Help, DIY cree light driver advice needed.

[gav6280]

Hello, i could do with some advice before making an expensive error.

I have purchased :

A Polymer Li-Ion Battery Pack: 7.4V 5000 mAh from batteryspace
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=4075

4 of Cree XR-E Q5 Emitter on Premium Star (228LM at 1A) from DealExtreme
http://www.dealextreme.com/details.dx/sku.2394

Also a Lens : http://www.dealextreme.com/details.dx/sku.1915

I am building a light for SCUBA Diving so driver modes have no importance but brightness and reliability essential.

All 4 LED's will be on at the same time and on full brightness for around 1 hour using the battery pack.

In what configuration? and with what driver should I power this Cree set-up?

I am hoping to get around 1000 continuous lumen for at least 1 hour .

Many thanks.

Gav.

 

[Jarl]

You've got just under 40 watt hours to play with. Since it's a dive light, I'm going to pretend you've got 30 watt hours to play with. 4 XRE's would be about 16 watts, factoring in driver inefficiencies and you're talking an hour and a half on full power.

As for a driver, all 4 LED's in series with a shark boost driver would probably be your best bet. A shark/remora would be useful if you want multi-modes, if not the shark by itself will happily power your setup.

How do you plan to waterproof it? How do you know the DX lens won't shatter at high pressures from diving? are a couple more questions you should be considering IMO.

 

[gav6280]

No idea what a shark is so just had a quick search through the forum.

Man that thing looks scary and complicated? Where do you get them.?

My battery is a lot....lower than the forward voltage of all 4 led's in series?

Is there an easier solution bearing in mind all the factors in my original post?

Even more confused now...

As for waterproofing that's not a problem as it's going off to a specialist company, that prototype underwater housings.

 

[Jarl]

Man that thing looks scary and complicated? Where do you get them.?

http://theledguy.chainreactionweb.com/product_info.php?products_id=721

It's not complex at all. You have to be good with a soldering iron, or know someone who is, and you also want a multimeter. Connect everything up- LED+ to +ve of first LED, then wire everything in series from then on, with -ve of last LED going to LED- on the shark. Connect the multimeter on the amps setting, twiddle the pot till you get to 1A (or thereabouts... bear in mind that you shouldn't turn the pot much- it's rated for ~20 swipes. Set and forget, not an adjuster. If you want an adjuster, you need an external pot)

My battery is a lot....lower than the forward voltage of all 4 led's in series?

Hence the shark. It increases the voltage to the level required (up to 26V, but the Vf of 4 XR-E's is far less than 26V so you're fine) until the current set by the pot to flow through the circuit.

Is there an easier solution bearing in mind all the factors in my original post?

The shark is IMO the simplest solution. It's not very scary- the worst part is the soldering.

As for waterproofing that's not a problem as it's going off to a specialist company, that prototype underwater housings.

That's good to hear. I still have doubts about that DX lens- will you have a big glass window in front of it? If so, you're probably better off with separate, higher quality lenses which will reflect better.

 

[steve6690]

The Shark is probably your best option TBH, bearing in mind that you've already bought the battery pack so you need a boost driver. It needn't be complicated either, in fact it's fairly straightforward as long as you know how to solder. I have used that lens from DX with 4 of those Led's and I think it will work very nicely as a dive light. Wire the led's in series...
Get the Shark from here :

http://theledguy.chainreactionweb.com/product_info.php?cPath=48_49_61&products_id=721


steve

 

[gav6280]

Cheers chaps, for all your advice much appreciated. I am going to order one.

One question though my battery has a capacity of 5000mah and the max input according to the supplier is 4A.

Is that going to be ok then?

As for the external lenese on the front of the lamp it's 4mm toughened glass.

Does anyone know of a supplier selling a better quad optic?

 

[gav6280]

Anyone....

 

[Jarl]

max input for the shark is 4A. So, you work out how many watts you'll be outputting (worst case is 15W including driver inefficiencies) and the worst case battery voltage (6V) So, at 6V input current for 15W would be about 2.5A, well within 4A.

As for a better quad optic, you may be better with 4 separate optics?

 

[LukeA]

As for a better quad optic, you may be better with 4 separate optics?

Multiple discrete optics are more difficult to focus than one quad.

 

[gav6280]

just spotted a much better battery going cheap.

It's a 14.8 v 3000mah.

Can someone have a look at my numbers below:

(4 led's * fv * Amps ) so 4*3.7*1 = 14.8 watts + extra 2 for the shark driver so totall is around 17 watts right?

Ok. so 17 watts / 14.8 volts gives 1.14 Amps per hour?

