Cree in a Duo

[Agrophobic]

Pete-I Hope i can help you with your figures, the efficiency is 85% power out compared to power in. your power out calculation is correct but as the input voltage is higher the input current is lower.
At 100 % efficiency 3.8w/4.8v=0.79A(from battery)
At 85% efficiency (P in=3.8w/0.85=4.47W) 4.47w/4.8v=0.93A
so 930mA in at 4.8v gives 1A out at 3.8v

using 2650mah batteries- 2650/930=2.8 hours. (in theory)
however- efficiency improves as battery voltage drops so you'll get a bit more than that.
and........the figure of 2650mah is quoted from discharging the batterys at 500ma until they drop to 4v.
so in reality you'll get less capacity by discharging at 1A but still get usefull light when the batterys drop below 4v. the only way to really tell is to time the dishcharge to a usefull light level, as you have done.

 

[Agrophobic]

Footleg- the p7s get verrrrrryyyy hot and need a lot of heatsinking. if you just want to take them out when you'r photographing then they should be ok on the outside if you have a protective cover for transit. they are waterproof but the solder will corrode and the leds would easily get knocked off their little ally plates if you drag them around caves unprotected.

 

[Pete K]

Nice one mate. I'm finding all this a steep learning curve. Should have paid more attention in school after all!

At highest power level but one I managed 6 hours full brightness and a further 2 hours on lower settings (it auto lowers power as batteries draw below a certain current). The lower setting is still brighter than a Tikka Plus.

 

[Agrophobic]

sounds great. eight hours of usefull light and most of it very bright. compare that to your old halogen duo and have a good laugh.

That looks like a great driver you're using, shame about the price being so high but you get what you pay for.

 

[van the man]

Well 1st trip out with new head lamp........

Running on a dodgy set of Ni HD and all went well

Great illumination, thoug more spread than focused beam

Heat seemed to be well sorted, no probs with case getting warm

Did notice that getting dimmer as trip progressed but still better than I usualy get and Biffs LED still working as a back up

Go on have a try, my Duo can still be retro fitted with the 14 LED array but the new setup is so much better!

Thanks again to all for your help

Michiel

 

[footleg]

Footleg- the p7s get verrrrrryyyy hot and need a lot of heatsinking. if you just want to take them out when you'r photographing then they should be ok on the outside if you have a protective cover for transit. they are waterproof but the solder will corrode and the leds would easily get knocked off their little ally plates if you drag them around caves unprotected.

Yes, my initial experiments with my 2.8A drivers running one P7 attached to an old Intel Cerelon CPU cooler heatsink resulted in that heatsink getting uncomfortably hot to touch in a matter of minutes. It remains to be seen whether a larger heatsink will provide adequate cooling inside a waterproof box. I'll post details when I have tried it!

 

[Agrophobic]

I'd be keen to hear how you get on footleg. i've only tried the p7 in the worshop so far.

I also modded my old zoom as another spare. very simple to do using a cree q5 mounted on a 50mm diameter ally disc in a stripped out zoom head. cheap single mode driver from dx fits nicely in the back of the head unit and is smothered in hotmelt glue.
powered from 4 18650 3.5Ah nimh cells which just squeeze into the battery box.
switching is done with a magnetic reed switch operated by a magnet in the rotating part of the head in order to keep the rotate to turn on function.
compared to an old halogen zoom its amazing, great spread and throw.

keep up the good work guys

 

[footleg]

I'd be keen to hear how you get on footleg. i've only tried the p7 in the workshop so far.

I ran my P7 for 35 minutes on full brightness yesterday, with the LED mounted on a large Intel P4 cooler heat sink, and separate heat sinks attached to both sides of the driver board (which also gets very hot). The driver reached around 45 degC and the LED heat sink around 40 degC. So I think this will be OK in a sealed plastic box for using underground as a video light. I'll try to box it up and see how hot it gets inside the box.

 

[potholer]

For my experimental P7 light, I just used a diecast aluminium box (~60x60x25mm), and cut a piece of perspex to replace the lid.
With some silicone sealing the lid, it's water resistant, if not actually waterproof, and it doesn't seem to get ridiculously hot.

 

[Agrophobic]

That sounds encouraging. What current do you drive your p7 with? and what batteries do you use? i'm still experimenting with bright leds so its good to hear of other folks successes.

 

[footleg]

I think you were asking potholer this, but for the record I am driving my LED at the maximum rated 2.8A with the plan to mount it in a waterproof box with a clear lid (off the shelf from Maplin). The switch will mean it is not actually waterproof, but I've not found a cost effective way to deal with that. Running off 10 x AA NiMh cells, the driver draws 1.23A off them.

 

[potholer]

That sounds encouraging. What current do you drive your p7 with? and what batteries do you use? i'm still experimenting with bright leds so its good to hear of other folks successes.

