From: bobnospam@gmail.com   
      
   On 12/6/2021 7:49 AM, Jim Wilkins wrote:   
   > "Bob F"  wrote in message news:sok163$kfc$1@dont-email.me...   
   >   
   > On 12/5/2021 9:23 AM, Jim Wilkins wrote:   
   >>   
   >> How did your project to salvage the Saft NiCds go?   
   >   
   > I still haven't done much with them The one I played with did seem to   
   > charge OK.   
   > So many projects, so little time.   
   >   
   > I am doing an experiment with a NiMh battery pack in an old panasonic   
   > wireless phone designed for NiCd's. I bought some NiCd replacements that   
   > turned out to be NiMh. Fried a couple of those in the phones. They'd   
   > last about a year, then quickly and completely die from overcharging. I   
   > put a AC timer on one phone supply set for an hour a day with the last   
   > NiMh battery. It started about 2/3 charged, and has stayed there for 2-3   
   > weeks so far. Maybe they will last a lot longer. I will adjust the   
   > charge time if the charge level drops.   
   >   
   > -----------------   
   >   
   > Unlike Li and Lead, the voltage on a NiMH doesn't indicate state of   
   > charge very accurately, because their discharge voltage curve is nearly   
   > flat. Battery data sheets are very helpful to understand them. The rule   
   > of thumb to run power tool batteries down before recharging prevents   
   > simple timer-controlled fast chargers from overcharging nearly full   
   > battery packs. It isn't inherently necessary even for NiCds, but it   
   > covers all common battery types and chargers adequately without having   
   > to learn and remember each one's particular needs.   
   >   
   > Adjusting the charge timer is an easy solution as long as you can   
   > determine the setting that just reaches full charge. I think 1.5 to   
   > 1.55V per cell is a safe and conservative choice for a 'dumb' charger   
   > without feedback.   
   >   
   > Once the cells reach full charge the internal chemical process changes   
   > and any further current heats them, although their voltage may continue   
   > to rise. The process change in fully charged 'wet' lead-acids is to   
   > electrolyze the water into hydrogen and oxygen which escapes out the   
   > vent and doesn't damage the cell until the level drops below the plate   
   > tops, other sealed battery types are less tolerant of the change. That's   
   > why charging rates and times are supposed to be limited.   
   >   
   > It appears that prolonged charging at the C/10 rate or below is safe, C   
   > being the Amp-hour capacity rating of the cell. You won't get far   
   > designing a faster 'smart' charger unless you can monitor the cell   
   > voltage and current. Although it doesn't guarantee a full charge,   
   > stopping the charge when the voltage rises to a preset limit appears to   
   > work without much complication. I've read and observed several choices   
   > for that limit, from 1.5V to 1.7V per cell. Another fairly simple way to   
   > end a rapid charge is to watch for temperature rise by taping a   
   > temperature-sensing thermistor to the pack. That appears to be how the   
   > multi-voltage NiMH charger for my Dewalt-clone NiMH packs operates, via   
   > the third terminal. I opened the charger and connected test point wires   
   > to the battery socket so I could record a charge cycle.   
   >   
   > My cheap homebrew datalogger is an old laptop plus TP4000ZC DVMs, which   
   > can record voltage, current, resistance or temperature. It can also   
   > record the discharge of a cell to measure its actual capacity. You   
   > import the file of recorded values into a spreadsheet to do the math,   
   > such as summing the individual Amp-seconds to get the Amp-hour total.   
   >   
      
   You are motivating me. Maybe I should make using those batteries a   
   project this winter.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)