the gain quickly when stopped, so longer runs help the charge stick.

What is the 369 design? Three 16ga coils, three 20ga coils, nine rotor magnets. The name comes from that 3-6-9 pattern. The 20ga coils make a strong compact field that helps push the rotor fast once timed right.

Related on this site

• How to Build a Pulse Motor (Parts, Coil Placement & Circuit)
• What Is a Pulse Motor? How It Works (Beginner Explainer)
• Pulse Motor vs Bedini Motor: What's the Difference?
• Pulse Motor Battery Charging Experiments
• Best Neodymium Magnets for Pulse Motor Rotors

Watch this experiment on YouTube

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