Shark driver using 1x18650 **ADVICE NEEDED**

[Slickseth]

I'm planning on building a 1x18650 edc using a shark driver to power 4 Cree xp-e emitters in series at a minimum of 500ma each (6.44 watts). Technically this should draw about 2amps from my 3.7v 18650. According to the specs, the shark can operate all the way down to 2.7v, so in theory this **should** work.

But I'm having a hard time finding any info on using the shark driver with a 3.7v source.

Does anybody have any experience with this? Will it work?

 

[Justin Case]

http://candlepowerforums.com/vb/showpost.php?p=1246655&postcount=2

A general rule of thumb to use the Shark.

1) Determine the number of LEDs you want to drive in series. Example: 4 Lux3s.

2) Determine the series voltage of the LEDs at the desired current. Example: 1A which means ~4V/LED and 4LEDs = 4 * 4V = 16V (approximately)

3) Determine the operating and min battery voltages using the total Vf output. Operating is > 1/2 output and min is approximately 1/3 Vout.

Operating should be greater than 1/2 of 16 Volts or a fresh battery pack should be 8+ volts.

At end of battery life your battery voltage should not drop below ~ 1/3 Vout or 1/3 of 16 = 5.3V

In this example a 9V stack of AAs batteries or a 12V stack of AA batteries would be fine for this example. What won't work is 2AAs, 4AAs since the current demand will approach the limit of the regulator.

Example 2:

Three low Vf LuxV. say you have 3 LuxVs with Vf of approximately 7V @ 700mA. That's 21V which is below the 22V open circuit protection (with J1 jumpered).

1/2 21V is 10.5V and 1/3 21 is 7V.

A 12V battery pack would suffice for this application. A 9V battery pack would be marginal for this application.

 

[Slickseth]

Thank you for the info. However, my situation doesn't quite match either of those scenarios.

My total led vf (in series) will be 12.88v @ 500ma. If I decide to drive the four emitters in a 2s2p configuration, then my total led vf will be 6.44v @ 1000ma.

Having said that, I'm comfortable with the vf-in / vf-out ratio. My question is whether or not the shark driver is able to perform properly when the input voltage range is so near the driver's minimum specification.

 

[Slickseth]

Does anyone have any experience with this? Anyone???

 

[Justin Case]

Thank you for the info. However, my situation doesn't quite match either of those scenarios.

My total led vf (in series) will be 12.88v @ 500ma. If I decide to drive the four emitters in a 2s2p configuration, then my total led vf will be 6.44v @ 1000ma.

Having said that, I'm comfortable with the vf-in / vf-out ratio. My question is whether or not the shark driver is able to perform properly when the input voltage range is so near the driver's minimum specification.

3) Determine the operating and min battery voltages using the total Vf output. Operating is > 1/2 output and min is approximately 1/3 Vout.

Your output is about 12.9V. Thus, Vop > 6V and Vmin > 4.3V. It seems to me that your 1x18650 power source fails on both counts.

 

[Slickseth]

If I wire the LEDs in a 2s2p configuration, then the vf of the led string will be 6.4v @ 1000ma. This gets the vf - in / vf - out ratio into spec.

But my main question still remains. Will the shark driver operate correctly if run so close to it's minimum voltage (2.7v)?

 

[Justin Case]

Why would you run your 18650 all the way down to 2.7V?

 

[Slickseth]

Because these are the new 2900mah panasonic ncr18650 batteries which can be discharged to 2.5v.

 

[Justin Case]

I doubt driving the Shark at low voltages is a good idea, which may be why you aren't getting any feedback from anyone who has tried it. No one is wasting their time with such marginal implementations.

The Shark's boost IC is rated at a typical 4A max input, but the minimum max input can be 3A. Wayne conservatively recommends holding the max current draw requirement to 2A. At 2.7V input, you are very close to that 3A limit, and definitely way over 2A. In addition, the Shark is going to run hotter at low Vin and its efficiency will suffer. Thus, an assumption of 80% or 85% driver efficiency may be invalid, and the current draw could be even greater than calculated.

Typically, running at the limits of devices isn't a good idea anyway.

The Blue Shark runs cooler than the Shark and may be a better bet. However, Wayne has stated that his rule of thumb still applies where the full battery range (fresh to depleted) should be greater than 1/2 of Vf of the LED string. Given that, it would seem to me that your envisioned implementation is not a good one. To meet Wayne's rule of thumb, you'd have to run your Panasonic only to about 3.3V, wasting a significant portion of the cell's capacity for a 2A or higher draw.

For a more definitive statement, you probably should post your question to Wayne on the Shoppe's CPF sub forum.

 

[Slickseth]

I should have specified that I will be using a BLUE shark for this.

I'm going to give it a shot. If it doesn't work, I can always use the shark for another build. At the very worst, I may just end up using two gd1000s to supply the 6.44 watts to the emitters.

With a nearly depleted battery (2.7v), assuming that the efficiency is around 70 percent, it still will be drawing less than 3.5 amps from the battery in order to deliver 6.44 watts to the emitters.

Granted, a higher voltage battery supply would make the shark more efficient, but my goal is to use a single 18650 size host. 2x18350 could supply the higher voltage, but the the capacity (and quality) of 18350 batteries just isn't anywhere near that of these 18650's.

Perhaps I will direct this question to Wayne. He should be able to give me more specific info on the capabilities of the shark when used near it's minimum voltage input specifications.

 

[yellow]

up to 500 mA it should work
I have a MC-E driven from three C Ni-Mhs and it works till about 500-600

but: when reducing to three led, it will surely work and I have - somehow and only for me - come to the conclusion, that I can put three led much better into an exisiting housing (read: small), then four.


PS: dont forget to mount the Shark in direct contact to thermal/mounting sheet, or metal housing of light

 

[Slickseth]

That is good news. 500ma is as much I care to push emitters. The emitters are R3 bin xp-e's behind a 25mm khatod optic. This is going into a Surefire 6p host. Should be good for 600 lumens, at 6.44 watts (at the emitters). I just need to figure out the best way to design the heatsink to dissipate the heat from the emitters AND the shark.

 

[Justin Case]

up to 500 mA it should work
I have a MC-E driven from three C Ni-Mhs and it works till about 500-600

but: when reducing to three led, it will surely work and I have - somehow and only for me - come to the conclusion, that I can put three led much better into an exisiting housing (read: small), then four.


PS: dont forget to mount the Shark in direct contact to thermal/mounting sheet, or metal housing of light

Can you clarify what you mean by "500mA"? Is that a tail current draw, total drive current, or drive current per MC-E die? I would assume that you are talking about a 2S2P MC-E.

 

[Slickseth]

I was assuming he meant that he had the mc-e wired in a 4s configuration, pushing 500ma to each die. That would make for some pretty decent output. But... Indeed, please clarify.

 

[yellow]

thats it, correct. Sorry for not typing it.
MC-E fully wired in series, current measured at the led
(so total drive current and drive current per die)

(anything other and especially led wired in parallel is crap, imho)


I have a drawing for a sink, is there any other way?

the better/thighter the fit in housing, the better.


PS: that quad setup really fits into a 6P housing?

 

[Slickseth]

PS: that quad setup really fits into a 6P housing?

The outer diameter of the optic/mcpcb is 25.4mm. The height of the two together is about 13mm. Luckily there is some room to machine down the diameter of the mcpcb, but the flashlight body will need to be opened up a bit as well. With a snug fitting heatsink below the mcpcb, I think it will fit. I'm still waiting to get a few parts, so I'll add an update when everything is confirmed.