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Discussion Starter #1
Hi folks,

Just wanted to post here to see if I can get a bit of help as well as just collecting my info together to try and sort this out & get it all straight in my head...

What I'm planning is to run LED lights direct from the stator (no battery, it's not actually a streetfighter, but a KTM 380 EXC supermoto that I'm building. I figure the lighting theory would be relevant to other bikes as well and you could just as easily run it from a bike that uses a battery - so hopefully this can be informative for anyone else thinking of building their own headlight from scratch). Here's the basics, I just need to fill in the bits in the middle:

Power Source: 12V, 130W

LED: CREE XP-G2 (3-up on star PCB), planning to use 2 of these in series
Stats for individual LED
8.4Vf (typical forward voltage at 350mA)
1500mA maximum drive​

I've been trying to find which driver to use. Ideally I'd like to have one driver for both LEDs to keep the install nice & minimal and parts/weight to a minimum. But driving two of these in series means that the Vf increases to 16.8V. The only driver I've seen so far that could handle this is a FlexBlock boost driver, but the max output is 700mA. I'd like to be able to drive the LEDs at something closer to their max, for whenever I need hi beam. (Not that I'm ever likely to need to use hi beam continuously, but I'll be using a heatsink anyway so I'm not worried about heat damage etc.)

I found that FlexBlock driver on LEDsupply.com via their driver calculator.

I also found some much cheaper, basic drivers on LEDsales.com.au. These are only $3 each compared to $18 for the FlexBlock driver, so it almost makes sense to use one driver for each LED: Bare switchmode LED driver for one 1W LED

First thing that confused me was the description for that switchmode driver. It says it will drive a 1-watt LED at 350mA. So a 1W LED is one that has a max drive of 1,000mA? Is that correct? But then why only drive it at 350mA...? If someone can help me figure that out I'd really appreciate it.... :help0:

Regardless of which driver I use and what power I drive the LED at, I still need to figure out how to run a hi/low beam... From what I've been able to learn so far, to do it properly i would really need another driver on the low circuit lets say? Or I guess I could wire in resistors after the driver to drop the current for the low beam... placing the resistor after the driver - would that still result in a fairly constant current? The current into the resistor would be constant, so current out should be... but I'm not at all an electrically-minded person.

Another option is a dimmable driver, and wire it up so that the hi/low light switch just dims to preset values? But those drivers are $20, and only 700mA and that's the only suitable one I've found so far.

Thanks for any help that folks can offer on this. I will probably have more questions, but need to get these couple of things straight in my mind before I start thinking about other stuff.
 

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Elbow Grease is Cheap
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Interested in any help offered. Considering doing the same.

Hopefully you are running the power after the R/R. the stator voltages will be all over the place and also AC current.

And I would definitely check the voltages with the bike running. it will usually be a slight bit more than 12v, possibly up to 13v.
 

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I would look into a variable 24V driver. They can be found cheap on ebay and will provide what you need in both current and voltage.
 

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Discussion Starter #4
I forgot to mention that I have no idea if two of those LEDs will provide sufficient light, I'll be doing some testing to see how they compare against my Gixxer headlight. I'm prepared to use more LEDs or even use completely different LEDs so I'll just have to see how that goes...

In case no one picked up, I'm not only a CF n00b, but also an electrical n00b. Haha. I figured I'd have to get my head around this whole "electricity" dealy-o so I watched some vids on YouTube and did some reading. I had a couple of things wrong so hopefully I have got this straight now (feel free to tell me if I still have anything wrong here!)

Above I said "So a 1W LED is one that has a max drive of 1,000mA?" Well that's just wrong... :jpshakehead.sml:
mA is a measure of current and a watt is... well it's just a watt (I guess you could say it's a better measure of "power" rather than just looking at how much voltage or current something runs on). To find the wattage you multiply the Amps by Voltage, so a 1W LED would be one that has a 350mA peak drive and runs at 3.4V (.35 x 3.4 = 1.19, good enough to call 1W I guess).

