# Driver, LED choice& battery - desiging a bike lamp, CREE XML T6 or P7 etc?



## fishpie (Sep 29, 2011)

Hello, 

Any input is welcome please as I'm new to this but have been doing some homework...

I'm designing my first offroad bike lamp and am from the school of more is better. I am aware of the difference between buck, buck/boost and PWM but having difficulty choosing a suitable driver here in the UK.

I want to be able to drive up to 3 x of today's most efficeint LEDs (?) i.e CREE XM-L U2 and want to run them around their max 700 lumens each for up to 2+ hours.

I haven't chosen a battery pack yet but aint afraid of carrying a lot on the bike frame to support this long runtime/high output. 

I'd really appreciate if anyone advise a suitable driver, batteries choice, and alternate LED if required. Even advice on reflectors will win you my helpfull fella smiley.

Thanks folks, much appreciated


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## NathanV (Sep 29, 2011)

For a good first shot at the in's and outs of building a bike light i suggest looking at bikeled.org, or googling "diyled"

It's a few years old, but other than the older emitters it still seems like current info. The recommended driver and batteries are still sold and still great.


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## wquiles (Sep 30, 2011)

I know this does not answer the question directly, but I wrote this as a guide to getting started, and it might have a few data points to help with your selection:
http://www.candlepowerforums.com/vb/showthread.php?257554-Introduction-to-modifying-flashlights-...

As to LED drivers that are efficient with a wide battery input range, I recommend the LED drivers from TaskLED.

WIll


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## Inkidu (Sep 30, 2011)

You might want to consider LiFePO4 batteries.
They are different than other Li chemistries. 
They have a very flat discharge. You might just be able to direct drive a XM-L
The link shows the smallest of the "brick" cells. If your not worried so much about the weight,5Lb/2.25Kg for (3) 3.3v "bricks", having a pack with 20Ah capacity would be great. Another benefit is that they can be charge 1500+ times and that is when you beat on them i.e. discharge them deeply or at high amps. Something that with your setup probably would not even happen. The case is bullet proof and easy to work with. They don't self discharge and are safer than other Li cells. 
I use a123 LiFePO4 pouches for my lawnmower and I happy with them. They are much lighter than lead batteries and will last much much longer. My only complaint is that the pouches are not hook up friendly. Something the bricks solve.

Hope this helps.


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## wquiles (Sep 30, 2011)

Inkidu said:


> You might want to consider LiFePO4 batteries.
> They are different than other Li chemistries.
> They have a very flat discharge. You might just be able to direct drive a XM-L



+1

Absolutely, in fact, for my current project I am direct driving a P7 from an "F" size LifePO4 cell (IFR32900P 4500mAH 3.2V). I am actually under-driving the LED, but I have no need for a driver (less wiring, components, etc.), since the discharge is flat I have "built-in" regulation (fairly constant brightness as the cell discharges), and with no driver that also means that I have 100% efficiency (even the best drivers achieve only about 90% at high current levels).

Will


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## fishpie (Sep 30, 2011)

Thanks gents, I'm always impressed with the response I get from the several forums i use on my many embarrassing hobbies. I'll have a wee peruse of the links and do some more homework.
Shamefully, I'm into larger scale rc gliders so am already armed with some pretty fancy intelligent chargers and the like for high cap LiPos. If you look at the rcgroups.com, http://www.rcgroups.com/batteries-and-chargers-129/? , there's a battery/chargers section which may be of interest to some here.

will no doubt be back asking about reflector beam angles from you guys for single track mounting biking

Mucho thanks


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## jtr1962 (Sep 30, 2011)

I'll add here that the brightest, most efficient LED isn't necessarily the best choice. I just discovered this in the process of building myself a bike light. I had bought some R5 XPGs and 10mm optics last year for this project, but didn't get around to it until recently (still not finished, but the light engine part is built). It turns out that due to the large die size of the XPG I'm not getting as much throw out of the 10 mm optics as I could be. In retrospect a better choice would have been the best bin XP-E (currently R3). Fewer lumens, but probably about 2-3 times the lux I'm getting from the XP-Gs due to the smaller die size. For the same reason an XM-L really isn't a great choice here even though it's the most efficient LED available. The huge die means you'll need a huge optic for any given amount of throw. You _can_ get good throw from an XM-L, but you'll need something like this.

Bottom line-more efficient LEDs usually have larger dies. This in turn means you'll need larger optics for any given amount of throw.


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## fishpie (Oct 1, 2011)

Thanks JTR,

Maybe a rethink required of led and reflector required if throw is going to be an issue?

The housing I'm using has and internal diameter of 65mm but could stretch another couple of mm on the lathe if required. The depth can be as required so taller relfectors not an issue. I thought I might even overlap some if they were to overlap slightly in the centre with some carefull shaping, what do you think?

PS, I realise some don't like to advise particular LEDs/reflector combinations in case of being held accountable for a duff project but that's not going to be the case here - I welcome any input as this is going to cost me very little outlay 

Thanks


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## fishpie (Oct 10, 2011)

Am I looking at the following LED specs too simply? Seems too good to be true...

Could I use a boost Driver to achieve the advertised 900lm at only 250mA @ 25V??? surely not, as this is only 6.25W theoretically for such a low amount of heat/current.

