What temperature will your Cree XRE operate down to?

On my ride home tonight my homemade triple cree bike light cut out on me after about 15-20 minutes. Tonights temp was -1 with a windchill of -20. My light flickered a little then kicked into low with no adustment (bflex) then nothing. Once I got home and got it inside it was wigging out, turning on and off on low alot, so I unplugged it and opened the light up to warm up. After about 15 minutes, everyhting was back to working order.

I've tested them down to -55C with no problems, including thermal cycling.

I'd be looking at connections, converters, and batteries if you are having issues.

NewBie said:

I've tested them down to -55C with no problems, including thermal cycling.

I'd be looking at connections, converters, and batteries if you are having issues.

Click to expand...

Thanks, just trying to open a dialog on real world use. I measured my batteries as soon as I came in and they were putting out 14.38volts (AA x 12 NIMH) while not great, sufficient.

Send George an email or PM.
He will want to know.....

Sounds to me like you probably had a contact come loose due to the effects the metal cooling down and contracting. The LED itself should be able to handle the cold fine -- if anything it should operate better.

(AA x 12 NIMH) therein lies your problem, the batterie's at those temps will drop out of regulation.

i had same battery pack (12x nimh) - no problemo

I had the same problem with nimh cells in a GPS while it was 15 degrees. It totally stopped working. Go with lithium batteries for very cold weather.

Y-Wrench said:

On my ride home tonight my homemade triple cree bike light cut out on me after about 15-20 minutes. Tonights temp was -1 with a windchill of -20. My light flickered a little then kicked into low with no adustment (bflex) then nothing. Once I got home and got it inside it was wigging out, turning on and off on low alot, so I unplugged it and opened the light up to warm up. After about 15 minutes, everyhting was back to working order.

Click to expand...

I guess that at minus 15 celsius the runtime may reduse by 50%
what was the runtime at "noarmal" temperature?

Welcome to CPF !

Question, where did you get a TriCree Bike-light ?
Home made ?

Y-Wrench said:

On my ride home tonight my homemade triple cree bike light....

Click to expand...

On the first line it says homemade

Indeed you should use Li-Ion with temperatures like and below that !!

However, if you use regulation-electronics, they meight as well have problems with low temperatures..

But by the sound of it.. I'd say its the batts..

Another point: The wind only cools the unit more rapidly towards the -1 degree environment-temperature. Windchill is the aparrent temperature you seem to feel with a combination of the actual temperature and a certain windspeed!


Regards,

Ra.

Thanks for the replies on this one guys:goodjob:

As suspected by most, I'm gonna blame this one on the batteries, or one in particular to be exact. I went through all the cells individually and in one group of 4, three read 1.1, and the last read .83. I threw all four in the charger and the weak link read .36 after charging. So I guess something happened inside the battery that must have freaked everything out. Even at 14+ volts I should have had no problem, so that battery must have been reversing, or cutting voltage, or something funky.
I didn't get an exact duplication of conditions tonight. At a balmy 4 degrees with -16 windchill (the windchill is more important in regards to me, the rider ), I took the long way home tonight and went over the hills and through the woods. After a little over an hour out there, no problems. The batteries do get to a point where at 1mA level 5 and 8 are indiscernable from each other and the light draws down a little, but it still is kickin'.
The words of everyone in regards to Li-Ion are well heeded, and in fact I already have a Li-Ion battery pack on order, but it got back ordered on me. Instead of waiting around and only running one or two LED's I just broke out some AA's and made a temporary battery pack. Which is also a pretty good plan to have a setup like this if you want a relatively cheap backup battery "just in case".

Just saw the thread, glad you have it resolved.

Given that the LEDs and converter will self heat, they will be at a 'happy' temperature pretty soon into the ride. All the parts on bFlex are rated to at least -40C operating, so if YOU can ride, it can run

I've tested bFlex in the freezer and it will start happily at those temperatures - which it should.

Finally, given the low temps you will hit in your application, condensation is a real issue. I'd recommend for long time reliability of the electronics that you either seal them in a small sealed box with a fresh desiccant packet or use a spray on conformal coating over all the components and PCB.

cheers,
george.

Thanks George, I was thinking that condensation might also have played a role. Without the opportunity to get out under the same conditions, I guess I won't know for certain until next year (I hope ). Sealing up the B flex is definitely in my future, I have it resting between some rubber in a 1" square tube right now.