Nitecore UM4 failing to terminate C-cell NiMH at 0.5A ?

Batteries and Chargers Chargers
1

I just got at Nitecore UM4, and I’m testing it out with some brand new Tenergy Premium NiMH C-sized cells.

I have no experience charging C-sized cells. I usually charge AA and AAA Eneloops using a Gyrfalcon All-88. I often put it on 0.1A, and it seems to work fine.

I’ve found that the Nitecore UM4 will just go forever (like 20 hours) on 300mA. It eventually seems to stop right at 20 hours, maybe because of a fail-safe timer.

At 500mA, it also seems to go for quite a long time. I have one cell on there now, and it’s been going for 6+ hours at this point.

As a sanity check, I tried charging some Eneloops on the UM4 and Gyrfalcon in parallel. I did 300mA on the UM4 and 0.25A on the Gyrfalcon. Both worked and terminated just fine (the UM4 was slightly faster, as expected). Several hours later, the two test AA Eneloops are at 1.423V and 1.420V. Good stuff.

Then I put brand new C-sized Tenergy Premium NiMH cells on each at 500mA.

The Gyrfalcon finished at 4:19. The UM4 is still going at 6:12. I will let it keep going to see what happens.

Do you think it’s that there’s not enough current at 500mA to get a proper -dV/dt drop at the end?

I’m guessing that charging at 1.0A would work better on the UM4…

But then why does the Gyrfalcon not have this problem? Is it simply a better and more sensitive charger?

As a matter of habit, I generally charge Eneloop AA at 0.1A on the Gyrfalcon. I have noticed that sometimes, it goes 10:00 and then stops. Now I’m realizing that it’s probably failing to -dV/dt terminate when that happens.

I guess I should charge them at 0.25 always then? They do get warm when I do that, but now I understand that the warmth is what triggers the voltage drop in the first place.

(And if the Gyrfalcon is fine, why bother with the UM4? I need a USB charger for a solar setup that I’m working on).

2

I had opposite problem with my tenergy cells, with other chargers, they would terminate too early. current settings did not seem to help. But in your case it is easier to adopt than look for reasons why, that is if you find it at all.
In general you need to pour 150% capacity into a nickle cell to charge it fully, ideal current is 0.5-1c, your C cells are 5ah, so it would be safe to charge them 2A+ that is if your charger has that ability. So set for 1A you need to pour 7AH into a cell, set your time out timer to 7 hours, in best case delta V would kick in and stop, if not, timer will. Or you can increase current/decrease time, to stay in 150% window.

3

Are you talking about a simple egg or kitchen timer, separate from the charger? Or do some chargers support time-outs like this? I don’t know any charger that I have that has the ability to set a custom timeout (not Xtar, Gyrfalcon, Nitecore, etc…)

4

I was talking about charger setting, at least 1 of mine has that function, you mentioned yours stopped at 20 hours, time out safety, can you change that setting?
Worst case if you set 350ma, 20 hours will be just the amount of time you need to fully charge. I know it is slow, but at least you would be able to charge.
Charging nimh is a tricky thing, i’ve been dealing with this phenomenon for about 20 years, some sells charge great, delta v kicks in, others not so much, actually tenergy are the ones i have issues with charging in smart chargers as well.

5

Try charging them at one amp, or higher, to help trigger termination.

300mA is what? .1C …05C?

Chris

6

Yes, I will try charging at higher amperage and see what happens.

Currently, it’s been going for 9+ hours at 500mA.

I do wonder what the Gyrfalcon All-88 is doing differently to terminate.

Regarding chargers with adjustable timers, which one do you have that has that?

UM4 manual mentions the 20 hour cutoff, but not how to change it:

The Gyrfalcon manual doesn’t seem to mention the 10-hour limit:

https://www.planetofthevapes.co.uk/forums/attachments/gyrfalcon-a44-a88-user-manual-pdf.197074/

Also, if Tenergy cells have this problem, is there some C-sized NiMH that is better? I do have the Eneloop plastic C adapters, and those work fine, but the capacity of AA is so low (that’s the whole point of the C-battery form-factor… more capacity, right?)

7

Okay, another test on fresh-out-of package Tenergy Premium C-sized NiMH cells.

One in each charger at 1.0A each (in the Nitecore UM4 and the Gyrfalcon All-88). Let them run last night.

Gyrfalcon finished in 2:03 and shows 1.43V at the end.

Nitecore UM4 is STILL going this morning… 11:00 hours later, it’s showing 1.45V, and it now claims the cell has absorbed 9999 mAh. Essentially, the mAh display only has 4 digits, and it has overflowed.

