Varta battery :
Waiting 'til tomorrow to measure battery voltage again, following Rob's instructions, but that does not mean I am inactive !
I am so upset about my lab power supply that's not up to the job, can't set current limit low enough for the task at hand, and can't even monitor current, not enough resolution on the display.
I want a better supply !!! One day.....
In the mean time I thought hey ! Why not use that as an excuse to make my own little constant current charge/discharge circuit ?!
Like.. using a Wilson current source, say ?! That would be fun !
So I looked at the trannies I had in stock, found some TO-39 2N2905A, checked the datasheet, looks plenty capable enough for my modest need here.
So picked 3 of these and wired everything up on my breadboard. Current can be set with a pot from 3.7mA to 13,5mA. Battery is 110mAh so C/10 is 11mA. So I wanted to be able to adjust it around 10mA.
First time I make a Wilson mirror I think, was excited to see if that would work, it's quite magical... and it does work
It's so cool, just turn the pot and hey presto you can control the output current.
I used my brand new Metrix MX554 bench meter to monitor output current, of course
So tomorrow, once I have measured the battery voltage, I will be able to discharge it in a controlled manner... then charge it again in total control... how cool is that ?
Only thing I am not too sure about, is the current "mirror" is a twisted mirror.... output current is a bit higher than asked. Like, to get about 10mA or so at the output IIRC, I had to set the input current lower than that, 8.75mA.... is that "normal" / expected with that kind of circuit ? Or is just that my trannies are so old that one is very low on Beta, and/or there is a big Beta mismatch between the 3 trannies and that screws things up ?
It's so cool what you can do with just a handful of components !