need help understanding constant current driver wiring

so im gonna need a driver that accepts 12vcd in, and aprox 2100ma-ish out. i wanna power 10 xml t6 to roughly 700 lm as im a bit leary of the reflectors. i thought i wanted this
http://www.luxeonstar.com/2100mA-Externally-Dimmable-BuckBlock-Driver-p/a009-d-v-2100.htm

It says in the description:
"Due to the nature of the buck regulator, the input voltage must always be higher than the total forward voltage drop of the LEDjunction(s) connected in series. For example, for a series string of four junctions having an average forward drop of 3.15V each, the required minimum input voltage will be 24VDC. Refer to page three of the technical documentation for the max Vout/Vin ratings for the various drive currents."

So, how would i have to wire the xmls ? im kinda clueless at this point. originally i thought i would wire all leds in series, as i do with my meanwell house driver(110vAC in )
then i read out voltage must be lower than input, so i thought - 5 pairs of 2 in series? i hope someone will chime in here, as using a constant current driver on an automobile is new to me.

btw, this is for my off road vehicle, my atv. this is primarily gonna be used for plowing snow from my long driveway. thanks!

1 power supply will not work for 10 of those. If you have a car input on 12v, you would only be able to drive 3 XM-L's in series . You will need to get 3 drivers, and power 3 XM-L with each driver. Here is a wiring diagram of how you can do this.

They also do offer a FexBlock which you can wire all 10 in series, however there is only a 700mA output, versus the 2100mA output so it will be Significantly dimmer. i would recommend then using the Cree XT-E, XP-E or XP-G since there would be a big cost savings on the LED cost. With the FlexBlock you can actually wire 14 of them with 1 driver to.

If you buy everything from LEDSUpply, you can get the 14 XT-E's and Flexblock for $71.19, and the 10 XM-Ls and 3 BuckBlocks for $141.1
Output of the 14 XT-E's will be around 3976 Lumen, the 10 XM-L's would be about 6400 Lumen
the XT-E's are much more cost effective.


Wiring with BubkBlock and XM-L;s

thanks for the detailed response.

I already have a most of the xml t6 around, and ordered some 30' and 45' reflectors so i wanted to go that route.
I was afraid i might need multiple drivers..

Is there a more "cost effective" way to drive these xmls as suggested @ 2100ma or is the buckblock my best bet?


Also, i am curious as why the xmls would only produce 3987? is that with a 700ma driver? i thought cree datasheet said xml @2100ma= 690ish lm each

Thanks!

Edit: im curious how cree light bars are put together . Do they also use multiple drivers?
And besides, im primarily only gonna use this to plow snow, so its more than likely gonna be cold out, as im in the Northeastern states. i wanna drive the leds hard for more light output as the heatsink will work flawlessly

I'm curious why you only want to drive the XML at 2100 mA, when it's rated for 3A. If you're worried about melting the reflectors, you should be more worried about burning out your LEDs.

An H6CC or h6Flex from Taskled could drive 6 XML at up to 3.3A each or 9 at 2.2A each. Or the HBFlex can run 10 at up to 2.1A, or 6 at 3A. The nice thing about the HBFlex is you can run all the LEDs in one string, which eliminates any concerns about different forward voltages, or one failed LED causing others to get overloaded (and destroyed).

poolman966554 said:

Is there a more "cost effective" way to drive these xmls as suggested @ 2100ma or is the buckblock my best bet?

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For a cheap and not-too-nasty alternative you could maybe try using multiple AMC7135 chips tied in parallel; if using the newer 380mA ones, you could use six in parallel to drive 3x XM-Ls @ 2280mA, or the older 350mA ones will give you the 2100mA. At those currents 3x XM-Ls will need a bit under 10V, so the 7135's will need to burn off ~2V, so 4-5W of heat there. Whack 'em on some aluminium exposed to the external air and it should be OK?

Rinse and repeat three times.

Check out fasttech, 10x 7135's cost about $2 shipped, so you can pick up 20x for under $5. Just solder them up in parallel.

You can get AMC7135's on boards built up at dealextreme and kaidomain pretty cheap if you don't want to build your own board.

But the vehicle voltage while running is likely to be closer to 13.8V than 12. In some vehicles it's over 14V. So you need to plan on burning off 3.9+ volts. Even at the lower 350 mA, that's 1.4W per chip. That would require excellent thermal management to keep them from overheating. It's not the total amount of power, it's getting it out of the chip that's tough. Not saying it can't be done, but you have to know what you are doing.

But it gets worse. Max supply voltage in an AMC7135 is 6V. So even if you use the trick of using the Vf of two LEDs to increase it, you will still be 7.2V, which the 7135's won't like at all. Running 4 LEDs may work, but only if the vehicle voltage is high enough to run 4 LEDs plus about 0.2V. Even then, if you do something silly like turn off the headlamp, or disengage the starter while the LEDs are on, the resultant surge could still overvoltage the 7135's.

Maybe you should check the B/S/T forum and see if there's an automotive driver thread there, or check out the automotive forum and see what others are doing.

As to how light bars are built, I suspect every one is different. I think it's CPF member BigToy that sells a light bar he made with 6 LEDs, either XML or SST-90, I forget. IIRC, he made a custom board with dual drivers for the 6 LEDs. As I posted earlier, there's no reason you can't drive 6, 8, 10 or more LEDs with single driver. You could build one big protection circuit, then use dozens of 7135's to drive LEDs. Is that one, or dozens of drivers?
Every design choice involves tradeoffs, and no two people will always make the same choices. Looking at what others have done is an excellent learning opportunity. But don't expect a single answer. There's very often not a single best design.

