Update, final one I believe. Gonna go the above-mentioned route, though not with bare charging modules like the ones above. I had a spare TP4056 module with battery protection (DW01 + 8205A), and of course I've tested the stuff by attaching 2S cells to its P/B+ and Bā terminals. Of course it works right, the DW01 shuts off the circuit when 2S voltage is on the terminals, the TP4056 leds remain off even if power is applied to the board. Removal of the overvoltage condition (relays change cell arrangement) makes it work again. This, Sir, will kill. :-)
Thanks for pointing out these boost charging modules, HKJ. I had not even bothered looking up for that sort of stuff.
The cells I'm gonna use in this setup come protected (built in BMS), and the load won't pull above 1.5A from the 2S battery in any case (no more than 8W into the driver). Should work rather well. Upon 5V PSU connection a momentary short-circuit may happen on the cells (relay coil timing), a no issue since they're protected.
I have the feeling this topic has been beaten to death but still i would like to have your guys opinion.
I also want to charge two lipoās the cheapest way possible but also do balanced charging.
Looking at all the information online i have come up with the following (cheap) solution trying to use only ONE relay for two battās.
Or would the two way relay be better?
Please let me know what you guys think or are there better (small+cheap) solutions
i think this should workā¦
For anyone reading this and thinks this are tested circuits.
THERE NOT!
If you build them, please do, and let me know if they work
IF i build them iāll let you know here what my results areā¦.
For anyone reading this.
I have ditched the idea for 2s because i could not find a 2s BMS (CHARGER).
So iām 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.
But this is not really balance charging, itās just individual termination and bypass when one of the cells is fully charged (isnāt it?).
So you have to continue charging until both cells are fully charged.
I think you also need a current limited input.
Itās probably not advised to let the BMS limit the charging current.
Thatās 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?
Thereās always very little information in those listingsā¦
Oh, another thing, regarding those USB charging boards with protection circuit.
I donāt 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 canāt 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 doesnāt reach 4.2 Volts when thereās that protection circuit in between.
Something like thatā¦
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
But then still, itās 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 itās fully charged.
What does āterminal of the charger using high voltage deviceā even meanā¦
If those BMSs donāt shut off power to the battery when charging is completed then the DC DC converter will continuously ātrickle chargeā the lithium cell at CV which is horrible.
Well iām ditching the 3s idea alsoā¦.
Itās just all really confusing.
Anyway iām probably stick with the PT4065 and a disconnect circuit, not sure on the relais thoughā¦
I made a overview of the type of board that are out there.
This is partially guesses so not sure on everything
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 ātrickle chargeā?
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.
I no offence guys but in the batteryuniversity this is stated:
āThe absence of trickle charge further simplifies the charger. ā
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.
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.