Thanks for all the replies. I just want to knock something together using what I've got lying around to get some life in to the battery just now. I'll just make a quick adjustable LD1084 (LM317 equivalent) and tweak the voltage whilst monitoring the current in to the battery.
Would a constant current supply, with the max output voltage limited to 4.2v do the trick longer term?
I was doing that for a while, yeah, it will do the trick but
poorly.
The LM317 load regulation is not that great. Under load, your 4.2v will be pulled so far down thus current become so low that it takes much longer than healthy (not for the battery but for me, life is not that long, you know...)
So, I manually re-adjust the output to bring in a better current flow while keeping the loaded voltage as high as possible while below 4.2V. Trouble is, as the battery charges, the decreased load increases the voltage - eventually load decreases to a point where the voltage exceeds 4.2V so it needs constant readjusting to keep it at around 4.2V.
Getting tired of such constant readjustment, I hire an Italian guy call Arduino to do the job. "Mr. A" brought along his two assistant called ADC and DAC. They are brothers, I think. Easy thing for Mr. A's team. With the ADC brothers, one is blind and just adjusts the voltage, the other is a reader who just monitor the
voltage and current then tell his brother to step up the voltage or step down. You see, ADC was born an ADC, it can read voltage and current like a charm. But DAC was born a PWM, cross dressed to become a DAC... Enough gossip about DAC's private life. I will just add that DAC is quite a leader. Where the DAC leads, the LM317 will follow.
The contraption works nicely but far too complex for a simple task.
So, I decided to fire them, hired a Chinese guy called
TP4096 TP4056. For 1/10 of the cost, the job gets done - simple, no blinking lights, no LCD screen... It just gets done. "Mr. A" now has a different job.
EDIT- may be silly to edit a dead thread but so as not to confuse myself or others... it is
TP4056, not TP4096. I confused myself when I had to search what I wrote...