The cell is quite warm, almost hot to the touch. A contact griddle thermometer is showing 100F after about 10 seconds of contact.

Obviously, I’m going to stop it from cooking the cell. But this behavior is troubling.

I’m also wondering if the Gyrfalcon is under-filling the cell after only 2 hours. Though this would mean the cell absorbed 2000mA, which might be about right, given that they ship pre-charged to some degree.

But anyway, what “magic” is the Gyrfalcon using here that the Nitecore UM4 is missing?

And if the UM4 really does suck in comparison, I guess my quest for a good USB-powered NiMH charger must continue…

8

I think this is most likely cause.

It’s a little dated now, but are you aware of HKJs site?

Hard to know why, perhaps the charger is more sensitive, perhaps you just got lucky with the sample you have.

Is there a reason you’re looking to solar charge NiMh C cells? Lithium chemistry generally much easier to charge (Constant Current, Constant Voltage).

9

Yes, I am a longtime student of HKJ! That’s why I have a Gyrfalcon All-88.

The UM4 was also a “Two smiley-face” rating, and it’s USB, and it does NiMH, and it has 4 slots, and it has user-adjustable current, and it goes down to 300mA (which would be good for AAA), so that’s why I picked it.

As for why I want to charge NiMH with Solar… well… I want a setup where I can charge everything that I might need to charge. Though I use 18650s and friends in most flashlights, I still have Eneloops in some mission-critical things, like my Garmin GPS. We also use Eneloops all over the house for all kinds of things. Like… this Korg guitar tuner sitting on my desk. Or my Fluke Multimeter.

If there was an extended power outage at some point, we might need to charge some Eneloops.

The idea for solar is to get a BigBlue 28W, and then hook that to an XTAR PB2SL with some fat 21700s in there. Then use an XTAR VP4C for Li-Ion cells, and use the UM4 for NiMH cells. And if I need to charge some very long cells, I can also use a VC8 Plus.

But so far, I’m not happy with the UM4 for NiMH when plugged directly into the wall (no solar, no power bank so far).

The Woyum ZK6 is NiMH-specific, but I’m having trouble tracking one down. If I can get one, I’m hoping that it works better.

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10

From the Enova (Gyrfalcon) rep:

The termination algorithm for NiMh batteries is more complex than that for lithium-ion batteries. It typically involves -dV, 0dV, cut-voltage, and timeout. In the All-88, these algorithms are executed simultaneously, and charging can be terminated as long as any one of them is satisfied.

11

Why is it that my Maha charger (only charges nimh) charges 4 batteries from empty in 20 minutes. In a multi chemistry charger (no matter what the brand) it takes hours. Sometimes 7-8 hours for four batteries. We are talking about new Eneloop’s.

12

UM(S)4 use slot-sharing, Slot 1&3, 2&4 share the selected current; not sure if anyone is aware of that

Charged 2 C-cells with 2000mA with my UMS4, the cells getting at the end a bit more than handwarm, that´s OK for NiMH

Use 500mA for AAA and 1A for AAA, works in most ways good. With good cells it terminates perfectly and have one of the lowest temp at charge end.

But the Nitecore have problems with cells which don´t reach 1,45V and above, in this case it would charge till the 20 hours emergency stop.

Could it be that the voltage is less than 1,45V)

@zoulas

You have to be more detailed. The MH-C9000 shows charge is ended while it charges stil 2 hours with a top-off-charge. And full cells in 40 Mins mean you charge them with a much to high current, AAA-cells with capacity below 1000mAh with 2000mA?

Dunno what you do, lots of my chargers charges 2000mAh-AA in less than 3 hours with cahrge current of 1000mA, some others in ca. 2h - 2,5 hours

13

I have the MH-C980

And

Miboxer multi chemistry charger.

But this has nothing to do with brand of charger or batteries.

The multi chemistry chargers take many, many hours to charge nimh batteries. The C980 takes 30 minutes.

14

My charger is the UM4, not the UMS4, which means it only goes up to 1.5A, I think.

Also, I was testing this with a single cell by itself, so I guess slot sharing wouldn’t be a factor.

I could try another fresh C-cell at 1.5A and see what happens.

After 11 hours, the UM4 was showing 1.45V on the display, but still not stopping… Gyrfalcon indeed stopped at 1.43V

Is there some better C-sized NiMH cell than these Tenergy Premiums?

15

I used the Amazon Basics 5000mAh with 2000mA charge and Wilhelm 4500mAh with 1500mA charge, worked flawless in my UMS4. I don´t look always on the charger but it exceeds the 1,45V

I know you have the UM4 but except the max. charge current the chargers should be similar, at least in theory.

