What Happens When You Draw Too Much Current From A Battery

nlaham

And so I accept learned that all batteries have an internal resistance which will limit the current that it tin can output, so that you can't belch a huge battery in a separate 2d because of that internal resistance. But what I am wondering is, at what betoken is it dangerous to draw likewise much current on lithium ion batteries.

I took an 3.7V iPhone battery out (1900 mAh) and found the internal resistance to be very depression through a couple tests, effectually 0.2 ohms or something. After, I attached the leads to a very low ohm resistor and measured the current (like 0.1 ohms, barely annihilation). I actually maxed out the electric current on my ammeter, which is 10 amps, and then I went over that mark. Hopefully I didn't mess up my meter, but I removed it chop-chop. The resistor also burnt out, only basically this tells me, I can pull a TON of electric current from this tiny trivial battery when information technology'south not hooked to all the circuitry in the phone. Normally, it would exist limited to only allow 500mA or something of the like.

I am wondering, is there a skilful dominion of pollex that will tell me what electric current is unsafe to draw off a lithium ion battery? I would think at some bespeak, if I shorted the bombardment out for more than a few seconds, the internal resistance in the bombardment would get very hot and destroy, explode or catch the battery on fire.

I just desire to be safe hither. I am not into short circuiting batteries, but I want to know how much current I can safely draw off of a lithium ion battery without causing it harm.

mfb

I would retrieve at some point, if I shorted the battery out for more than a few seconds, the internal resistance in the battery would get very hot and destroy, explode or catch the battery on fire.

That internal resistance is not a dissever component, it is an constructive description of the battery itself and emerges from its style to store and release energy.

Endeavor to detect some data sheet. The maximal current the iPhone requires gives a (weak) lower limit for maximal current.

nlaham

That internal resistance is not a separate component, it is an constructive clarification of the battery itself and emerges from its way to store and release energy.
Try to observe some information sheet. The maximal current the iPhone requires gives a (weak) lower limit for maximal current.

Thank you guys. I think the iPhone requires at about i to two amps when it'south being used heavily (high processing ability). Are you proverb that the the bombardment then will have that as its max as a lower limit? What is the upper limit then? I am hoping I can depict 3-4 amps off of it safely, but there is no "C" rating on it.

mfb

Are you maxim that the the battery so volition accept that as its max every bit a lower limit?

If the iPhone tin draw 1-2A (that is a lot), I doubt that this value is dangerous for the battery (otherwise information technology would be a poor blueprint). However, it could tolerate college currents, likewise.
Perhaps yous can use multiple batteries in parallel?

nlaham

If the iPhone can draw ane-2A (that is a lot), I uncertainty that this value is dangerous for the bombardment (otherwise information technology would be a poor pattern). Still, information technology could tolerate higher currents, likewise.
Maybe yous can use multiple batteries in parallel?

That is a good idea, I didn't consider that. I might be able to arrange 2 smaller batteries easier that style too.

Thank you for the tips.

mrspeedybob

I took an three.7V iPhone battery out (1900 mAh) and constitute the internal resistance to be very low through a couple tests, effectually 0.2 ohms or something. Afterward, I attached the leads to a very low ohm resistor and measured the electric current (like 0.one ohms, barely anything). I really maxed out the current on my ammeter, which is x amps, and so I went over that marker.

In lodge for a circuit to draw 10+ amps from a 3.7 volt source the total resistance must be iii.7/x ohms or less, and then your ascertainment of x+ amps with a load of 0.3 ohms is plausible. I'm just wondering how you measured the cells internal resistance. I may be wrong but from your post it doesn't audio like ohms police is something yous were familiar with, only that's the merely way I can think of to measure a cells internal resistance.

nlaham

In order for a circuit to draw 10+ amps from a three.7 volt source the full resistance must exist 3.7/ten ohms or less, and so your observation of 10+ amps with a load of 0.3 ohms is plausible. I'grand only wondering how you lot measured the cells internal resistance. I may be incorrect but from your post information technology doesn't sound like ohms law is something you were familiar with, but that'southward the just mode I can think of to measure a cells internal resistance.

I take been familiar with Ohm'southward constabulary, just not too familiar with batteries and internal resistance. Well, I should say I was more familiar when I was in schoolhouse, only forgot all of those things and needed a refresher, I'k only a Mechanical Engineer. I as well have never really applied these principals to actual applications so I am sort of relearning some concepts.

Anyway, I measured the internal resistance using the second equation here. http://en.wikipedia.org/wiki/Output_impedance#Batteries

I measured no load voltage, and then put a load on it, and measured current and loaded voltage. I had to measure out the 2 separately since I only had one multimeter. Since the voltage keeps dropping off equally I continue the electric current running and draining the battery, I can't exist sure my loaded voltage and current measurements matched upwards exactly, but it was pretty close. The best manner to do information technology would be to use two meters, and record my values at the aforementioned time. Hence the reason I said ABOUT 0.2 ohms. It could have been 0.fifteen or 0.25.

I want to test it again, but equally of now I believe it's a really depression internal resistance, so depression that the max current I can draw off the battery would in fact be a dangerous level for a Li-Ion batery. I have been reading that 1C to 3C is a safe discharge rate for most Li-Ion batteries. (C beingness the chapters which I think is 1900mAh for iPhone 4, so anywhere from 1.9A to 5.7A would exist prophylactic for this battery, probably closer to the middle). Cheers to CWatters for this explanation on discharge rates.

I may beginning using a Lipo battery, since those can discharge at much higher currents, some every bit high every bit 60C (or 300 amps according to the bombardment CWatters pointed out.http://www.overlander.co.britain/batteri...ry-4400mah-3s-11-1v-60c-farthermost-pro-1010.html

CWatters

Something else to watch is the belch voltage - you may need to build a voltage cut off to prevent the cells existence over discharged. They can react desperately to that.