Discharge protection test

Batteries and Chargers Rechargeable Batteries
1

Discharge protection test



There is frequently asked some question about the discharge protection in batteries:

  • Does it work at low current?
  • At what voltage does it work?
  • How to reset it?
  • How much extra capacity is there at low voltage?


In this article I will try to answer these questions.

I will look at a couple of batteries in detail (i.e. with lots of curves). The batteries used are not new batteries, they are from the batteries I have reviewed over the last few years.



Keeppower 18650 3400mAh (Black)



I selected this battery as the first one to test. The 3400mAh cell is very common today.
The cell can be discharged down to 2.50 volt according to the datasheet.
This battery uses a protection circuit with hysteresis.



The protection trips at about 2.50 volt and when I apply the charge pulse it is reset again and the battery recovers up to 3.25 volt.



Here I have zoomed in on the trip point. I apply a current pulse after 30 second and reset the protection.



With 0.3A discharge there was 17 minutes (85mAh) more in the battery.



But to reset the protection the battery needed two pulses.



Going down to 0.1A I can get another 22 minutes (40mAh) runtime.
Again the protection trips at 2.50 volt, but the pulse does not reset the protection. I have to use many pulses before the battery has high enough voltage to reset. I looks like the protection need 2.9 volt on the battery before it will reset.
I have added a dark red line with the estimated battery voltage during this charge.



Here my charge pulses can be seen, each pulse is 10 seconds with 10mA, then I wait 20 seconds, before trying again. This makes the average charge current about 3mA. Using a more powerful charge pulse will, of course, reset the battery much faster than the 1 hour I used.



With 30mA load I do get about 27 minutes (14mAh) more, but the battery need more charging before it will reset the protection.



The protection does still trip at 10mAh load, resetting it requires some charging.



The extra runtime with 3mA is not real, a lot of it is due to charging above to reset the protection.





The 0.1mA or 100uA trace did take a long time to test, 6500 minutes is about 4½ day.
But as can be seen the protection works perfectly, it still trips at 2.5 volt.

After this test, where the battery has been at around 2.5 volt for days, I did a final capacity measurement and it showed that the battery had lost 10mAh in capacity. On average the battery is supposed to lose about 2mAh for a charge cycle (30% capacity loss during 500 cycles), i.e. the battery may have been damaged slightly, but nothing to worry about.



Here I have collected the different discharge segments in a table.

For this battery the protection works fine at any current and gives protection from over discharge.


Enerpower+ 18650 2900mAh (Blue)



A slightly older Panasonic cell, but it is still rated for 2.5 volt discharge.



The protection trips at around 2.3 volt and it looks like there is some hysteresis, before it can be enabled again at 3 volt.



Discharging with lower current makes it much more obvious. The battery must be charged to 3 volt before it will be enabled again.




My longest test. The protection did trip, even with a 0.1mA load.



It is very little energy that is left after the first time the protection trips, but with low enough current draw it can last a long time.



Xtar 18700 2600mAh (Black)



Next battery is a 2600mAh battery, these battery usual has a lower voltage or 3.0 volt or 2.75 volt (Xtar does not specify minimum voltage for this battery).



The protection has a rather low trip voltage of 2.40 volt.








At 1mA it does still trip perfectly at 2.40 volt and does only need one pulse to reset the protection.



Interesting curve, the battery is still recovering when I apply the load again. It continuous recovering for about 10 hours.
This time it was a bit harder to reset the protection, two pulses was needed.



This time it recovers for 3½ day with the 100uA load applied, before the voltage starts dropping. It takes nearly 10 days, before the protection trips at 2.40 volt.






TrustFire TF18650 3000mAh (Flame)



How does the protection work on a cheap battery. For this I have used a Trustfire battery, it is rated as a 3000mAh battery, but the real capacity is around 2600mAh.



The protection trips at 2.50 volt and a single pulse resets the protection.









Here the protection is a bit slow to reset.



A close look shows that after a few seconds (6 seconds) with the charge pulse, the protection resets.



Even at 100uA the protection works fine.





Sibeile IMR18650 2600mAh (Black)



Next battery is another 2600mAh, but this time I will only do a few tests.



I did only test down to 0.1A, but that protection is at a very low voltage.



The battery did not loose any capacity during this test.



Fenix 18650 ARB-L2 2600mAh (Black)



Just a check of protection voltage at 1A.



The protection kicks in at 2.50 volt.





Resetting protection

Many chargers can do it, if I specify that the charger will charge with at 1mA at 0 volt, it will reset protection (Lower currents will probably also do it).



If the charger cannot reset the protection, it can be reset with another battery. It is best to use partial charged battery, but a fully charged can also be used. Connect them as the photo shows. Depending on how much hysteresis the protection has, the needed time can be below a second to a minute or two.



Test setup



The test setup is fairly simple, I uses a electronic load to discharge the battery until the protection trips. Then I wait 30 seconds, before applying a 10 second charge pulse with 10mA to reset the protection. I do keep the charge current fairly low, to avoid charging the battery.

Because this setup is mostly for low current test I have not used 4 terminal connections, this means that I will have some (small) error in voltage at 1A.



Conclusion

It looks like 2.0 volt to 2.5 volt is very common for under voltage protection, independent of the specified minimum voltage for the battery.
The protection works both at high and low currents, but on some batteries it is more difficult to reset the protection when it is tripped, especially at low currents.
When the protection has tripped there is very little energy left in the battery.


Notes

Do hold these result against any specific brands. I have only tested a couple of brands, but I will expect that all brands works the same way.