So battery pack has 3000mah so 3 / 1.148 = 2.61 hours or 156 minutes run time ?

 

[Jarl]

Personally I find it easier to work out capacity of the battery pack in watt hours (in this case, 14.8*3=44 watt hours) then divide by the watts= 2.6 hours. But yes, your method also works.

Problem with the 14.8 is that it's 16.8V hot off the charger, which means Vs>Vf of your LED's, so a shark wouldn't work. You'd need a high voltage buck/boost (because Vs starts above Vf, and drops below Vf as the batteries discharge) driver, and I don't envy you if you need to find one of those....

 

[steve6690]

just spotted a much better battery going cheap.

It's a 14.8 v 3000mah.

Can someone have a look at my numbers below:

(4 led's * fv * Amps ) so 4*3.7*1 = 14.8 watts + extra 2 for the shark driver so totall is around 17 watts right?

Ok. so 17 watts / 14.8 volts gives 1.14 Amps per hour?

So battery pack has 3000mah so 3 / 1.148 = 2.61 hours or 156 minutes run time ?

If you're going to change the battery pack you could stay with Li-ion but go for 3 cells in series to give you 11.1 volts nominal ( 12.6 volts(ish) off the charger. This would give the Shark less work to do. As for the DX quad optic, it will be fine, trust me. I have tried it...

 

[gav6280]

Lost now. It clearly says that the shark board can handle input voltages from 2 to 20 volts.

My new battery is 14.4 volts nominal.

The forward vlotage of my 4 cree's will be 14.8.

So what's the problem?

All i can foresee is that for the first few minutes i will be in direct drive, then as the voltage drops the shark will start to boost.

Or how about adding a resistor or a 5th q5 led ?

 

[Jarl]

If Vs>Vf, your shark will die (it actually says in one of the threads "the shark MUST be running a boost configuration at all times!" or words to that effect) rather than DD'ing.

14.4V nominal at 3.7V/cell means 4 cells. A freshly charged li-ion is 4.2 hot off the charger, which means Vs would be 16.8 (4*4.2), ~2V larger than Vf, and break the shark board. A 5th Q5 or resistor (About 3 ohms, 5 watts) would work. Obviously the Q5 would be better for efficiency reasons, though you may struggle to find a 5 cree optic.

HTH.

 

[gav6280]

Deleted this post myself, please continue.

 

[gav6280]

How about a direct drive solution?



+16.8V

R = 2.2 ohms

• each 2.2 ohm resistor dissipates 2425.5 mW
• the wizard says the color code for 2.2 is red red gold
• together, all resistors dissipate 2425.5 mW
• together, the diodes dissipate 15540 mW
• total power dissipated by the array is 17965.5 mW
• the array draws current of 1050 mA from the source.

 

[gav6280]

Or maybe a buckpuck with 2 series strings of 2 leds per string?

http://www.ledsupply.com/02008b-1000.php

What happens to a buckpuck if the Vin drops below VF, does it cut out or go into melt down?

 

[yellow]

damn, I am SURE I did post in this thread. Should have been post #3, or so.
Somehow lost it and the questions/problems rose, while I covered exactly those problems
I will make it quick:

1st: skip those optics You linked, they are CRAP.
Compare that to using prescription goggles from the 1 $ shop --> are they good?
Use single reflectors from the Sandwich shoppe, 27 mm if You have the space. They are focused the most and thats what You want underwater. If not so much space in housing, get the 19 mm (I like them best, but their beam is a bit wider)
... sure not a cheap solution, but is diving a cheap hobby?

2nd: using the same number of Li-Ion cells (4) and led (4) does not work. Its better to have an uneven number to be able to use boost, or buck drivers. If You want to use the 14.4 V pack and have enough space, change to 5 Led and SHARK; or reduce to 3 and a buck driver. Or 2 strings with buck drivers and 2 led in series each.

3rd: what material will that "custom housing" be?
Because You want to drive the led hard and this means heat production, much heat.
Maybe, when using a thick Aluminium mounting plate for the emitters, a plastic housing might be enough underwater. I would try to get a metal one, and the mounting plate in direct pressed-in contact to the housing. Thats how powerful led lights have to be made.

4th: whatever You do, dont have them run on more then 900 mAh. That way they might survive 1st mounting effort (its still "learning").

I would go for the SHARK solution, but direct driving will also work. You have to play around with the resistor, but when the light runs at 800-900 mAh after the 1st high voltage spike is settled (after 5 mins of running), the output will be quite nice.

PS: when using SHARK and the 7.2 V Pack, the driver has to be mounted on the backside of the mounting plate for cooling. Will draw about double what is needed, so about 2 Amps.