Lithium Ion charger hack..

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dacflyer
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Lithium Ion charger hack..

Post by dacflyer » Mon Oct 22, 2018 2:13 pm

hi guys..i got a new one for ya..
i bought a handful of these li-ion single cell charging boards ( tp4056 with protection ) and the chip has the ability to monitor the temperature of the cell, but it is bypassed in the schematic. i'd like to hack my board to be able to use a NTP sensor as shown in the schematic, but there is no chart of the value to use. anyone have any ideas ? i already looked at the schematics. no help tho.

link to the ones i have. ----> https://www.hotmcu.com/index.php?main_p ... o5d0f0bom1

schematic -----> https://www.sunrom.com/p/lithum-battery ... n-microusb

essentially i could carefully lift pin 1, and add in the thermo probe, but i have no ideas what value to use. i have many that i salvaged from li-ion laptop and tool packs. may try them and see what results i get.
but ideas are welcomed in the mean time.

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haklesup
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Re: Lithium Ion charger hack..

Post by haklesup » Tue Oct 23, 2018 5:09 pm

following the link from the schematic page to the part you do get a reference schematic with the NTC included but you need more than that device, you will need the voltage divider it forms with R1 and R2.

the web page says "Thermal feedback regulates the charge current " So I presume the voltage on pin 1 is that proportional control signal and when grounded it does not limit charge current, as it rises to the supply voltage it reduces output current proportionally. So I would select a value that gives you that voltage range over the relevant temperature range you are controlling perhaps 20C to 100C or whatever max temp you want to allow. At that temp, the control voltage on pin 1 should be approaching VDD. The exact balancing point is unclear and the optimal temperature probably depends on the cell you are using and how it is assembled into a pack. So use the voltage divider formula with R1 on top (to vdd) and the NTC and R2 in parallel on the bottom (to ground) along with the R vs. T curve for the sensor to solve for the values.

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dacflyer
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Re: Lithium Ion charger hack..

Post by dacflyer » Tue Oct 30, 2018 12:46 pm

sounds complicated.. i more concerned to monitor the temps of the cells.. some have gotten quite warm during charging, and i had to pause the charging for an hour or so.. was probably because the battery was so low at 1st.. when i resumed charge it stayed cool.
i may take the probes i have now, and wire them into a OP amp, and an alarm to let me know if they start to heat up.. sounds simpler.. just build a separate monitor, maybe to set an alarm off and disconnect the charge..

dyarker
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Re: Lithium Ion charger hack..

Post by dyarker » Tue Oct 30, 2018 3:05 pm

Two components and three connections complicated?????

The NTC is in physical contact with cells. It's resistance changes with temperature OF THE CELLS. The junction of NTC and a fixed resistor is wired to (pin 1?) of the IC. The IC circuitry measures the voltage to control the charge current.

The other connection of the NTC goes to supply common. The other connection of the fixed resistor goes to Vcc.
Dale Y

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dacflyer
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Re: Lithium Ion charger hack..

Post by dacflyer » Mon Nov 05, 2018 9:56 am

complicated as in, figuring out the resistor to use, and the NTC's i have, i don't know their values ,
how do you determine their value ? And is it measured hot or cold or room temperature ?
the ones i have handy are from out of old battery packs.

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Re: Lithium Ion charger hack..

Post by dyarker » Mon Nov 05, 2018 10:57 am

Wiper of a pot to IC temperature measuring pin. Ends of pot to Vcc and common. Adjust pot till IC cuts the charging current. Measure voltage at wiper.

Warm NTC to temperature where cell charging should stop. Measure resistance of NTC.

A touch of algebra (or longer way with Ohm's Law) gives resistance value of resistor to put in series with NTC. Pick next higher standard value. Max power to be disapated by resistor should like 65%, or less, of resistor's power rating.

Cheers,
Dale Y

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dacflyer
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Re: Lithium Ion charger hack..

Post by dacflyer » Tue Nov 06, 2018 2:07 pm

ok, i'll try that. if it works for me, i'll report it..
I'm gonna have to be careful, I'll have to lift a pin on a SMT chip. and it's really really small.

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Re: Lithium Ion charger hack..

Post by dacflyer » Tue Nov 13, 2018 3:11 pm

well, i give up..unable to get enough room under the pin to make a connection, and if you lift the pin up too far, it snaps off..

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