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

I happen to have some cheap TP4056 charger modules on the way to me from eBay. But I’m not smart enough to do any of that stuff. Sorry. :person_facepalming:

No worries.
Any feedback is good :wink:
If anyone can help out please do! ;) ;)
(especially on the single relay circuit)

For anyone reading this.
I have ditched the idea for 2s because i could not find a 2s BMS (CHARGER).
So i’m switching to 3s as there seems to be a good one for that!

Described by this guy:

search on ebay for:

3s PCB BMS Protection Board For 3 Packs 18650

NOTE! you have to see/get the one from he video as it has a proper charger IC on it.

honestly I would search for a 2S BMS instead this solution, cant be hard to find a proper one

Something like this:

https://www.ebay.com/itm/2S-20A-7-4V-8-4V-Li-ion-Lithium-Battery-18650-Charger-PCB-BMS-Protection-Board/202358675893

But this is not really balance charging, it’s just individual termination and bypass when one of the cells is fully charged (isn’t it?).
So you have to continue charging until both cells are fully charged.

I think you also need a current limited input.
It’s probably not advised to let the BMS limit the charging current.
That’s only a protection feature, not intended to regulate your charging current.

So, what you would need with this kind of BSM is some boost circuit (5 Volts to 8.5 Volts) with a constant current output.
I guess you could use a LED boost driver for that?

There’s always very little information in those listings…

Oh, another thing, regarding those USB charging boards with protection circuit.
I don’t understand this:
It seems to me that the outputs are mislabeled.
B+ and B- seem to be OUT+ and OUT- in reality.
And so OUT+ and OUT- seem to be B+ and B- in reality.
Because the OUT connections come straight from the TP4056, and usually go straight to the battery (on versions without protection).
And then comes the protection circuit to prevent discharge-over-current and over-discharging based on voltage.

I tried both options (according to the labels and according to my (possibly faulty) logic).
I found that it worked better according to my (possibly faulty) logic.
Unfortunately i can’t remember exactly what the problem was when you go by the labels, but i think i lost some voltage to the cell or it would take much longer to terminate charging.
Because the TP4056 stops charging when it sees 4.2 Volts over the output, but it doesn’t reach 4.2 Volts when there’s that protection circuit in between.
Something like that…

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?