P7 in one head, and a Q5 in another ... one battery?

[jontawn]

Dear CPF!

I wonder if you can help!

I am still planning my cateye ABS bike light conversion/build, and have planned thus far:

I plan on using one housing to put in a P7 and an appropriate 2.8a driver, the other housing is to have a Q5 and also a driver within the housing. I'm planning on using 6x 18650's, wired in parallel which, iirc, should give me the same 3.7v but, a whopping 16.8A of current, theoretically, giving me a runtime of both lights on @ 4hrs 40mins or so? (if i've worked that our correctly)

How does that sound?

Kind Regards,
Jonathan

 

[Packhorse]

Sounds good to me. Although from my limited experience I have found the Vf of P7s to be quite varied. I got 2 in one order from DX and one was 3.11V and the other was 3.7V.
Get a low Vf one and you should be able to drive it at 2.8amps for just about all of the battery run time.
The Q5 may be a different story. They seem to have a higher Vf and you may not get full current to it all the time.
If you can you may be better to series parallel the battery pack to 7.4v 8.4 amphour. But then its only an issue if you want full power all the time.

Oh and dont forget to consider heat sinking the LEDs

 

[jontawn]

Hi there,

Thanks for coming back to me!

How do I go about checking the vF on the LED?

Are LED drivers (the likes from DE & KD) capable of being over-volt'ed - the last thing I want to do is melt them!

I'm still working on the heatsink design/integration with the lamp body to offer maximum thermal efficiency!

cheers,
JT

 

[Packhorse]

While using the correct driver to drive the LED measure the voltage out of the driver. That is the Vf od the LED.

No you shouldnt run them at higher than rated input voltages. Even if you run them at the upper end of the voltage rating they will get very hot. You may need to heat sink them.
THIS is rated up to 18 volt so could be a good place to start for your Q5.