Where do I start looking?

[Stardust]

Hi everyone,

I am complete noob on designing a flash light for cycling. I have just purchased 3 Cree XR-E star emitters and I am not sure what other parts do I need. Please point me to the right direction thanks.

I have done a couple of years of electronics and I have knowledge of circuit analysis ( a bit rusty though, havn;t touch the stuff for ages!!).

Thanks!!

 

[Doh!Nut]

If you have the emitters then you need a constant current source and a battery.
The LED should be run in series so you need 3*3v to 3*3.8v = 9 to 11 volts Vf

So you either need at 12v+ battery and a buck regulator
or a 7ish v battery and a boost regulator

I suggest batteries from Component-shop.co.uk
regulators from dotlight.de or led-1.de
or from sandwich shop or taskled

Depending on what facilities are available to you the tricky bit will be mounting the LED in a light, sturdy, correctly heatsinked unit that does not look like Jade Goodey has knocked it together.

Nick

 

[Stardust]

So what are the minium tools I need to take on this project?

Potential casing.. HA you guested it right I havn't got a casing for the whole thing yet. At the moment I am looking at Timson's and KonradC's bike lights for ideas.

I think I want two stars either side to flood while the center star doing spot
as my overall beam pattern.

More ideas and tips are most welcomed.

Thanks in advance.

Edit:
----------------
Ok here is the check list of stuff I need at the moment:
1. LEDs ( I got them 3 x Cree XR-E)
2. Batteries from Component-shop.co.uk
3. LED drivers from various places mentioned above
4. Casing for the whole thing, not sure where to get it from
5. Mounting Clip from lumicycle
Edit 2:
----------------
6. optic or reflector

Please feel free to add to the list thanks.

 

[chimo]

I would start by listing your requirements:

Beam profile
Beam Brightness
Power Source
Desired run-time

One you have those, you can better choose the components to install.

The BEAM PROFILE will tell you if you want an optic or reflector.

The BRIGHTNESS, POWER SOURCE and RUNTIME will help you determine an appropriate driver and help you determine the cooling requirement.

HTH,

Paul

 

[Stardust]

Hi chimo,

>> Beam profile
humm.... I am not sure what you mean but if what I have said in my last reply counts then here they are again. I would like to have 3 leds side by side. The center one I would like it to be a spot light and the other two I would like it to flood.

>> Beam Brightness
I do city communting most of the time and I am not riding my bike during the night yet coz I am not that good and crazy about cycling. But I sure am getting serious into cycling. So yeah I might do night rides one day. Well taking the Cree XR-E that I will be receiving from Download the rated lumans are between 80.6-87.4 lumans each. So if I combine the three at standard current 350mA each I will have between 241.8 to 262.2 lumans in total. I have no idea of what this amount of lumans can do. I don't really want to over drive things beyond their rating so if the datasheet tells me I have to run them in 350mA then I will run it at 350mA.

>>Power Source
I would like to have an external battery that hangs on my bicycle frame and I heard that Li-ion batteries are rather dangerous but they are the good energy source. I don't mind NiMH batteries but I know they don't have as high energy density as the Li-Ion. So I am a bit torn and am not sure what to choose. I thing a little water proof might be needed as I will cycle in the rain if it is not too windy.

>>Desired runtime
I would like to have the battery last for at lease 6hrs coz I will most likely to cycling 6 hrs per week between various places in the city. Or I don't mind to charge it everyday coz I can just plug the battery in first thing I arrived at the office every morning. But I would like the battery to be as small and as light in weight as possible.

Thanks for your suggestion, it really made me think about the requirements and hence to have something to work with. I hope I am not being vague about the requirements.

Thanks,
Paul aka Stardust

 

[nightrider]

Welcome to CPF Stardust!

Check out my signature links for some of the lights that I've built (especially the Triple Cree) and note that I have some additional instructional links in that post as well.

Also, CPF member Andytiedye has put together this accumulation of bike light related posts here on CPF.

http://www.candlepowerforums.com/vb/showthread.php?p=1755372#post1755372

That should keep you busy for a while!

- Allen

 

[Doh!Nut]

OK
If you are city cycling then the object is to be seen, not to to throw a huge beam to light up a trail, the mix of one spot and two flood sound about right for that.
The XR-E are rated up to 1000ma (this changed last week previously 700ma check Cree web site this applies to ALL XR-E)
However I think you will get enough light from a 350ma drive current and get the double benefit of the increased efficiency at lower drive levels.
Power required - Vf ~10v*0.35a = 3.5watt
3.5w /0.85 (converter efficiency) = 4.1w power drawn from battery.
4.1*6hours = 24 watt hours battery capacity required.

Or if you really valued the flashing function then the TaskLED bflex may be best
powered by 10aa *2400mah = 28.8Wh = 7hours.

I know you can get higher capacity batteries but component-shop packs made from tabbed aa are 2400mah

Nick

 

[Stardust]

@NightRider: Thanks for the welcoming, behonest your project logs have put the nail in the coffin for my internal struggle about rather to build my own light or buy a kit from master modders on CPF. And I thank you for your inspration and good info.

@Doh!Nut: Thanks for the time and effort in all the calculations you have done for me. I started to have more concrete specifications for my project hopefully I can get the light designed and all the parts sourced somewhere so that I can use it before the winter is gone. I don't really like flashing front light coz it dazzles me, but I am ok for the back light to flash coz it is not dazzlling me .

I think I want 2 maybe 3 levels of lights, so maybe 350mA, 750mA and 900mA or something I need to fix these current points by looking more closely at the lumans vs. current graph.

Question:

1. How do you convert Wh into mAh?
2. Are there safe Li-Ion battery packs out there that can support the following battery requirement?
3. How does the light level works with the drivers? Do I do one click to Low, one more to medium and one more to max level?
4. Battery calculation:

Say I need to have 750mA for 7hrs runtime @ 12V then:
Battery Capacity in mAh = RunTime X Driving Current
Battery Capacity =750mA x 7hrs = 5250mAh

10 * 1.2V@2700mAh in series will give me 12V@2700mAh then
2 * 12V@2700mAh in parallel will give me 12V@5400mAh

Therefore the required battery ratings for this project and I need 20
of those 1.2V 2700mAh AA cells then. Please check calculation!!

Now I am thinking of machining the casing for my light, I don't have access to any machines I can only do simple screw driver type of things. So if anyone can offer machining service I would love to hear from you.

Paul

 

[Doh!Nut]

Paul
Volts*Amps = Watts
Volts*Amps*Time= Watt Hours Wh
One aa = 1.2v*2700mAh (2.7Ah) = 3.24 Wh
You then have the option to connect 10 of these in parallel for 1.2v 27Ah
or in series for 12v 2.7Ah
or any combination inbetween
All will have the same Wh, I only really thought about Wh when I was trying to compare different voltage battery packs.
Try all-battery.com for Li-Ion packs - super cheap but I have not seen if we can get them in without paying duty on them.

N

 

[Stardust]

Doh!Nut,

I am looking at some Li-Polymer battery packs from all-battery.com. I am quite interested in this product:
7.4 volt - 5400mAh Li-Polymer Pack with PCB
If that's the case then I need boost driver rather than a buck driver, the reason I am thinking about this battery pack is that all the 14.8V Li-Polymer packs are too expansive. Also I think all-battery.com will not ship their products to UK as stated in their Shopping FAQ.

Does anyone knows where I can get some Li-Polyer packs within the UK?

Thanks