Question for the light guru's - driver/LED confusion

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Question for the light guru's - driver/LED confusion

26 posts & 9 voices | Started 1 year ago by stumpy01 | Latest reply from Luminous

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stumpy01 - Member

With the help of Trout, Chucky@vortexracing and probably a few others, I managed to convert one of my Lumi LED cans (and a mates too) a while back with on of the Teapot/BlackCatTech drivers and Cutter LEDs.

It works pretty well, but I am not sure that I need the run time I am getting from the light as it stands. I ran both lamps set to high as a test and got 7hrs 20 mins run time. My mate ran his last night on it's own as he's doing the D2D solo and he gave up this morning after it had been running for 13.5hrs and he had to leave for work!! I am assuming he'd have got 14hrs 40 or so from the single lamp....

I am tempted when I convert the next one to go for a bit more oomph, but am unclear how to best go about this, being an electronics Neanderthal.
If I use the same driver but use a 4-LED board instead of 3 will output of the driver be divided by 4, rather than 3, resulting in the same overall output (just lower per LED)?? Or does each LED get the 675mA output, making it a 1/3 brighter than the 3 LED one?

It would be cheaper I guess to swap the LED driver for the 975mA version, but would this cause overheating problems with the driver, as it has no heatsinking....? And as I understand it, the LED output tapers off as you get to the upper ends of it's operating range so this might not give as much light?

I guess for the full whammy I could get a 4 LED board and a higher output driver?

Posted 1 year ago #
stumpy01 - Member

Trout......

anyone.......?!

Posted 1 year ago #
funkynick - Member

Without knowing the particulars of the driver, it's almost impossible to say exactly, but I would expect that the 3 LEDs are currently in series (wired one after the other) so the full 675mA flows through each.

Now, adding a 4th LED in there might be a little tricky, as when you pass the current through an LED about 3V-ish is dropped across it. With them all being in series, one after the other, this voltage gets added up. So with 3 LEDs they have a combined voltage of about 9V (probably more like 10V though). Adding a 4th LED in will raise this to around 12-13V which is getting a little close to the battery voltage (14.4V for Li-Ion), or may even be above it if you are using NiMH (13.2V).

Does that make any sense?

Anyway, why not just stick with what you have and get a smaller battery?

But if you really do want more light, I'd say that you'd probably be better off going for 3 higher current LEDs (or the same LEDs you have if they can handle the extra) and driving them harder with the other driver board.

Posted 1 year ago #
funkynick - Member

You know, this 'ere LED stuff might actually catch on one day... I might have to design my own driver for these... *thinks*

Would having it USB programmable be a little bit overkill?

:o)

Posted 1 year ago #
Luminous - Member

if I use the same driver but use a 4-LED board instead of 3 will output of the driver be divided by 4, rather than 3, resulting in the same overall output (just lower per LED)??
Or does each LED get the 675mA output, making it a 1/3 brighter than the 3 LED one

Depends, if you've wired them in series, then yes, they all get the same current of 675ma, being delivered to them from the driver.

As you know, Trout is our resident BCT LED driver expert, apart from the chap who produces them, of course.
So, I can't say whether the BCT driver needs significant, dedicated cooling.

LEDs are more efficient at some point down the curve, away from their peak output.

This leaves us facing the choice, do we add more LEDs and enjoy each LED operating closer to its peak efficiency, or do we keep the number of LEDs to a package space friendly quantity, and just up the current.

Its my humble opinion that between 3 - 6 LEDs should be enough.

What voltage battery are you using ?.

Any pics of these converted lights ?

Posted 1 year ago #
Luminous - Member

Would having it USB programmable be a little bit overkill

Where do I sign ?

Posted 1 year ago #
stumpy01 - Member

Yeah - they are the MR11 LED boards from Cutter and I believe they are on the board in series. The conversion stemmed from the thread about a year ago that Chucky@vortexracing started up after he converted some Lumi halogens.

I see what you mean about the voltage across the LEDs perhaps being a bit tight to the upper limit with the 4th LED - thanks for the explanation. I am using the Lumi Endurance battery which I think it 6.6A/h 14.4V.
I could go for a smaller battery, but thought it would make more sense to tinker around a bit more with the cans. It seemed to make more sense to get more light out of the existing battery than having to purchase a new one.