To simplify things even more you can think of Voltage as being like the pressure pushing water through a pipe. Current is like describing the amount of water coming out of the pipe. Increasing the pressure causes more water to flow, and increasing the voltage also causes more current to flow. Which all of a sudden makes sense as to why you need to increase the forward voltage when running LEDs in series... more voltage to push the same current further down the line. Got it!

So going back to the XP-G2 LED I was considering, each emitter has a forward voltage of 3.1V @ 1500mA (max drive), making the emitter 4.65W. Let's say 4.5W. The actual LED has 3 emitters, so 13.5W per LED, 27W of light with two of those LEDs on max drive... could be promising!

Anyway - DecepticonDon, what exactly do you mean about running the power after R/R (just haven't seen that abbreviation before)? I was not too worried about the voltage fluctuating, all of the drivers I've seen (aside from those cheap "bare" drivers, need to get a datasheet on them) have a fairly wide range. For instance the FlexBlock has an input range of 10-32V so you're pretty safe there.

Cheers mvrk10256 for the tip on eBay, just had a quick look now... However now that I have an accurate gauge what kind of wattage I need (13.5W per LED max) I will need to re-think what driver I'm using... I think I'll put a hold on that for the moment, I need to get my hands on those LEDs first up and see what kind of mA i'm going to be happy running them at, then choose a suitable driver. Seems like the best way forward.

Also if anyone has experience using these newer LEDs I'd be interested in any input about the brightness at different mA. I was also looking at the CREE XM-L2.
 

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Elbow Grease is Cheap
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R/R is short for regulator/rectifier. Not only does it regulate the power, but also changes the AC power coming from the stator into DC. I'm pretty sure you need DC to run the LED's.

Scratch that, it can be done on AC. But what I saw was from constant voltage from a wall outlet. and more complicated circuits. also, your light will change throughout the rev range.

I don't know too terribly much about LED's, except for wiring a few into some guitar pedals and amps. Found this to be really useful. :D
http://ledcalculator.net/

This guy just posted this. may want to ask him a few questions.

http://www.customfighters.com/forums/showthread.php?t=65099
 

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Discussion Starter #6
Ahhh... R/R, gotcha! That would be the heatsink looking thing that usually bolts onto the frame somewhere...? No problems, was planning on using that, just using the stock light wiring for these LEDs. DC is definitely the way to go (making this kind of thing from scratch is tricky enough for me without added trickiness!)

Cheers for that LED Calculator link, that will definitley come in handy when I get around to building the indicators and brake light.

And thanks for the heads-up on that other thread - that definitely answers some questions!

So looking at these comparison shots here we can get an idea of what kind of light an XM-L (or two) puts out at 2100mA.

Both LED and incandescent lights on:


LED only:


Incandescent only (on high!):


So, I don't think any more light than that is needed! Those picture show 2x XM-L being driven at 2100mA. For comparison we can look at the datasheets to get some kind of idea as to how an XP-G2 will compare. 2100mA on the XM-L means it's being driven at 75% of maximum (3000mA max). So we'll compare the XP-G2 being driven at 75% of max. as well:

XM-L @ 25ºC
2100mA = 625lm

XP-G2 @ 85ºC
1050mA = 299lm * 3-up = 897lm

I multiplied the XP-G2 lm rating by 3 because I'm looking at using a 3-up star LED. The XM-L is physically larger emitter, only available 1-up. The datasheets only show that info for XM-L at 25ºC, whereas XP-G2 shows it at 85ºC. The lumens output will decrease with temperature increases so the XM-L data has an advantage there, but from that we can expect that a 3-up XP-G2 LED will be noticeably brighter. I just based the calculations on neutral white, taking a lm rating from around the middle of the bin ranges (different bins have different specs, some lower & some higher light output).

Based on that I'm kind of thinking that a single XP-G2 will be fine for "low beam". The other thing that you'll notice from the comparison photos is that the LED is visible from a large angle, easy to blind oncoming drivers. Those photos show it using an elliptical lens, so that's better than a plain lens (at least the beam is wider than it is tall). But I'm going to search around and look for a reflector as that will give much better throw and also avoids the problem of someone accidentally looking directly into the LED. Not sure how much the elliptical lens obscures the LED, but looking directly into a power LED is a big no-no. The other worry is that if I happen to pass an oncoming police car and he happens to look into the light, most likely he would get blinded and turn around to give me a ticket. One defect notice is one too many... and I've already had that experience!

