constant current source for typical red high power led

[kenwood96]

Hi,

I can't seem to find a suitable constant current driver for a 350ma led.

it should be fine running of a rectified 6V shimano hub dynamo...

Can anyone point me in the right direction? I have 3 of those red leds, is it possible to put them in parrallel and use 700ma driver for 2 leds?


tnx!

 

[tylernt]

You could use three LuxDrive BuckToot 7027-D-350 drivers (one per LED).

You could theoretically use one BuckToot to drive all three in series, but you'd need a source voltage of ~9V or more.

 

[kenwood96]

thanx! I'll look into that!

 

[Lion251]

A hub dynamo acts more or less like a current source. Depending on the model, you get 400 mA (for a 2.4W dynamo) or 500 mA (for a 3W dynamo).
Voltage will rise if you pull less current. If you short-circuit the dynamo, the current will rise only insignificantly.
I have a Seoul P4 as a front light, just rectified, no further electronics.
I would put all three leds in series, behind the rectifier.
If current is too large then, just put a resistor in parallel over the three leds to bleed off excess current.

Putting a regulator (especially a switching one!) after the rectifier is a recipe for disaster if you sometimes ride a bit faster.
The regulator limits the current that you draw, so the dynamo voltage will rise.
It can then rise above 10, 15, 20 Volts, or even higher.
Switching regulators are especially bad; they diminish current draw when voltage rises, resulting in an even further rising current.

I'd stick with just the 3 leds in series behind the rectifier.
Possibly one electrolytic capacitor directly over the leds to diminish blinking at low speeds.
But, in that case, make sure that the leds are connected directly to the capacitor.
I have blown my first headlight by a capacitor that was charged to 40V when the led had a contact fault, then discharged through the led when contact was re-established.

 

[kenwood96]

I have a solar force l2m in front now, I must say it works really well from the dynamo.

I don't know what the specs are of a l2m driver ...

Could I add 3 350ma leds @ the rear ?

I ride an e bike so speeds of 40 kmh are no exception.

Sent from my HTC Wildfire using Tapatalk

 

[kenwood96]

So un regulated my cree in front will dim a lot? Adding 3 @ the back also not regulated will dim even further not ?

Sent from my HTC Wildfire using Tapatalk

 

[tylernt]

If current is too large then, just put a resistor in parallel over the three leds to bleed off excess current.

Won't a resistor make it harder to pedal?

 

[kenwood96]

So I hooked up 2 red leds (350ma) after the rectifier, without lenses or anything... MAN WHAT A LIGHT!!!!!!

I got a really big flood that can be seen miles away during daytime
they came on @ about 7 km/h with a little flickering and full blown light starting at 10km/h

I recently added a 10V 2200Mf capacitor out of and old PSU, put the leds didn't light up anymore... after about 500metres, the cap blew and killed my leds too...


any idea how this happened?

 

[Mr Happy]

I recently added a 10V 2200Mf capacitor out of and old PSU, put the leds didn't light up anymore... after about 500metres, the cap blew and killed my leds too...

any idea how this happened?

I just saw what was written higher up the thread:

I'd stick with just the 3 leds in series behind the rectifier.
Possibly one electrolytic capacitor directly over the leds to diminish blinking at low speeds.
But, in that case, make sure that the leds are connected directly to the capacitor.
I have blown my first headlight by a capacitor that was charged to 40V when the led had a contact fault, then discharged through the led when contact was re-established.

Maybe something similar happened here?

 

[kenwood96]

I just saw what was written higher up the thread:



Maybe something similar happened here?

I doubt that, it was securely soldered...
Does the cap has to be physically connected to the "legs" of the led? Mine was soldered along the wires of the led....

I soldered a 4.8V 700mah nicad battery in parallel too, leds were fine until battery was dry. When I drove the bike the leds wouldn't come up either.....


I regret messing with my fine setup now....