Homemade Battery Recharger w/ Regulator -- HELP!

[MrAl]

You missed the point of the info I posted. NI-MH has an exothermic charge reaction so it gets hot by charging. It will show a rise above ambient long before it is fulluy charged.

Hello,

Well that's really too general compared to what i was trying to show in my own post. The cell can easily be profiled to find out the best temperature rise. The cell is exothermic but not 100 percent exothermic so it doesnt start heating up as much as when it is fully charged, that's what makes delta Temp possible.

Delta Temp is obviously the better choice, but it means a more complex measurement system to go along with it. If the cell is turned off after a certain temperature rise (determined by profiling, and note this is temperature RISE not absolute temperature) it would be charged enough for many purposes, and without damaging the cell in the least (actually prolonging life compared to some minus delta V techniques).

I dont think the linear long term sample and holds will be accurate enough for this task, but it's been quite a while since i looked into that kind of thing with the advent of cheap microcontrollers.

So the choice is to measure temperature rise and use a much simpler circuit, or use delta temperature and require a more complex circuit.

 

[ronv]

"The fact remains the picture you posted shows a normal temination on temperature"

I guess I should have been clearer: the figure 2 that I posted above is a good example of why simple temp measurement is not good for NI-MH: the cell temp rises to 41C. It's from a Linear-Tech data sheet pimping one of their products. If you don't mind running the cells above 40C at end of charge it's great.... now ask a battery maker how long the cells last if you cook them that hot on every charge cycle.

If you look close at that curve the charge would not have terminated at a lower temperature using - delta V.
It would appear that now days the temperature spec. is 45C and many "smart chargers" use all of it.

You can trade charge time for temperture like you said.

https://crypto.com/chargers/