Although there is also the option of a collimator. Reflectors provide spot and spill, I think it's the spill that is the problem for oncoming drivers... It seems that collimators tend to absorb more light, but the light that the do put out tends to be much more in the spot - say 80% in the spot and 20% spill, whereas a reflector would be more like 50% spot and 50% spill.

So the plan now has evolved to use a 1000mA driver, with a switch between the driver and 2nd LED to turn it on for "high beam". That seems like the most simple solution... I would like to use a driver with dim function and always have both LEDs on at the same time, but I'm not sure how to wire up a switch to a preset dim level. Maybe I will try and find something there... it would be a much nicer solution for sure.

I will post back when I anything new to report...
 

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Hi folks,

Just wanted to post here to see if I can get a bit of help as well as just collecting my info together to try and sort this out & get it all straight in my head...

What I'm planning is to run LED lights direct from the stator (no battery, it's not actually a streetfighter, but a KTM 380 EXC supermoto that I'm building. I figure the lighting theory would be relevant to other bikes as well and you could just as easily run it from a bike that uses a battery - so hopefully this can be informative for anyone else thinking of building their own headlight from scratch). Here's the basics, I just need to fill in the bits in the middle:

Power Source: 12V, 130W

LED: CREE XP-G2 (3-up on star PCB), planning to use 2 of these in series
Stats for individual LED
8.4Vf (typical forward voltage at 350mA)
1500mA maximum drive​

I've been trying to find which driver to use. Ideally I'd like to have one driver for both LEDs to keep the install nice & minimal and parts/weight to a minimum. But driving two of these in series means that the Vf increases to 16.8V. The only driver I've seen so far that could handle this is a FlexBlock boost driver, but the max output is 700mA. I'd like to be able to drive the LEDs at something closer to their max, for whenever I need hi beam. (Not that I'm ever likely to need to use hi beam continuously, but I'll be using a heatsink anyway so I'm not worried about heat damage etc.)

I found that FlexBlock driver on LEDsupply.com via their driver calculator.

I also found some much cheaper, basic drivers on LEDsales.com.au. These are only $3 each compared to $18 for the FlexBlock driver, so it almost makes sense to use one driver for each LED: Bare switchmode LED driver for one 1W LED
http://www.ledsales.com.au/catalog/...roduct_info&cPath=148_182_184&products_id=614

First thing that confused me was the description for that switchmode driver. It says it will drive a 1-watt LED at 350mA. So a 1W LED is one that has a max drive of 1,000mA? Is that correct? But then why only drive it at 350mA...? If someone can help me figure that out I'd really appreciate it.... :help0:

Regardless of which driver I use and what power I drive the LED at, I still need to figure out how to run a hi/low beam... From what I've been able to learn so far, to do it properly i would really need another driver on the low circuit lets say? Or I guess I could wire in resistors after the driver to drop the current for the low beam... placing the resistor after the driver - would that still result in a fairly constant current? The current into the resistor would be constant, so current out should be... but I'm not at all an electrically-minded person.

Another option is a dimmable driver, and wire it up so that the hi/low light switch just dims to preset values? But those drivers are $20, and only 700mA and that's the only suitable one I've found so far.

Thanks for any help that folks can offer on this. I will probably have more questions, but need to get these couple of things straight in my mind before I start thinking about other stuff.
Interesting post. I think your post is helping lots of individuals and now I am considering to get these led lights very soon
 

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Discussion Starter #8
Cheers RaymondWarner. (And welcome to the forum!)
I was sure that I wasn't the only person out there wanting to know more about LEDs... hope this thread does help out some people, because it sure isn't as simple as wiring up a small $0.05 LED onto an AA battery!

