Come in and join me....

[coolwaters]

well wat ballast r u using? is it that 700mA 12-28VDC?

if so your using way too many LEDs. @.@

 

the max should be 7 or 8 LEDs.at 700mA

[evilc66]

Yeah, you'll need to give us some info on what driver you are using. But I think Coolwaters is on the right path thinking that you may be driving too many LEDs from one driver. Give us more info and we can hook you up.

[snowlancer2720]

yep, its that one that you, coolwaters, told me about on ebay - http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...em=160156511950 the only thing that i can think of is that the leds pull .6 ( i believe the driver is 20wmax and the leds came out to 20.6 or something like that) more watts than the max for the driver. I guess ill try disconnecting one of them tonight and see if that fixes it.

[evilc66]

your problem seems to lie with the voltage. If you have LEDs at 3.4v (for example) and a max voltage from your regulator of 28v, you could only run 7 LEDs (7*3.6=25.2v, one more would push you over the limit). Give us the specs on the LEDs and we can go further and show you how to get your array set up properly.

[snowlancer2720]

the specs of the leds from future electronics are:6x "cool white"Part Number: LXML-PWC1-0070

Manufacturer Part Number: LXML-PWC1-0070 Price: (USD)

Price Break Unit Price Extended Price

1 3.4100 $3.41

Manufacturer Name: LUMILEDS LIGHTING

Future Part Number: LXML-PWC1-0070-CT-LF

Packaging: CUTT

Description: Lambertian Emitter, Cool White, 70 Lumens, 6500K

Datasheet:

In Stock: 1,000 +

Manufacturer Package Quantity: 250

RoHS: Y

Radiation Pattern: LAMBERTIAN

Color (wavelength/CCT): COOL WHITE

Flux-Typ: 130lm

Intensity-Typ:

Forward Current: 700mA

Forward Voltage: 3.40V

Lead Free: Y

Mounting Feature: SURFACE MOUNT

 

and 2x "Royal Blue"

Part Number: LXML-PR01-0225

Manufacturer Part Number: LXML-PR01-0225 Price: (USD)

Price Break Unit Price Extended Price

1 2.9700 $2.97

Manufacturer Name: LUMILEDS LIGHTING

Future Part Number: LXML-PR01-0225-CT-LF

Packaging: CUTT

Description: Lambertian Emitter, Royal Blue, 225mW, 455nm

Datasheet:

In Stock: 67

Manufacturer Package Quantity: 500

RoHS: Y

Radiation Pattern: LAMBERTIAN

Color (wavelength/CCT): ROYAL BLUE

Flux-Typ: 400mW

Intensity-Typ:

Forward Current: 700mA

Forward Voltage: 3.60V

Lead Free: Y

Mounting Feature: SURFACE MOUNT

 

any help you guys can provide will be really appreciated

[evilc66]

Sorry, looked back and missed that you were using Rebels. Are you using 2 or 6 royal blues? You mentioned 6 a few posts back. Either way, you can only run up to 8 white LEDs on one driver, and up to 7 royal blues. If you are to mix them, only 7 LEDs total. No more! To drive all the LEDs you listed in the last post, you will need 2 drivers to get the job done. You could use a Luxdrive Buckpuck and run 10 (32v max, but you will need a DC power supply). I think where you made the mistake was in not adding the voltage drop across each LED together correctly.

 

Keep in mind too that an LED with a 3.4v rating is only it's average voltage. An LED can increase or decrease its voltage as it requires, and multiple LEDs will have different average running voltages too. Basically what I'm getting at is you don't want to be running at the drivers max voltage. Just under is better.

[snowlancer2720]

thanks a lot man, ill have to take out one of them whites, i was running 6 white and 2 blue just off of that one driver. I guess i forgot to carry the one or something when i was adding them all up, lol. No biggie, ill just take one off tonight and hope that solves the problem. Thanks again.

[coolwaters]

i wouldnt max out the voltages. but w/e u want.

try to use at least 1volt less cuz of the resistance for wires and the LEDs..ect.

 

evilc66 low voltages and high amps is better right?

 

im trying to pry off the adhesive without destroy the LEDs but its pretty hard since i used the thermal epoxy...from arctic silver...strong stuff.

