AA Battery Charger using TP4056

Thread Starter

Prashant Saxena

Joined Nov 6, 2022
1
Hello,
I'm trying to build a AA rechargeable battery charger. Targeted battery is duracell 1300mAh-1.2V and the board is TP4056. The board produces 4.12V ~ 4.2V and 1AMP output. I need to step down the voltage to 1.2 V. Board manufacturer suggested to change Rprog resistor R3 if you want to change the output voltage. Instead of changing R3, I would like to add a resistor at output to reduce the voltage. To calculate the dropped voltage I'm using this link.

Input Voltage = 4.2V
Output Voltage = 1.2V
Current Draw = 1A
It gives me a 3 Ohms resistor.

Q1 Am I on the right track or doing something wrong?
Q2 Is there a better alternative to do it. May be another board.
Q3 Is 3 Ohms resistor is the correct solution?

Regards
Prashant
 

Ya’akov

Joined Jan 27, 2019
6,856
Hello,
I'm trying to build a AA rechargeable battery charger. Targeted battery is duracell 1300mAh-1.2V and the board is TP4056.
Welcome to AAC.

The TP4056 is designed to charge lithium chemistry cells. Information is scarce, but as far as I can tell it is unsuited to use for rechargeable alkaline cells. The charging strategy of CC/CV depends on knowing the target voltage which for the TP4056 is 4.2V.

The information I can find suggests that a pulse charging strategy is used. The charger sends pulses to the cell and checks the voltage between the pulses. When the OCV (Open Circuit Voltage) of the cell reaches ~1.5V no pulse is sent. The periodic measurement of the OCV continues and when a sag is detected pulses resume. This process is repeated until no more sagging is detected and that is considered full charge.

I don't think it is safe to assume that simply scaling voltages will make the TP4056 work. You need to find a good source for the change curve and strategy for alkaline rechargeable cells and follow that. There may not be a packaged solution available.
 

Audioguru again

Joined Oct 21, 2019
5,418
Since they know nothing about electronics, Amazon's ad for the Duracell battery is completely wrong.
It is NOT alkaline, it is Nickle-Metal Hydride (Ni-MH).
Its voltage is 1.2V when almost completely discharged. A Ni-MH charger should be used and charges it to 1.4V or 1.5V and stops charging when the voltage quickly rises in a bump.

It is a cheap Chinese knock-off battery that has poor performance. I bought some with a charger from Costco and they are junk.
 

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Ya’akov

Joined Jan 27, 2019
6,856
Since they know nothing about electronics, Amazon's ad for the Duracell battery is completely wrong.
It is NOT alkaline, it is Nickle-Metal Hydride (Ni-MH).
Its voltage is 1.2V when almost completely discharged. A Ni-MH charger should be used and charges it to 1.4V or 1.5V and stops charging when the voltage quickly rises in a bump.

It is a cheap Chinese knock-off battery that has poor performance. I bought some with a charger from Costco and they are junk.
In Asia, there are two versions of the DC1500 (from Duracell's website):

1667748690090.png

Also, there are rechargeable Alkaline cells which are particularly useful if you need the 1.5V output. It seems, though, that Duracell isn't making them.
 

bassbindevil

Joined Jan 23, 2014
639
I think the best strategy for NiMH is to detect temperature rise. None of the allegedly smart chargers I've used will reliably stop charging based on that voltage rise effect.
 

Irving

Joined Jan 30, 2016
3,190
The Revolectrix PL8 charger (sadly discontinued) I have very successfully detects the 'NiMH bump' to terminate charging but is a bit overkill to charge 2x AA cells. I've used the MAXIM DS2715 NiMH charge controller before, datasheet attached, that uses the temperature rise (dT/dt) termination method. These days I wouldn't use NiMH for 2xAA replacement, I'd use a LiFEPO4 3.6v AA cell (14500) and a dummy cell.
 

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Audioguru again

Joined Oct 21, 2019
5,418
I do not store battery acid in my refrigerator in an orange juice container and I do not have 3.2V AA or AAA LifeP04 battery cells.
They are crazy to make such different voltage batteries in exactly the same sizes.

I use a Duracell Ni-MH battery charger that was free when packaged with some poor quality Chinese Duracell AA and AAA Ni-MH battery cells. It quickly charges the low capacity Chinese cells but takes longer to charge higher capacity Energizer cells.

I have not yet electrically compared older Japanese Energizer AAA Ni-MH cells to the newer Chinese Energizer AAA Ni-MH cells.
The Chinese cells weigh 8.7% more than the Japanese cells but both are marked 800mAh.
 

Irving

Joined Jan 30, 2016
3,190
I do not store battery acid in my refrigerator in an orange juice container and I do not have 3.2V AA or AAA LifeP04 battery cells.
I agree with not storing battery acid in the fridge ... or anywhere else for that matter - I've long ditched lead-acid... but I don't get your issue with LiFePO4?
 
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