I hadn't forgot about this thread - just that the lights were always a low priority until I get the rest of my build nearing completion. Still glad that I started looking into this when I did because it's taken many hours to find a combination of optics (reflectors, lenses etc.) that will (hopefully) be suitable for use with the 3-up XP-G2. Now I've got the optics, or at least two possible options sorted, I was just getting ready to order some bits and pieces and realised that I need to select an appropriate heatsink as well. Well... Now I start to understand why larger emitters like the XM-L exist...

Going back to the comparison and adding in the newer XM-L2, this time also comparing the driven wattage, which will determine the size of heatsink required:

XM-L @ 25ºC
2100mA = 625lm
6.6W (94lm per Watt)

XM-L2 @ 85ºC (U2 bin)
2000mA = 728lm
6.3W (115lm per Watt)

XP-G2 @ 85ºC
1050mA = 299lm * 3-up = 897lm
9W (99lm per Watt)

The lumen ratings for XP-G2 and XM-L probably aren't so accurate since I just estimated those figures based from graphs etc., didn't get the numbers by using an actual bin for reference. An interesting side point on "bins", I finally found out what they're all about. The bins represent a 7% increase in efficacy. So you start off with more common bins like T2, then it goes up to T3, T4... I think the U bins are currently the highest, U3 being the best you can get. So if you have the option of choosing between a T3 and a U2, better to go for the U3 option and get more light!

So the 3-up XP-G2 ends up being a 9 watt LED because of the 3 emitters on the one board! I won't go into all the details, but I just spend a little bit getting a quick overview on thermal design (there's a great video here if you want to learn about that. It's not all that difficult, same principle as basic electronic circuit design: http://youtu.be/8ruFVmxf0zs)

Anyway if I understand this all correctly, here's what it should work out as:
Based on using this heatsink (44mm dia. x 40mm high) in a steady-state setup, just sitting in free air, no active cooling.
Using an XM-L2 driven at the above specs, based on 35ºC ambient temp (just to give a good margin since I'm in Australia after all) I worked out the LED junction temperature would be 148ºC.
Using the 3-up XP-G2, based on same ambient temp. and driven at the above specs, on the same 44x40mm heatsink the LED junction temp. would be 210ºC.
Now keeping in mind that the maximum junction temp. for both LEDs is 150ºC, the XP-G2 would fry itself! The XM-L2 is very very close... actually I didn't take into account the PCB between the heatsink and LED emitters, so that would add about 2°C/W (this is the amount that the temperature rises when you apply 1W of power), so that brings the XM-L2 to around 161ºC, the XP-G2 would be around 228ºC.

That shouldn't be surprising since that heatsink description says it's suitable for 1W to 3W LED, so the only solution is going to be to throw a bigger chunk of aluminium at it... but after those rough calculations I'm thinking that it may not be worth using the XP-G2 3-up LED after all. Unless I did add a little 12V fan to cool things down, but I want to keep this as simple as possible.

Looking for higher power LED heatsinks, you can definitely get them - for example something like 95mm dia. x 39mm high can apparently be used for a 40W LED! But that has much better thermal performance of 2.2ºC/W compared to 15.5ºC/W of the heatsink in the above example. Also if you look at LED downlights and LED globes, they all seem to have a self-contained heatsink that doesn't seem all that big - plus they're just sitting around in a ceiling cavity with not much airflow, so it makes me think that a good heatsink design is key - there should be a way to get sufficient cooling without having a crazy big heatsink.

Anyway, back to Google now while I try to find a better heatsink. Then I've still gotta find out if it's feasible to wire the LED driver to work with a dim function from the hi/low switch... I'll probably be back in another month! :shootme:
 

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Elbow Grease is Cheap
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How about modifying a heatsink from inside a junk computer? check out this heatsink from a Pentium II processor. Yes its large, but The cooling fins are deep(about 1 inch) and its shape could easily be altered to fit your application. the smaller one still on the circuit board is from a junk guitar amplifier.



 

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Discussion Starter #10 (Edited)
Yeah, CPU heatsink would work I'm sure - guaranteed if you had a fan on it! But for this I'd prefer to use something that I know the specs of. Not especially for this light I want to build now, but after this I'll probably do an endurance style headlight for my Gixxer so the experience I gain in building this one will just help later.

