Nitecore UMS4 and new unprotected 21700 cells

10 posts / 0 new
Last post
marcosgg
marcosgg's picture
Offline
Last seen: 2 days 15 hours ago
Joined: 05/10/2022 - 14:51
Posts: 69
Location: Argentina
Nitecore UMS4 and new unprotected 21700 cells

Hello, this is my first time with unprotected cells, these are Liitokala 21700 4000 mAh, 3.7v, 40A batteries…

I bought them here at Argentina and put them in this charger, it said 3.60 v at start, so they where empty.

Now one of them is at 4.20v, full, but the others are at 3,98v…still charging.

0)
I think I have a big problem here with the length of the battery: it measures 5mm less than the original Imalent ones… it’s not something that a drop of tin will solve, is it? any ideas?

1)
Why did those charged so much slower than the first one?

2)
And, BTW, is there something else I should look for or take care for using unprotected cells?
I am a bit scared of their danger, I already know that I don’t have to short-circuit them, and I have to take good care of them, store them in an appropriate place…

3)
These cells are for Imalent R60C and MS08. Original Imalent batteries are 35A
Will the liitokala 40A produce more power/lumens?

Edited by: marcosgg on 06/18/2022 - 11:27
Correllux
Correllux's picture
Offline
Last seen: 1 day 23 hours ago
Joined: 04/27/2019 - 22:23
Posts: 1496
Location: USA

I’m not familiar with those lights and the cell lengths they can accept but maybe someone has a solution that doesn’t involve buying new cells.

As for the cells not finishing the charge at the same rate, it could be a couple of things. If the cells are not very similar in their internal quality then the charger may be attempting to provide current levels/duration at what it thinks is best for what it sees. Often the China-manufactured cells have a little wider spread in quality than what we see from the majors like Samsung, etc. If the spread is wider than normal then it might be smarter not to use them in this light (ok for single cell lights, though) and look for a set of cells where each one is more closely matched to their mates in performance metrics. Some people buy ten cells and pick the best three of the bunch but that’s not completely necessary.

Maybe more likely is that the charger is sensing different resistance levels – most chargers are notorious for this and imperfect at resistance measurements. The charging sequence is determined by measuring voltage and resistance and choosing a rate programmed into the chips that is safe/not likely to overheat the cell. If it thinks it sees high resistance it will lower the current for a little bit or even the whole time. The contacts on the cell or on bay terminals might not be clean, or it could be that the clamping pressure the slot is providing is not consistent between bays, or the pressure is not firm enough, or it could be actual higher resistance inside the cell itself. I would discharge and recharge them a couple of times and take notes…if they have been stored for a long time it may fix itself with a little energy use. Also, you could select a manual charging rate, say 0.5A or 1A and see how they compare that way, so the chip is not deciding anything (it will still terminate the charge normally this way).

Taking care of cells…mostly just don’t drop them, try to keep them at lower humidity and at room temps or cooler if possible, replace the heat shrink wraps with new ones as they get damaged. It’s a good idea to note their new charged voltage and capacity, as best you can, and then see how close that stays to the same numbers over the first several cycles of the cells…and if you can let them sit still after charging, it’s smart to take voltage readings with a multimeter after a day, a few days, a week (or longer if you can) to see how they maintain their resting voltage (should only drop very little…many will settle at 4.15v give or take, but if they keep dropping or start to drop below 4.1v then they may not be good quality/new cells). Most people will recharge when voltage (after rest/rebound from use) is from 3.4v to 3.2v – it’s ok to go lower but you don’t get much benefit and it could shorten lifetime a little bit. The important thing is to make sure they never drop too low, like 2.5v or lower…can often still be used/charged but there is a possibility of internal chemistry changes when the voltage goes very low and/or is allowed to stay there for awhile (like a light was turned on and drained very low in a seldom used backpack and nobody knew about it until a week or month later). If that ever happens, the charger may provide a very low trickle charge to “wake them up” a little…just keep an eye on them and feel for normal temperatures…check resting voltage/voltage drop…if anything is out of whack then recycle them and replace with new ones. They’re pretty safe overall, don’t be too worried. Don’t drive nails into them with a hammer. Smile

Tatteredmidnight
Offline
Last seen: 6 hours 34 sec ago
Joined: 09/11/2021 - 19:32
Posts: 145
Location: United States

I have an issue with my Thrunite TN20 V2 not working with a Vapcell k62 26650 because it is much shorter than the protected cell it came with. Currently I am using a magnet with this, but that solution has many problems.

As a longer term solution. I have some flat to button top adapter PCBs on order from Convoy. This would be the 21mm version https://www.aliexpress.com/item/3256803132204249.html?spm=a2g0o.store_pc...

Both of these lights seem to run the cells in parallel, so there is less risk of using unmatched cells than if they were in series. Having said that, it is always best to use cells of the same brand and batch in multi cell lights. As you run the batteries down, your lights may be stressing the cells unevenly.