I guessed your cells are have this low voltage which let the Nitecores charge forever, know this problem with bad/ over-discharged cells.

Most multi-chemistry chargers don´t provide more than 1A charge current for NiMH, I guess in my not so small charger collection only the Nitecore UMS4 provide 2A NiMH-charge, the Accupower IQ338XL provide 1500mA.

But I can´t still agree with your statements because it makes no sense if you use the same charge current with Multi-chemistries and NiMH-charger.

It´s true that 1A charge current on different chargers is not the same, in my experince all Xtars are very slow (almost 3 hours) while the Nitecore UMS4 with max. 2 cells (Becasue of slot sharing) is very fast and fill 2000mAh–AA with 1000mA charge current in 2h and some minutes. This time cannot be beaten by my pure NiMH-chargers like Skyrc NC2200 or Powerex MH-C9000 Pro.

I don´t have a MiBoxer but it seems to be made by Dlyfull, I would think it´s modified A4-chargers. This charger have terminating problems (charger longer than neccessary) and are not very fast overall.

16

It has taken me as much as 5 hrs to charge two AAA batteries in a multi chemistry charger. This is unacceptable.

As mentioned the Maha does it in minutes.

I am attributing this to the fact that the Maha is purpose built for nimh.

17

Jep, Maha Powerex is specialized to NiMH

Some multi-chemistry-chargers are not the fastest but -if the termination works- I´m far away from needing 3 hours for charging AAA (except maybe Xtar and my Infinity Voltage 4 is also a bit slow). Some chargers (mostly Xtar) are very slow in general with NiMH and also reduce the selected charge current because of high IR, but 5 hours for AAA sound like charge current 200-250mA

But charge AAA in minutes is a confusing statement, minimum with max charge -which the cells are not made for- is 30Min for a 1000mAh-AAA in theory.

I wouldn´t charge AAA with 2A, except I want hot fingers and very bad longevity

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18

Than is something wrong. Even my slowest Combochargers for NiMH, Xtar VC4SL and Dlyfull A4 need not more than 3 hours with 500mA, except the termination fail and lead to almost endless charging

I have the UM2 and UMS4 again, there are more differences that I would expect.

I had the UMS4, was a bit angry because of the slot sharing which make it to a 2-slot-charger, sold it and buy an UM2.

The UM2 generally terminates NiMH at 1,48V, looks not like it would go for the DeltaV while the UMS4 charged with good NiMHs 1,51-1,55V

The UM2 react much slower at changing charge current, needs longer to go in the energy save mode for the display.

The UMS4 was much better for me, so I get one again. The UM2 is only used if I don´t want to charge the NiMH really full

19

When I say minutes, I meant 20 minutes. Give or take.

20

I guess the question remains: what evidence do you have that this Powerex charger is doing a good job at charging those cells in 20-30 minutes? I tried to look it up on HJK’s site, and that particular charger isn’t listed. Has anyone done an in-depth review of it? Has anyone measured the current over time during the charge? Has anyone taken a look at the termination behavior?

For example, here is HJK’s in-depth review of the Powerex MH-C9000, which is a dedicated NiMH charger:

https://lygte-info.dk/review/Review%20Charger%20Powerex%20MH-C9000%20UK.html

You can see that at 2A, it “finishes” charging after about 50 minutes and then trickle charges to top-off all the way up to 175 minutes. But the battery isn’t full at 50 minutes. The trickle charge afterward is necessary to completely fill it. That’s about 3 hours total.

Now look at the Gyrfalcon multi-chem charger, which is using 1.0A to charge an Eneloop AA:

https://lygte-info.dk/review/Review%20Charger%20GyrFalcon%20All-88%20UK.html

It uses -dv/dt termination, ending the charge at about 120 minutes. So you can see that to actually fill the battery, this is faster than the 175 minutes of the dedicated Powerex charger…

I’m guessing that Powerex chargers are telling you that the charge is done, when it’s not really done… the battery isn’t full yet after 20-30 minutes. But it’s “full enough” to use.

I generally try to charge my cells as slowly as possible, to prolong their life. I’ve never ever charged my AA Eneloops at 1.0A, for example. I do 0.1A if I’ve got the time, and 0.25A if I’m in a semi-rush, and 0.5A if I’m in a real rush. But they definitely get much warmer during the charge the higher the amperage. Maybe I’m totally misguided when doing this. Maybe I’m just wasting time, and cell life at 0.5A charges is identical (or even worse?) than cell life at 0.25A charges. But I read long ago that keeping cells cooler is better, so I’ve been doing that ever since.

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