Coin Batteries that won't die!

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,894
This is totally weird. Another AAC user and I have been corresponding on a different subject. Meanwhile I mentioned that I had a few coin batteries (2032) that I can't use in my remote garage door opener buttons. Wanting to toss them into a bucket along with other useless batteries I decided I wanted to fully deplete them (kill them) before tossing them into a bucket. The potential for shorts and fire were my concerns.

I took a couple white super bright LED's (3.2 forward volt) and simply slipped them over the batteries. That was Wednesday, November 23rd. I didn't think it through because I didn't expect them to last this long. At this very moment they are still lit. One has grown visibly dimmer than the rest, and only recently did I start checking the voltage of the batteries.

Lets call them BL1, BL2 & BL3. Yesterday I measured and recorded the voltage for the first time (recording the numbers). BL1 had a voltage of 2.564, BL2 had a voltage of 2.611 & BL3 had a voltage of 2.614. These voltages were measured WITH the LED's connected and glowing. A week ago I tested the batteries to see what would happen if I connected a motor in parallel (small DVD spin motor) and all three tests spun the motor but only BL1 went almost completely out. It continued to glow but barely, hardly discernible. 2 & 3 ran the motor with little dimming. At present there isn't enough power in any of the BL's to spin the motor, so the batteries ARE draining.

What I am most curious about is why are these batteries NOT burning up my LED's? They've been operating for a week and a half at present. Continuous, non-stop luminous output. Keep in mind I do not have any current limiting resistance on the batteries at all. If I were to connect an LED to a double A battery I would expect to burn out the LED, so the coin batteries must not be capable of delivering very much current.

If you have ANY insight as to why these batteries are able to drive an LED for this long even after their useful life has been spent, please share. I'm almost tempted to take a new coin battery and do a full charting of the voltage and current and track them over time just to see how long the LED will continue to burn. However, I don't think I want to perform an experiment that may take months to complete.

FYI, for Halloween I took a gourd that looked like a snake and put two tiny red LED's in it for eyes. Stuffed a 9V battery and a current limiting resistor on each to make sure not to blow them out. Come evening time I turned it on. By the end of the evening the LED's were still glowing but barely. I suppose I may have used a weak battery to begin with, but given the size of the battery and the test that is under way on my work bench, I would have expected the 9V battery to have lived much longer. Now I'm thinking that next year I'll use coin batteries and set the gourd out there all week - day and night. If weak, near death batteries can last this long then why not sitting in a pumpkin or other gourd for days on end?!

Your thoughts?

RECAP:

……..Yesterday….Today
BL1….2.564v…...2.556v (V drop 0.008)

BL2….2.611v…...2.602v (V drop 0.009)

BL3….2.614v…...2.615v (V increase 0.001) ? ? ? ? ?
 
Last edited:

dl324

Joined Mar 30, 2015
11,243
What's a "Throwie"?
It's a CR2032 type battery with one or more LEDs taped to the terminals and a magnet. People like to throw them at ferrous metal objects so they'll stick.

And how would I calculate how long they might last?
CR2032 specs (Energizer):
upload_2016-12-3_12-9-17.png
When battery voltage drops to the vicinity of the LED forward voltage, current draw will be low and the lifetime can be hundreds of hours.

Self discharge on that type of battery is very low. My daughter did a "Which LED is brighter" experiment when she was in middle school (6-7 years ago). The similar but higher capacity coin cells I used still operate her display.
 

MrChips

Joined Oct 2, 2009
21,639
You can see a similar effect with supercaps.

Take a 1F 3V to 5V capacitor and charge it with two AA batteries to 3V.
Connect a blue LED across the capacitor without any series resistor and see how long it will stay lit.

The I-V curve of the LED is an exponential, i.e. it is highly nonlinear. As the voltage drops, the current drawn decreases exponentially. But the blue LED is still visible well below 1mA. Hence the LED stays lit for a very long time.
 

hp1729

Joined Nov 23, 2015
2,304
This is totally weird. Another AAC user and I have been corresponding on a different subject. Meanwhile I mentioned that I had a few coin batteries (2032) that I can't use in my remote garage door opener buttons. Wanting to toss them into a bucket along with other useless batteries I decided I wanted to fully deplete them (kill them) before tossing them into a bucket. The potential for shorts and fire were my concerns.

I took a couple white super bright LED's (3.2 forward volt) and simply slipped them over the batteries. That was Wednesday, November 23rd. I didn't think it through because I didn't expect them to last this long. At this very moment they are still lit. One has grown visibly dimmer than the rest, and only recently did I start checking the voltage of the batteries.

Lets call them BL1, BL2 & BL3. Yesterday I measured and recorded the voltage for the first time (recording the numbers). BL1 had a voltage of 2.564, BL2 had a voltage of 2.611 & BL3 had a voltage of 2.614. These voltages were measured WITH the LED's connected and glowing. A week ago I tested the batteries to see what would happen if I connected a motor in parallel (small DVD spin motor) and all three tests spun the motor but only BL1 went almost completely out. It continued to glow but barely, hardly discernible. 2 & 3 ran the motor with little dimming. At present there isn't enough power in any of the BL's to spin the motor, so the batteries ARE draining.

What I am most curious about is why are these batteries NOT burning up my LED's? They've been operating for a week and a half at present. Continuous, non-stop luminous output. Keep in mind I do not have any current limiting resistance on the batteries at all. If I were to connect an LED to a double A battery I would expect to burn out the LED, so the coin batteries must not be capable of delivering very much current.

If you have ANY insight as to why these batteries are able to drive an LED for this long even after their useful life has been spent, please share. I'm almost tempted to take a new coin battery and do a full charting of the voltage and current and track them over time just to see how long the LED will continue to burn. However, I don't think I want to perform an experiment that may take months to complete.

