modifying a phillips saferide led bike light

[mutmost]

Hi All,
I want to mod my phillips saferide bike light to run off a 12v supply I have at the handlebar from a DC-DC convertor from the bike battery.

The light is great but the run time on high is now only 20mins which is too short for my commute. It use to be longer but seems to have dropped from when I came off in the ice.
(The 20mins seems to be a common problem with them)

I have measured the voltage across the LEDs and got 5.6V on low and 6.63V on high so with that i planned to get one of the convertors linked to in the other LED light thread and turn the voltage up to 6.63 and thought that would be it.

I have since read that LEDs need a constant current so looked at constant current drivers on deal extreme but in my mind I can't work out if it is a constant current what voltage would be supplied or does it not matter.

I then read about the bflex drivers from taskled which are probably overkill and all the modes confused me .

So in short do I need one of these:
LM2596HV DCDC Step Down Converter Adjustable + Heatsink | eBay
one of these
3.6V~16V 925mA Constant Current LED Driver Board for Cree and SSC LEDs (4-pack) - Free Shipping - DealExtreme
or something else.
Thanks
Mutmost

 

[Alan Quay]

If all you are doing is connecting the output of the dc converter into where the battery(s) were connected, then you have no need to worry about current limiting - presumably its managed internally. All you need to do is match the dc converter output to the original battery voltage.

It's possible that I've misunderstood something though....

 

[mutmost]

Mike,
thanks for the suggestion but I am looking to get rid of the current electronics and go straight to the LEDs as just replacing the batteries with the DC-DC convertor does not get round the 20 min then off problem.
Thanks

 

[Alan Quay]

Ah, I see. I'd assumed it was a battery problem.

 

[Scimitar]

Is it overheating on high and the electronics are actually protecting it?

 

[103Alex1]

Off Bikeforums :

""Keep in mind that the newer production models have an annoying "feature": the light will run on high for only 70mins and then automatically switch to low and continue to run for another 165 mins - it refuses to switch back to high until you charge the batteries or just take them out and put them back in (which is not very convenient on the road). I have an earlier production model which runs for the promised 2 hours on high and then turns off.""

Sounds like some form of timer or voltmeter function in the light itself is doing this. Probably on the driver circuit board. Light spec says this which might help you get input from those more knowledgeable than I ...

Self-contained with no wires
Excellent switch and fuel guage
2 High powered Luxeon Rebel LED

Sounds to me like what's causing the auto-dim is down to the light design inside the housing and swapping out a different driver board might not be easy or even 'cure the problem' ... but if you just matched the input voltage of the current batteries (4 AA 2,450ma NiMH rechargeable batteries = 9.8V) you might at least get to run them off your supply and then if there's a voltmeter behind the auto-dim, it might not be triggered as you'd have a far greater capacity in the supply you're feeding than the pack the lights run off. If it's some form of intelligent timer the lights will still dim or turn off after the prescribed amount of time.

Just a thought applying logic rather than any significant knowledge. Hopefully someone more knowledgeable will comment on these ideas and help you get your answer ...

 

[mutmost]

Thanks all for the comments but it is the electronics on the current board are faulty (or set to turn off high after 20 mins) regardless of battery condition, so replacing seems to be the way forward, the question is which board, a current limiting or voltage limiting?

Thanks

 

[103Alex1]

You may need both. If they are LEDs you I believe you need a current limiting board ideally, to stabilize supply current. Plus you have to feed a voltage that the new driver board accepts so you may need a buck/DC-DC unless the driver board you choose accepts variable voltage input within the range you are feeding from your supply.

You will also have to be able to wire the emitters to the new board, by-passing the current control circuit. Only way to see if you can do that is open it up and see if the wires can be switched over.

Such is my understanding anyhow.....