Balancing current with LED's

Voxboy · 05/11/2012, 10:04 PM

Starting my build tomorrow. Pretty sure I have it all figured out thanks to members here.
The only concern I have is....when I go to balance the current and have to swap LED's how is this accomplished due to them being epoxy to the heatsink???

HaKs310 · 05/11/2012, 11:10 PM

Is this two separate questions? Adjusting driver current and moving LEDs around?

What type of drivers will you be running?
How will the LEDs be mounted? Thermal adhesive or thermal grease and screws?

tomservo · 05/12/2012, 07:59 AM

You shouldn't need to move around any LEDs if all your strings are made up of the same number and type of emitters.

As far as moving LEDs; if you used epoxy, you will pretty much have to chisel them apart. Good application of technique might make the emitter reusable if it still works.. However, for this reason, I recommend using a silicone based thermal glue (like aquastyle provides/sells). The silicone stuff doesn't hold as strong, though it is plenty good for use with stars.

Voxboy · 05/12/2012, 02:03 PM

Quote:

Originally Posted by HaKs310

Is this two separate questions? Adjusting driver current and moving LEDs around?

What type of drivers will you be running?
How will the LEDs be mounted? Thermal adhesive or thermal grease and screws?

I am jrunning the MW LPF 90D 48...3 of them. 36 parallel per driver. Mounted with thermal adhesive from aquastyle.

I am a real noob when it comes to this electronic stuff.
Now that you mention it I guess my question does have 2 parts.

1. Do I check for balance before I use the thermal adhesive.
2. What do I set my meter on to check the various things I need to check.
This is the meter I am using.
http://www.doitbest.com/Box+connecto...sku-563269.dib

HaKs310 · 05/12/2012, 03:03 PM

Wiring in parallel, not series?

Voxboy · 05/12/2012, 08:09 PM

Quote:

Originally Posted by HaKs310

Wiring in parallel, not series?

Parallel. 3 strings of 12 from each driver.

HaKs310 · 05/12/2012, 09:39 PM

Aahh, can't help you there boss. Haven't wired LEDs in parallel other than small inexpensive projects.

kcress · 05/13/2012, 04:08 AM

Quote:

Originally Posted by Voxboy

Starting my build tomorrow. Pretty sure I have it all figured out thanks to members here.
The only concern I have is....when I go to balance the current and have to swap LED's how is this accomplished due to them being epoxy to the heatsink???

I hope you're including the fuses and resistors recommended for typical parallel builds.

If so, you're set. Turn down the current on your driver and proceed.

My recommendation, if you're gluing down your LEDs, is to just rewire the target LED. It doesn't matter how long the leads are inside your fixture.

You definitely do NOT want to try balancing without mounted LEDs. A big aspect of the balance is the thermal situation of the running strings. I doubt unmounted LEDs would even give a viable result. Furthermore, you would likely toast a few in the process. You cannot run them un-sinked for as long as you would need to.

Make sure your build is entirely commissioned before ever powering it. If you properly commission it you will know it will light-up correctly - without shorts or opens - and all the hassle that comes with those situations.

Please go to this thread and start reading about POST #60. It explains how to completely test a build. It includes nice pictures too.

http://www.reefcentral.com/forums/sh....php?t=1973462

3 out of 4 parallel builds require no balancing. In your glued case, as I say, just run wires to the neighboring LEDs you want to swap. It will make no difference to your light footprint.

Voxboy · 05/13/2012, 12:27 PM

Quote:

Originally Posted by kcress

I hope you're including the fuses and resistors recommended for typical parallel builds.

If so, you're set. Turn down the current on your driver and proceed.

My recommendation, if you're gluing down your LEDs, is to just rewire the target LED. It doesn't matter how long the leads are inside your fixture.

You definitely do NOT want to try balancing without mounted LEDs. A big aspect of the balance is the thermal situation of the running strings. I doubt unmounted LEDs would even give a viable result. Furthermore, you would likely toast a few in the process. You cannot run them un-sinked for as long as you would need to.

Make sure your build is entirely commissioned before ever powering it. If you properly commission it you will know it will light-up correctly - without shorts or opens - and all the hassle that comes with those situations.

Please go to this thread and start reading about POST #60. It explains how to completely test a build. It includes nice pictures too.

http://www.reefcentral.com/forums/sh....php?t=1973462

3 out of 4 parallel builds require no balancing. In your glued case, as I say, just run wires to the neighboring LEDs you want to swap. It will make no difference to your light footprint.

Good advice.
Going through the thread...my meter has different numbers..I don't have 2k on mine and still slightly confused as to probe placement at what setting for what measurement.
Thanks for the input...appreciated

thor109 · 05/13/2012, 01:43 PM

If you have a resistor in each string you can measure the voltage going through the resistor which will tell the current in the string. If not you have to install your meter in series on each string one at a time. I had 12 string and all were within 50 ma. So I didn't have to move or rewire. I screwed my leds on just on case.

Voxboy · 05/13/2012, 03:18 PM

Quote:

Originally Posted by thor109

If you have a resistor in each string you can measure the voltage going through the resistor which will tell the current in the string. If not you have to install your meter in series on each string one at a time. I had 12 string and all were within 50 ma. So I didn't have to move or rewire. I screwed my leds on just on case.