DIWdiver said:

But it gets worse. Max supply voltage in an AMC7135 is 6V.

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Ah. My bad.

Sorry i screwed up that math of the brightess of the XM-L's . it will be closer to 6400 Lumen, my bad...


DIW Diver - the LEDDynamics BuckBlocks are only rated at 2100mA as their highest output driver. I've spoke with them and last i heard they dont have plans for a higher output driver. As wel the 3 buclBlock drivers are almost the same cost as a H6CC and they come fully potted and waterproof already which makes them a bit more convenient to work with.

Thank you guys very much for your responses.

DIWdiver said:

I'm curious why you only want to drive the XML at 2100 mA, when it's rated for 3A. If you're worried about melting the reflectors, you should be more worried about burning out your LEDs.

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The reflectors i got are plastic, made in china.. 10 for $7 shipped.. reviews said they were a little thin, and could melt under high power. Still awaiting shipment, so i dont have one to test.


Im gonna search through the auto thread, and see what i come up with. Alternatively my options are to use a h6flex or 3 buckblocks.

question about installing the h6 flex: solder input voltage wires(with switch), solder all leds in series and connect to led + and -.. What else should be done to this driver? heatsinking wise. i imagine it will get hot running that voltage.
thank you guys again! this can be quite confusing without having much experience!

Taskled ships a small rubbery thermal pad with each unit. It's adhesive on both sides, so you use it to stick the board to your heatsink. That should be sufficient for anything the board can do. The efficiency is pretty high, so there's not a lot of heat to deal with.

mds82 said:

1 power supply will not work for 10 of those. If you have a car input on 12v, you would only be able to drive 3 XM-L's in series . You will need to get 3 drivers, and power 3 XM-L with each driver.

Click to expand...

Im sorry for seeming "thick headed" but after reading the datasheet for the 3rd time, http://www.ledsupply.com/content/pdf/led-driver-luxdrive-flexblock_documentation.pdf and looking at fig. 10 and 11, why cant i run my leds like fig 11 ? Fig 11 shows soldering the led series input to Vin, and running 6-14 leds in series as normal to led -

I do see a discrepancy between the part numbers, as this datasheet is for the 350/700ma buckblock. I would assume the 2100 would follow in the same manner?
What am i missing here??

why go thru all that, simply purchase a mean well driver in the voltage and current you require- but remember to spec it to 75-80% above what you really need. that is to say- depending on how you decide to wire it. LED prefers a constant current source for power. However, that is the beauty of the mean well drivers they are very adjustable- both IO and VO, and usually over 85% efficient.

kodi41 said:

why go thru all that, simply purchase a mean well driver in the voltage and current you require- but remember to spec it to 75-80% above what you really need. that is to say- depending on how you decide to wire it. LED prefers a constant current source for power. However, that is the beauty of the mean well drivers they are very adjustable- both IO and VO, and usually over 85% efficient.

Click to expand...

i was looking at meanwell drivers on mouser.com, got confused. i cant seem to find one in my Vin range, and not sure exactly what i want in Vout or amperage. Thats what im asking here. what driver will run a series of xm-l's around 2100ma?

Do i want a driver that has 12Vdc input and 3.2v output and 2100ma? wire all leds in parallel?
or try and find a driver that has 32v output at 2.1a out and wire them all in series?
My meanwell lcp-35-700 dont care about voltage, i just run leds in series and it'll run them at 700. I imagine the input voltage being that high (110vac) has somrthing to do with it
Im not sure of the "rules" of the proper calculation. hence why im asking a community of people that share the same interest.

The driver in your original post is a BuckBlock. The datasheet you seem to be reading now is for a FlexBlock. They're very different animals, not only in output current, but in construction and application as well. The BuckBlock cannot be operated in the Boost-Only mode, which you are looking at in Fig 11.

DIWdiver said:

The driver in your original post is a BuckBlock. The datasheet you seem to be reading now is for a FlexBlock. They're very different animals, not only in output current, but in construction and application as well. The BuckBlock cannot be operated in the Boost-Only mode, which you are looking at in Fig 11.

Click to expand...

So if i buy the flexblock i can wire accordingly to fig 11? and get the results im after?

Edit: wait..flexblock only goes to 700ma

heres where im getting confused.
http://www.ledsupply.com/led-drivers/buckblock-2100ma-constant-current-led-driver-with-dimming
the data sheet on this page is for a flexblock

well before I can give you a correct answer, please tell what the LED is with it's exact specs and how many, also what will cool these LED? thank you

kodi41 said:

why go thru all that, simply purchase a mean well driver in the voltage and current you require- but remember to spec it to 75-80% above what you really need. that is to say- depending on how you decide to wire it. LED prefers a constant current source for power. However, that is the beauty of the mean well drivers they are very adjustable- both IO and VO, and usually over 85% efficient.

Click to expand...

THe meanwell drivers are mostly AC/DC, he needs DC-DC . They do offer 2 DC/DC Drivers however they are not much different than the BuckBlock's

Poolman - Basically Flexblock is 350/700mA, either in a step down or step up. the BuckBlock is up to 2100ma and is only a step down driver meaning the input voltage needs to be higher then the output voltage.

The voltage of leach XM-L will be around 3.2, so you would only be able to run 3 of them from a 12v source if you use a step down driver.