Re: Voltage regulated P/S as Li-ion charger
Hello wasBlinded,
I use a power supply to charge Li-Ion cells with the following settings:
WARNING
NEVER charge Li-Ion UNATTENDED
I would caution you to charge on a non-combustible surface as well. I use a Corningware dish on a hot pad.
1. My power supply is plugged into a timer. I have noticed that it takes about 3.5 hours to charge the cells that I am using. With that in mind I set my timer for 4 hours. If for some reason I loose track of the charging, the timer acts as a back up to shut everything down.
2. I set my voltage with my Fluke 8060A to 4.230 volts. My power supply has a meter on it, but it is not accurate enough for Li-Ion. Please note that some power supplies exhibit voltage drift as they warm up. If the direction of the drift is upward, you could end up overcharging the cell. This can result it reduced cycles, overheating, and there is a possibility of "rapid venting with flame." It is best to keep an eye on things and I often keep a volt meter hooked up while charging so I can watch what is going on.
3. I short the leads together and set the current for less than 1 C of the battery capacity. I have been working with some 2400 mAh cells. 1 C would be 2.4 amps. I choose to charge these cells at 1.0 amp. I have other cells that are about 600 mAh. I charge them at 0.5 amps. Li-Ion should not get warm during charging. If your cells get warm, reduce the charge current. I am charging at room temperature (about 72 degrees F), by warm I mean 78 degrees F. Mine are usually 73-74 degrees F.
4. I terminate the charge when the current drops to 50 mA.
Following this procedure, my cells come off the charger at 4.21 volts and quickly settle down to 4.2 volts. After sitting a few hours, their resting voltage is in the neighborhood of 4.185 volts.
Rechargeable cells have a limited cycle life. You can decide if you are interested in having more capacity per charge, or more total cycles.
I did a test and charged Li-Ion cells to 4.5 volts. I had great run time, but only got 6 cycles... and then the cells were dead.
Terminating the charge at 4.2 volts should give you 300-500 cycles and this is considered a full charge.
When you terminate the charge at 4.1 volts, your capacity drops to somewhere around 88% of what you would get from a full charge, but you are good for something like 1500 cycles.
When you purchase a charger, the manufacturer has set everything up for you and you plug the cell in and go. When you purchase a power supply, you get to make all the decisions and trade offs, and of course live with the consequences... /ubbthreads/images/graemlins/evilgrin07.gif
Have fun.
Tom
