Newb project, CREE Q5's for automotive use?

I am an avid off-roader (4-Wheeling) and I want to build some "Rock Lights"

(Basically a way to illuminate the ground under my truck at night)

These will not be used to make my truck look cool, they will be purely utilitarian!

this is a similar/identical project
https://www.candlepowerforums.com/threads/196510

Goals

• I want to use 8 or so CREE LED's with a chunk of aluminum as a heatsink and a chunk of lexan or similar plastic as a "lens"
• Simple to wire to the 12V system
• Bright
• as FLOODY as possible, the distance from the light to the ground would be about 2-3' (this will probably depend more on my "lens" which is basically a frosted lexan cover)

Questions:

• I hear the buck pucks by LUXDRIVE are common and easy but I was wondering if there was a cheaper way, also how do I wire these? do I need one per LED? is there a cheaper LED buck driver that I can use?
  
• I want to make these so I can wire 12v to the led assembly, this will be switched, if this is exceptionally more expensive then I will use one driver for more then one LED.
  
• I am not worried about the mounts, I understand that I need a decent heatsink and use thermal epoxy to mount the LED to the heatsink, thats not the issues... I am a mechanical engineering student and sorta struggle with the electrical world.

How do you recommend I do this? I want to learn how the electronics work and why, but I want them to be simple to wire. I know my friends will want a set once I finish the first batch in my manufacturing class.


here is a picture of a product made by Vision-X, this is the effect I am looking for but I want something brighter, thus the CREE Q5's
http://www.wanderingtrail.com/Mods/JKmods/Tantrum/images/IMG_3641.jpg

-Zach

How about using 3 per side ( 3x 3.7vf= 11.1v) and wire them up using a resistor. Not the most efficient way but for a car who cares! Also very robust.

It's not just efficiency! A resistor with three LEDs in series will mean there will be quite a bit of variation in the voltage the LEDs get when the engine is running and when it is not. It's so easy to avoid that problem, and suitable drivers start from under $2 each. http://www.videofoundry.co.nz/ianma...pe=buck&v_in_min=10.5&v_in_max=14&order=price

BTW, posted pics should be 800 pixels max width, and are you paying for its hosting? http://www.candlepowerforums.com/Rules.html#siglines. (It's a nice pic though.)

Picture will be re-hosted tonight, for the time being I changed it to a link...

A cheap driver makes sense but the resistors would work too. I have to admit that my electrical understanding here is pretty limited. Would the variation in current be an issue? Won't that only affect the brightness of the LEDs? This should only be used when the engine is running ~14.4 volts

-Zach

Assuming a max of 14.4 volt and a minimum of 12.4 volt there is a 2 volt swing. Calculate your max current for the max voltage and accept that it will be dimmer with the engine off ( as will all the other lights on the truck but to an even greater lever hue to them being incans).

No its not the best since its not constant current but it is very simple, reliable and robust.

Phantomd aka zach said:

Would the variation in current be an issue? Won't that only affect the brightness of the LEDs? This should only be used when the engine is running ~14.4 volts

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Yes, it would only affect the brightness (possibly significantly), but if your engine will be running whenever they're used you avoid that issue, so either a resistor or driver would work well.

With the engine running, as Packhorse said, efficiency won't be an issue - you won't be wanting to get the most possible light before your battery goes flat, for example.

Packhorse, sounds simple enough...

as long as I dont overdrive the LEDs the only consequence would be heat from the resistor and a lower light output when the voltage drops, assuming I set it up to see a max of ~14.5volts?

I am assuming that if I were to set up each individual LED with it's own resistor (so I can just wire 12v directly to it) it would be far more inefficient and create more heat then wiring them end to end with one resistor driving them all(in series?)

This would be because it has to limit far more current PER LED then if I were to have them in series?

as I said earlier my electrical knowledge is not the best.

I found a DX product that is a drop in that has a driver built in, although its an R2 bin... ~$8 USD at the quantity I would need, might be a simpler way to do it.

I was planning on sourcing my parts from wither newark.com or DX

-Zach

Phantomd aka zach said:

I am assuming that if I were to set up each individual LED with it's own resistor (so I can just wire 12v directly to it) it would be far more inefficient and create more heat then wiring them end to end with one resistor driving them all(in series?)

Click to expand...

If the LED is run at a high current the resistor would get toasty hot - melt plastic, burn fingers. For example, dropping 10 volts at 1 amp means 10 watts heating the resistor. That's when a driver really is a better idea. (Mind you, even 3 W dissipate by a resistor feeding three LEDs still produces enough heat to melt plastic.)

Wow, alright... I guess I will go with a driver...

however, now I will need more handholding...

I dont know anything about how they work...

could I get a buckpuck and wire all 8 LEDs into it?

-Zach

Phantomd aka zach said:

could I get a buckpuck and wire all 8 LEDs into it?

