Serial battery charging with in series TP4056 modules? Sort of YES! :-D

the main problem is that the 2S charge circuits with 5V boost to 2S simply charge the battery
and depend on the balancing BMS board of the battery pack

an example

So you need both.

But then still, it’s only balanced when both cells are fully charged.
You often see this on cordless drills too.
They strongly advise you to charge the battery pack until it’s fully charged.

There are plenty 2S BMS models: https://www.aliexpress.com/w/wholesale-2S-BMS.html?SortType=price_asc&SearchText=2S+BMS

540 hits I am seeing.

To charge a 2S battery, use a CC/CV DC/DC converter. They're cheap as chips (at least ≈6.5V of input required for constant current regulation):

Also, do not expect balancing boards to do jackshit below well above 4.2V/cell.

Cheers :-)

What does “terminal of the charger using high voltage device” even mean…

If those BMSs don’t shut off power to the battery when charging is completed then the DC DC converter will continuously ‘trickle charge’ the lithium cell at CV which is horrible.

Well i’m ditching the 3s idea also….
It’s just all really confusing.
Anyway i’m probably stick with the PT4065 and a disconnect circuit, not sure on the relais though…

I made a overview of the type of board that are out there.
This is partially guesses so not sure on everything :wink:

PDF with overview of LIPO chargers:
http://realretro.nl/SharedPics/LIPO%20charging%20types%20of%20boards.pdf

A BMS shuts off charging power to the battery if overvoltage condition is reached, this won't happen with a DC/DC module with carefully adjusted voltage output.

What do you mean with “trickle charge”?

A DC/DC converter tunes a fixed output voltage, technically this is not trickle charging as it can't overcharge a battery unless a too high output voltage is tuned. Battery voltage cannot raise above output voltage and current flow tapers exponentially to ridiculous levels after a while in CV mode. You're supposed to remove the battery from the charger once charging is finished anyway.

Cheers :-)

This is definitely a trickle charge, a battery needs to settle a bit after being charged.

I no offence guys but in the batteryuniversity this is stated:

“The absence of trickle charge further simplifies the charger. ”
In below piece of text

Summary
Charging lithium-ion batteries is simpler than nickel-based systems. The charge circuit is straight forward; voltage and current limitations are easier to accommodate than analyzing complex voltage signatures, which change as the battery ages. The charge process can be intermittent, and Li-ion does not need saturation as is the case with lead acid. This offers a major advantage for renewable energy storage such as a solar panel and wind turbine, which cannot always fully charge the battery. The absence of trickle charge further simplifies the charger. Equalizing charger, as is required with lead acid, is not necessary with Li-ion.

Consumer and most industrial Li-ion chargers charge the battery fully. They do not offer adjustable end-of-charge voltages that would prolong the service life of Li-ion by lowering the end charge voltage and accepting a shorter runtime. Device manufacturers fear that such an option would complicate the charger. Exceptions are electric vehicles and satellites that avoid full charge to achieve long service life.

This is a copy from this website:

Thanks for all your help and comments!
Cheers

I do not hope that was a comment on my post.
With LiIon you charge to a specified voltage (Usual 4.20V) then you continue to charge until the current is dropped below a specified level (Termination current). When this happens you stop charging and let the voltage drop a bit.

The termination current it usual stated in the datasheet for batteries, continuing to charge will increase the wear on the battery. The problem is not using a different termination current that stated (100mA or 50mA is a minor detail), but not terminating at all.

Do the TP4056 modules not terminate when they reach the end of the charge cycle?

The TP4056 is a well behaved LiIon charger and will terminate.
When used in this module it may not because the output power is drawn from a combination of battery and TP4056. It requires something more advanced it you want a good control in these circumstances.

yes they do as far as i have read/seen online.
On this video is the proof ;) ;)

That is not what trickle charging means.
A lithium cell self-discharges, especially when it has just finished charging at 4.2V it will drop by several tens of millivolts.
By keeping a constant 4.2V attached to the battery, you are trickling energy into it continuously to keep it topped off at 4.2V.
This current fed into the battery to keep it ‘topped off’ is trickle charging, and this is what damages lithium cells.

