Overdriven Cree XPGs

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betti254

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Hi,

I'm building a light for scuba diving purposes and I want it to output a serious amount of lumens. I'm also after the simplest solution possible.

I want to use a Cutter 7-up XPG board (wired in series), and am wondering how hard we can run the XPG's in practice. I'm somewhat prepared to accept a reduced lifespan of the LEDs, though would need at 50-100 hours of burn time over 1-2 years at a minimum.

Please keep in mind that this is for underwater use only, so the metal PCB will be heat sunk against an alloy block, which in turn has a good thermal path to the alloy housing (immersed in water).

I've briefly used a similar setup using a Cutter 4-up XPG board run at 1800-2000ma (direct driven with 14v battery). Again, when run in the water it was only wildly warm and heat wasn't a problem but I've only run this under test conditions for 5-6 hours. Light output at this level was awesome, though keep in mind that underwater the light gets eaten up and throw/punch is something we don't get much of.

So my ultimate question is given this, does anyone think it to be possible to run the 7-up at 29v/2700ma? If I can do this I presume I can direct drive the LEDs from my lithium battery pack (8S). I'll accept that as the battery runs down my light output will decrease, though at this level of output I'd be happy to accept that.

Thanks, damien
 
I doubt that the bondwires can handle 2,7A. As far as we know most cree leds can only handle 2A, then the bond wires melt, no matter how well your heatsink is.
 
Hi,

Thanks for the reply. Pardon my ignorance (I'm a relatively noob), but by bond wires do you mean the wires that connect the LED diode to the square board?

In any case, nice to know that there is a practical limit. I'll aim to cap things at 2amp.

thanks, damien
 
Does not seem like a smart thing to do to me.
1st the efficiency really drops when pushed at these current levels but most importantly reliability is going to be highly compromised. Since you plan to wire them in series as soon as one blows then all the rest will stop working leaving you with no light.

As for the test in that link, chances are the LED's were only driven for very short periods of time. I doubt you would get very long from a XP-G driven at 2600ma


IMHO the beam produced by the choice of optics is much more important that the sheer amount of lumen produced.
Will the 7up optic really give you the beam you want?
 
Thanks again for the comments - they're much appreciated. I think 2A will be my limit.

I'm planning to use the 6 degree optic listed by Cutter. Our bench tests show this to produce a ~25 degree beam which is quite nice for lighting a ship wreck underwater. We'll get a 20-30% beam tighter underwater too due to the flat glass port refraction, which will only help our cause.

I'm going to build an 8 cell lipo battery pack in series, giving me 29.6v. My initial thinking was to use 2xRCD-24 1000ma buck drivers in parallel to power the board.

thanks, damien
 
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Another option is to use only 6 LEDs instead of 7.
This opens up a few different options for wiring them up.
2P3S
3P2S
6P
6S
Probably not an option you will take but worth thinking about all the same.
 
I did think about other configuration, but having to build the actually boards scares the crap out of me. Sadly my skills just aren't there at the moment, so for now anyway I'm limited to whatever I can buy as a board.

I'm not too concerned about the whole series problem with one LED taking out the lot. From a risk perspective we have been dealing with that for years with single HID bulbs, so always carry heaps of backup light. This particular 7-up light will be a wreck diving weapon, so that typically means short (< 60min, using 20-30min) burn times.

thanks again, damien
 
Just use the 7 XP-G board and dont wire the centre one up. I think some of the Solus lights used a 7 LED optic but only 6 LED's.
The only reason I mention it is because it opens up more options for drivers and battery packs.

You could even wire the 7th LED up through its own driver in a semi redundancy set up.
 
You raise an interesting point, but to be honest I don't really understand how the Cutter 7-up boat is wired.

I presume the gold pad next to each LED allows for some kind of individual addressing, though I can't seem get any to individually light up. It seems all or nothing, though I presume I'm missing something obvious.

Any enlightenment here would be appreciated.

ds
 
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