Click to expand...

From the specs in my list, no. They can drive a maximum of six LEDs in series, but you don't have enough voltage for that. If you put the LEDs in two parallel strings of four LEDs each string that wouldn't give you any headroom for the driver to operate (normally 0.5~1.5 V above the total volts needed by the LEDs at whatever drive current you've chosen). Four parallel strings of two LEDs each would be doable, but then each string would only get about 250 mA if you were using a 1,000 mA Buckpuck - not bright enough. Also, small differences in the forward voltage of the LEDs will mean the parallel strings will draw uneven shares of the current. Drawing more current will mean they'll heat up more, and so get hotter...

Do you know what parallel and series means? (Forgive me if that's too basic a question.)

And the buckpuck looks quite expensive compared to many you could buy that would do the job - for example, there's a four pack listed just above it (alphabetically) for under $7 that would do for all 8 LEDs. In the last post in the other project thread you linked to, Nitroz recommends the Kennan driver, which has been superceded by drivers like those in the 4 pack.

Are you thinking of one LED in front of and behind each tyre, as mentioned in the other thread? Or two LEDs on each corner? For both of those setups it would probably be easiest to get four drivers, each one driving the two LEDs for each tyre.

Either way, with your headlights turned off you should have plenty of light. This is a really cool project. Hm, I could make some AA-powered magnetic mount ones...

Ok, I am going to totally re-write this post... I have learned lots since I posted it.


So here is what I was thinking...

Run two XR-E P4 leds (sku 3417) using one Driver (sku 13557) make a heat sink out of some aluminum (like the greatlakes4x4 guy **link below**) and a plexyglass cover "lens" use some thermal epoxy to seat the LED to the aluminum.

I would wire these in series correct?

do I need to worry about heat-sinks on the drivers? The DX page has some issues with the diodes failing, but since I am running DC I should be fine... correct? or I can bypass the diodes.

great lakes 4x4 rock light page
http://www.greatlakes4x4.com/showthread.php?t=81920

-Zach

I dont see which drivers and 4-packs you are talking about? EDIT: FOUND IT! that page is difficult to read for me, it does not handle the long text box well.


I like the 2 LEDs per driver per tire suggestion. I keep editing this post simply because I keep learning and understanding more. I guess I need to look up some data sheets on the LEDs I want to use. I dont yet understand the relationship between output current from the driver and how that would effect the two LEDs in parallell/series, in parallel they would see the full current but half the voltage? or would that be series??

EDIT: read the XR-E data sheet here, 350mA is the suggested but you can go up to 1A, what would be the consequence of running them at 700mA? These will probably be running for up to 4-5 hours at a time, so I would assume that a lower drive current will reduce heat?

OK, here are some DX links...

can I use this driver to run 2 Leds?(EDIT yes) (mr16 base driver)
http://www.dealextreme.com/details.dx/sku.13553

the leds being these ones? (q5 bin)
http://www.dealextreme.com/details.dx/sku.11022

These ones are cheaper! (p4 bin)
http://www.dealextreme.com/details.dx/sku.3417

I dont know what those are supposed to be driven at though... (EDIT 350mA to 1A)


can you tell I am trying to do this as cheaply as possible? and that I have no idea what I am doing? however I am learning A LOT!
-Zach

Click to expand...

Those aluminium and plexiglass LED holders are great - they're simple and effective, and the aluminium would act as a pretty good heatsink. Yes, the two LEDs would be wired in series.

Yes, the rectifier diodes in the MR16 drivers can be bypassed if you're going to have them permanently connected. You could probably use the 700 mA version (sku.13557) without heat issues, or maybe even change the set resistor to run it at 1 amp. With the two LEDs in series being fed 1 amp (or whatever), each LED will get 1 amp and enough volts for it to draw 1 amp, however many volts that might be - the constant current driver changes it to suit, in order to keep to the set current level.

Honestly, doing a project cheaply sounds like a really good idea if it's your first project. You'll probably enjoy doing it more if you're not as worried about stuffing it up or it being a very costly learning experience. Using the 16 mm round base will be very handy for inserting the LEDs into a machined aluminium panel.

Can you please post in the driver list thread to explain the trouble you're having viewing the list.

Hi,
I've found these to be adequate and cheap for mounting leds http://www.dealextreme.com/details.dx/sku.8941 you can remove the fan, use some thermal epoxy to mount the driver and then pot it in epoxy resin. I made a light for a mechanic mate some time ago now using one of the drivers Torchboy is recomending and it's still working ok
Torchboy. Would it also be a good idea for Zach to connect a capacitor as supplementary protection for these drivers as in for the buckpuck in this thread? https://www.candlepowerforums.com/threads/208756 I've had a couple of the cheap MR16 drivers fail (without capacitor) when using an old Scalextrix transformer but the buckpucks are still going strong. The MR16's had been fine for months until I changed the power supply to the current very possibly "dirty" one?