Speaking of super-duper high power LED lights - I think I found a solution!! These guys have a bunch of heatsink options, and you can either use them as a passive sink, or you can add their active cooling element as well. The good thing is that it's not actually a fan (less moving parts, they say the cooling unit will outlast the LEDs by a long way, up to 100,000 hours), not sure exactly how they do it but there's some oscillating diaphragm inside the cooler that moves air over the sink. Even better they have outdoor models available which are waterproof, shock & dust resistant etc. Good stuff: http://www.nuventix.com/led-cooling/led-heatsinks/

Another option are these ones: http://www.led-heatsink.com/products.php?scateID=82&tag=CATE348

I did some more quick calcs and using the Nuventix 34W sink would bring the 3-up XP-G2 down to 97ºC and the XM-L2 would end up at 69ºC. The MechaTronix 70mm dia. sink would be okay just for the XM-L2, putting it at 92ºC. I'm sure the actual heats would be lower on the bike because of the moving air, but I'm just wanting to play it safe and leave some decent headroom. Not only because an overheated LED will have a shortened life, but it will also reduce brightness and even change the colour of the light. "Plan for the worst, expect the best" has been my motto...

Seeing as I will have two LEDs (of which ever I end up going with), I don't really want to have two massive 70-90mm diameter heatsinks there... but the calculations get a bit more complicated when you add two components to a single sink. No idea how that all works out, so this is a part where I will have to kinda wing it. Although I did find something of a rough guide that could be useful...

As a general rule of thumb, for a well-ventilated heat sink, there should be 10 square inches of heat sink for every 1 watt of power dissipated. The use of pinned heat sinks, however, is not recommended.
One other thing I should keep in mind is that all the calculations so far have been at the max. power I'd be driving the LEDs at, which would basically be high beam, so not actually used all that often for me on the bike this is going to - just there for safety and to provide some appearance of road worthiness and compliance with Australian Design Rules!

I think I've just about got everything straight in my head now. I'll use a 45mm dia. reflector, with a 20mm elliptical lens placed at the base of that to try and cut down on the amount of spill. Will probably have to modify the reflector to fit, but no problem. The LED will sit directly behind the lens, and it will be mounted to the heatsink. That's still the tricky bit because I'm imposing some fairly tight fitment requirements on myself! I'm aiming to make a headlight unit that looks something like this:



Except that it's not actually a headlight to start with, but I'll be trying to squeeze the lights into that lower section where it just looks like there's a grille.

Only remaining thing to sort out is the driver and hi/low function. I am fairly certain that I have this sussed out, but earlier today I posted on an electronics forum to try and get some clarification on this.

The driver I'm looking to use is the A009 BuckBlock, here's my plan to wire up hi/low, and an on/off switch for track days or whenever I need to tail someone:

EDIT >>
Uploaded new diagram, since my first one was full of n00b errors. Haha.
Not sure if it makes a difference whether the on/off switch is wired to Vin or DIM, but the data sheet only mentions on/off function associated with DIM, so I put the switch there. I suppose it could be on Vin, still don't know if there's any real difference?



This will also give a low beam trim through the use of a potentiometer, so the brightness of low beam can be adjusted (if wanted, this could easily be replace with a resistor once the right brightness level has been found).

But I'm just not sure on this diagram that's in the driver datasheet:



Now I just can't figure out how that functions as an on/off switch??? The way I see it, there will always be current flowing through the red highlighted section, you could remove the switch and it would function just the same?

It does look like possibly a more simple option to give high/low beam functionality? Since the highlighted area would be like an always-on low beam, and once the switch is closed/activated there should be full current flowing? (The POT remains live, but the switch can pass full current?)

If anyone can please explain that to me I'd be massively appreciative!

EDIT >>
The on/off switch there would only control the POT function. Basically giving a hi/low switch only. Current will always flow through the POT which gives your low beam, and when the switch is engaged the current will take the course of least resistance through it, bypassing the POT to give high beam. Just thought I'd better explain that for anyone who started wondering the same question as I did.
 
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