I perhaps need to e-mail teapot (BCT) regarding the potential heat build-up of the higher current driver.

I only have beam shots of the converted lights, Luminous. I thought I had posted them on here, but can't find them. I didn't bother putting pics of the conversion up as they are pretty much the same as here:

http://www.singletrackworld.com/forum/topic/lumicycle-halogen-to-led-conversion-with-piccies-and-a-step-by-step-guide

The light is pretty bright to be fair, and if I converted the second can that would be plenty enough. But, I thought it wise to question whether I should convert the second one in the same manner or do something a bit different.

Posted 1 year ago #
nockmeister - Member

Was a brilliant conversion...mine, used in anger last night

Posted 1 year ago #
stumpy01 - Member

Yep, it is a very neat conversion - I didn't bother with the external heatsinks as I had some heatsinks made that attempt to increase the area in contact with the side of the can. Seems to work, although hard to know.

nockmeister, I only did one can initially to see what it was like and whether it seemed reliable. What driver did you go for? 675mA or 975mA? If you went for the higher one, how do you find the heat build-up....?

Posted 1 year ago #
nockmeister - Member

Yep using the 975ma BCT. I've got a 10mm Ali slug in both cans which the LED boards are epoxied to with Artic Silver and still they get very hot, can't quite remember the temps, but with airflow it's not a problem. I did the resistor thang, so always swith to half power when still.

Can't wait to suppliment them with Trouties DIY head mounted project!

Posted 1 year ago #
stumpy01 - Member

Hmmm, might give the 975mA ones a go for the second can.
I'll probably use that with the 'medium' optic for some flood and keep the 675mA one using the narrow spread.

I just bought a spokeshirt light for use on my helmet so I think I am getting towards not only being over-biked, but over-lit!!

If 2x675mA ones lasted 7hrs 20mins, the 675/975 combo should still manage 5hrs or so on high, with the option of switching to low.

Posted 1 year ago #
stuey - Member

Nockmeister - great heat sinks did you make them yourself or can they be easily purchased?

Posted 1 year ago #
TandemJeremy - Member

I would go for the 975 driver - you get a bit more light ( but less efficiency) that way

usualy the drivers don't need heatsinking - its the led boards that do. When I converted a lumi can I use a bit of 5mm alloy behind the led board that was a tight fit in teh can to get good heat transfer - this was OK with airflow but not when still - but I used a taskled driver which you can alter the power levels and has a thermal cutout on it

http://www.taskled.com/bflex.html

Posted 1 year ago #
BlackCatTech - Member

Sorry I'm a little late in to this thread.

My feeling is that the halogen can isn't up to dissipating the heat from three LEDs at 1A without an extra, external heatsink. A larger internal slug helps but really you need the surface area and preferably a thicker can in the first place.

You can go to 4 LEDs if your battery has the voltage - assuming XPGs these are about 3.3V at 1A each so 13.2V for four. Then add 1V drop across the driver gives a 14.2V load. The driver doesn't appreciate being run at full wack as it gets hot - really you need 16V to comfortably run four XPGs. It would run from 14.4V but you'd need to take steps to heatsink the driver as well otherwise you will be shortening the life of the IC.

Drivers will be available again shortly, I'm working on the group order for the DIY project first.

Posted 1 year ago #
stumpy01 - Member

stuey - I seem to remember them being heatsinks for R/C car motors. I think they are tthe right size for 540 motor heatsinks....

Like these, I think:

http://www.blacksmithproducts.co.uk/products.asp?cat=259&gclid=CLC7-NKMsKQCFUU14wodRQka1Q

Posted 1 year ago #
stumpy01 - Member

Cheers TJ & BCT.....

My heatsinks have a 6mm base with a thin sleeve that extends forwards from the LED board to increase the surface area against the can and is a very tight fit.

I think I will try the higher current driver and perhaps look at getting some of the external heatsinks I have linked to above.

