Newbie Q about driving

[OldBoy82]

Hi all. been lurking a while here and trying to design a light but am wandering about driving the LED.

basically i want to install the driver down with the battery and have a switch on the output to turn the light on and off. the main reason for this is to reduce the weight at the bars and also to make the light head as compact as posible.

my main concern is with the electronics. i realise drivers work completey differently to transformers but do they still draw power/current if permanently attatched and switched on the 'back side'?

hope you understand what im trying to do.


look forward to your suggestions.


Mark

 

[LukeA]

It depends on the driver, but most of them will shutdown due to overheat or burn themselves out. In short, output open-circuit is very bad for LED drivers.

You can either mount the driver in the light head or mount it with the battery and wire from the battery up to the switch, back to the driver, and finally to the LEDs.

 

[OldBoy82]

ok so a bad idea then. i think running a wire up from the battery to a switch and back to the driver is my best option. would also give me the option of putting the switch anywhere i like aswell.

thanks alot


M

 

[georges80]

Many drivers are fine with an open circuit.

Generally a buck (step down) driver will be ok with an open circuit. If the output circuitry is rated to handle the input voltage, a buck converter will handle an open ok. With a buck the output voltage can't be more than the input voltage.

Some boost drivers are also ok with an open circuit. Circuitry will limit the open circuit voltage, i.e. rather than trying to boost to infinite voltage (trying to current regulate a non-existent load), they will transition to voltage regulation. Examples are maxFlex and CCHIPO (2 of my drivers), they both will limit open circuit voltage to a safe level. Some boost drivers will be destroyed without a load (example, Fatman, another of my drivers).

The danger that is often ignored is to the LED(s) themselves.

Lets say you have 4 li-ion cells, so ~16V fresh off the charger. Assume we have a buck converter and we're driving say a single LED (to assume a pretty bad situation). Now we open circuit the load (switch). The driver now sees no load and the output voltage will rise to ~16V (same as the input), the output capacitors of the driver are now fully charged to the same ~16V. You now flick your switch and for the instant that it takes for the output capacitors to discharge to the LED Vf (say 3.5) and the driver to start regulating you will have a high voltage/high power spike applied to the LED. More than likely the LED will sustain damage if not be destroyed outright.

With a smart driver (like maxFlex, bFlex etc), you could have batteries and driver remote, run 2 wires from your control switch (very very little current) down to the driver from the bar (i.e. remote mounted switch) and 2 wires back from the driver/battery to the bar mounted light.

cheers,
george.

 

[OldBoy82]

@ george

so my best bet is to run a bflex with a 'remote' switch and another line up to the light to power it. is this more eficient than my previous method of switching the input to the driver? or are they much the same?

just trying to work out the most cost effective design but have a nice small light head.


M


ps. im in the uk and have thus far not found many supplyers of components ( led's, drivers, optics etc). if i wanted one of your circuits do you ship them here?

 

[georges80]

@ george

so my best bet is to run a bflex with a 'remote' switch and another line up to the light to power it. is this more eficient than my previous method of switching the input to the driver? or are they much the same?

just trying to work out the most cost effective design but have a nice small light head.


M


ps. im in the uk and have thus far not found many supplyers of components ( led's, drivers, optics etc). if i wanted one of your circuits do you ship them here?

You could run bFlex at the battery pack end and run 4 wires (2 from bFlex to the LED(s) and 2 from the remote switch to bFlex.

Or, you could install bFlex in the LED housing (it is a pretty compact driver) and then run battery power up to the LED/bFlex combo and still have a remote switch on the bar. Lots of options - just depends on what you want to build.

Most folk install the bFlex in the light housing and often have the control switch in there too. They then run a battery cable from the light housing/bFlex to the battery pack using some quality connectors. This allows easy removal of the battery pack for recharging.

You can look around the bike forum here and see lots of various build ups.

Yes, I ship drivers all over the world.

cheers,
george.