Looking for advice on building my first 4x CREE XM-L based video light 8)

[mattst]

I am new to this so please be patient.

Am wondering if I can run 4 XM-L's in a 2S2P config with a H6Flex powered by 2 LiFEPo4 10000mah in series..

if I am understanding things right the LED array will have a fV of 6.7V and current draw of 6A. is that right?

thanks for any advice you might have.

matt--

 

[hellokitty[hk]]

At fV ≈7v+, vin must be at least 8v to work with that buck driver, preferably more.

 

[mattst]

🙁
well I do have 4 bats but I was hoping to make 2 lights not to mention the pack is a lot bigger

thanks for the reply HK

can anyone recommend a battery set that would give 1 hour (min) burn on high 6A that might be smaller?
I am looking to mount the pack to the bottom of my camera housing

thanks in advance

 

[Codiak]

I'd just build a single canister with 6 18650s 3s2p. You won't notice A tube any more then a box under the camera

This is an old setup http://picasaweb.google.com/BeaverLakeNe/350Demo#5436468850822402850

 

[Klem]

Forward voltage of an XM-L at max recommended current (3A) is 3.35V. In 2s2P that's 6.7V, plus 1.0V for the driver...let's say 8V to be sure.

What you need to consider is the cut-off voltage of the batteries when 'empty', which is commonly 3V per cell. If the battery is 2S then it will be 8.3V full and deplete to 6V when 'empty'. Your configuration needs 8V to run properly at max lumens and with the usual voltage drop at high power draws your system will be compromised from the start.

You need to have a minimum 3S battery configuration. 3S is 12.4V full and 9V when 'empty'... 9V is above the operating voltage (8V) and that gives you max lumens for the entire depletion of the battery. That Flex driver works up to 21V, meaning whatever batteries you choose they must be either 3S, 4S, or 5S. Only those 3 lithium options will work with your settup.

 

[mattst]

thank you for the help.
I will post some pics soon, the head design is almost finished.

I have one more question.
That driver, is there a max led lead length? or can I put it in the can to separate the thermal issues?

 

[mattst]

thanks again for the help!

 

[Codiak]

thank you for the help.
I will post some pics soon, the head design is almost finished.

I have one more question.
That driver, is there a max led lead length? or can I put it in the can to separate the thermal issues?

I think George once stated 8inches, but it was highly suggested not absolute.

If the heat sink is water cooled your not really going to have to worry about it stayin cool

 

[350xfire]

You can buy a simple to assemble 3 XML module from Cutter electronics for about $50...

 

[mattst]

ok was looking on Georges site for the H6Flex dimensions and found a reference to 8" max for the momentary switch wire.

anybody have dimensions for the H6Flex?

and on the battery situation for now I am thinking I will bite the bullet and use the 4 LiFePO4 cells I have in series should give me a 14.4 nom voltage.. unless you guys say that just wont work..

next project will be can lights w/ 3x XM-L and 18650 cells probably use the DX tri-led reflector.
but that is for next month

 

[Klem]

All the specs including dimensions are found on his website;
http://www.taskled.com/techh6flex.html

Your 4 cells will work fine. Frankly, if you want to be drawing around 42Watts of power (approx 4*10W) which is a huge amount then you need a generous amount of everything to ensure you realise all those theoretical specs. With voltage drops/inefficiencies, overstated battery capacities by manufacturers, loss of condition by ageing and loss of capacity by high power draw...things tend to be more conservative in reality.