Hey I'm new to posting on CPF but having been sifting for a while!
I am looking at building up a new light for nightriding and looking for a little advice.
Light specs will be as follows:
2 x XML (series) driven using a Lflex at 2.8A (7.4v battery)
How much surface area would be recommended in the housing for this setup?
Any recommendations for Lenses or reflectors?
I know I need 7.2v to run the 2 LEDs in series. I want to maximise burntime. What battery config would you recommend? 2S2P at 5600Ahr will only last 1.5hr at max (appx). I was thinking 6 or 8 cells instead of four - has anyone else attempted this config before?
With a side by side design, do you think mounting the light to be on the centre line is important? Or mounting it off to one side would be sufficient?
is this for road use or trail? I've been pretty happy with the Ledil Rocket SS lens for the XR-E on my commuting bike. Seems to fit the width of the road nicely without putting too much light right in front of the bike where it impacts my night vision. Considering the power that you are using, I'll just guess that this is for the trail.
I've been contemplating putting together a battery powered light for another road bike, and trying to figure out the risks of charging lithium batteries. Seems a little more risky than just tossing NiMH's into the charger and walking away.
The best burn time is going to be achieved by maximizing efficiency. Switching regulators tend to be most efficient with a small difference between the input and output voltages. Batteries are more efficient at lower currents than high (less loss to the internal resistance). And, of course, you'll get the best runtime by making sure that you can use the batteries down to the full (or nearly full) discharge voltage.
Using multiple batteries does complicate things because you'll want to avoid having one cell discharge before the others. If you use cells in series, then you run the risk of reverse charging the cell that discharges first. Are the cells protected against this by built-in circuitry?
I have two XM-Ls tamed to street use driven by a H6Flex. Current battery won't supply more than the 1.4 A level so I have no info (they'd be a bit blinding at 3 A, anyway). The lights are about 7 square inches and the one with the driver gets warm but not hot in street use. This suggests the 'rule of thumb of 1 inch per watt heat sink air interface area with a very good thermal path in minimal, 1.5 better, 2 ample. My XP-E and double XP-G light is about 11 watts @ 1 A with 7 square inches and it needs a cool or windy night to run at full power on steady. On flash mode in the day, it gets toasty, but not too hot to touch.
The 'firewall' if aluminum needs to be at least 1/8 inch think to move heat form a central LED to the light body. A solid machined piece is best but polished with thermal paste or epoxy will work if the contact area is big enough.
2 fully driven XM-L's will yield a lot of lumens to the ground, and the edges, and the air around you. If you ride in any fog at all, you will not see much so be sure to have lower modes available, down to the 10% range.
1st I would recommend an over/under setup, near field using a wide beam (XM-L won't require much reflector offset for this) and a far field using a thrower reflector (deep well focused). I would also recommend independent control for whatever conditions prevail.
Maybe use an 2P2S for each light? Runtime indeed will be limited if you really want nearly 2000 lumens full time. You will also have to consider thermal measures running these at full bore if you will be running in warm summer nights.
For reference, I run 350ma on an XP-G and find I have great visibility only wanting for more when I face oncoming headlights. the XM-L and the XP-G put out about the same lumens at 350ma. At 1A to the emitter, I get a lot of light. I'm sure you have your reasons for wanting 20 watts of light so I will leave it at that.
ok....so the light is going to be primarily for the trail, but also for commuting. I am going to try and keep it as small as possible with the use of 16mm optics from Gaggione. The Lflex will form the heart with the 2 XMLs in series. Because of the size I will prob run it at max 2A but maybe 2.4. Its going to be moving most of the time which will keep the heat right down.
I will try to design a swing mount so that it can be adjusted on the fly when on the helmet or on the bar. Lets see how that goes!
Batteries will be 2800 mah 2s2p x 4 or maybe I'll put together a 6pack!
I've got a friend with solidworks, so I'll see how our design comes along. Stay tuned. He also works somewhere with a 3D printer that i can utilise - this is going to be fun!
Good luck, it sounds fun. I am thinking of making another light, dual XM-L or dual MC-E, I had my eyes on the Ledil IRIS lenses. You might want to check them out for a combination long throw and wide flood. I have found though, that the Ledil smooth spot lenses for the MC-E are actually sufficient for trail riding,whatever that angle is. Keep us updated.
Both the above have a good selection of Ledil lenses. I just had a delivery from rs-online yesterday, quick delivery and acceptable del cost. I noticed that Farnell was charging something like £15.95 delivery