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Hello battery experts.
I have a project where I am using a 5000mAH (flat pack) LiPo battery from a seller on Aliexpress.
I am attempting to charge it with a 5V 1A TYPE-C Micro USB 18650 TC4056A Lithium Battery Charging Board also from Aliexpress.
I have used several of these boards in other projects but always charging lower capacity Lipo batteries e,g 650mAH and 100mAH without any issue.
Normal operation:- When charging there is a red LED on the charging TC4056 pcb that is lit whilst charging. As the battery voltage reaches 4.2V the charger stops charging,
the red LED goes out and a blue LED illuminated to indicate that the battery is fully charged.
The problem:-
When charging this new battery, the TC4056 board charge current is adjusted to 1/2C (500mA) but the battery the voltage NEVER reaches 4.2V.
Consequently the charger never switches from red to blue to indicate fully charged. So without connecting external DVM's I don't know what state of charge the battery is in!
It could be almost 'flat' or have a full amount of energy.
The clues:-
Whilst monitoring both charging current and battery voltage simultaneously I have noticed that as the battery voltage approaches between 4.05 and 4.1V (never a precise set point) the charging current keeps
intermittently falling to a low level or dropping to zero, and then almost immediately jumps back up to full charge current.
It's as though the BMS (Battery management/protection system) pcb built into the battery, is intervening in the charging process and preventing the charging from ever completing?
Questions:
Has anyone else seen this strange behaviour?
Does it look like I have a faulty battery or am I missing something?
I could live with 4.1V for this application but I can't see a way to 'fool' the TC4056 into thinking the battery is fully charged.
There is a Texas LiPo charging IC that has a switchable 4.06V or 4.2V 'set point' but no cheap modules available sporting this chip!
I am loathe to buy a second battery (from a different vendor) until I understand what is causing this phenomenon!
It's a mystery.
All help/comments appreciated.
Thanks in anticipation.....
Dave
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You're in kind of no man's land of charge termination. A fast charger is on the order of 2 hours and a slow charger is 8 hours, you're right in the middle. The 4056 is designed as a "fast charger" which means that it looks for a decrease in charge current- set by a resistor (Imin) after reaching the constant Voltage level (4.2v nom). At 500 mA, you're charging at C/20- pretty slow, you say in your notes that this is C/2? There is also a EOC current threshold set by a resistor- this means that the charge current had to be above this and fall to Imin for termination. The data sheet has the values for a a half amp charger. It needs to charge at > 350 mA and must drop below Imin for termination. Look a these two levels, you're not satisfying one or both. Most chargers also have a "fast" charge time limit, I can imagine pushing fast charge current for 5 hours will exceed this time. Some (not most) TP4056 have a 3 hour limit fast charge limit (very approximately), this could also trip you up. The premium LTC4056 has a settable timer. These no name chinese clones might use something similar- you'll have to see how it behaves. Is the charge current going down to the trickle level or does it just keep pushing .5 amp. Look at the R's on the board, you should be charging at 1 amp and you'll have to adjust your threshold and I min. That's a big battery for this charger. It should work. There are better chargers, the 4056 is sort of the minimum Li solution.
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I have exactly the same issue trying to charge a new 5000mah lipo prism cell, only charges to a max of 3,75v and the blue led comes on when soc is under 4v, did you find a cure/fix?.
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Your charger is just a typical TP4056 charger with protection built in. If you monitor the charger's supply voltage and battery voltage when charging a smaller battery, what do you see? Does battery voltage get up to 4.2V? Does the supply voltage stay at 5V all the way through? Then when it's done charging and you disconnect the battery, what's the battery voltage an hour later?
From the picture, I suspect the new battery also has a protection circuit. Its over-voltage protection could be triggering at too low a voltage, and shutting things down. But first, we need numbers on how the charger performs with another battery, to see what the difference is.
I would also say that if you have the charge rate resistor selected for 500mA, the charger will supply that without regard to the capacity of the battery. It doesn't know how big the battery is. So if it works for one, it should work for another.
Did you say how you are powering the charger?