I have posted some beamshots of the Spokeshirt light compared to one converted Lumi can here.....
http://www.singletrackworld.com/forum/topic/spokeshirt-light-beam-shots-pics-of-helmet-mount

BCT - I noticed you are a bit snowed under providing drivers for Trouts DIY class! I will keep my eye open on your eBay site for drivers. I also noticed you mentioned a Lumicycle driver on that thread.....what's the deal with that one??
The one I purchased previously was your 'normal' one that allows resistor dimming. Worked perfectly with a 200k resistor, so I'd be looking at trying the 975mA version of that, I think....

Posted 1 year ago #
BlackCatTech - Member

Hi Stumpy, The lumicycle driver is designed to solder direct to the LED board via a hole in the centre of the heatsink. It also keeps the driver out of the way as it sits inside the heatsink. It does mean however that the size of the heatsink is limited - about 3mm thickness at the centre. It has the dimming mode built in as well as the shutdown so you just wire the switch to the board with no external parts needed.

Otherwise it's the same circuit, just packaged a bit differently.

Posted 1 year ago #
stumpy01 - Member

a hole in the centre of the heatsink

Is this a particular heatsink design of yours, BCT? I remember you mentioning that you were working on a heatsink and specific Lumi driver a while back.

I'd be interested in getting hold of these, if they are available at 975mA. Do you have any drawings/pics of the design? It would be nice to have an integrated design as getting all the bits to fit in the original conversion was erm, interesting!

Right - that's enough for today!

Posted 1 year ago #
BlackCatTech - Member

Have a peek at the lumicycle conversion thread, I've just posted two pictures on there. The drivers can be set at 970mA, personally I'd recommend less than that for the halogen can but it is up to you really!

Posted 1 year ago #
fergusd - Member

My feeling is that the halogen can isn't up to dissipating the heat from three LEDs at 1A without an extra, external heatsink. A larger internal slug helps but really you need the surface area and preferably a thicker can in the first place.

Nah, I was skeptical also, but have been running 3 x XPG in a standard lumi can with no extra cooling with your 975mA regulator with no hassles for the last year, using a 8mm heatsink bonded to the MCPCB and coupled to the can using transfer grease . . . works fine so long as you are using it in moving air or a cold enviro . . . even then there is plenty capacity . . .

Posted 1 year ago #
trout - Member

Stumpy Hope you dont think I was ignoring you on the other thread
but by the time I looked here you had a load of answers .

Nice light NM be interesting to see/hear the comparison when you have do a Vagina light

Posted 1 year ago #
stumpy01 - Member

BlackCatTech - Member
Have a peek at the lumicycle conversion thread, I've just posted two pictures on there.

Oh yeah - I think I found them.. drivers with straight sides & curved ends?

No problems Trout - I figured you were busy....don't quite know how you are administering all those e-mail orders for LED parts that are flying around.
Why is your DIY light called a Vagina light....??

Posted 1 year ago #
trout - Member

some of the more cynical on here would probably say any **** could build one

but it rhymes with Regina the reflector

Posted 1 year ago #
Luminous - Member

Nockmeister.

One of the best looking conversions I've ever seen, good stuff

Stumpy, imo, you can never have too much cooling, its just about what the end result looks like, to a certain degree.

The RC motor cooling fins on NM's lights are a great touch.

Anyway, seems like you've a good handle on all this, so all thats left is for us to wait and see what you come up with.

I will try to get to the D2D on Saturday, to rec'y the course, if its makred out by then.

I've not entered, but I'd like to see the course.

You ride a Carbon HT specialized, no ?.

I'll either be on a black Stumpy FSR, or a black Kinesis HT.

Posted 1 year ago #
stumpy01 - Member

You ride a Carbon HT specialized, no ?.

I'll either be on a black Stumpy FSR, or a black Kinesis HT.

I shall keep my eyes peeled....!

No, I've not got a Spesh carbon HT. It's a Carbon Stumpy FSR - bare carbon & dark red bits......and I imagine it'll be sporting some fetching white crud guards.
Here's some gratuitous pics.....
http://www.singletrackworld.com/forum/topic/top-marks-for-specialized-warranty-new-stumpy-frame-content

Posted 1 year ago #
Luminous - Member

Yeah, thats the bike I thought you had.

Very nice.

Posted 1 year ago #

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