Some VERY interesting LED modules

Interesting that there is a bridge rectifier on the board.

Robert G8RPI

Useful notes about selecting LED drivers here: **LINK**

https://docs.rs-online.com/6263/0900766b814dedba.pdf

MichaelG.

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… especially as the data-sheet appears to say it should not be reverse connected.

MichaelG.

Looking at the track pattern in the picture, the AC terminals of the bridge rectifier seem to be routed to the power input connector.

In which case, reversed polarity supply would not be a problem.

JimB

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Exactly my point, Jim

[would not be a problem … except that it is ]

… which is why it is essential to read the data-sheet.

MichaelG.

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Edited By Michael Gilligan on 09/01/2023 08:49:48

The information in the manufacturers datasheets should sometimes be taken with pinch of salt.

I saw the bridge and the diode packages on Michael's first picture but did not (and still have not, followed the track layout) but from the text in the Plessey datasheet one might infer that the diode was before the bridge, but in that case why even have a bridge rectifier.

If the bridge rectifier is across the incoming supply then why the warning about reverse polarity I wonder.

Ian P

Right then-cut to the chase-has anybody got them working yet. Being somewhat chicken I have a couple of them on the workbench while I fret over how to power them without killing them.

Doug

Whether you need to fret or not depends on what power supply you have, also depends on whether you just want to see them light or operate them continuously.

For continuous operation at 700mA they would need a heatsink.

Ian P

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There is a suitable driver module winging its way to me, Doug

… I will report back a.s.a.p.

MichaelG.

This is a 60 degree version running in an otherwise unlit room (white ceiling):

It's pretty bright!

It's running from a lab PSU in CC mode, current clamped at 700mA , voltage was 43.4V at that current.

Not having a suitable heatsink I just perched it on top of a piece of 2.25" Ali bar, fresh from the workshop so at about 10C. I ran it for maybe 2 minutes - the aluminium back of the LED was stone cold after that but the metallised plastic housing was warm.

I'll rig up a thermocouple and get proper measurements anon.

Robin.

Edited By Robin Graham on 09/01/2023 22:12:38

PS. I guess the fact that the array didn't blind the camera at that angle shows that the 'optics' work pretty well in directing the beam - the overall illumination comes mostly from reflection from the ceiling, about 6ft above the device.

Does anyone know how to calculate heatsink requirements for continuous running?

Thanks for sharing this discovery Michael - I think I might have to order more if they're still available at this price.

Robin.

I just got my 25 degree one and it is very bright. I expected this as they are spotlight replacements.
The "turn-on" voltage on mine is 34-35V (1mA @ 35.5V) .
Heatsink is easy
Maximum operating temperature is 90 deg C. and the power is 31W @ 0.7A. The heatsink requiement is 90 - ambient temperature /31. So for a consertaive 35 deg. ambient it is (90-35) / 31 = 1.77 deg / W.
Which is quite big. An example:

https://uk.rs-online.com/web/p/heatsinks/1898280

Robert G8RPI.

The two that I ordered arrived today. I found a suitable heatsink to use.

Here are some measurements of voltage against current

100 mA 40.24 V
200 mA 41.21 V
300 mA 42.07 V
400 mA 42.80 V
500 mA 43.29 V
600 mA 43.76 V
700 mA 44.15 V

Even at 100 mA it was quite bright.
Many thanks to Michael for pointing them out.

Les.

I too received a pair of these modules and thank Michael for spotting them.

Regarding the voltage/current values just posted by Les, I would like to point out to (less electronically aware readers) that it is current rather than voltage which is the main consideration when selecting a power source.

The voltage across an illuminated string of LEDs (which varies slightly with temperature anyway) may be of interest but its not critically relevant, with these modules a 'constant current' supply (with an unloaded output higher than 45 volts (ish) is how they should be used.

I have not powered up mine yet but I not try to connect them direct to a regulated DC supply even if it was set to 44.15 Volts

Ian P

Ian makes a good point as beginners may be tempted to drive them with a constant voltage rather than a constant current. As well as the voltage for a given current changing with temperature it can be different between samples of LEDs. This is why it is a bad idea to drive LEDs in parallel. (Unless they are matched.)

Les.

Thanks for the heatsink calculation Robert - I thought it would be more complicated than that!.

Can you - or anyone else - rationalise this from the datasheet:

"Do not expose the module to liquids such as adhesives or thermal paste. No thermal paste
should be used as a TIM between the module and the heatsink. Do not remove the product
barcode".

My bold/italics. It seems common sense to me to use thermal paste. Am I missing something?

Obviously no one in their right mind would remove the barcode. One shudders to think of the consequences...

Robin.

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It confused confuses me too, Robin …

As for the barcode [the little titchy one on the edge] … it’s interesting to note that it’s not the part number, so it might be something to do with batch traceability.

MichaelG.

I'd not spotted the note about thermal paste. Most of these are based on silicone oil and a filler (typically zinc oxide).
The Silicone oil tends to bleed out of the paste and creep across surfaces. I can only assume that some component of the assembly is not compatible with silicone oil. Given the large surface area of the assembly and low power rating I would not have thought compound was needed anyway. Its more typivcally used on small components or those with a lot more power.
My heatsink calculaton do not allow for the thermal interface as I conservatively assumed all the input power turned to heat. In rality only about 60% is heat so more like 18W.

Robert G8RPI.

Silicone polishes were banned from strowger telephone exchanges after a contractor used some on a floor instead of beeswax. The oil crept all over the contact surfaces and oxidised to silica if there was any arcing. Result, one exchange out of service. As the design of the light just has some kind of mechanical contact between bare wire and some sort of barb arrangement that may be susceptible to the same problem?

Can somebody tell if this LED system is dimmable with, for instance, an Euchips 30 Watt Constant Current Dali and1-10 Volt Driver 550-900mA, with dip switch settings 700mA-43VDC?

Or even simpler with a 0-10V dinmming with a 100kOhm potmeter?

Regards,

Jouke