# power coil so battery does not blow up?

Discussion in 'General Electronics Chat' started by ElectromagnetNewbee, Sep 18, 2014.

1. ### ElectromagnetNewbee Thread Starter Member

Jul 13, 2014
69
0
if i connect a car battery to a large copper coil, what do i need to help regulate the voltage/amps so my battery does not overheat and blow up? 8 gage coil that is 10 pounds is what i want to power.

2. ### #12 Expert

Nov 30, 2010
16,685
7,323
A resistor.

An 8 gauge coil of ten pounds weight is about 200 feet long and has .1257 ohms, so just calculate R = 12.6 volts / the current you want to flow, to decide on the ohms. Be sure to calculate the power (P=IE) to be sure the resistor is large enough that it doesn't overheat.

You can also use car light bulbs to limit the current safely.

Last edited: Sep 18, 2014
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3. ### ElectromagnetNewbee Thread Starter Member

Jul 13, 2014
69
0
what size resistor?

4. ### #12 Expert

Nov 30, 2010
16,685
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How many amps?

5. ### faley Member

Aug 30, 2014
94
13
I must ask ElectromagnetNewbee, what are you trying to accomplish, a better way to heat your still?

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6. ### wayneh Expert

Sep 9, 2010
12,382
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That's my vote. A typical headlight is something under 5A. You can place them in parallel if you need more.

Any resistor you use will be expensive since it will require a high power rating. How high depends on your answer to #12 regarding the target current. Lightbulbs are relatively cheap, provide visual feedback, and are purpose-built to dissipate heat.

7. ### PackratKing Well-Known Member

Jul 13, 2008
850
216
Just guessing here... whether OP is looking to make a large electromagnet.. an Iron core would help... Although considering the amperage potential of a car battery, wouldn't either heat up drastically in short order ??
I have " played the fool ", and laid a tire-iron across battery terminals, and it got cherry-red rather quickly...

Would a 12v sealed-beam headlamp in parallel mitigate the tendency to overheat?

I have a collection of kitchen-range oven coils, and burners to use for high-power resistors, for all that is worth...

Last edited: Sep 19, 2014
8. ### #12 Expert

Nov 30, 2010
16,685
7,323
No. This guy is talking about 8 ga. wire. NEC limit is 40 amps.
Crazy as this seems, he has the right to experiment, and I will help unless he starts talking about ways to get injured.

9. ### PackratKing Well-Known Member

Jul 13, 2008
850
216
In effect, he is courting some serious burns in this adventure... I too, will not deny the right to experiment... just as you said...

10. ### wayneh Expert

Sep 9, 2010
12,382
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For the record, I would put the bulb in SERIES with the load. It won't limit the current in parallel.

I would not recommend an iron core, as that starts to look like a railgun if the geometry is off. I might feel better if we could see a picture.

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11. ### alfacliff Well-Known Member

Dec 13, 2013
2,449
428
what happened to the 0ther post on this subject? the #8 wire and such sounds famiar, last time it was with a power suply, I think.

12. ### tcmtech Well-Known Member

Nov 4, 2013
2,111
1,751
I have suspicions that you have not yet read up on and come to understand the concepts of ampere turns and how they directly relate to magnetic field strength as of yet.

So if you have a 12 volt vehicle battery and you are using approximately 200 feet of 8 ga copper wire with an estimated resistance of about .125 ohms your amp draw will be a little less than 100 amps which will not hurt any decent sized lead acid battery in the least bit.

What you will get however is a very strong magnetic field and a large coil that will start to heat up after a few 10's of seconds run time so the duty cycle will be somewhat limited by how hot you want your coils to get.

That said for example a typical junk yard electromagnetic crane runs around 250 - 300 volts DC at 50 - 100 amps of current resulting in a magnetic strength that if equated to ampere turns would be anywhere between 12,500 and 30,000 ampere turns of magnetic field force but its spread out over a rather large surface area.

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13. ### faley Member

Aug 30, 2014
94
13
Maybe the OP can't afford a carbon-pile rheostat and simply wants an alternative method to run a load test on the battery. Just kidding. Without understanding the desired goal, as we all know, there is no answer.

14. ### wayneh Expert

Sep 9, 2010
12,382
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The OP has previously been trying to generate a strong magnetic field and has been advised of the amps versus turns issue, as well as using magnetic field permeability to concentrate the field. Beyond that, I have no idea what his plan is. Hoping to avoid splattering copper.

15. ### alfacliff Well-Known Member

Dec 13, 2013
2,449
428
also not mentioned, if the wire is insulated or not.

16. ### ElectromagnetNewbee Thread Starter Member

Jul 13, 2014
69
0
railgun.. i never thought of that. it is kinda a cool idea. but im def not building it for that.

17. ### wayneh Expert

Sep 9, 2010
12,382
3,238
Right, but my point was that anything you place inside your coil could potentially become a projectile, whether you want that or not!

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