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I have exactly the same issue trying to charge a new 5000mah lipo prism cell, only charges to a max of 3,75v and the blue led comes on when soc is under 4v, did you find a cure/fix?.
sounds like you got the LiFe / LFP variant of the IC. -
Hi thanks for your considered replies.
So in desperation I decided to dismiss the TP4056 charging module and connect the LiPo battery directly to my Farnell PSU.
Of course setting the current limit to 500mA as previously attempted with the charging module.
So carefully monitoring the voltage and current values over 1/2 an hour I noted down the progress.
Results:-
The battery voltage jumped to 4.14V as the constant current source (Farnell PSU) was connected.
After around 10 minutes the voltage suddenly dropped to 4.08V and the current dropped to zero.
Almost immediately it jumped back to 4.14V and the current returned to 500mA.
There then commenced a frantic on/off episode lasting a few seconds before the voltage returned to 4.15V where it then remained for the rest of the test period.
I then disconnected the battery from the power supply and dumped a 500mA load across it's terminals.
I left this connected for 15 minutes before reconnecting the constant current source. At this point the 'on load' voltage was 3.97V.
The battery voltage jumped back to 4.13V and slowly climbed to 4.15V where the same 'switching behaviour' happened again.
I have not tried just leaving the battery connected to the Farnell PSU for hours unattended, so cannot report if the battery voltage ever progresses beyond 4.15V
I think I have now successfully discounted the TP4056 as the culprit and just wonder why this particular LiPo is presenting this behaviour?
It has crossed my mind to just split open the end of the battery an remove the BMS board and try charging the LiPo again from the TP4056 module.
But is this safe?
Please feel free to comment and add any further tests/ideas I can try.
Thanks in anticipation.....
Dave
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I don't think that should be happening. So you had your power supply set to 500mA with a voltage maximum of 4.2V? I suspect another battery would not behave that way.
The picture you posted originally shows the standard TP4056 module with built-in protection (the DW01 chip, or equivalent). So you already have protection, and don't need another instance in the battery. If you can physically do the operation, taking that circuit out of the battery, or just connecting the battery's negative terminal directly to ground so the protection is bypassed, would probably solve this problem, or at least limit it to what the TP4056 does.
But there's an odd thing in your picture. It's hard to see, but it looks like you have both of the black ground/negative wires soldered to the OUT- pin. That's what you would do to bypass the protection circuit on the TP4056 module, but if you do the equivalent to the battery, then you need to separate those connections. The protection circuit operates by connecting, or disconnecting, the battery negative terminal to/from the charger/system ground. The high side goes right through without any switching. If you look your module, you should find that OUT+ and BAT+ are directly connected by a wide trace.
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Almost:-
I had the PSU set to 500mA current limit and watched the DVM connected across the battery terminals. (making sure it didn't go above 4.2V)
However in the time I sat watching it the voltage never got higher than 4.15V and it just kept having crazy episodes where the current kept switching between 500mA and zero very rapidly.
As I understand it the pcb incorporated within these LiPo batteries is NOT a charge management system but a battery protection unit.
Preventing over voltage/over current and total discharge prevention so it should (like all my smaller LiPo batteries) just allow the battery voltage to achieve 4.2V whereby the BMS in the external charger (TO4056) would intervene and reduce the charging current and display the 'full' LED indicator.
It's almost as though my battery has the 'over charging' protection set point set too low, or the wrong board fitted in the battery that is designed for a different battery chemistry.
Maybe I shouldn't have bought the 'best deal' (cheapest) LiPo off Aliexpress, maybe this is why these were being sold cheaper than their competitors?
Lol!
Dave -
Switching between 500mA and 0 very quickly sounds like:
1. Charger applies V_charge with I_charge_max current limit
2. Voltage on battery rises above BMS V_ovc (overvoltage cutoff)
3. Battery BMS opens the FET
4. Battery charger turns off charging voltage/current regulator once I_charge < target_C/10 (no current can flow through the open FET)
5. BMS releases OV lock since there's no longer any overvoltage
6. Return to step 1
At a basic level, the BMS is there to make sure the customer doesn't blame the battery supplier when the battery explodes due to overvoltage.
