Help with Homopolar Motor

You probably have too much current....

http://www.instructables.com/id/Homopolar-Motor-With-Five-Speed-Manual-Stick-Shift/

Yea I've seen that video and he is using a battery as well. Getting it to spin with a battery works just fine.

I've tried varying voltages and amperages to no avail. Everything from 1V to 30v and from 30ma to 800ma. I could push the currents higher with my supply but I shouldn't have to I wouldn't think.

I think you may have removed the rotor part of the motor by removing the battery...the magnet on the battery varies the electromagnetic field causing the Lorentz effect and torque necessary to make the motor work....

Hmm perhaps I'm not understanding. This is how I tested it long ago and to this day can still get it to spin with no issues

http://upload.wikimedia.org/wikipedia/commons/a/a5/Homopolar_Motor_Large.jpg

I essentially replace the battery with a steel rod measuring 3mm x 60mm and hook my positive lead to the to of the rod and allow a screw with the magnet dangle from the bottom of the rod. I then tap the negative wire to the magnet and nothing. I never really had the magnet touching the battery to make it spin as it was on the bottom of the screw.

Is there a magnetic field rotating....? There must be an electromagnetic field rotating with one end of field attached to the magnet to vary the field effect....this is what produces the Lorentz force....Perhaps if you draw a diagram of your model, with the electromagnetic field lines in place, this will show what the problem is....

Maybe you could attempt something like this.....

Equipment List: ·

• 0-20 V, 40-A, DC power source ·
• bus strip with resistive load wire ·
• momentary contact switch ·
• 2-mm thick copper disk, 15-cm diameter, on a mounted axle ·
• glass liquid trough that holds 2 ml mercury ·
• horseshoe magnet ·
• 5 banana plug wires

http://www.rose-hulman.edu/~moloney/AppComp/2001Entries/e11p/homopolar.htm

Does the rotating magnetic field powered from a battery differ from a DC PS of the same voltage? I was under the impression that electron flow consists of two counter rotating fields running through a wire. I mean I do understand how the lorentz force operates and it should turn but yet it stands still.

I thought that it could be some sort of protection in my variable PS that could be cutting current so i put a lamp in to be sure there was an actual load and not just shorting out the PS through a magnet and screw. Still no turning.

I also took into consideration that this is a very low torque motor so perhaps the tip of the screw was pressing too hard against the steel rod (in place of the battery from the pic above) so I lowered the size of magnet on there to no avail. I also tried larger magnets with the same effect.

Yes you get different wave patterns depending on the type of DC produced....

You could probably rectify(oh no you didn't) the situation with a smoothing capacitor.....

http://forum.allaboutcircuits.com/showthread.php?t=67094

You might just build your own capacitor.....it's easy...

http://www.wikihow.com/Build-a-Capacitor

Total back EMF is unity. Just a guess.....

Current still flowing? Then my guess is wrong.

"How much current you got now?"

While that is a bit different than my setup the principle is the same. Instead of a liquid contact I'm essentially using a brush. On difference I do see is the addition of the bus bar. I mean I can't really see that as having any real effect but perhaps I'm wrong?

You might have a problem with the brush. The outer rim of the wheel is pretty far from the axis of rotation and a little bit of friction requires quite a bit of torque to overcome.

These things worked better back in the day when folks didn't worry about playing with mercury.

Lol I also don't happen to have a bowl of mercury laying around. I do have some gallium I could heat up and try. But I think that may be over complicating it vs just using a brush at first.

Yeah I think the mercury might get a little messy....

You didn't post a picture of your version without the battery.

Two suggestions:

.

1. Use a multimeter to compare things like resistance and voltage and amperage in the operating circuit.

.

2. Try the setup with a dead alkaline battery in place of the steel rod when using the power supply. Hysteresis may be sufficient with the steel rod that it is too much for the low torque to overcome. Larger magnets would probably only exacerbate the problem.

The battery is supplying far more current than you think. I'd bet >4A. Your power supply current is insufficient. Assuming the new connections are correct, the motor should work IF you use a power source that can supply at least 4A of current @1.5V

Good answer...

Ripple is not a problem, the lack of current is! This is a low resistance setup. Get a PSU with 30A capability at all voltages. If you run a linear PSU at lo output Volts, it will just foldback the Volts to stop the Amps increasing. When you have lo O/P Volts, the pass transistors have to get rid of the rest of the Amps and Volts = WATTS = HEAT.

I once had a linear PSU where I accidentally had a short across the output. The meters read zero Volts and 25 Amps output. When I touched the heatsinks, I realised where the Amps and Volts were, in the pass transistors.

there is something O/P Current listed in Model section
the alkaline can supply above 5A at fresh (Heavy Duty 1-s might go over 10A)

Anyone ever get this problem licked? I'm trying to replicate the motor aspect of the Faraday Disc just because.
Powersupply is 750watt converted PC to benchtop PS
3.3v 22A
5v 25A
12V 85A
The bearings I have in place require a touch of torque - literally a feather can move it.
The connection is good, the amps make the connections glow hot. N42 magnet, 3" annular attached to the bottom with an iron plate 5" diameter and copper foil on top.
It is a vertical assembly in a paint can with decent bearings.
The amps I'm pouring into this should cause some movement as a proof of concept and the servo discs I've seen operate at 7V - 24V.
Thoughts are magnet based but any suggestions will do. And I'm aware that this thread is old as dirt but the interweb is surprising in it's dirth of amateur scientists.

Are you using slip rings?

No, I'm trying to duplicate spriteelemental's experiment but with a power supply from a PC. But I'll invest in slip rings.

https://www.youtube.com/watch?v=s2JW7uaPjy8
I have posted a similar question on his page.

I'm having a devil of a time locating a source for cheap high current slip rings. Do you know of any?

An eBay search for 'slip rings' returns over 4000 items.

I'll keep the slip rings in mind. But I should see some torque by manually connecting it.
The assembly weigh a bit, 4 or 5 pounds. The bearings are adequate. 5" diameter discs. But 6V and 15A doesn't yield anything.