_"Description
_

_LED, EASYWHITE, LUM FLUX 900LM_
_ Series:MP-L_
_ LED Colour:White_
_ Luminous Flux @ Test:1000lm_
_ CCT:4000K_
_ Forward Current @ Test:150mA_
_ Forward Current If Max:250mA_
_ Forward Voltage @ Test:25V_
_ Power Dissipation Pd:11.3W_
_ Viewing Angle:125°_
_ LED Mounting:SMD_
_ No. of Pins:6_
_ Power Dissipation Pd:11.3W_
_ Termination Type:SMD"_
_Here's a link to the blurb: _http://uk.farnell.com/cree/mplezw-a1-r100-0000d040f/led-easywhite-lum-flux-900lm/dp/1846636


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## Steve K (Oct 11, 2011)

Yep, too good to be true. 

the datasheet (linked to from the Farnell site) says the neutral white produces 260 lumens at 700mA At 3 volts, that's 124 lumens per watt. Not unreasonable. You can put up to 3A through this LED, so getting 1000 lumens out seems likely. Vf is nominally 3.35v, so dissipation is 10 watts. 

This is different from "900 lumens at 250mA", though. I'm not sure where the "Forward current If max: 250mA" came from. It didn't come from the datasheet.

Steve K.


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## PapaLumen (Oct 11, 2011)

Look at the second data sheet. (986.22). Its an "easywhite" multi die led. 19.9w @ 250ma, 26.5v. I dont know much about these though. Do they have multiple connections like an mc-e?


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## fishpie (Oct 11, 2011)

hmm, I'm confused though - it boasts _'Luminous Flux @ Test:1000lm'_, _'Forward Current @ Test:150mA'_, at _'Forward Voltage @ Test:25V_'.

Is it unreasonable to think I can achieve this i.e. 800lm, close to at only 150mA? 

A 7.4V pack into a 25V output boost driver at only 150mA would mean the inefficiency wouldn't be an issue? That would be ideal for my project.

Thanks for any education...!


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## ifor powell (Oct 11, 2011)

Forget the easy white, no good optics for your use and not as efficent as the xml.

3 Xml in series. You need to choose the colour tint, maybe a mix?
4 cell lithium cells of whatever flavour you want. 
H6flex driver from TaskLed.
All that is left is the optics and the hard mechanical bits...


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## fishpie (Oct 12, 2011)

Bosh! Straight talking from _ifor_ there.

Fair enough, I'll take your advice - Ignoring colour choice at this stage, which XML, this for instance, or lower fwd I?:

LED X LAMP XMLA 1200LM


 Series:XML
 LED Colour:White
 Forward Current @ Test:700mA
 Forward Voltage @ Test:6.2V
 Viewing Angle:110°
 LED Mounting:SMD
 No. of Pins:2
http://uk.farnell.com/cree/xmlezw-00-0000-0000s630f/led-x-lamp-xmla-1200lm/dp/1892513

I can get the driver from TaskLed in the States as I have family in Houston to purchase and post to speed it up a bit.

Thanks for the help fella

Edit:
hmmm, just spotted this on TaskLed's site
NOTE: No orders processed or shipped from
*** 12 Oct - 14 Nov 2011 ***
ORDER SOON

Any alternatives?


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## Justin Case (Oct 12, 2011)

fishpie said:


> Am I looking at the following LED specs too simply? Seems too good to be true...
> 
> Could I use a boost Driver to achieve the advertised 900lm at only 250mA @ 25V??? surely not, as this is only 6.25W theoretically for such a low amount of heat/current.



The MP-L has three strings. Your calculation is for one string. Multiply by 3. The MP-L datasheet says 19.9W total power at 250mA drive, for all 3 strings.

This boost driver appears to be designed for the MP-L.


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## PapaLumen (Oct 12, 2011)

Thats another easy white xm-l. 

Heres is xml-u2 from cutter (australia but i get mine from there) - http://www.cutter.com.au/proddetail.php?prod=cut1095

Or xml-t6 from cutter too - http://www.cutter.com.au/proddetail.php?prod=cut1023


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## Justin Case (Oct 12, 2011)

fishpie said:


> Bosh! Straight talking from _ifor_ there.
> 
> Fair enough, I'll take your advice - Ignoring colour choice at this stage, which XML, this for instance, or lower fwd I?:
> 
> ...



You could try the Shark Buck and configure it for 3A (sense resistors of 0.1 ohm and 0.05 ohm). If you want multi-mode, add a Remora. Assembled gets very expensive. Assemble yourself is cheaper. For some reason, The Sandwich Shoppe's web site doesn't show any Shark Buck 3A boards. So you may have to get a Shark Buck 1A or 2A and install your own sense resistors anyway.


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## fishpie (Jan 20, 2012)

The light's near complete, just need to pot the proper external cable into the housing and I'm done. Hopefully these pics are visible and not too large: 

http://i389.photobucket.com/albums/oo335/HaggisFuelled/MTB light/DSC00711.jpg


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## Toaster79 (Jan 21, 2012)

Remove that diffuser plastic on 225 reflector/optic to get tighter hotspot, other vise it will be only wide "hot spot".


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## fishpie (Jan 22, 2012)

Thanks, I didn't realise it would have any great impact on the spot. I'll give it a go.


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