With nothing better to do on the plane, I charged, discharged and charged the LiPoly battery to see how much capacity it really had. I got some strange results:The battery is a Thunderpower 2100, with a manufacturing stamp on the label of 6-4-04
- 6-28-04: I set the Triton charger to charge at 2.1 AH, 11.1 volts. It ran for 69 minutes. Final charge was 12.56 volts, 1.796 AH put into the battery
- 6-29-04: I set the Triton to discharge at 2.1 AH down to 9 volts. After 56 min, the Triton stopped at 10.5 volts, having discharged 1.635 AH.
- 6-29-04: I set the Triton to charge at 1 AH. It started charging at 10.69 volts and finished at 12.56 volts, having put 1.654 AH into the battery after 110 minutes.
So, what’s up with the Triton only drawing down to 10.5 volts? And why did it only pull about 1.7 AH instead of 2.1 AH? I called Sal at NESail and he had a lot to say.
First, he warned me very sternly (!) that I shouldn’t ever ever ever discharge a LiPoly on a charger. There’s no need to and it could damage the battery by drawing the battery down too much. Discharging in a charger is bad because, if a LiPoly is brought down too flat, it’s capacity will be permanently significantly diminished; a charger discharges the battery too slowly to hit the obvious 3 volt/cell wall. If you are flying, the high drain on the pack lets the drain work correctly. In addition, a good speed control will tell you when it’s time to come in for a charge. You shouldn’t drain the battery more than 75% or they’ll go bad on you. That’s 1.575 AH on a 2.1 AH battery.
It sounds like the Triton company is aware of this 75% rule. That’s why they the charger only draws down to 10.5v on a 3 cell 11.1 v pack. The Triton charger seems to have a user interface problem. On the discharge cycle, the options it gives are “3v”, “6v”, and “9v”. The obvious implication is that it will draw the cell down to the specified amount but it doesn’t. It draws the pack down to what is considered “safe” flat… on the “9v” setting, it draws to 10.5v. Instead, it should give options like the following: “1 cell”, “2 cell”, “3 cell”. Or “3.7v”, “7.4v”, “11.1v”. Or “3.5v”, “7v”, “10.5v” because that’s what it draws down to.