Last night was nothing but playing around with the magnets, not much progress was made. However with me messing with it I realized that the resistor and coils are getting too hot, I need more resistance but in the form of magnetic coils. Can I get away with putting the coils in series to increase the resistance that way? Right now each coil has 7.5 ohms each and that will increase it to 0.91A. If I rewire them to 10 ohms each I'd be right at 0.6A.

So here’s it is with the coils wired in series, please let me know if you see anything wrong with it. (just rewired the coils to be in series)

Yes it looks as if it should work.

As for the original schematic: If you use 2x 10 resistors in series the power dissipation for the resistors and the total current will decrease. Is 500mA not enough to create the desired magnetic field strength with the coils you have? This way you wouldn't need to rewire your coils... again.

 

Congrats on the progress!

The LEDs won't be much for technical to add on, you are over the hump!

 

Yes it looks as if it should work.

As for the original schematic: If you use 2x 10 resistors in series the power dissipation for the resistors and the total current will decrease. Is 500mA not enough to create the desired magnetic field strength with the coils you have? This way you wouldn't need to rewire your coils... again.

You're right about wiring up those coils, I really don't want to do it again. Just because I paid top dollar for the wire and I had to by it in a pack of 3 different guages of spooled wire.

I was playing with the resistor configurations last night, putting 2x 10Ω in series produced a very faint magnetic field. then I put one 10Ω in series and the magnet were working great at 948mA, however the wattage of the resistor needed to be 13w because it was getting hot with just running it for a short period of time (noting that the coils were fairly cool to the touch). With that logic, I'm not sure if putting the coils in series without the 10Ω resistor is going to be a good idea because the 30awg wire is going to assume all that current and heat up.

There are so many options, I could wire the coils in series (15Ω) and put 2x 10Ω in parallel to give me total of 20Ω at 13V which is 650mA, not sure if that is enough current flow though. Or 3x 10Ω resistors in parallel a total of 18.3 leading to 710mA. Hmm.

A question that I have is, when I put two 10w resistors in parallel, is the wattage additive? Meaning that now I have a 5Ω resistor at 20w? and how about, I wire 3 in parallel that will give me 3.3Ω at 30w?

Congrats on the progress!

The LEDs won't be much for technical to add on, you are over the hump!

Thanks,


This should be something that can be added after everything is said and done, the only thing that I would need clarification on is the right resistors to add inline to get the right voltage to the LED's.

 

Try the coils in parallel and in series you put two series resistor pairs in parallel. That's 880mA total, 2W for each resistor at 12V and 3.6Ohm coil resistance.

 

If the coil ohms are already low, surely putting the coils in series is the best bet?

The resistor wattages do add up, wattage is based on resistor size so 2 resistors can dissipate twice the wattage of 1 resistor.

I would run each coil pair in series, then with a extra series resistance to set the desired current. That series resistance can be any combination of resistors that adds up to the correct ohms and will stay cool.

How much current do the coils seem to need to pull the rotor magnet? If the air gap is small and the rotor is on a bearing it should only need a few hundred mA or so.

 

How much current do the coils seem to need to pull the rotor magnet? If the air gap is small and the rotor is on a bearing it should only need a few hundred mA or so.

Apparently about 400mA to 500mA, he had 950mA total for two coils in parallel.

@JCOX
If you put the coils in series and then 15Ohms in series with the coils that's 22.2Ohms total, at 12V about 500mA. Coil current as per my previous post will be 440mA per coil, assuming their resistance is equal. Connecting the coils in series will guarantee that the same current flows through them, when in parallel it could be slightly different.

 

At lunch today I was able to put the coils in series and added two 10Ω resistors in parallel and each set of coils with the resistors had 19.1Ω at 680mA, which seems to be perfect I ran it for at least 5 minutes and the resistors were slightly warm to the touch and the coils had a trace of warmth. So I think that series is going to be the way to go simply because I don’t have to have 4 of those big resistors on the circiut.

I have been working on making a case to hoouse everything, more to come.

 

At lunch today I was able to put the coils in series and added two 10Ω resistors in parallel and each set of coils with the resistors had 19.1Ω at 680mA, which seems to be perfect I ran it for at least 5 minutes and the resistors were slightly warm to the touch and the coils had a trace of warmth. So I think that series is going to be the way to go simply because I don’t have to have 4 of those big resistors on the circiut.

I have been working on making a case to hoouse everything, more to come.

I hope you tested the device , i.e. if the rotor turns, before making a case etc..

"slightly warm" and "trace of warm" sounds good.

 

i have tested it and it works really well. the one thing that doesn't work really well is the random portion. the jumping from one speed to the next is so drastic that the magnet stops spinning and just wiggles between pulses. I am in the process of messing with the pots to see if I can dial it in to where the changes are slow and gradual.

 

i have tested it and it works really well. the one thing that doesn't work really well is the random portion. the jumping from one speed to the next is so drastic that the magnet stops spinning and just wiggles between pulses. I am in the process of messing with the pots to see if I can dial it in to where the changes are slow and gradual.

Changes will always be abrupt. I guess the frequency is too high when it wiggles. Try to slow down the D-FlipFlop refresh rate by decreasing the upper left schmitt trigger oscillator frequency. This will give you more time to analyze with the scope. Then play with the offset and gain pots.

That part will also work if you put the same effort into analyzing it as you did until now.
Great job! I wish all threads would make progress like this.

 

Some flywheel mass for the rotor will help a lot too. Maybe a brass disk that holds the barmagnet?

Or even a 5/8" thick clear acrylic disk, with the bar magnet embedded into it (since you looked to have CNC machining capabilities). The clear disk would allow the students to see the important working parts like the magnet and coils interacting.

 

I was thinking the exact same thing. and instead of using a bar magnet I will use two separate magnets on the ends. almost ready to snap some pictures of it.

 

That part will also work if you put the same effort into analyzing it as you did until now.
Great job! I wish all threads would make progress like this.

this project was fun, I enjoyed the entire process. I need to come up with another idea, so that you can draw me up another schematic... maybe something a lot more complicated...

 

An "antigravity" suspended (or levitated) clear globe using controlled electromagnets?

They are fun for students and have a cool factor.

 

An "antigravity" suspended (or levitated) clear globe using controlled electromagnets?

They are fun for students and have a cool factor.

I was thinking if that can that be done with ferrofluid... Having a mass of levitated ferrofluid would be really nice...

JCOX: I was hoping you said that (about new projects), and you did. Looking forward to hear from you

 

Here's the box, I incorporated a fan to keep the big resistors cool.

 

He, really well made.

I assume the rotor part is not ready yet?

Thanks for the update.

 

no not quite there yet.

 

no not quite there yet.

No problem , no one is putting pressure on you.

If you do all your projects this way people here will be more than happy to help you out next time.

 

That is one slick looking enclosure!

Bandsaw or laser cut?