Creating large DC Motor for Funzies. Won't work.

[Flyingwing12]

Everybody hold their horses before we lose focus.

I have included a diagram of fairly accurate measurements regarding my design layout.

I don't have the information of the car battery because they could all be different depending on a lot of factors. But I am assuming that it is a perfect battery :P

Will a regular 60 watt bulb work in this series setup? I was wondering if the 60 watts was coming from the suggested 120v usage.

I realize that my calculations are excluding the Bulb which would obviously reduce current. But I Don't know what the readings for the bulb will be. Any help is appreciated.

If I can get this series setup to work. Then I can worry about finding out how powerful of a magnet I will need.

 

[NascentOxygen]

Will a regular 60 watt bulb work in this series setup? I was wondering if the 60 watts was coming from the suggested 120v usage.

A 60w 120v bulb has a resistance around 240Ω. (V*V/R = 60)

This is a new rotor you have wound, is it? One that has 130Ω resistance? How many turns of wire?

I realize that my calculations are excluding the Bulb which would obviously reduce current. But I was in the moment and thought " What the heck"

If I can get this series setup to work. Then I can worry about finding out how powerful of a magnet I will need.

If you add 240Ω in series with your new rotor of 130Ω then it will reduce the current but I'd expect the rotor will still turn. However, with a rotor of 130Ω there is no necessity to "protect" the battery, except against accidental short-circuits. If the rotor gets hot and starts smoking, then that means 12v is too much for it, and you can incorporate some series resistance like you've shown, to reduce the voltage that the rotor sees. But 130Ω is nothing like a short-circuit, so the car battery won't be overloaded.

Once it starts spinning, the "slip-ring" contacts you have will impose their own resistance to current flow, so that 130Ω will be further increased, and the motor will draw less current once it gets spinning.

You have now abandoned the idea of getting your original egg-whisk rotor to turn?

 

[Flyingwing12]

no, I just need a really strong Magnet.

 

[Flyingwing12]

But the Bulb would be hooked up to 12v. So the wattage and current would be different right?

The setup I tried earlier was having the whole thing in series, without a lamp to reduce current, which was probably 2 amperes. The volt meter showed only 9vdc coming from the battery charger. But I should be using something else. The car charger was explained to have a rectifier that was making short jumps of current. Cutting to the chase, the small 1/16th copper wires leading form the sides of my motor melted and I was not surprised.

The eggbeater is shown on page 1 I think. It is only one continuous line of 5/64 inch copper wire.

I know there is a way to make this work. I was able ot get a similar design of smaller scale to work. SO why wouldn't this?

BTW FOR ANYONE WHO CAN ANSWER: My multimeter has Ohm settings of 20,200,200k, and 2000k. Why are these in 2's?

Also, my multimeter never seems to stick to one reading on Ohms. it always jumps between a high and low number. How can I get it to give me a straight reading?

I'm using a cheap 30 dollar multimeter form sears btw.

 

[NascentOxygen]

But the Bulb would be hooked up to 12v. So the wattage and current would be different right?

Sure they'll be different.

The eggbeater is shown on page 1 I think. It is only one continuous line of 5/64 inch copper wire.

Are you saying that half a dozen pieces of 5/16 inch copper wire soldered in parallel give a resistance of 120Ω?? Not likely.

Also, my multimeter never seems to stick to one reading on Ohms. it always jumps between a high and low number. How can I get it to give me a straight reading?

When you connect a resistor or lightbulb or anything across your meter, the resistance reading jumps around and never settles?

 

[NascentOxygen]

I got the small single wound job to spin continuously yes.

It has to be possible for this thing to spin.

I think I just need a very strong magnet.

You could try bar magnet(s).

And how would this commutator work? This keeps being mentioned and yet no one says how I should hook it up?

On DC motors, the function of the commutator is to allow current in only the rotor winding that is most effective in maintaining rotation at that particular moment. In your egg whisk rotor, current in the upper wire is not aiding rotation (it's slightly opposing it), so allowing that current is counter-productive.

You could retrofit a commutator to your rotor (see my sketch). Cut the rotor wires near one of the hubs and rejoin each in a strong mechanical joint using heat-shrink tubing, while at the same time ensuring that there is no electrical connection inside that join. You have 8 wires, you need to cut and rejoin in a total of 7 places. (You could do 8, but 7 is exactly as good.) Perhaps include a tiny piece of matchstick inside the heat-shrink to keep the two ends of the wires apart.

You make this modification at only one end of the rotor wires, so that's 7 cuts-and-rejoins needed. This now means that electricity can't get into that end of the rotor via the axle, so remedy this with a flexible bare copper wire bent into a J-shape and positioned so it will make good contact with that end of the one rotor wire nearest the magnet. You can hold this sliding contact in your hand while you optimize its shape and positioning, for maximum rotational speed.

As I cautioned, if your egg whisk rotor shows no inclination to move, then increasing the current or adding a commutator will not change this.

Happy experimenting! https://www.physicsforums.com/images/icons/icon14.gif

 

[Flyingwing12]

I am following the design process. But I am not seeing how you're J shaped wire will work. The motor is supported by two copper pylons. The pylons are about an inch and a half wide, so the wire would need to touch the pylon right?

Here is what I think you're sketch is telling me to do.

 

[Flyingwing12]

It also goes through two pylons of copper that support this eggbeater. The cooper is also oxidized. So the resistance should be a tad higher than pure silky clean Cu.

The ohm meter jumps around when I measure the resistance of wires. It usually jumps form 168-30 and then quickly stops at .3Ω and I have a belief that the resistance is probably lower than that.

But hey, how accurate is a 30 dollar meter going to be?

Still don't know why they marked all the measurements off in twos...

 

[NascentOxygen]

I am following the design process. But I am not seeing how you're J shaped wire will work. The motor is supported by two copper pylons. The pylons are about an inch and a half wide, so the wire would need to touch the pylon right?

Here is what I think you're sketch is telling me to do.

You have to disconnect the voltage from the support at this end, and instead feed the current into the ribs of the rotor by means of a rubbing contact using springy wire. The springy wire needs to rub against that part of the egg beater to the left of the heat-shrink so that as the rotor turns, current switches to a new rib of thick copper wire, goes along that rib and out of the motor at the support at the other end.

I'm using the word "rib" to describe anyone of the thick wires comprising the egg whisk.

 

[SirAskalot]

One word; Homopolar motor. Actually that is two words, non the less it might be a good/better solution than your design, because you don't need a commutator. Google it.

You also might want to skip the car battery, it gives a pretty nasty arc if its shorted. And can result in injury. Since it just going to rotate in free air without any loading, for a short time, regular (D-cell, 9V, 4.5V etc) batteries would be sufficient.

 

[NascentOxygen]

I am following the design process. But I am not seeing how you're J shaped wire will work.

The J shaped wire is a sliding contact to "brush" against the rotor and put current into the rib that at that moment is closest to the magnet.

 

[dlgoff]

The J shaped wire is a sliding contact to "brush" against the rotor and put current into the rib that at that moment is closest to the magnet.

Brushes? What's next, ... a commutator?