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Automatic Ni-MH battery charger woes
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VanMarco:
Hello people!
I am building this circuit here https://www.eleccircuit.com/wp-content/uploads/2013/07/ni-mh-battery-charger-circuit-using-tl072.png
I start in advance by saying that I have added an increased level of difficulty to this build by using mostly used parts, I changed the TL072 with an LM358, and the transistor with a 2N6667. The issue I am having is that the LM358 got hot and likely died. The first error i made was to put D1 in reverse (as you can see from the full page link the 1st image shows it one way, the second the opposite). I since put the diode back as it needed to go, replaced the IC, and now the red led does not turn on nor it charges, also pressing the button "to start" does not seem to do it. I replaced the BC 327 with another one, it was new and the multimeter says it's not faulty.
The only difference between 1n6667 and mje listen is that there is a big difference on the base current. It is possible the small elec. capacitor is faulty but I am not sure it would cause such problems based on schematic.

I have no idea why such a simple circuit does not work.
Full page link https://www.eleccircuit.com/automatic-ni-mh-battery-charger-can-make-by-yourself/
Ebay page of a seller that has exactly the same thing i am doing https://www.ebay.com/itm/Ni-MH-Charger-Auto-Stop-Circuit-board-1-to-10-cell-800mA-MJE2955T-12-16VDC-/140353600313

thanks in advance!
BravoV:
The circuit's explanation does not mention about how it detects full charge state, which is the "secret recipe" in charging algorithm for Nickel based cell (NiMh or NiCd), without it, it will ruin the battery really fast.

Charging LiIon is much-much more simpler.
Buriedcode:
It looks like a crude delta V charge termination using the opamp as a comparator, with D4 and C4 holding the max voltage of the cells, and R8/C5 the actual voltage of the cells.  When the voltage across the cells starts to fall, the voltage on C5 will drop below the voltage of C4, making the opamps output high, turning off charge.  R2 and D1 look like they add some hysteresis (the diode to stop C4 discharging through R3 when charging), so charging is held off until the button is pressed again.

Kind of a cool circuit, but I would use an actual comparator instead of an opamp.  The TL072 has inputs that can sense up to VCC but not to its negative rail, so in this circuit it cannot sense Vbatt below about 2.5V.

Using "used" parts is problematic for a couple of reasons, namely that you don't know if they are in any way damaged, and also that their specs may differ enough from the intended parts to negative affect the circuit.

NiHaoMike:
Looks like a simple voltage slope detector. That said, nowadays it's a lot better to do it in a microcontroller.
http://www.ultrasmartcharger.com/phpBB3/viewtopic.php?f=3&t=5
VanMarco:
thanks for your reply. So i should buy TL072? all the other parts looks fine, i could put new 1n4148s.
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