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Puffin  NMH  cells         650mAh     1050mAh       1400mAh

In Q&EFI magazine, May 2004, Bob Smith reports his discharge tests on 10 cell packs of these cells.

I have used his data to produce the tabulation below. The capacities are less because I have cut-off the unusable tail-end of the discharge. Data for Konion 1100 cells is included for comparison.

In this note, the calculations are not shown, but the methodology used is the same as in my note on Konion cells.

When comparing the performance figures be aware that the 1050 and 1400 cells have been tested at a very high discharge rate [probably in excess of what most flyers would use], while the other two cells are tested at a rate below the max allowable. This has a marked effect on the power parameters.

Ideally, each cell type should be tested at four discharge rates. One at 60 minutes. One at the max allowable rate, this being the most significant.  And at two intermediate rates. How we define "max allowable" is open to debate.

Abbreviations:

g      gram                            W    watts                                WM    watt minutes

A    amps                              AM    amp minutes                     WM/g    watt minutes per gram

M    minutes                          mAh    milliamp hours                W/g    watts per gram

V    volts                                                                              W/lb    watts per pound

 
"per cell" where applicable

650

1050

1400

Konion 1100
weight

11g

19g

23g

41g
discharge current

6A

13A

18A

10A
discharge duration

5.5 M

4M

3.8M

6.9M
average EMF

.98V

1.02V

.91V

3.17V
discharge capacity 6A * 5.5M           = 33AM     =550mAh 13A * 4M              = 52AM                 = 867mAh 18A * 3.8m             = 68AM                  = 1149mAh 10a * 6.9M              = 69AM                   = 1155mAh
discharge energy 33AM * .98V        = 32.3WM 52AM * 1.02V        = 53WM 68AM * .91V           = 61.9WM 69AM * 3.2V            = 221WM
average power 32.3WM / 5.5M =5.9W 53WM / 4M          = 13.3W 61.9WM / 3.8M      = 16.3W 221WM / 6.9M         = 32W
energy/weight 2.94WM/g 2.79WM/g 2.69WM/g 5.4WM/g
power/weight .54W/g              = 244W/lb 1.02W/g              = 461W/lb .905W/g                = 410W/lb .77W/g                  = 349W/lb

To summarise.

For the same weight, the lithium ion cell has about twice the energy of the NMH cells.

It's a pity that the cells were not all tested at their max discharge rates. This makes power/wt comparisons less valid. At max rates, the Puffin 1400 and the Konion 1100 would probably be very similar, at about 400 watts per pound.

It is unusual to see that the 1050 is better, on both counts, than the larger 1400.