Electronics > Repair
18V/3A HY1503 PSU - weird CC/CV behavior while charging battery cells
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iMo:
The problem was with slow charging batteries - see above details. Removing 100pF from 741's pin 5 to its output cured the issue fully.
No idea on the stability when pulsing the load, it needs some equipment to create, then I will look at it with o'scope.
It needs more tests on the HW, anyhow...

iMo:
 :palm:
The story continues.. Another issue I have not identified till today. While manually switching a 10ohm load into/from the post (playing with settings and watching some nodes on the pcb) I found out sometimes the output voltage drops by aprox 0.9V after inserting the banana into the post. That was not caused by CC setting but a random process.  :scared:
So again I tracked the stuff and again it stops at the 741. The noninverting input sometimes set itself to a 0.1xx volt. There is the C11 1u (in orig schematics) at the other side of the 7k5 resistor so I thought it is perhaps a faulty capacitor, after removing it happened still the same.
There is the C1* 100n between 741's inputs in the schematics not populated on the pcb, therefore I tried to put there something and after several xx nF experiments I finished with a C3=330pF (C3 in the LTSspice) which was enough and which helped.
I also replaced the 1uF C11 with a 22nF ceramic (C4 in the LTspice).
The latest schematics of the affected part below.
I do not know - perhaps is the 741 somehow faulty or it is a clone..too much issues around it to my taste..
What still needs to be understand better is the RC in the feedback of the 741 opamp..
gupa:
Hello, I'm ignorant but I'm learning, somewhere I saw that with four ICs, unconnected operational amplifiers are connected to the ground so that they don't make a mess. And I see that the plus pin goes from the LM324 to the problem IC. So maybe I don't drink too much water.
iMo:
Yep, the 324 in this PSU is using only 2 opamps, the other 2 are free, not connected to anything on the pcb.
That is actually great :) as it saved me replacing the entire 324 as I smoked one of the opamps inside while experimenting, so I took the spare one and it works now. But sure, the not used opamps in the package have to be handled accordingly.
All the issues I had here are around the LM741 which is a single opamp in DIL8 so no spares handy :)
I have the chips in my junkbox somewhere, but I am too lazy to disassemble the entire PSU in order to replace the chips, so I've been trying to debug it under a "minimal effort" methodology..  :D
xavier60:
If it's because of oscillation, try changing the 2N3055 B-E resistor to 100 ohms as well as trying to find the best compensation.
I'll do some experimenting here as I get time.
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