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post #1 of 17 (permalink) Old 12-16-2015, 12:36 PM Thread Starter
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LED driver help

I have little electronic question: I'm working on my DIY LED and all is going well, except that I am using Steves LEDs drivers and I ordered a mix of 700ma drivers and 1000 ma drivers; but, when I got the package, none of the drivers were labeled and I can't see any differentiating marks on any of them. I hooked up one of my 1000 ma LED strngs and tested the current and all five drivers read the same: betwee 224 ma and 226 ma. What can I do to figure out which divers are which before i hook up the 700ma strings? Can I test the current when hooked up to a large resistive load, like a heating element? I have a bare finnex 300 watt element (no thermostat or other electronics, just the heating element).Does anybody know more about electronics and is able to give some advice? Jeffkrol?

Thanks,
Justin

Last edited by jrygel; 12-16-2015 at 02:27 PM. Reason: typos
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post #2 of 17 (permalink) Old 12-16-2015, 02:34 PM
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Can you take pictures?


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post #3 of 17 (permalink) Old 12-16-2015, 03:19 PM
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Quote:
Originally Posted by jrygel View Post
I have little electronic question: I'm working on my DIY LED and all is going well, except that I am using Steves LEDs drivers and I ordered a mix of 700ma drivers and 1000 ma drivers; but, when I got the package, none of the drivers were labeled and I can't see any differentiating marks on any of them. I hooked up one of my 1000 ma LED strngs and tested the current and all five drivers read the same: betwee 224 ma and 226 ma. What can I do to figure out which divers are which before i hook up the 700ma strings? Can I test the current when hooked up to a large resistive load, like a heating element? I have a bare finnex 300 watt element (no thermostat or other electronics, just the heating element).Does anybody know more about electronics and is able to give some advice? Jeffkrol?

Thanks,
Justin
Wel you are either measuring wrong, have to low of voltage, or are somehow dimming..

What is your power supply and the amount of serial LED's and their respective V(f) @ 1000mA

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post #4 of 17 (permalink) Old 12-16-2015, 04:38 PM Thread Starter
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Wel you are either measuring wrong, have to low of voltage, or are somehow dimming..

What is your power supply and the amount of serial LED's and their respective V(f) @ 1000mA


I am using a Meanwell LRS-100-24. Now that you mention it, I think the voltage is set to around 21 V, I turned it down initially so I wouldn't fry anything while testing.


The string I am testing is composed of all Luxeon ES: (3x) cool blue, (2x) royal blue, and (2x) cyan V(f) @ 1000 ma are: 3.3 V, 3.0 V, and 2.95 V, respectively, so total voltage should be 21.8 V.


I assume that the driver is taking something, so probably I need to turn my power supply up from 21 V to 23 V or so, but will that make much of a difference in the current? I have one of the drivers hooked up to the bluefish, and the others have the pot. terminals bridged with no PWM dimming hooked up, so should have no dimming. I got the same results whether measuring one of the bare drivers or the one hooked up to Bluefish set to run @ 100% - did see a change (as I should) if I turned the channel down.


I am measuring by hooking my multimeter into the circuit in series as if it was another LED. Is that correct? It does appear that all of these LEDs are working properly and getting full voltage: subjectively, the string looks like it is running full power, it's certainly not running at 1/4 power.


I got in touch with Steve's tech support this morning and am going to take pictures for them, that I can post here.


Thanks in advance for whatever help/advice is offered!


-Justin
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post #5 of 17 (permalink) Old 12-16-2015, 06:24 PM
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Steve's led drivers use the OnSemi CAT4101 led driver IC in their design. The CAT4101 IC is a low side regulator. The driver needs to see between .5V &.8V over the led string voltage to operate properly. Try setting the voltage on your power supply to no more than 24V(25V is the chip's limit). Find your led string with the highest Vf and then adjust the voltage down from there. Once you reach .5V-.8V over the string voltage, leave the voltage setting alone. Hopefully all of your led strings have approximately the same Vf. If not, the CAT4101's driving the lower Vf strings will run hotter, and less efficiently.


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post #6 of 17 (permalink) Old 12-16-2015, 07:58 PM
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Quote:
I am using a Meanwell LRS-100-24. Now that you mention it, I think the voltage is set to around 21 V, I turned it down initially so I wouldn't fry anything while testing.


The string I am testing is composed of all Luxeon ES: (3x) cool blue, (2x) royal blue, and (2x) cyan V(f) @ 1000 ma are: 3.3 V, 3.0 V, and 2.95 V, respectively, so total voltage should be 21.8 V.
so assuming the ps is maxed around 24v and your divers are no more than 1000mA then the only thing to worry about (unfortunately) is overheating the driver..
driver will control the current so you won't "overvolt" nor "overcurrent" the LEDs.

running at 21 and considering the voltage loss per O2.. you are way underdriving the LED's thus the low ma output..

As mentioned though, getting fairly equal v(f) strings is much more important w/ Steves drivers than say LDD's which, for the most part, wouldn't give a hats rass if one was 3v at 1000mA and another is 20V at 700mA..

driver temp will tell you if you are on the right track..

