I purchased 16 of the SAFT NiMH cells through Ralph Weaver and finally finished testing them on my Turbo 30. I tested them at a 5 amp discharge and at a 20 amp discharge and used a 4 amp charge rate. Discharge was to 0.8 volts which represented only an additioal 10 or so seconds of runtime at 5 amps. I will not present all the data here, just the most interesting.
Best cell:
5A DISC time = 2074 secs | 5A avg DISC Voltage = 1.19 Volts 20A DISC time = 516 secs | 20A avg DISC Voltage = 1.08 Volts Charge time to peak at 4 amps = 2798 seconds. Voltage at peak = 1.53 volts. Computed charge efficiency = 92% Computed Internal Resistance = 0.0073 ohms Capacity in AH at 5A = 2.88AH Capacity in AH at 20A = 2.87AH
Worst cell:
5A DISC time = 1848 secs | 5A avg DISC Voltage = 1.20 Volts 20A DISC time = 465 secs | 20A avg DISC Voltage = 1.09 Volts Charge time to peak at 4 amps = 2507 seconds. Voltage at peak = 1.53 volts. Computed charge efficiency = 91% Computed Internal Resistance = 0.0073 ohms Capacity in AH at 5A = 2.57AH Capacity in AH at 20A = 2.58AH
Median cell:
5A DISC time = 2008 secs | 5A avg DISC Voltage = 1.19 Volts 20A DISC time = 502 secs | 20A avg DISC Voltage = 1.09 Volts Charge time to peak at 4 amps = 2669 seconds. Voltage at peak = 1.53 volts. Computed charge efficiency = 94% Computed Internal Resistance = 0.0067 ohms Capacity in AH at 5A = 2.79AH Capacity in AH at 20A = 2.79AH
Comments: These cells do not appear to need any sort of breakin. They are completely consistant for the first 6 cycles. NiCd’s wander a bit after being idle for a few weeks. They are not usable for any sort of competition except for all up last down where a long run time at a low weight is the most important thing. I think they will be perfectly fine for Sport use if the lower voltage under load is acceptable. Compare to a typical RC-2000 cell (Disc to 0.9V)
5A DISC time = 1475 secs | 5A avg DISC Voltage = 1.23 Volts 20A DISC time = 360 secs | 20A avg DISC Voltage = 1.14 Volts Computed Internal Resistance = 0.006 ohms Capacity in AH at 5A = 2.05AH Capacity in AH at 20A = 2.00AH
Because of the lower voltage at 20 amps you will need to add an additional cell to the pack for every 23 cells in order to see the similar performance due to the voltage drop. To me this is probably going to be very slightly noticable on my 16 cell pack. At higher currents of course this would be worse.
My worst cell is quite a bit worse than the 2nd worst cell (116 secs less runtime at 5A, 19 sec at 20A) and I really wish I could replace it as I know I will be reverse charging that cell at the ends of the discharge. I guess we will see how well they handle this.
Mine will be going into my LT-25 and since I see typical flght times of 12 minutes with 1700SCRC cells I expect to get nearly 18 minute flights on these NiMH cells with no increase in weight. An increase of about 1.5 times.
If you were using 1200MAH cells in 1989 you could replace your pack with one of these and expect an increase in duration of 2.3 times at no real change in weight. The only known disadvantage is the long charge times (about 40 minutes). It remains to be seen if you can get hundreds of cycles on these cells like you can with NiCd cells.