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View Full Version : Two quirky DIY LED lighting questions/problems?


balto777
06/26/2012, 10:50 PM
Just finished a 12 LED RapidLED build with the dimmable driver. The LED's work perfectly (for the most part), and I am completely happy with them. However, I have two issues that I would like feedback about.

1) When I dim the driver with the pot - the lights go completely out. This is a good thing since many people find the lights stay on very dimly with this driver. However, when I touch any part of the aluminum U-channel, the LED's light up very dimly - not even enough to be noticable unless you look directly at it. Wondering what could cause this since I tested for shorts between the aluminum and stars without any indication of one and the light otherwise works perfectly.

2) The other problem involves unplugging the driver. When I unplug the driver, the lights flash very brightly once after about 15 seconds - almost like a capacitor is discharging. It only flashes once, but would be annoying to see everytime the power is turned off.

Thoughts on bopth of these issues please . . .

reefermad619
06/26/2012, 11:37 PM
1: sounds like a short to me. I've seen this happen to a friends units and he did have a very small short. Wire was too long and a single strand of his 22ga stranded wire was touching the heatsink.

2: that's exactly what's heppening. That's why some say to use a controller and dim down gradually and don't completely shut off led. That way capacitors stay charged, so they don't blink when going off and don't get such a large inrush of current upon start up.

pfi$h
06/27/2012, 09:11 AM
I would agree with reefermad. I did the same DIY LED build and I don't have these issues.

balto777
06/27/2012, 09:29 AM
I would agree with reefermad. I did the same DIY LED build and I don't have these issues.

Not even the second issue? It seems that this wasn't a problem but just how the drivers discharge after they are unplugged . . .

ghellin
06/27/2012, 10:01 AM
I use an apex to control 4 ELNs and after the ramp all the way down they apex kills power to the drivers via the eb8 and I never see a flash

balto777
06/27/2012, 10:34 AM
I use an apex to control 4 ELNs and after the ramp all the way down they apex kills power to the drivers via the eb8 and I never see a flash

That is my plan on my full build for my 40 breeder, this was a test run for a coral QT tank. It doesn't happen everytime, but often enough. I have tried unplugging both the pot and driver at the same time, the pot first, the driver first - it doesn't really matter. Hope to find some help here because this one is annoying.

unkel j
06/27/2012, 10:46 AM
I have the same issues with mine. Mine used to light up when I touched the heatsink. That was a short wich I fixed, now it does not light up when I touch it. I talked with Rapid and they told me that it is normal for the leds to stay lit ever so slightly unless you kill the power to the drivers wich will cause them to discharge, or add a small resistor across V+ and V-. I choose to kill the power to the rapid controller only because it seems pointless to spend 30 min dimming them off just to brightly flash at the end. Rapid said that staying on slightly like that will not hurt anything or shorten the life of the leds. If they light up when you touch the heatsink that is a short. You should check again really close. If they only light up when you touch the heatsink AND your other hand is in the water, that is stray voltage in the tank.

balto777
06/27/2012, 10:53 AM
I got some video to show what I mean - hopefully this helps:

Issue #1: Lights coming on when I touch the heatsink:

http://www.youtube.com/watch?v=xePsotVaXiM&feature=youtu.be

Issue #2: Lights flashing when turned off:

http://www.youtube.com/watch?v=0oooSy3uIUA&feature=youtu.be

balto777
06/27/2012, 10:56 AM
What is the best way to find shorts? I have already used my multitester, and I cannot find it. I am using plastic screws and washers, so unless there is a stray wire or glob of solder I don't think anything would cause a problem.

unkel j
06/27/2012, 10:59 AM
If you unplug the drivers they will discharge and flash. That is normal. You have to use a controller and leave the drivers pluged in to stop that.

unkel j
06/27/2012, 11:04 AM
To find a short set your meter to continuity. Touch the two leads together and you should hear a beep. Now hold one lead on the heatsink and toch the other to every solder joint on each led. If you hear a beep, that led is shorted to the heatsink.

unkel j
06/27/2012, 11:07 AM
I noticed only some leds light up when you touch it. That is EXACTLY what mine did when it had a short.

balto777
06/27/2012, 11:20 AM
Thanks for the reply Unkel J.