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Last edited by jeffkrol; 12-16-2015 at 09:24 PM. Reason: edit
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post #7 of 17 (permalink) Old 12-16-2015, 09:08 PM Thread Starter
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Thanks for the help! My LED strings are all between 20.8 V and 22.4 V, so there won't be too much excess voltage. The drivers are attached to a pretty heavy aluminum heatsink with a fan. (BuildmyLED premium 6x20).
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post #8 of 17 (permalink) Old 12-16-2015, 09:33 PM
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Starting at like 23.5V (check to see if outputting max current) and working your way down till you reach the sweet spot w/ the highest string.. then you should be all set.
you should have all drivers outputting their designed current..

21.6-28.8V is approx adj. range..
4.5A max output..

Using a shunt resistor and checking the current w/ a VOM will allow you to do it a bit more precisely than the "eyeball" method..
voltage can fluctuate as the temp of the diode changes.. but current should stay relatively stable.. AFAICT



Quote:
Example of calculation
As an example a shunt resistor is used with a resistance of 1 mOhm. The resistor is placed in a circuit, and a voltage drop of 30 millivolts is measured across the resistor. This means that the current is equal to the voltage divided over the resistance, or: I = V / R = 0.030 / 0.001 = 30 A. The same calculation could be made, but now with the resistance value unknown and the voltage and current known. This is used to calibrate shunt resistance
Read more http://www.resistorguide.com/shunt-resistor/

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Last edited by jeffkrol; 12-16-2015 at 09:53 PM. Reason: edit
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post #9 of 17 (permalink) Old 12-17-2015, 02:58 PM Thread Starter
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Jeff, I understand the math and method behind the shunt resistor, but is there an advantage to doing this vs. measuring current directly with my multimeter?

I turned the voltage on the power supply up to 24.8 V and tested the current with the LED string on all five drivers last night. All five read right around 1000 ma. A 700 ma driver should not be able to provide 1000 ma of current, correct? This means I have five 1000 ma drivers, right?

-Justin

UPDATE: Just heard back from Steve's tech support and based on my measurements and the photos I sent in, it looks like all five drivers were 1000 ma, so they are sending me a couple 700 ma drivers.

Last edited by jrygel; 12-17-2015 at 03:04 PM. Reason: new information
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post #10 of 17 (permalink) Old 12-17-2015, 04:56 PM
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Originally Posted by jrygel View Post
Jeff, I understand the math and method behind the shunt resistor, but is there an advantage to doing this vs. measuring current directly with my multimeter?

I turned the voltage on the power supply up to 24.8 V and tested the current with the LED string on all five drivers last night. All five read right around 1000 ma. A 700 ma driver should not be able to provide 1000 ma of current, correct? This means I have five 1000 ma drivers, right?

-Justin

UPDATE: Just heard back from Steve's tech support and based on my measurements and the photos I sent in, it looks like all five drivers were 1000 ma, so they are sending me a couple 700 ma drivers.
It is a bit more accurate usually and you also don't need your meter "in line"
hot swapping LEd's on some drivers can cause an inrush of current and burn them out.. like if a meter clip lets go and you reattach it..

If your ammeter is accurate, not really necessary though. most really aren't..Having a good calibrated shunt resistor is important though..

Usually they were used to measure large Amp ranges.. Maybe I'm just old school..

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post #11 of 17 (permalink) Old 12-17-2015, 05:36 PM
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Modern meters are accurate measuring amps. They have ports for 10A and mA.


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post #12 of 17 (permalink) Old 12-17-2015, 07:19 PM
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UPDATE: Just heard back from Steve's tech support and based on my measurements and the photos I sent in, it looks like all five drivers were 1000 ma, so they are sending me a couple 700 ma drivers.

Just an FYI... There's really no difference between the 1000ma and 700ma drivers. A small Rsense resistor is used to "program" the driver for set current values. 569 ohms = 1000ma 768 ohms = 700ma. If you ever want to get fancy and add infinite 0- 1000ma current adjust ability to your drivers.... wire a 10K potentiometer in series with the 569 ohm resistor. With that in place, you'll be able to adjust the drivers current with just the twist of a knob. I still don't understand why Steve's Led never incorporated that into their driver design?


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post #13 of 17 (permalink) Old 12-17-2015, 09:50 PM
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wire a 10K potentiometer in series with the 569 ohm resistor.
Why 10k .. wouldn't 5k be better (5549 max) ?
and would an audio taper pot be more fun?

The spec sheet only goes to 100 mA at 4990 Ohms,
There is no problem going a lot lower???
Does look to never quite go to zero..

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post #14 of 17 (permalink) Old 12-17-2015, 11:33 PM
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The point being..... You don't have to replace the entire driver. A resistor swap is all that's needed. Going the extra mile by adding the pot makes the driver even more user friendly.

An audio tapered pot would be more fun.....linear's are boring in that they're soooo predictable

100ma isn't the lowest they'll go, but what's the point with going so low with "3 watt" LEDs? Might as well go back to using "gumdrops leds" if you're only pushing 20ma.


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post #15 of 17 (permalink) Old 12-18-2015, 02:15 AM
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I was thinking more about the log nature of the rset response..
Log pot would be more "predictable" than a linear one..




My point about the high ohm resistance was if there were some circuit limitations.. i.e going too low (thus questioning the 10k) NOT that you would want to do it but "what if" you do it?
What if you went to 20K, or 50k? any consequences or just dribble current? Or can this be a manual "pot dimmer???
somewhat related is the problem of low (or zero) Ohms on the rset..
Seems that would create "out of spec" output and burn out the chip...

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Last edited by jeffkrol; 12-18-2015 at 02:27 AM. Reason: edit
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