My Cateye ABS Halogen to Cutter/Cree LED conversion project

Well I think this will be my second or third post on here. Already I've learnt racks from trawling through various posts and I'd like to say a big thankyou to everyone who posts up their thoughts and shares their expertise.

I have a plan and before I start spending money I'd just like to run it by folks here for comment to see if there is anything I could learn and maybe do better.

The starting point for the project is a set of cateye abs 35 lights. The end result I'm looking for is 2 sets of lights that will be suitable for mountain biking on the trails here in North Wales

The starting point



Cateye ABS 35
Batteries = 2 x (6 Volt 3000mAH) = 36 Watt hours
Low = 15 watt flood = 2.4 hrs
Med = 20 watt spot = 1.8 hrs
High = 15 watt flood + 20 watt spot = 1 hr
Weights
Cateye abs 35 = total 1.15kg (approx)
2 x batteries = 0.75
2 x head units inc bulbs = 0.25kg
1 x cable set = 0.15kg

The bulb holder is the key element in this and here are a couple of photos

The plan is to split the system in two and create 2 lights from it. I'm intending to use the Cree MR11 from Cutter with the Maxflex driver.

Each light system will be like this

here's an incredibly dodgy drawing that shows how the led's, optics and driver should sort of fit into the head unit



This should give me 2 pretty good lights with usefull run times

LED Vf = 3 x 3.5 Volt LED's = 10.5 Volts

Battery = 6 Volt 3000mAH = 6 volts x 3 amps = 18 Watt hours

@ 1000mAH
1.0 amp x 10.5 Vf = 10.5 watt + 20% inefficiency = 13.125 watt draw
18 watt hours / 13.125 watt draw = 1.37 hour battery life

@ 750mAH
0.75 amps x 10.5 Vf = 7.875 watt - 20% = 9.84375
18 / 9.843 = 1.8 hour battery life

@500mAH = 2.75 hour battery life

@350mAH = 3.9 hour battery life

The weight should be in the half a kilo area

I'm planning of using one of these switches


as made by the team thats put together the stunning Min-T. See here http://candlepowerforums.com/vb/showthread.php?t=172053&page=5

Queries I've got at the moment are

1. I don't know how deep exactly the LED & Optic assembly is including the board the LED's are mounted on

2. I'm going to mount the MCPCB onto a 42mm dia disk (made from an old trangia pan I think) so that the bezel with hold all the optics in securely. This will either work perfectly or be a bit crap. How should I attach the disc to the mcpcb? Thermal epoxy (not actually sure what that is or where to get it:duh2 or small bolts

3. how to secure the maxflex board in the housing so that it doesn't rattle around or short circuit. I've seen a photo of a board wrapped up in something to protect it and insulate it but not sure what it was. I guess its got to be heat resistant and non conductive.

These head units seem ideal for the purpose. I brought a replacement for a damaged one a year ago for £20. They are aluminium so should conduct and disipate heat pretty well. The mounting brackets for handle bars (inc oversize) work well (I also have a plan to adapt one to make a simple helmet mount) and spared are available

So then folks what do you think? any problems you can see?

All comments and opinions gratefully recieved

Hi Iggs
That looks like a good modding platform since it is an aluminum body -just make sure you have good contact with the inside fins.

Here is the size of the Cutter optic and MCPCB



Cutter also has Arctic Silver adhesive which you can stick the board and heasink together with.
Or Photon Fanatic has a large range of similar adhesives
http://www.cpfmarketplace.com/mp/showthread.php?t=85330

Maybe a few blobs of Sikaflex or RTV silicone around the edges of the maxflex to hold and isolate from the housing?
You may have to heatsink the maxflex as well -someone should know about that.

Looks good

Nice switch BTW

Cheers
Dom

Thanks for the reply Dom.

Particularly thanks for the measurment of the mcpcb and optics. Its actually got me quite excited as it looks like the plan is going to work better than I could possible have hoped.

If my calculations are right then the bezel will hold everything in place and apply a bit of pressure so that the contact is good between the ali disc and the fins/housing

The silicone blobs idea is perfect. What I havent decided is whether the board needs insulating from the heat that will be conducted to the housing or connected to it to allow disipation.