[Hans Dorn]

Hi snowlancer,

 

you can boost your LED driver by carefully adding a small DC power supply in series to it - see attached schematic.

 

 

Your LED driver can deliver 12..28V to your LEDs, falling slightly short of the required voltage.

By adding another 5V, you get an output range of 17-33V, and should be good.

 

Be careful and don't boost the voltage too much, or you might fall out of regulation.

Minimum expected voltage for the rebels is about 2.9V, IIRC, adding up to ca. 23V for 8 LEDs.

 

The minimum output voltage for your boosted driver should stay well below this voltage to be safe.

The 2 shottky diodes aren't strictly necessary, but they will protect your driver and power supply in case of

a short circuit.

 

 

Regards Hans

[coolwaters]

thats a interesting idea. you combined a DD power supply with a constant current supply. can anyone confirm that its safe?

 

if i connect it with something that is 12v and like 3amp+ would that work?

[evilc66]

Hans, would putting a voltage regulated power source on a current regulated circuit create issues with current draw? I'm not terribly familiar with doing this in this particular instance.

[Hans Dorn]

Well.

 

I was waiting for someone else to chime in

 

A LED driver basically works by adjusting its output voltage until the desired current is reached.

 

A perfect driver (like a lab supply) would go from 0V (in case of a short circuit) to a certain max voltage (when running without a load).

 

By adding a voltage regulated supply, you get a non-perfect current source that only works above a certain voltage.

 

You have to make sure your LEDs always have more combined forward voltage than the minimum output voltage of your driver.

 

Otherwise your LEDs will run with a constant (too high) voltage, your current increases and your LEDs will most likely burn out!

 

You need to know the minimum output voltage of your current source, and the combined Vf of your LEDs to decide what voltage source to use.

Your best bet is to meausure the Vf of your actual LEDs, because the datasheets aren't very specific.

 

To give an example, I'm planning to do the following:

 

Take a 3W 350mA regulator with a voltage range of 0.5 - 10V : SLP03SS

 

and boost it with a 31V 1.6A switching power supply: Surplus switching PS

 

to drive 12 Cree LEDs.

 

Minimum combined output voltage is 31.5V, or 2.625V per LED.

This is low enough to not cause any problems.

 

Maximum output voltage is 41V, or 3.42V per LED.

This is just high enough to get the LEDs safely running @ 350mA

 

Your DC supply must be able to deliver the required current, that goes without saying.

BTW: If you have an LED driver with DC input, you can't use the same DC supply to boost it!

 

 

The combined VF of your LEDs at the desired current MUST lie within the minimum and maximum output voltage of your driver.

 

To be safe, don't go above 2.8V minimum voltage per LED:

VF drops while the LEDs age, and it drops when they heat up.

 

At an expected LED life span of about 50.000 hours, your cooling fans WILL fail before your LEDs burn out,

so make sure your driver also works when the LEDs don't get any active cooling.

 

 

Regards Hans

 

P.S:

If you look at the specs of snowlancer's LED driver, you'll see it's minimum output voltage already is at 12V.

Looks like the manufacturer pulled the same trick

[coolwaters]

i had one of those (but the 35w version at 700mA 24-48v)) i wired 8 LEDs to it. it seems that my combined forward voltage on all 8 LEDs were below 24v...so it just blinked off and on (at 10mA or something really low) i guess its a safety thing. im pretty sure the other ones do the same thing.

 

i'll be using 3 regulator boards on the rest of my LEDs to make a array over 50watts.

is that the highest so far??? =)

[snowlancer2720]

well, i tried to take a few of them off, and still no avail, i hooked it up to a multimeter and without attaching the lights, it was giving me 29.4vdc output from the 120vac. As soon as i turned on the lights it went crazy in fluctuation, but usually down to ~4v then up to ~16, then back down.. so i think i fried it; can i do that? i trying to find a new driver. I looked at the buckpuck, it looks like i would need another dc power supply to go with it. any suggestions on that? Im looking to power 6-8 3.6v and 2-3 3.4v Rebels so im figuring a 36v driver would be ok..i couldnt seem to find one though, anyone else using something like that/ know of one. Thanks.