How to see if a battery is protected

2

Thanks HKJ, that’s great info. Based on that it seems that you really can just use protected cells in a light which has no low-voltage-protection on it’s driver.

3

Thanks for testing, it is very useful to see this tested. I still like the low voltage protection to kick in at 3V, so I prefer a driver that does that.

It is good to see that the protection of the Trustfire also seem to work fine ( at least on this one sample).

4

Thanks for sharing your knowledge again. Hopefully I'll be able to apply this.

5

Very interesting results. Did you by any chance test an unprotected cell? I was under the assumption that even though the cells are “unprotected”, they have some sort of built in protection of their own.

6

I did not, they do not have any protection against over discharge. In the link at the bottom of the article I do have a bit about the protection in unprotected cells. In short: that protection is not to protect the battery, but to protect the user from flames or explosion.

7

As always a very professional overview of an important subject.

Thanks for taking the time to do this for us. I don’t actually run protected cells in anything simply because I don’t trust the protection and I don’t personally feel the need for it in any of my lights. However, I do see why many people choose to use protected batteries and this is very useful information for them.

8

Thank you so much.

9

Thanks for the efforts with some amazing information. I found it interesting that the protection circuits did not reset the same way each time, meaning that depending on how it was discharged is how it reset. Do you have any idea why this was happening? Thanks again, orsm info.

10

When discharging at low current the cell will not recover as much voltage, this can affect the protection. There is, of course, also different protection chips that works different.

11

When I used to use protected cells I noticed that on a few Panasonic’s if I discharged them with low current they would NOT reset at all. I would have to jump start them by feeding them current from another battery. I ended up simply stripping the protection off of them after a while. I wonder how many people have “dead” panasonics that this would work on.

Have you ever run across that?

12

Thanks HKJ. Silly me thought it was the protection circuit not even thinking it was the battery voltage preventing it from resetting.

13

I cant see why this would be Panasonic related, they dont make the protection circuits. That same circuit is likely to be on other battery brands too.

14

Thank you sir. :beer:

15

I’m sure it’s not only panasonic, just that this was the battery that I had the problem with. As far as I know Panasonic and Sanyo are the same company now right? Also Like you said I’m sure others use the same protection. Might even be different protection used on the same cells at times. I know a bunch of us bought these same ones though. It was a group buy from Wallbuys I believe. I thought I would say something in case other people had “dead” batteries that are actually still good, just that the protection refuses to reset.

16

FWIW, while one may own the other, they don’t suddenly become the same company. I have not followed it closely, but I assume that R&D and manufacturing are still mostly separate between the two entities. Branding may change, but they still have separate product lines and technologies. (Probably ;-))

When those cells stopped working did you try “jump starting” them as described in this thread?

17

[quote=wight]

Yeah that makes sense that they would still have their own product lines. It would be like Chevy buying Ford, you might end up with some parts being ordered for both but you would still have Mustangs and Camaro’s.

On the jumpstart. I suppose I shouldn’t recommend this but it’s what I do. I keep a battery with wires taped to both ends. I’m always using it to test lights with. Drivers and things before I turn the light on, etc etc. I just use that. Positive to positive and negative to negative. Just a few seconds does the trick. It will bring the amps up high enough that a charger will detect it too if it has been taken down too low. Try this at your own risk. 0:)

18

Don't all protected Panasonic batteries have the protection added by another company? In HKJ's review of the protected NCR18650B with Panasonic wrapper, he says, "This battery is not made by Panasonic. The cell inside the battery is from Panasonic, the protection cirucit and the assembly work is done by somebody else." The battery looks like it keeps the original wrapper, adds the protection, then adds a second clear wrapper over it all.

19

I think I heard that Keeppowers were using Panasonic sells and I’m sure there are others. I like Panasonic sells I just don’t use the ones with protection, not because they are all bad or anything, just that I don’t need it. Their 3400’s were on sale for a while and they are great batteries for all kinds of lights. And yes the Panasonics that I have taken apart just have an unprotected Panasonic with the green wrapper under it. I don’t have any idea if Panasonic is wrapping them or if all of them are wrapped and protected someplace else under license maybe, maybe not?

20

No licence is my understanding. The cells are designed to be wrapped as laptop battery packs and the like, higher drain for power tools etc. 3rd parties divert them to other purposes and fit the protection circuits, or not. Essentially all Panasonic branded protected batteries are fake. The cell is Panasonic (assuming the cell isnt a fake), but the assembled battery as we know it is a not theirs. The KeepPower because they wrap it in their name, with their choice of circuit, are genuine KeepPower using a Panasonic cell, it would still be a genuine KeepPower with a Sanyo cell or any other.

Whether Panasonic and the like turn a blind eye I cant say, but it does seem apparent they are trying to at least keep themselves distant from that repurposing. They may actively try to prevent it too for all we know. The cells are volatile and Panasonic rightly would not want to see them in the hands of mad scientists and be potentially liable for the choices they make.

On a side note, no need to look at Ford and GM, GM already has demonstrated shared R&D and suppliers with for example the same basic V6 finding its way into GM models from Pontiac, Chev, Buick and Holden in Australia. They all had variations on the same basic engine. Theres plenty more parts that were the same way, in the 70s there was the T350 and T400 transmissions, and in the 80s or 90s the T700s for example. Theres a huge saving by not doubling up on R&D costs. A recent Pontiac GTO was a rebadged Australian Holden that in the UK was sold as a Vauxhaul, the same basic car was sold as the G8 too (4 door version I believe). The Vauxhaul Vectra was sold in Australia as the Holden Astra.