Here is text and a picture from taskled.com

"The picture below shows the top view of MaxFlex. The exposed rectangular tinned area just above the (C) TaskLED is a direct thermal interface to the bottom of the switcher IC (on the other side of the PCB). If the power dissipation of the MaxFlex board exceeds about 1W it is recommended to affix a heatsink or copper tab to a heatsink to the exposed area. The exposed area is at Ground potential - i.e. electrically connected to the battery GND and LED- pads. This means it is safe to mount the tab to a heatsink that connects to the body of a flashlight, IF the body of the flashlight is the same as the Battery negative or ground. "


At the moment my plan is to have it set up as just a high/low light with 750mAH as the high and 350mAH as the low as my batteries aren't that good. If I get a better set of batteries then I might move up to a 1000mAH setting. 1 amp is obviously right on the boundry of needing heatsinking. Be really fiddly to do in there.

This being my first tinkering project I think I've fallen on my feet with the housings I've got. There certainly seems to be plenty of options. Here in the uk they are still available as spares for about £20 per housing from http://www.zyro.co.uk/product_list.asp?cat1=lig&cat2=spacat
You'll also see all the various brackets that would be needed too. I'm using these at the moment on a weekly basis and they work really well

Hey Iggs
Yes -very good and cheap housing -haven't seen anyone using these before.
Very good find.
Someone will chip in on the maxflex heatsinking
There is a good discussion about it here if you haven't seen it yet.
http://candlepowerforums.com/vb/showthread.php?t=176391

There are links on the second page to a good mod Tino Ale is doing with the maxflex.

Cheers
Dom

Right then having re read the text from Taskled I realise I'd completely misunderstood the heat sink issue with the board.

and now I have a question because I dont understand the issue :-S

If the power dissipation of the MaxFlex board exceeds about 1W

How do I work this out?

The exposed area is at Ground potential - i.e. electrically connected to the battery GND and LED- pads. This means it is safe to mount the tab to a heatsink that connects to the body of a flashlight, IF the body of the flashlight is the same as the Battery negative or ground.

What does this mean? Seeing as I'm not using the body of the light as a ground I assume this means I cant connect it straight to the body which is the heat dissipation route.

So do I need to worry about dissipating heat from the board?

If so how do I do it?

Thanks Dom, that link has sort of helped. Its a long time since I've done this sort of maths. Weirdly I'm really enjoying it!

So I'm going to be using 3 emmiters @ 3.5 volts each with up to 1000mAH going through them

@ 1000mA
3 x 3.5 x 1 = 10.5 Watts
Say 90% efficiency = 1.05 Watt being disapated by the maxflex board

@ 750mA (my planned high rating)
3 x 3.5 x 0.75 = 7.875 Watts
90%= 0.7875 watts

So at 750mA no problems, at 1000mA its on it's limits. Thats ok and fits with my plans at the moment

Bit more info, this time on costings of this project if starting from scratch

Light head unit
£20 - Light Housing
£ 5 - handlebar mount
£50 - Cutter's Cree MR 11 with (+£5 with Maxflex)
£10 + p&p - Remote switch
£10 - bits and bobs including heat paste, heat shrink and cables

£95

Battery and charger - NiMH about £30 (14.4volt 2400mAH)

So, another question is - what comercial lights are available that give out this sort of light that this project should and how much do they cost

...thrill at telling your riding buddies you made the brightest light they've seen...priceless.

iggs said:

@ 1000mA
3 x 3.5 x 1 = 10.5 Watts
Say 90% efficiency = 1.05 Watt being disapated by the maxflex board

Click to expand...

If your driving them at 1000ma the Vf will be atleast 3.7 possibly a bit more, I'm sure somebody will be able to confirm that.

Depends on the specific LED and bin (and production day), but all my Crees (P4 and Q2 bins) have been at or under 3.6V at 1A. My Q2s in fact are much lower, around 3.4 average at turn-on (before heating effects), but my P4s were right around 3.6 and reports are the Q5s are also around 3.6, so that's a pretty "safe" starting figure for Cree LEDs.

Well the first one is complete





Quite pleased with my switch and recycled innertube mounting system







More photos of the build here > http://s17.photobucket.com/albums/b79/iggs/LED Bike Light Project/

One thing I haven't really resolved is the heat sinking of the maxflex board, still pondering that.

The sealing is a bit rough at the moment on this one. I've got to change the battery connectors and faff with it a bit. Once that is done I'll wrap it up nice and tight with silicon and shrink wrap

I'm not completely happy with the settings I've got on the UIB yet either. I haven't quite got to grips with my multi meter either so I've not got it sussed in my head how much battery is being used

And of course a bit of helmet cam video of the above light in action > http://uk.youtube.com/watch?v=yJE39-fZaZs

Thanks for all the help from everyone so far, really appriciate it, I've learnt racks and now have a really great light to boot