# How do I draw high Current from battery

Discussion in 'General Electronics Chat' started by Link068, Jan 27, 2018.

Apr 10, 2017
30
1
Hi.

I am working with electromagnet which has a resistance of about 100ohms. I want to put about 4amps through it.

Could this be done with 4x 12v SLA 1.2ah battery’s? Or 6v 4.5ah sla battery’s?

And if so how do I draw 1amp from each battery ?

Cheers

2. ### Ylli Member

Nov 13, 2015
449
114
To draw 4 amps with a 100 ohm load requires 400 volts. See Ohm's Law.

3. ### WBahn Moderator

Mar 31, 2012
23,552
7,207
If you want to put 4 A through a resistance of 100 Ω, you are going to need 400 V to do it.

To do that from a lower voltage battery pack, you would need a suitable DC-DC converter. To go from a 48 V battery pack you would need to increase the voltage by a factor of 8.3. and would need to draw 33.33 A. Allowing for about an 85% efficiency and you will actually need to pull closer to 40 A.

4. ### wayneh Expert

Sep 9, 2010
15,512
5,739
Driving 4A into 100 ohms requires 400V, so no.

5. ### Sensacell Moderator

Jun 19, 2012
2,125
680
Not to mention the 1.6 kW of energy, that's one hell of a heater.

6. ### WBahn Moderator

Mar 31, 2012
23,552
7,207
Not very many batteries are going to last very long, either. Those 1.2 Ah batteries will last less than two minutes.

7. ### Alec_t AAC Fanatic!

Sep 17, 2013
9,173
2,163
You could use one battery and a DC-DC inverter to charge a capacitor up to 400V or more, then discharge it through the resistor: but your 4A pulse would last only a few milliseconds at most, unless you can afford a lorry load of large capacitors.

8. ### sghioto Active Member

Dec 31, 2017
641
87
I just want to know where the OP got a 100 ohm electromagnet. Maybe 10 ohms but 100 ohms,WTH
SG

Last edited: Jan 28, 2018
9. ### shteii01 AAC Fanatic!

Feb 19, 2010
4,461
706
Using Ohm's Law, I=V/R. V is constant, battery voltage. The only way to adjust current I is to adjust resistor R. Resistor R in this case is a load attached to the battery. Therefore to have large current I you will need resistance R to be small.

10. ### mcgyvr AAC Fanatic!

Oct 15, 2009
5,394
1,194
These are the types of posts that make me wonder how there aren't just constantly stories on the news of kids/people just killing/electrocuting themselves, blowing up their houses,etc...
Also wonder why people think electronics/electrical projects are just so simple/harmless that they can just jump right in without any basic knowledge what so ever...

"Hey guys... watch this".... BOOM...

11. ### WBahn Moderator

Mar 31, 2012
23,552
7,207
How many of us played around with electricity when we were kids? How many of us really had any idea what we were doing? How many of us got zapped now and then or let the magic smoke out of something from time to time?

I remember winding bare wire around a big nail to make an electromagnet and connecting it to some big-ass dry cell batteries that my dad brought home from work (they were the used batteries from their burglar alarm system) and wondering why things got hot but almost nothing got picked up. I was perhaps eight at the time. That night my dad introduced me to the notion of "electrical insulation".

watchmania, recklessrog and sghioto like this.
12. ### WBahn Moderator

Mar 31, 2012
23,552
7,207
I just did some searching and I'm pretty sure those batteries were No 6.

13. ### Ylli Member

Nov 13, 2015
449
114
Put out as much current as a modern AAA alkaline.

14. ### WBahn Moderator

Mar 31, 2012
23,552
7,207
I don't know what the peak current is, but the capacity of 40,000 mAh is a wee bit more than a modern AAA alkaline.

15. ### Poor old sod Member

Jul 25, 2017
77
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If you read/study darwinawards.com u will find a few experimenters whom paid dearly for being uniformed, or just stupid.

smooth_jamie likes this.
16. ### smooth_jamie Member

Jan 4, 2017
99
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+1 for Darwin Awards, great website. Have you seen the movie? some of them are true stories.

17. ### WBahn Moderator

Mar 31, 2012
23,552
7,207
Yep. And most of us could easily have been among them at several times in our lives. Then again, I doubt that there's a single person that's ever lived (that made it to the age of five or so) that wasn't a Darwin wannabe at least once.