FYI, for Halloween I took a gourd that looked like a snake and put two tiny red LED's in it for eyes. Stuffed a 9V battery and a current limiting resistor on each to make sure not to blow them out. Come evening time I turned it on. By the end of the evening the LED's were still glowing but barely. I suppose I may have used a weak battery to begin with, but given the size of the battery and the test that is under way on my work bench, I would have expected the 9V battery to have lived much longer. Now I'm thinking that next year I'll use coin batteries and set the gourd out there all week - day and night. If weak, near death batteries can last this long then why not sitting in a pumpkin or other gourd for days on end?!

Your thoughts?

RECAP:

……..Yesterday….Today
BL1….2.564v…...2.556v (V drop 0.008)

BL2….2.611v…...2.602v (V drop 0.009)

BL3….2.614v…...2.615v (V increase 0.001) ? ? ? ? ?
250 mAH battery, LED that works down to 1 mA. Could get 250 hours out of it.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,894
Yesterday I noted a slight increase in the voltage present on BL3. It was up by 1 mV. Today it's up even more, up by 3 mV. Using the same meter as always. BL(s) 1 & 2 are both down by 7 mV & 13 mV. BL1 is growing even dimmer and BL2 is showing visible signs of dimming. BL3 remains bright, but not as bright as when I started this test.

Here's some pictures to compare November 29 to today: Batteries are arranged in order, BL1 on the left, BL3 on the right. The glow on the static mat signifies the brightness. In the November picture it's almost impossible to see the outline of the clear 5 mm super bright LED's. This morning's photo shows the outline of all three test pieces.
 

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RichardO

Joined May 4, 2013
2,271
Yesterday I noted a slight increase in the voltage present on BL3. It was up by 1 mV. Today it's up even more, up by 3 mV. Using the same meter as always. BL(s) 1 & 2 are both down by 7 mV & 13 mV. BL1 is growing even dimmer and BL2 is showing visible signs of dimming.
Were these voltages measured with the LED connected? LED's tend to have about the same temperature coeficcent as silicon diodes -- about -3mv per volt of forward voltage drop per degC of . (-2mv for a silicon signal diode). You are likely measuring temperature of the diode. ;)
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,894
Voltage tests are done with LED's connected. Room is approximately 73˚ F. This room tends to hold heat better than most of the house. Otherwise the temp when testing at other times may have been 72˚ F. Just used an infrared thermometer. Said the diode temp is 74.5˚ F. I'll start testing temperatures when testing for voltage. The voltage just read was 2.614 v. Yesterday's voltage was 2.615 v. Maybe heat has something to do with it.

The meter is an EXTECH. I generally have faith in its readout. Been accurate enough. I'd assume that measuring the same voltage the same way on different days shouldn't produce inconsistent results. As to why I tested 2.618 this morning, perhaps it has something to do with the ambient temperature in my lab. It's certainly not an environmentally controlled lab, just a basement.
 

RichardO

Joined May 4, 2013
2,271
Try this: Put your voltmeter on the battery/LED. While watching the voltage, squeeze the LED between your fingers. I would expect that to raise the temperature a measurable amount. I am guessing that the voltage will drop by tens of millivolts.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,894
I've never held the batteries in my hand while testing them. Always been on the desk.

Starting voltage: (BL1) 2.535. At 30 seconds holding battery between fingers, 2.538. After one minute, 2.538. After two minutes, 2.538. After 3 min (one min holding the LED itself) 2.538. Only saw a 3 mV rise while holding the battery between my stubby spicy hot Italian fingers.

I am guessing that the voltage will drop by tens of millivolts.
Didn't drop. Increased 3 mV. After 5 minutes on bench, no touching, no heat sources: 2.540 v. I have no idea what I did.
 

RichardO

Joined May 4, 2013
2,271
Starting voltage: (BL1) 2.535. At 30 seconds holding battery between fingers, 2.538. After one minute, 2.538. After two minutes, 2.538. After 3 min (one min holding the LED itself) 2.538. Only saw a 3 mV rise while holding the battery between my stubby spicy hot Italian fingers.

Didn't drop. Increased 3 mV. After 5 minutes on bench, no touching, no heat sources: 2.540 v. I have no idea what I did.
Dang. Another great theory shot down by reality. :(
More thought required here...
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,894
Did both. No significant change. After holding the battery for two minutes, I held both the battery AND the LED for an additional minute. Saw no change when I started holding the LED.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,894
Results coming in now.

Yesterday BL1 was at 2.41 v, BL2 was at 2.45 & BL3 was at 2.549 v. All three were still glowing but barely detectable.

This morning, BL1 is at 2.034, BL2 is at 2.181 & BL3 is at 2.405. Only BL3 is showing any sort of light.

Next is to put red LED's on them to see where they go.

[edit]

With Red Superbright LED's on the batteries,
BL1 is at 1.764 v and glowing.
BL2 is at 1.793 v and glowing.
BL3 is at 1.807 v and glowing.

All 3 are lit but 1 & 2 are close to being too dim to see. #3 is glowing dim but brighter than the other two.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,894
BL1 no longer glows. It's voltage reads at 1.4 volts initially but steadily climbs the longer I hold the test meter probes on the battery. So I think it's acting more like a capacitor now than a battery. BL2 & 3 are almost as low but are still glowing on the red superbright LED's. I suspect this will be my last entry regarding this silly experiment. I only wish I had started with full documentation from the beginning, charting current as well as voltage. Oh well, maybe next time I replace a garage door remote battery I'll set up to test for all these parameters.

Hey everyone - have a good holiday season.
 

AlbertHall

Joined Jun 4, 2014
10,226
I found an old 2032 and I thought I might repeat the experiment. The test didn't last long. Its voltage was precisely zero even without an LED :(
 
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