I’m thinking of a NiMH Mag build as usual. Iwant something that can use straightforward/cheap AMC7135 based driver board + “safe” NiMH technology (cells, charger, etc all usable without supervision).
here’s the current state of the union:
Silverfox did some good destructive charge-cycle testing here (back in 2008, but nothing has changed): http://www.candlepowerforums.com/vb/showthread.php?114943-Cycle-Testing-Observations%85&p=1370657#post1370657
(scroll down to Round 3)
I’d say his discharge rate is a little low and his charge rate is a little high, but that was really the point to him I think.. he’s trying to firmly establish the effects of fast-charging. Personally I think his results look great… 100 cycles with almost no damage is pretty great. I’d like to know the effect of a higher discharge rate, maybe coupled with a more reasonable charge rate…
but wait…..
drumroll….
http://www.candlepowerforums.com/vb/showthread.php?219301-Eneloop-Performance-Details-for-Experts
there we go. granted this is straight from Sanyo Europe but it does look pretty legit. 200 good cycles charged at ~1C (2 amps in this case) and discharged at 2A is awesome! Granted they don’t show the voltage-over-discharge curve that Silverfox does, so we can’t know how that looks… but I think it’s safe to assume that it’s probably nicer looking. Now it would be nice to see the middle ground, 2C charging (4A). Somewhere there’s probably a fine line that damages the cells though, I assume that 1C is well on the safe side of the line and an hour really isn’t that long to wait…
these discharge graphs at different loads (linked from the second link above) were also interesting to me:
http://www.eneloop.info/home/performance-details/discharge-current.html
so if I was to wire up, say, 3s2p in a maglite (6 cells in pairs of 2, fits fine) I’d be looking at between the red and blue lines (1.5A current per cell). Driving a Cree XM-L at 3Amps, we’re going to need ~3.35v (typical) to the emitter according to the datasheet. In order for the AMC7135 to stay in regulation we need 0.12v above vOUT (which they call vOUTL). So we need 3.47 volts from the batteries to stay in regulation… with a standard single-mode driver I’d say we should drop out of regulation after 1700mAh (per cell, 3400mAh per pair of cells….) have been expended. As we expend the next 100mAh or so (per cell) we should notice it drop out of regulation and get dim really, really fast. Dim is relative here, it’s going to be pretty interesting to see how an LED which can produce 260-300 lumens at only 2.9vF is going to react to the batteries falling off.
Really I’d rather still have a protection program in place @ 3.0v that uses PWM dimming and blinks the LED every 5seconds to warn you so you don’t damage the cells. The Budget Light Forum Versatile LED Driver has that feature of course.
Anyway since we are using a linear regulator we just burn off any excess volts so runtime is easy to calculate. 1hr8min before it drops out of regulation (assuming all my numbers above are good). Not bad but to do better in a 2D mag will take some doing. 7.4v Li-Ion @ whatever they can muster (4000mAh? 3000mAh?) and an expensive TaskLED H6CC buck driver would double runtime. You’d still want a control board in there though to get voltage protection and probably some modes. Expensive, Expensive, Expensive.
Cost projections for a build with good prices:
- $15 – incan mag 2D
- $14 – H22A flat top heatsink
- $9 – XM-L on MCPCB from Illumination Supply
- $5 – Shipping @ Illumination Supply
- $5 – 8xAMC7135 driver board from Kaidomain (or backup source @ Illumination Supply for $7)
- $8 – Arctic Silver Alumina thermal adhesive / epoxy
- $20 – 8x Eneloop AA’s (6 of which get used)
- $15-35 – looks like the charger may be something of a bitch for a 3s2p pack. Figure $30.
probably get the whole project done around <$110..
