Strongest Electromagnet using 2 AA bateries

[Nigel Goodwin]

Im angry that that thread was deleted. It took me an hour to make. None of the questions were repeats. They were magnetism/physics central questions. Not AWG/internal resistance/H bridges to reverse polarity etc. All it deserved was a move to the physics/math discussion section. I want to remake it in the right forum, but knowing how fair the world is, it would be deleted and I would be banned from here.

You've started one thread, don't make duplicates about the same question - they WILL be deleted, and you WILL be banned - moderator.

 

[Trisorion]

Thank you nigel.

 

[Hero999]

It makes me smile when Nigel speaks like this, when I read his stern moderator posts I hear the voice of a very strict teacher.

 

[Willbe]

Are you allowed to parallel your battery with a capacitor?

 

[Willbe]

I thought that resistance lessened when the battery heated

Me too. A car battery so weak it can barely crank the engine can be boosted by running the headlights for a minute or so.

 

[Trisorion]

I could run a capacitor in parallel, but please excuse my inexperience, what would that do?

Also I think that the internal resistance heating/cooling relationship might be different depending on battery chemistry. Car batteries are lead acid, but I always thought NiCd was known for its high discharge potential, but I will do some tests either way. And I will make the coil slightly less resistance than I calculate it needs.

This post got lost in the shuffle. Does anyone know the answer to that question?

 

[audioguru]

Forget about using a lead-acid battery. You said the rules spec'd two 1.5V batteries but lead acid is 2V per cell.
Maybe the rules do not allow Ni-Cad or Ni-MH batteries that are only 1.2V per cell.
Alkaline batteries are 1.5V per cell. Two alkaline D cells might produce 5A.

Your question about adding many coils and overloading the battery was answered by me. The internal resistance of the battery will show its ugly head which reduces the voltage to the coils which reduces their current.
Then most of the power of the battery will heat its internal resistance instead of powering the coils.

Forget about heat causing the internal resistance of the battery and resistance of the coils to rise. The temperature takes time to rise and it won't rise much in only 20 seconds with maybe only 5A of current.

Forget about connecting a capacitor in parallel with the battery. A capacitor's voltage drops sharply when it discharges because it is not a battery. It would need to be as big as your house to provide 5A for 20 seconds.

 

[Willbe]

I could run a capacitor in parallel, but please excuse my inexperience, what would that do?

Picking up clips = transient domain; holding many clips = steady-state domain.

Short circuiting an ideal capacitor gives you infinite current for zero time with the area under the spike "curve" <> [not equal to] 0; definitely transient domain.
Discharging a cap with low ESR into a low resistance gives you a current spike over and above what the battery is delivering; definitely transient domain.

Discharging a cap with low ESR into a low resistance in series with an inductance gives you something I'd have calculate.
If this series RLC circuit is underdamped (Q factor > 1?) you'd get a decaying sinusoidal current waveform (which I don't know if that would help or not). Overdamped, you'd get a big decaying current spike, probably modeled in the time domain by the sum of two e^x terms.

You'd hook the cap to the battery first, then switch on the coil.

I'll have to get back to you on this; I haven't done Laplace domain stuff for decades.

We're definitely having fun, now.

It would be good, after all this effort, if you actually won.

 

[audioguru]

Transient magnetic power.
Enough power to draw paperclips within one kilometer? One centimeter?

I think paperclips would just twitch a little then the capacitor is discharged.

The power comes from the battery. If the battery is used to charge a huge capacitor then the battery will be weakened. The capacitor uses up the battery's power.
You don't gain anything except the ability to draw paperclips from a distance which is not needed.

 

[Sceadwian]

Depends on what you're allowed to use. You could get exotic and use the charge pump circuit from a disposable flash camera to charge a large capacitor bank to a few hundred volts from a single AA battery. Could do more than twitch a paperclip with that. I've always had the urge to use the stretch film we use at work and some foil to make a very large capacitor. Although it would be limited for pulse discharge by the inductance of it being a large coil I think I worked out the thickness of the film we have at work would alllow a safe charging voltage of 200 volts. A couple roles of super heavy duty aluminum foil and a few rolls of poly stretch film could be fun.

 

[audioguru]

A capacitor must be huge to provide high power for 20 seconds.