I modified a driver with a resistor and zener
(QLITE MT-G2 Zener Mod DIY Kit of mountain electronics)
I get 2.95A (8 x 7135) with fresh battery Panasonic 18650PF, Mtg2 on noctigon, but this only lasts a few seconds after about 30 seconds the 7135’s turn get very hot and the current and brightness drops to half!
This is so? Or is there something wrong?
The voltage drop across the chips with fresh cells is quite high at that drive current. Either additional heat sinking of them is needed or lower the input voltage or add more chips to raise current and led Vf consequently lowering voltage drop across the chips. Both the chips and the led produce heat so getting rid of excess heat is crucial to stable operation.
No, that's not normal and the driver shouldn't need extra heatsinking. That's how they behave without the zener mod, you got something wrong somewhere. The zener is probably the wrong way 'round.
Measure the voltage at pin #8 on the MCU.
Thanks for answers
I need a driver with good autonomy, so that the maximum is wanted no more than 3A…
I see the zener and is in correct way, I have 4.28V in #8 MCU in low mode and 4.18V in high mode.
Recheck everything and I can not see anything wrong… keep taking a lot of heat in a few seconds at high mode :~
You say “battery” (singular) in your opening post. You are using two cells in parallel, right?
Sorry, are 2 batteries in serial.
oops! yes, serial.
At 3 amps the MT-G2 needs about 6.2V meaning you are dropping 2.2V across 8x 7135, or 6.6W. It won’t hold that 8.4V long so realistically, within 5 minutes the batteries are probably at around 7.2V at 3 amps. This should be more than manageable for 8x 7135 being under 1/2 watt each.
I’m going to suggest you have a driver assembled with insufficient solder paste on one side providing poor solder joints.
Ok thanks I understand … with this mod it’s a driver not to use with only 8 x 7135 and freshly charged batteries :~
If I add more 7135 I’ll have better dissipation but also more current in the output…but I do not want this.
You suggest to me that somewhere there may be a poor solder? I will resolder…
At only 3A it is best to use some batteries with more voltage sag! PFs are too good! Panasonic Bs or maybe even some old laptop pulls would be a better choice. The MT-G2 has a low enough vF that even poor cells perform well.