It is hard to say which cell will be better. These are rewrapped OEM cells, and there are no guarantees that two cells branded and marked the same will actually use the same cell internally. Comparing between two differently branded cells is even harder.

As for the safety of using unprotected cells, it’s just a matter of being conservative and conscientious. One consideration when mixing them with protected cells in parallel is that if you run the protected cell low enough that the protection steps in and cuts the battery off, all the load will be shifted to the unprotected cells, and you may not be immediately aware of it. This can lead to those cells pumping out more current and heating up, so use caution.

The cells may be charging at different speeds due to a difference in internal resistance causing the charger to choose a different charging rate (assuming the charger is using such logic). Another possibility is that some chargers support different rates in different bays. This is something that Xtar tends to do, with the outer most bays supplying more current than the inner most ones can.

Good luck and enjoy your lights.

marcosgg
marcosgg's picture
Offline
Last seen: 2 days 15 hours ago
Joined: 05/10/2022 - 14:51
Posts: 69
Location: Argentina

Wow, Correllux, great explanation. I take note. Thanks

Tatteredmidnight, thanks for that link and for the explanation.

So that item from Aliexpress has magnets? that’s the way it attaches to the battery?

Do you think it would be safe to just add a 5mm tall drop of tin to the battery?

Tatteredmidnight
Offline
Last seen: 6 hours 34 sec ago
Joined: 09/11/2021 - 19:32
Posts: 145
Location: United States

marcosgg wrote:
Wow, Correllux, great explanation. I take note. Thanks

Tatteredmidnight, thanks for that link and for the explanation.

So that item from Aliexpress has magnets? that’s the way it attaches to the battery?

Do you think it would be safe to just add a 5mm tall drop of tin to the battery?

The linked item does not use magnets, I believe it is just a copper slug in a 21mm PCB. I think it would be safe to add a solder blob to the cell if you are careful not to heat the anode too much while soldering it. There are some informative threads about this on the site, so I encourage you to do a search and see peoples, experiences. I haven’t tried adding a blob to the cells personally so I can’t really comment on it well.

I’m not sure how well the adapters I linked work with a triple cell host like the ones you are using, but they are cheap enough that it probably doesn’t hurt to try. To be honest, I don’t even know how well they’ll work for my single cell light as I haven’t received mine yet, but that was the approach I am going to try for a similar problem, so I figured I’d share in the event that it was helpful to you.

Best of luck, I’m interested in hearing what you land on.

marcosgg
marcosgg's picture
Offline
Last seen: 2 days 15 hours ago
Joined: 05/10/2022 - 14:51
Posts: 69
Location: Argentina

Hello: yes, your idea seems to be very good! My father is an electrician, so he could help. Now… just 2 months from Aliexpress Sad

BTW: they did worked right out of the box on Imalent R30C on all the modes, even turbo.

On Imalent MS08 they work (I see less power on all the modes) but not on turbo… why? I mean: Imalent batteries are 35A, and these ones 40A, they should do turbo too.

Not working on R60C…

Anyway, I am happy about it.

Tatteredmidnight
Offline
Last seen: 6 hours 34 sec ago
Joined: 09/11/2021 - 19:32
Posts: 145
Location: United States

It’s much easier to list a spec than design a battery that actually meets it. 40A continuous for a 4000mAh cell is top shelf, Molicel P42B territory, I wouldn’t count on these cells coming close. HKJ has tested them and suggests that they reasonably top out below 20A.

Quote:
https://lygte-info.dk/review/batteries2012/LiitoKala%2021700%204000mAh%2...

Conclusion
The cells has the rated capacity and capacity is fairly constant with load, but they do get rather hot at high current. This means they may handle high pulse current, but 20A or more in constant current is not a good idea.

marcosgg
marcosgg's picture
Offline
Last seen: 2 days 15 hours ago
Joined: 05/10/2022 - 14:51
Posts: 69
Location: Argentina

haha, ok, good to know it: so Liitokala is somewhat lying about the 40A thing.

I concluded they are good for Imalent R30C (9000lm aprox) but not for MS08 (not getting the turbo at 30000lm aprox, “just” 10000lm on high mode but it does looks darker than with the original cells). Anyway I like them as emergency batteries.

I should be able to make them work on R60C and see what happens.

marcosgg
marcosgg's picture
Offline
Last seen: 2 days 15 hours ago
Joined: 05/10/2022 - 14:51
Posts: 69
Location: Argentina

Now I am able to import these ones:

Molicel/NPE INR-21700-P42A 45A 4200mAh Flat Top 21700 Battery

Tatteredmidnight
Offline
Last seen: 6 hours 34 sec ago
Joined: 09/11/2021 - 19:32
Posts: 145
Location: United States

Those are supposed to be some of the best high discharge cells currently on the market. I hope you don’t have issues with their length. I’m sure you won’t be disappointed in their performance assuming they do fit.