Configuring emitters with

[fefrie]

Hi, I'm interested in the 1000ma buck puck constant current driver, and it states that it is able to drive 6 3w emitters or 18 1 w emitters.

I would be using this in an automotive application where voltage varies between 11 and 14 volts.

Is it able to combine both 3 and 1 watt emitters?
If it is possible, how would that be wired?

I'd like to have 4 cree xre emitters (3 if it fits circuitry better) powered at 3w and 4 emitters at 1 watt.

If none of this works and they different wattage emitters have to be on different constant current drivers, how would 3,4,5 or 6 emitters need to be wired up?

I am guessing that with 3 or 6 emitters, emitters would be wired in series in groups of three, and groups connected in parallel to the power supply.

But how would a group of 4 or 5 emitters be hooked up?

Really technical questions.

Thanks so much

 

[bshanahan14rulz]

I would avoid wiring them in parallel. Probably be best to get a driver for each series of 3.

Not a lot of experience with buck puck, but generally you wire the LEDs in series on the output of the driver, not letting your total Vf go over the voltage your driver can supply.

 

[thepaan]

I believe the number of LEDs are suggestions based on the maximum parameters of the driver and not a strict rule.

For example the 7023 has a maximum input of 32V. Subtract 2V for overhead and you are looking at about 30V of LEDs you can attach. I connected the equivalent of 8 3W red emitters in series (actually two quad dies) to a 7023 for a total of about 20.8V which runs off an old 24V Sun monitor brick. If I had a higher voltage power source I could probably squeeze in 3 more. When connecting in parallel, you split the current but the voltage stays the same. So a 1000mA driver can drive two parallel strings of 500mA LEDs or, for an efficient setup, 4 strings of 350mA LEDs at 250mA.

The only thing I'm not clear on is the amp requirement going into the driver. Obviously, if you hook enough drivers up to a DC source you will run out of amps. I calculate one for one but it would be nice if someone knew for sure if 1A out of a driver requires 1A in.

 

[bshanahan14rulz]

I would avoid wiring them in parallel. Probably be best to get a driver for each series of 3.

Not a lot of experience with buck puck, but generally you wire the LEDs in series on the output of the driver, not letting your total Vf go over the voltage your driver can supply.

Also, best way is to calculate power in vs. power out. I don't know what a good number to use for generic driver efficiency, but basically
power out = power in*efficiency. 75% efficient driver would mean that your power out is 75% of the power in.

With power, you can divide by Voltage to get Amps (I)

Also, in theory running high-power LEDs paralleled is a great idea. In practice, not so much.

Edit: also, OP stated automotive use, so input voltage limited to ~12V

 

[evilc66]

I don't know if I would use a Buckpuck of any model for this. If 3 LEDs are connected in series, that's fine for ~12v, but if the voltage dips below that, and it will, the driver will suffer, and could be damaged. A buck/boost regulator would be better as it will handle any voltage you throw at it.

 

[fefrie]

When wired up, the system will only be powered on when the engine is running, so the system will always see at least 12volts, if not more closer to 13.5 volt. I'd measure the voltage with the engine running, but my stupid analog multi meter reads voltage in either 0-10v or 0-250v (stupid)

I talked to to the buckpuck supplier and he stated basically that the driver needs to be at least 2v above total Vf.

If I hooked up three cree emitter in series and run them at 1A, they will have a total Vf of (3.7v x 3emitters) 11.1V

If the system runs less than 13.1v, that can destroy the driver?

Maybe a constant current driver is not the best.

Can someone throw me a link for a buck/boost regulator? I'm not totally familiar with what that is.

 

[Steve K]

Hi, I'm interested in the 1000ma buck puck constant current driver, and it states that it is able to drive 6 3w emitters or 18 1 w emitters.

I would be using this in an automotive application where voltage varies between 11 and 14 volts.
I

Just a reminder regarding automotive electronics: the battery power bus in a car can be pretty nasty. Lots of voltage spikes, both positive and negative, and a lot of noise in general. If you have access to a technical library, check out the SAE J1113 document for some idea of how nasty.

In general, I'd advise hooking up a series diode between your circuit and the battery (wired so the diode blocks negative voltages). You might also want to consider a zener diode or transorb between the battery and ground connections, to limit any high voltage spikes that might otherwise damage your voltage or current regulator. A zener diode rated for 18v and one or two watts should be about right. In parallel with the zener, a capacitor or two would help clean up some of the noise. A ceramic 0.1uF cap wouldn't hurt.

A secondary benefit of one or two filter caps is that they would reduce the noise created by the LED voltage or current regulator circuit, which could possibly interfere with the other electronics in the car.

good luck,

Steve K.

 

[lilmarvin4064]

If you use 4+ emitters, why not just get the boost-puck version?

My understanding of the the buckpuck, is that if the input voltage drops below the Vf+2 of the LEDs, then the circuit just stops running, no damage. I have a few buckpucks that have taken some abuse. I belive they're protected from all kinds of things, reverse voltage, open circuit, etc...