I understand your conundrum a little too well, I think about this almost daily. :tinfoil:
Question: What cells are you using, CR123's or LiIon rechargeables - 2x17500 in the C3 and what in the C2?
Edit:
BTW I would prefer having the full-power M60 in the C3. One reason being that cells are less efficient (containing less usable watt-hours) at high drain rates. As the M60 will have a higher drain rate than the M60L, I'd rather let the more demanding LED module utilize three CR123's in series rather than two (~7.5v vs ~5.0v). As you can see from the data below, providing a greater voltage to the M60 regulation circuit results in a substantial decrease in overall current draw, which would be easier on each of the three CR123's. With the M60L, this is less of an issue -
that lower-drain module is far less demanding on the cells (no matter what the configuration), so your 2 CR123's will be at least comparably efficient in that case.
M60__from Regulated power supply,
Volts___amps___watts______,
3.0_____0.09____0.27__,
3.2_____0.22____0.70__,
3.5_____0.38____1.33__,
3.6_____0.51____1.84__,
3.8_____0.66____2.51__,
4.0_____0.86____3.44__,
4.2_____1.08____4.54__,
4.5_____0.85____3.83__,
4.7_____0.88____4.14__,
5.0_____0.80____4.00__, At 5.0v from 2x CR123, the drain should be 0.80 amps
5.5_____0.74____4.07__,
6.0_____0.69____4.14__,
7.0_____0.60____4.20__, For 3x CR123, this interpolates to ~7.5v, 0.58 amps - much easier on the cells.
7.9_____0.56____4.42__, This also results in sightly more overall wattage than from 2x CR123, 4.3 watts vs 4.0 watts - a brighter M60. :thumbsup:
8.0_____0.53____4.24__,
8.4_____0.50____4.20__,
8.5_____0.49____4.17__,
9.0_____0.47____4.23__,
9.5_____0.45____4.28__,
[comments above made by me]
I ran some calculations comparing these two situations a while ago and IIRC I came up with the result that CR123's could deliver ~10% more total watt-hours when in the lower amperage configuration (3x 2.5 =
7.5v and .6 amps) than in the higher amperage configuration (2x 2.5 =
5.0v and .8 amps). In other words, a small amount of
free energy from
each of the three cells compared to using just two cells.
(And again, this behavior shouldn't really show up with the M60L - it's much gentler on the cells to begin with, so you don't really gain any additional efficiency by going to the third cell.
Theoretically (regarding the M60L), that is. Check the following out:
Interesting thing:
The behavior of the M60L hasn't been documented as well as the M60 & M60LL on various voltages. What is most interesting is that the output of the M60LL, while rated for normal operation on
2x CR123, provides considerably higher output from
3xCR123 (& 2xLiIon) per data collected by BigWaffles in his 'Runtime Graphs' thread, resulting in less runtime than it has on 2xCR123 - very interesting behavior indeed.
The behavior of the M60L in this situation has not been documented, but if it had greater output (and less runtime) on the 'third cell' (as the M60LL does), this would complicate your choice somewhat.