Since it's an experimental light (and there weren't any suitable switch-mode drivers around when I built it), I just use 7x 7135 350mA drivers, and run the P7s at ~2.3A.
The 7135 drivers are easily available from kaidomain/dealextreme on boards of 1,2,3,or 4 drivers

I use one P7 as a flood, and the other one used to use a bodged oldham reflector, but now uses a reflector I recently bought to give a reasonable spot beam.
I only run one or the other P7 at once.

For power, I use 4xNiMH AA cells in an external holder. Since the wires on the PP3 clip connectors on such holders are pretty weedy, I went for a simple strengthened design, making 3 holes each side of the central rib, and threading some thick silicone wires through those holes and out through the holes in the top of the holder. The wires from the PP3 clip join onto the silicone wires inside the holder.
The threading of the silicone wires through the holes means they're physically very firmly attached to the holder. The wires do tend to push the AA cells out of the holder, but that's easily fixed with a reusable cable tie around the holder+cells.

I connect the P7 unit and battery holder together with Tamiya connectors, which are cheap (if you don't get them from Maplin) and pretty durable.

Pictures at:
http://www.potholer.com/tempstuff/P1121036.jpg
http://www.potholer.com/tempstuff/P1121037.jpg
http://www.potholer.com/tempstuff/P1121038.jpg
http://www.potholer.com/tempstuff/P1121039.jpg

 

[footleg]

Potholers images inline so save everyone having to click on all those links:

That looks like a very compact unit. How hot does it get running the P7 at 2.3A? How long do the batteries last?

I got around the thin wires on the PP3 style battery clip by just soldering thicker wires directly to the battery holder. Care is required not to melt the plastic holder with the heat transmitted through the metal you are soldering too, but it means there is one less set of contacts to go wrong, and saves buying a battery clip too!

 

[potholer]

That looks like a very compact unit. How hot does it get running the P7 at 2.3A? How long do the batteries last?

I got around the thin wires on the PP3 style battery clip by just soldering thicker wires directly to the battery holder. Care is required not to melt the plastic holder with the heat transmitted through the metal you are soldering too, but it means there is one less set of contacts to go wrong, and saves buying a battery clip too!

Batteries last around an hour (the Eneloops I use are 2000mAh cells, but are very good for high current drain, and likely to be pretty durable, compared to some higher-capacity cells).
Heatwise, it certainly gets warm in the hand, and warmer if left to run, but I tend to use it for short bursts, mainly for photography.
It did get accidentally knocked on for an hour in a carrier bag in a car boot, and seemed to survive OK.

I suppose I could have avoided using the clip and soldered direct, possibly using thin wire for the last bit of the internal connection to avoid the wire getting in the way of the cells, but that would still need some way of covering up the external contacts to avoid shorts.

 

[Agrophobic]

Thanks for the details guys. did the carrier bag survive its roasting Potholer? 
Nice to know it doesnt get unusably hot. my mate (Claustrophobic on here) is using the same 7135 drivers at 2.3 amp on high setting too. i'll get him to post his experiences once its finished.

Footleg- that sounds like a good driver you're using, should give you plenty of runtime.
if you want waterproof switching, magnetically operated reed switches are worth a try, they should work through the ally box. dunno if you can get one to take 1.5A but they should be available.

 

[footleg]

I did think about reed switches, but they all seem to have very low maximum switching current. I could add some electronic high current switching activated by the reed switch for future versions, but for my initial prototype I chose a cheap rocker switch as it has a low profile on the outside of the box and was only 79p 

I see what you mean about the battery contacts being at risk of shorting. While my battery box will be inside the waterproof box, there is a still a risk in something comes loose it could short out 12V of NiMh cells! I'll see if I can insulate the contacts with hot melt glue to guard against that.

 

[Agrophobic]

I've got a couple of single mode drivers using zxc310 chips, these have an enable pin you can use for low current switching but you'd need to parrallel the drivers up to drive a p7. yours sounds good for a prototype, good to keep it simple.

 

[footleg]

Finished building the unit last night. Now it just needs cave proofing (everything is loose in the box at the moment). But a new problem occurred to me. I chose a rocker switch because it was cheap and had a low profile. But I realise now it will be easily knocked on while in a bag being transported in the cave. I can't easily disconnect the batteries in transit because the lid to my box is held on with 4 screws. So I will need to protect the switch with some sort of cover to prevent accidental switching on.

That aside I am pretty happy with the finished unit. I just need to find a way to hold everything securely in place in the box to enable it to take the knocks it will get on a caving trip, and I am ready to try it out underground.

 

[Agrophobic]

i have some locking toggle switches like this-http://news.thomasnet.com/fullstory/531556
that are good for at least 6 amps, pm me if you want one. they're not waterproof tho.

 

[footleg]

Interesting website. I found these: http://news.thomasnet.com/fullstory/553143 waterproof (IP56) rocker switches. Not sure how cheap or easy to get hold of they are. I'm not sure the locking toggle switches are what I need. I think the toggle will protrude too much from the box and make it prone to damage. The rocker switches are low profile on the outside of the case. I just need to make some sort of cover to protect them from being switched on accidentally. I've already cut a hole in my case to fit the rocker switch I have, so I'll see how it holds up underground before I try anything else. Thanks.