It's your job to design a system where V_ovc is more than V_charge by some margin so the charger can function without tripping the BMS. How certain are you of those parameters for any of the components you've purchased? It's not clear you even have a datasheet for the battery cell.
4.1V is a pretty standard charge voltage cutoff. My EV runs a lithium nickel chemistry that's limited to 4.14V or so. Some cell phones charge up to 4.45V, some other devices use lithium iron chemistry that caps out at 3.65V but usually measures around 3.3V....
Maybe I shouldn't have bought the 'best deal' (cheapest) LiPo off Aliexpress, maybe this is why these were being sold cheaper than their competitors?
If you're buying random charger chips and random batteries (with unknown chemistry and unknown BMS) off Aliexpress without reading the datasheet, are you doing a good job? -
First, I don't know the potential quirks of the TC4056, but the charge of a Li-ion battery doesn't normally stop when the voltage reaches the max voltage.
The charger is in constant current mode until the voltage reaches the max voltage, then it goes to constant voltage mode and continues while monitoring the current until said current drops below a certain threshold, ofen C/10. The time that elapses in constant voltage mode can be significant. Just this first point to mention that the end-of-charge detection is not just that the voltage reaches "4.2V". Of course, if it never even reaches the max voltage, EOC will never be detected (but in that case, most charger ICs have a timeout and stop the charge automatically after some time), but just to mention that this isn't the EOC either.
Second point is that not all batteries have the same max voltage. You commonly have 4.1V and 4.2V batteries. So this particular battery may be a 4.1V max. battery. (Note that, while not at all a foolproof criterion, often a nominal 3.7V Li-ion battery will have 4.1V max and a 3.8V nominal one will have 4.2V. Ideally, check out the datasheet of the battery.)
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Good Morning Davebullock, I believe you are experiencing a phenomenon known as 'Lithium Battery Charging Histeresis'. Go here for more information: https://www.sciencedirect.com/science/article/abs/pii/S2352152X22005138
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How many mAh do you get from it after it's "full" at 4.15V? It may just be designed to stop charging at 4.15V.
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Thank you latest correspondents :-)
Well quite a bit to digest.
My first comment is ...as you suspect I have no datasheet for this particular battery, it's just listed as a 5000mAH LiPo battery with a voltage of 3.7V (printed on the label).
So fair comment about NOT being actually able to guarantee the chemistry.
In my defence I am using several similar looking batteries (smaller brothers) with identical packaging and all listed as LiPo chemistry and all have 3.7v printed on their labels.
The only difference I can see is that all the others charge to 4.2V and then stop charging. (their BMS NEVER trips in).
The project I am trying to use it in is to drive a 'Buck' converter to generate 2V d.c. instead of having to use lead acid technology. Because my setup needs to be reliable and charge automatically, you can see it's not reliable when exhibiting this behaviour.
This is a brand new battery and so I have never completely discharged it (yet) so don't know about any 'hysteresis' effects as I can't even get it to a fully charged state (even with a standalone constant current PSU).
I agree that it appears that the embedded BMS (or more specifically, Battery Protection System) is the culprit but why, I have been using smaller LiPo's from this same series for several years now and never seen this problem.
I thing it's getting near to the point where I open up the end of the battery and bypass the BMS and see if the battery voltage EVER goes to the expected 4.2V?
Certainly an annoying distraction from what was going to be a 'quick' modification :-)
Dave
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If you get 5000mAh +/- a few % when it stops charging at 4.15V then I'd say that was the intended end-of-charge voltage.
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Hi AMYK
You are probably correct but my point is that at 4.15V isn't a standard 'end of charge' set point for LiPo charging modules.
And as the general consensus is that one shouldn't rely on the batteries "Protection Management System" to end the charging cycle, plus without a dedicated charging management circuit there is no indication of 'full charge' it's a problem for an unsupervised application.
Thanks for all your input folks, in the New Year I think I will tear open the battery.
Merry Christmas everyone.
Dave