Paul.

Paul Baldwin said:

I've found these to be adequate and cheap for mounting leds http://www.dealextreme.com/details.dx/sku.8941

Click to expand...

I bought one of those a few months ago! I haven't got around to using it yet, but it certainly looks nice, and the fins have a nice ring when struck/plucked.

Paul Baldwin said:

Torchboy. Would it also be a good idea for Zach to connect a capacitor as supplementary protection for these drivers as in for the buckpuck in this thread? https://www.candlepowerforums.com/threads/208756

Click to expand...

Ummm... Sorry Paul, I'm not an electronics engineer, but I guess the only thing it would affect (apart from long term reliability and total project cost & hassle) would be efficiency - maybe - and even if it does we've already decided that isn't a big issue. Yes, you could add the capacitor/s if you were sufficiently keen, but I've only ever had one driver, er, LED driver die in my car. That was probably from overheating, not being spiked, so it hasn't been a big problem for me personally. If the LED lighting wasn't mission-critical I wouldn't bother.

If the maximum voltage coming from the alternator is 14.4v, and the drive voltage of the LEDs is 3.7v, you could just wire LEDs in sets of four in-series and not need any resistors at all -- the resistance of the LEDs will be sufficient to keep current flow under control. That's the simplest (i.e. most durable) solution.

Yes, it will dim when the engine is off, but if you've discovered a way to go rock-crawling with the engine off, I think you've missed your calling and you should be working on free-energy patents instead of LED lamps.

Having fully read that thread, like one of the posters I'm also not convinced the Buckpucks died from spikes. I would have thought venting with smoke would just about be lightning strike territory. An underrated or poor quality component overheating seems more likely.

And FWIW I think the driver that I mentioned died in my car actually went intermittent. I couldn't see anything obviously wrong and it wasn't worth trying to figure out if it was a poor solder joint or a dodgy component so I just replaced it with something that turned out to be better (one of the MR16 drivers - the on-board rectifier was ideal). Which perhaps raises a good idea: Get the odd spare driver.

fyrstormer said:

If the maximum voltage coming from the alternator is 14.4v, and the drive voltage of the LEDs is 3.7v, you could just wire LEDs in sets of four in-series and not need any resistors at all -- the resistance of the LEDs will be sufficient to keep current flow under control. That's the simplest (i.e. most durable) solution.

Click to expand...

Maybe. We had a discussion about it in one of the car cabin light threads. I've seen pros and cons for doing it, with the main one being the variability. As you said, it wouldn't be a problem if you never want to just show off while the engine is off.

Most LEDs need less than 3.7 V for 1 amp (even the highest Cree XR-E I've seen was only 3.6 V when cold), but with the wiring resistance you'd very likely have less than 14.4 V where it's needed anyway. So that sort of evens out. With reasonable heatsinking their Vf wouldn't drop very much, so current draw shouldn't get too high.

Simplest may not be the most durable when it comes to engine spikes. I honestly don't know how big a problem it is when starting the car, but it's something to avoid if possible. Is it possible to wire them so they get turned off when the starter motor is cranked?

The only other thought I have is the practicality of running a wire across or back along the car from the pair of LEDs for one tyre to the pair of LEDs for the next tyre. I suppose it would be about the same difficulty (ie, not very) as running power to each pair if they were using a driver.

BTW, this thread should be in the automotive section.

The wiring is not a worry, wiring under the truck is relatively easy...

The voltage should drop dramatically when the vehicle is started and will not pick up till the engine RPM gets moving, you should only see a spike with a bad alternator... the voltage should be pretty stable (at least no spikes).

I plan on running these from a fuse box that is tied directly to the battery on it's own cable. I will have some other accessories attached to their own fuses from this fuse box. (CB/HAM radio) so that worry about RF output is relevant to me.

-Zach

I just thought I'd point it out as being a potential problem as I'm making a worklight at the mo for a mates Landrover and thought it may be relavant, particularly after a conversation recently? I spoke to someone who had been selling the cheap 12v led lights to people on canal boats/caravans, they've had so many returns they stopped selling them. I just thought a few capacitors wouldn't hurt as they are only pennies and easy to wire
Great project by the way Zach :twothumbs some of those rock crawlers are impressive bits of kit!

Paul.

I didn't see anyone say this but I am using lm317's to control the brake lights and the undercarriage lights which are blue cree's (I am using them for the cool factor) all I am using is two pieces the regulator and a resistor setting the current to what ever I need. All the parts can be potted in some silicone for protection. I may need to add a cap I havent checked everything yet.All the parts for 15 regulators ( running around 3 white or 4 red leds each) were less that 30$ total.

Chris