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Old June 25th 09, 12:40 PM posted to alt.binaries.schematics.electronic
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Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.

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Old June 25th 09, 01:11 PM posted to alt.binaries.schematics.electronic
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On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
[email protected] wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


That is aluminum clad? There are holes through it? Are they isolated?

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Old June 25th 09, 01:21 PM posted to alt.binaries.schematics.electronic
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On Thu, 25 Jun 2009 07:11:19 -0400, Spehro Pefhany
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
[email protected] wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


That is aluminum clad? There are holes through it? Are they isolated?


The only holes are mechanical fixing holes, none go through the
copper.

To complete the prototype I'm removing the insulation layer around a
couple of holes to give bare aluminium on the top and creating an ac
ground with capacitors from 0V and +50V to solder tags secured by the
mounting srews.
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Old June 26th 09, 12:50 AM posted to alt.binaries.schematics.electronic
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Raveninghorde wrote:

Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb


Is that on one side ?


is not earthed causing problems with current control


What sort of problems ? Decouple every few LEDs to GND if it's HF ?


presumably due to much higher stray capacitance than we had on FR4.
Just got to find a neat way of earthing it.


So what material is that if not FR4 ?

Graham

p.s. 19k lumens ! What's it a replacement for ?


--
due to the hugely increased level of spam please make the obvious
adjustment to my email address


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Old June 26th 09, 02:20 AM posted to alt.binaries.schematics.electronic
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On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde [email protected]
wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.



Is there not a current limit resistor at each LED?

Capacitance has an effect? Improper design then.

Current limit resistors ARE the cheapest, most efficient "current
control".


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Old June 26th 09, 02:22 AM posted to alt.binaries.schematics.electronic
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On Thu, 25 Jun 2009 07:11:19 -0400, Spehro Pefhany
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
[email protected] wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


That is aluminum clad? There are holes through it? Are they isolated?



I think he is nuts. Looks like copper to me. What PCB houses use Al
clad media? What etching process works with AL cladding?

What solder sticks to Al cladding.

Current control should be easy and precise, even with ALL of them
floating without "earth" grounding.
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Old June 26th 09, 02:24 AM posted to alt.binaries.schematics.electronic
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On Thu, 25 Jun 2009 23:50:51 +0100, Eeyore
wrote:

So what material is that if not FR4 ?

Graham


G10 perhaps. There are others available as well.
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Old June 26th 09, 04:28 AM posted to alt.binaries.schematics.electronic
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On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
[email protected] wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


Why the 'S' pattern, and why copper-free areas (if thermals are an
issue)?

Must be a really hefty pre-heat for reflow. Are the leds compatible to
this fab step, at all?

RL
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Old June 26th 09, 04:39 AM posted to alt.binaries.schematics.electronic
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On Thu, 25 Jun 2009 22:28:13 -0400, legg wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
[email protected] wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


Why the 'S' pattern, and why copper-free areas (if thermals are an
issue)?

Must be a really hefty pre-heat for reflow. Are the leds compatible to
this fab step, at all?

RL



SMT LEDs are SMT capable (duh). That means a 500 F heat bath (or more
for RoHS). It can handle it, and likely more than one cycle.

The preheat remains the same. It is not like he used an 0.090" thick
PCB.
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Old June 26th 09, 10:46 AM posted to alt.binaries.schematics.electronic
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On Thu, 25 Jun 2009 17:22:21 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 07:11:19 -0400, Spehro Pefhany
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
[email protected] wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


That is aluminum clad? There are holes through it? Are they isolated?



I think he is nuts. Looks like copper to me. What PCB houses use Al
clad media? What etching process works with AL cladding?

What solder sticks to Al cladding.

Current control should be easy and precise, even with ALL of them
floating without "earth" grounding.



The pcb is an aluminium plate with a very thin insulator and a copper
layer.

http://www.aismalibar.com/archivos/8...pdf?download=1

Current control was stable on FR4 prototype but the higher capacitance
is causing interaction between current controllers.


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