All high quality chargers (even the TP4056 as mentioned in the posts above) will terminate charging, aka it send 0A and 0V to the battery after charging, it does NOT hold the battery at 4.2V.

Trickle charging the battery by holding it at a full charge voltage is common with SLA (and I think also NIMH), but should never be done to lithium cells.
You will also notice that phones and laptops will not begin charging until it is several percent below 100% charge, this is to prevent the charger from constantly feeding power into the battery, or having it cycle on and off as the battery voltage drops after charging and the charger thinking it needs to recharge again.

Just for curiosity, what about trickle charging at a lower voltage, say 4.0V or even 4.1V instead of “full charge”? Would it still be problematic? Is it the mere fact of keeping a steady voltage level that is the problem, or is there a lower level of voltage where it’s no longer an issue?

I’m not sure what the self-discharge curve of a lithium cell would look like, but clearly near full charge it drops voltage much faster than at lower charge %.
There’s probably some point where the microamps being fed into the cell will cause minimal damage, but I’m not sure at what voltage or what current.

It would be interesting if somebody wanted to test it scientifically. Maybe using four identical cells, a test rig could be set up to check level of damage over time. For this test, the one “control” cell would be fully charged, then discharged to optimal storage voltage, kept for an amount of time, and the cycle repeated continuously over the duration of the test. The charge/discharge/store cycle would approximate “usage” of the cell. The three “testing” cells can be kept at a non-terminating voltage level, one cell at 4.2V, one at 4.1V, and one at 4.0V, and “vital signs” of all four cells checked regularly (maybe once a week?) over several weeks, or even months, to see what damage occurs. Anybody want to do it? :smiling_imp:

0K people, so you are worried because of “trickle charging to whatever maximum voltage” which for li-ion happens to be 4.2/4.35V, mostly. This is a no issue for me with CC/CV modules. I've already built two dual voltage output custom chargers for power tools, consisting of XL4015 DC/DC modules with in series schottky diodes at the output for reverse polarity protection and a switch for changing the output voltage resistor divider value. For both setups I carefully measured voltage drop at the schottky for a current flow of around the balancing circuit resistor drop. With this in mind I adjusted maximum output voltage a little bit higher than Vmax plus Vschottky: 12.6V + 0.27V <= ≈12.93V for 3S. I did this because balancing circuits activate at a higher than maximum value, albeit in my experience it seems they may be doing it too high so I question their serviceability. For long lifespan Vout I tuned a variable resistor which could be engaged via switch, reducing Vout value close to 0.9V in the above example.

So trickle charge I fear not. Lots of reasons as you can infer from the above. Excluding NOR capacity tests on my Lii-500 I cannot recall when was the last time I fully charged a cell on purpose. Seriously.

Cheers ^:)

I don’t think you understand.
This is not about trickle charging to maximum voltage.
This is about constant trickle charging that keeps a cell topped off at maximum voltage.
The trickle charging does not stop when the cell reaches max voltage.
There is still current flowing into the cell to KEEP IT at 4.2V.
The harm comes from the fact that it never ends charging and just keeps putting energy into the cell, even though it never goes above 4.2V.

I fully understand.

Where is the source claiming the trickle charge is what damages the cell?

Is that the actual cause of cell damage, or is it the accelerated aging caused by the high voltage?

As I understand it, the actual cause is the latter.

Cheers :-)

https://batteryuniversity.com/learn/article/how_to_charge_li_ion_with_a_parasitic_load

“increase in the thickness of the solidelectrolyte-
interface (SEI) film that formed on the anode
over time because the SEI film formation involves lithium
ion consumption, which reduces the number of mobile
lithium ions in the cell.”