Thanks thor. I do have resistors for each string. What setting on my meter?

Thanks

kcress · 05/13/2012, 06:17 PM

Your meter settings don't have to match exactly. Try to understand what you are measuring so you have more confidence in how you measure.

All meters will have the same "type" of settings. They are just range settings. You need to set to ranges that are just larger than the value you are seeking to measure as that gives the most accuracy possible.

When measuring the current thru your strings you actually measure the voltage drop across the resistor and do some math. If you used the recommended 1 ohm resistors the math is absurdly simple. You divide the reading by 1.... And that is the current in amps.

Expect to measure using your meter on a low range, probably it's lowest range, that is above 1V. The voltage reading you get IS the current thru that resistor. And, since the current is identical in everything hooked in series that measurement IS the current thru that string.

Of course measuring the current should be well AFTER you've proven to yourself that there are no shorts to the heatsinks or opens in the strings by executing all the commissioning tests correctly as shown in the aforementioned thread above.

Feel free to ask specific questions. If you don't understand something in that other thread ask here. Refer to the thread number over there.

05/11/2012, 10:04 PM	#1
Voxboy Premium Member Join Date: Jul 2005 Location: Sault Ste Marie Posts: 410	Balancing current with LED's Starting my build tomorrow. Pretty sure I have it all figured out thanks to members here. The only concern I have is....when I go to balance the current and have to swap LED's how is this accomplished due to them being epoxy to the heatsink??? __________________ Like my Grandfather...I wish to die peacefully in my sleep....unlike the screaming passengers in his car Current Tank Info: 130g mixed reef.

05/11/2012, 11:10 PM	#2
HaKs310 Forever Learning Join Date: Nov 2003 Location: Whittier, CA Posts: 1,241	Is this two separate questions? Adjusting driver current and moving LEDs around? What type of drivers will you be running? How will the LEDs be mounted? Thermal adhesive or thermal grease and screws? __________________ IM Fusion Pro 20 Peninsula \| Nanobox Duo Plus M \| AquaIllumination Nero 3 \| XP Aqua Duetto Dual-Sensor ATO \| Eheim Jager 75w Heater

05/12/2012, 03:03 PM	#5
HaKs310 Forever Learning Join Date: Nov 2003 Location: Whittier, CA Posts: 1,241	Wiring in parallel, not series? __________________ IM Fusion Pro 20 Peninsula \| Nanobox Duo Plus M \| AquaIllumination Nero 3 \| XP Aqua Duetto Dual-Sensor ATO \| Eheim Jager 75w Heater

05/12/2012, 09:39 PM	#7
HaKs310 Forever Learning Join Date: Nov 2003 Location: Whittier, CA Posts: 1,241	Aahh, can't help you there boss. Haven't wired LEDs in parallel other than small inexpensive projects. __________________ IM Fusion Pro 20 Peninsula \| Nanobox Duo Plus M \| AquaIllumination Nero 3 \| XP Aqua Duetto Dual-Sensor ATO \| Eheim Jager 75w Heater

05/12/2012, 07:59 AM	#3
tomservo Registered Member Join Date: Feb 2012 Location: Manitoba, Canada Posts: 332	You shouldn't need to move around any LEDs if all your strings are made up of the same number and type of emitters. As far as moving LEDs; if you used epoxy, you will pretty much have to chisel them apart. Good application of technique might make the emitter reusable if it still works.. However, for this reason, I recommend using a silicone based thermal glue (like aquastyle provides/sells). The silicone stuff doesn't hold as strong, though it is plenty good for use with stars.

05/13/2012, 01:43 PM	#10
thor109 Registered Member. Join Date: Jun 2011 Location: Plainfield, Indiana Posts: 822	If you have a resistor in each string you can measure the voltage going through the resistor which will tell the current in the string. If not you have to install your meter in series on each string one at a time. I had 12 string and all were within 50 ma. So I didn't have to move or rewire. I screwed my leds on just on case.

05/13/2012, 06:17 PM	#12
kcress Registered Member Join Date: Dec 2007 Location: Central California Coast. Posts: 5,383	Your meter settings don't have to match exactly. Try to understand what you are measuring so you have more confidence in how you measure. All meters will have the same "type" of settings. They are just range settings. You need to set to ranges that are just larger than the value you are seeking to measure as that gives the most accuracy possible. When measuring the current thru your strings you actually measure the voltage drop across the resistor and do some math. If you used the recommended 1 ohm resistors the math is absurdly simple. You divide the reading by 1.... And that is the current in amps. Expect to measure using your meter on a low range, probably it's lowest range, that is above 1V. The voltage reading you get IS the current thru that resistor. And, since the current is identical in everything hooked in series that measurement IS the current thru that string. Of course measuring the current should be well AFTER you've proven to yourself that there are no shorts to the heatsinks or opens in the strings by executing all the commissioning tests correctly as shown in the aforementioned thread above. Feel free to ask specific questions. If you don't understand something in that other thread ask here. Refer to the thread number over there.