[coolwaters]

well u shouldnt test the LED driver. its voltage is the max rated with no load. it has a built in regulator so it gets "confused" when u use a multimeter.

 

again if u want to use a buckpuck

http://www.kaidomain.com/WEBUI/ProductDeta...spx?TranID=2982

this is a pretty good cheap replacement.

[snowlancer2720]

any idea then what is going on with the driver thats making it turn on and off? I looked at the buckpuck replacement from kaidomain, i would still need a dc power supply, and at least 3 of those. lol, i get so confused with this stuff, i should drop med school and go for electrical engineering, lol

[coolwaters]

its hard finding a good efficient DC adaptor the highest i seen was 90% and thats like the best PC poer supply u can get.

 

the cheap adaptor i got at wal-mart for $14 was like 76%...

 

hey i was really confused with this stuff to but once i started to read forums and asking the right people everything came clear.

 

the on and off thing is from the built in regulator i think and thats a safety thing since your driver has a min. req of about 4 standard high power LED. and a max of maybe 8. anything out of thos ranges will make the driver unusable. same thing happened to my 35w driver. it had about 7 min and 14 max.

 

it can also be that your solder or wiring is too thin. and theres too much resistance to transfer the required voltage.

[evilc66]

Like I mentioned earlier, the rated voltage drop across the LEDs are the average, and your actual voltage drop could be higher. If you were to take the averages of what you have you are at 27.2v and right at the limit. Try removing one more LED just to make sure you are below the rated limit. If it still has issues, there could be damage to the driver.

 

For a DC power supply, I wouldn't concern yourself too greatly with efficiency. You are going to pay a great deal of money for a very high efficiency PS. You should be more concerned with getting a PS that can regulate voltage accurately. The wall warts really are not that good. You can find surplus "laptop" style switching power supplies at places like MPJA and All Electronics for not much money, and they will be far superior to a wall wart.

[snowlancer2720]

coolwaters got me thinking with that soldering and resistance comment. before i installed the LEDs, i used thin gauge test wire just to make sure it worked correctly, now they are hooked up with thicker wire. Im thinking that the thicker wire is causing the problem because of the resistance. I think im going to take it all apart and use some thinner wire and see if that solves the problem. Thanks for the info evilc, if this doesnt work, i think im going to have to go with the laptop ps.

[Gomer]

I guess this place is as good as any to post a heads up for those looking to jump into the fray for a price lower then market costs.

 

I have a bunch of LEDs/partial LED projects that I'll be clearing out to fund some new stuff LOL.

I'll try and post in the market place tonight or tomorrow night after work

 

 

inc. K2, Cree, LuxeonIII, Luxeon 1, drivers, 5mm array.

[evilc66]

DO NOT GO TO A THINNER WIRE!!!!!!!

 

Larger wires have less resistance per foot than smaller wires. Unless you were using smaller than 28AWG it should not cause any harm. A poor solder joint could cause some issues.

[coolwaters]

i just a 22gauge wire since thats the only kind i have...except for the 30gauge ...but thats realistic...

 

it could be the thin piece of solder thats connecting them. i had the same problem with the rebels...u know how small the positive and negs are?

[snowlancer2720]

ok, mabye i wont try different wire, lol. maybe its just the soldering job, ill redo it tonight and mabye that will fix it..

 

edit: ok, nevermind..i resoldered all the wires and still nothing. I think I blew the driver somehow.

[evilc66]

Looks like you may have pushed the driver a bit too far with how you set things up originally.

 

Get this and this and you will be able to run the 8 LED setup you want. And all for under $30 shipped.

[Hans Dorn]

Hmmm...

 

From the BuckPuck spec. sheet:

 

DC input voltage from 5V to 32V. (The input voltage must be at least 2 volts higher than the forward voltage drop of all series connected LEDs.)

 

If you go with 3.6V per Led (to be safe on the high side), you'll have to supply the BuckPuck with about 30V to drive 8 LEDs in series.

 

You'd probably want to order some of coolwaters' flashlight drivers from Kaidomain instead, or try to find a 32V surplus power supply.