Leaving the drivers plugged in will not be a problem.

As for finding the short - I am at a loss. I used the multimeter and did just like you asked. I also did exactly as detailed by Kcress in this (http://www.reefcentral.com/forums/showthread.php?t=1973462&page=4) thread. I even went one step further and laid a piece of solder to create a short to make sure my multimeter would work properly - and it did???

unkel j
06/27/2012, 11:47 AM
Did you check every single tab on every led? It took me a while to find mine too.

unkel j
06/27/2012, 11:50 AM
This is one of the emails I got from Rapid:


Hi Josh,

This sounds like grounding. If when you touch the heatsink the LEDs get brighter, your body is acting as a partial ground source. This would allow the driver to increase its voltage between V+ and V- because your body is pulling V- lower when touching the heatsink. Increased voltage between V+ and V- = brighter LEDs.

If you have a multimeter, you can perform a continuity test, which will probably tell you why certain LEDs are dim or not lighting up: they are grounded (partially) to the heatsink somehow. Continuity refers to two things electrically connected. For example, if two parts are connected by a wire, they are continuous.

To perform this test, set the multimeter to measure continuity (usually the 'diode' setting) and ensure no power is applied to your LED string. Next, touch one probe to the heatsink and the other probe to each solder joint of every LED, going around your string until all joints have been examined. If you hear a beep or get 0.000 reading at a particular joint, there is continuity (conductivity) between that joint and the heatsink (this means there is an electrical path between that solder pad and the heatsink, which we call grounding). This solder joint will have to be re-done since the LED string should be completely isolated from the heatsink electrically for the string to work properly.

Remember all wiring must be complete before powering up the LED string.

Thanks,
Eric
Rapid LED

unkel j
06/27/2012, 12:19 PM
Here are some moer emails between Rapid and myself.

Hi Josh,

The lights may not shut off all the way with the MW driver. The only way to shut them off completely is to add a small resistor across V+ and V- or unplug them.

It is normal behavior for the lights to flash once briefly when power is cut from the driver.

Thanks,
Eric
Rapid LED


Thank you for the reply. I'm pretty sure that they used to shut off all the way. I could be wrong, maybe I just never looked close enough. I do not want to kill the power to the drivers. I would rather the leds stay on ever so slightly than flash like that. To me, it defeats the puorpose of dimming them off for 30 minutes. Unless it is bad for the drivers or anything else.

I have a few questions if you don't mind. Please humor me, I am not that great with electronics.

1-Is it bad to only kill power to the controller?
2-If the leds stay on just a tiny tiny bit always, will it shorten their life?
3-Will resistors limit the brightness or change the way the light works in any other way,
4-What type of resistors? What amperage?
5-Where exactly do I install them?

Thank you for your time.
Josh


Hi Josh,

1. This should not be an issue
2. The lifespan will not be shortened if the LEDs are on very dimly
3. Yes, but it should be insignificant, a few mA or less than 1% difference.
4. Resistors have a wattage rating. The wattage rating is their maximum power dissipation. When you run current through a resistor, it resists the flow of that current. Resisting the flow of current creates heat, which is measured in power (watts). Usually, resistor calculations are done with Ohm's law (Voltage = Current x Resistance). Resistance = Voltage / Current. The voltage for the DIM LEDs should be very small, and so should the current. I would try a 20 ohm 1/4 watt resistor, but cannot be sure.
5. The resistor should be installed between V+ from the driver and the first solder pad of the 1st LED in the string.

Please note the advice above is given such that I cannot guarantee the validity or performance of the recommendations. They're only recommendations and may or may not work.

As always never plug in the driver before all wiring is complete!

Thanks,
Eric
Rapid LED

nyquist
06/27/2012, 12:24 PM
what would happen if you place a switch (mosfet or otherwise) at the output of the controller and have that switch cause an open-circuit when the power is cut to the controller?