Can Someone help with Shark Converter math

[snipinglight]

I plan to run 4 Cree using 8AA's. My question is how do I adjust the Shark converter to feed 3.5V and 700mA into each Cree?

 

[DonShock]

If you hook up your LEDs in series, you don't have to try to balance the voltage across each one. The same current will flow through each. There is a potentiometer on the shark driver. Just hook up your multimeter in series with the LEDs, measuring current, and adjust the pot for 700ma. I usually use the multimeter to make the connection from one LED to another for this measurement, then once you have it adjusted you can replace the meter with the final pice of wire to permanently connect the LEDs.

 

[snipinglight]

I also read FAQ Shark at The Sandwich Shoppe that says

To drive muliple LEDs Jumper across J1. This will put the overvoltage protection to 22V and allow for Constant current control using the trim pot.

Jumper across J1 means solder a wire across the 2 points labelled J1 , is this right

After Jumpered J1 the voltage across the 4 Crees is 22V which means each Cree is getting 22/4 = 5.5V. The spec sheet for Cree is max at 3.5V. Does it mean that the Cree will be damaged at 5.5V each?

And if I jumper J1 can I still trim the pot to get a current of 750mA to each Cree? Do I use a DMM to do that?

 

[snipinglight]

If you hook up your LEDs in series, you don't have to try to balance the voltage across each one. The same current will flow through each. There is a potentiometer on the shark driver. Just hook up your multimeter in series with the LEDs, measuring current, and adjust the pot for 700ma. I usually use the multimeter to make the connection from one LED to another for this measurement, then once you have it adjusted you can replace the meter with the final pice of wire to permanently connect the LEDs.

So the output voltage across the 4 Crees is 22v with jumper J1, is this right?

So u connect your DMM in series with the circuit which consist of the 4 Crees and Shark Converter and trim the pot to the desired current?

 

[DonShock]

Not necessarily, 22v is just the max that the Shark is capable of. It will only output as much voltage as is needed to supply the current that you set it to. For example, I have a Shark driving 4 Crees at about 1 amp and the total voltage is a little over 12V, I forget the exact value.

 

[snipinglight]

Not necessarily, 22v is just the max that the Shark is capable of. It will only output as much voltage as is needed to supply the current that you set it to. For example, I have a Shark driving 4 Crees at about 1 amp and the total voltage is a little over 12V, I forget the exact value.

How does the Shark know the correct voltage to supply?

Max current for Cree is 700mA, u driving it at 1A! Can the Cree take it?

Curious to know what reflector are u using?

 

[DonShock]

Not sure of the exact design details, but I'm assuming it has a sensing resistor on the board that measures how much current is being supplied and it just raises the voltage until the output current is equal to what you set it to and then stops there. The Cree was recently rerated for 1A, but I was going to do it anyway. It's more fun to push the limits. And so far, I've only toasted one driver and one LED and that was by accident when I wasn't even trying to overdrive anything. I am using the McR-19XR reflectors. They are somewhat of a pain since they aren't self-centering like some of the reflectors for the Luxeon star LEDs are.

 

[snipinglight]

Not sure of the exact design details, but I'm assuming it has a sensing resistor on the board that measures how much current is being supplied and it just raises the voltage until the output current is equal to what you set it to and then stops there. The Cree was recently rerated for 1A, but I was going to do it anyway. It's more fun to push the limits. And so far, I've only toasted one driver and one LED and that was by accident when I wasn't even trying to overdrive anything. I am using the McR-19XR reflectors. They are somewhat of a pain since they aren't self-centering like some of the reflectors for the Luxeon star LEDs are.

Hi Don Shock thanks for all the help. What would your next choice of Cree reflector be ? Are there any self centering ones?

U are using the McR-19Xr reflector, did you make special shims to fit the Crees?

How about using MCR 20 for Crees?