Some VERY interesting LED modules

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Thank you, Robin ^^^

It really is a very clever bit of optical design and [in some situations] a massive improvement over the more common COB-LED units with their large area light source.

MichaelG.

The bit of Les' account you should pay attention to is " I would not advise anyone to buy one of these regulators to power the Plessey LED modules. "

Your test is not conclusive. To ensure a constant current generator is working correctly you must change the load, not the output voltage or current.
Assuming you don't have an ammeter, with your set up the test would be:

Set the voltage control higher than required for the maximum current you want to flow
Connect 3 resistors in series across the output
Set the desired current (for the test load) or turn down until the output voltage just starts to drop
Measure the voltage across the load. and not the value.
Short out one resistor
Measure the voltage across the load and ensure it changes to 2/3 the value for 3 resistors.

Your resistors look like 100 Ohm to me, but photo and screen colours are dificult. Assuming they do total 81 (3 x 27) Ohms, at 12.5V maximum current would be 150mA so if current was set to less than this, say 120mA, the voltage will drop (to 9.7V for 120mA). Shorting out a resistor will, if it is a constant current supply, cause the voltage to drop to 2/3rds (6.5V for 120mA).
Values will be +_ 10% typically.

If it is not a constant current supply you will find it very hard to set the voltage with the load connected and the voltage will not drop when you short out one resistor.

Robert G8RPI.

Edited By Robert Atkinson 2 on 29/01/2023 11:32:11

Robert - apologies for not responding earlier, I have only just got back to this.

I have now made experiments along the lines you suggested. My procedure and results:

- set PSU to 12V in CV mode

- adjust voltage pot on convertor to give 24.5V no load - PSU is indicating 10mA at this point.

- attach load (definitely 3 x 27 ohm 5W resistors in series) and wind down current pot on convertor to give 24.0 V

- attach voltmeter over the central resistor in load - 8.05V as expected. The PSU is supplying 660mA.

- short out one of the other resistors, momentary flicker, but 8.03V across the central resistor.

So that seems good - it's current limiting.

However...

Removing the short then turning the current limit from the PSU right down I find that:

- if I turn it up again straight away (within a couple of seconds) the PSU voltage / current return to 12V / 660mA immediately and all is as before.

- if I leave it for ~15 minutes with the PSU current down to zero, then turn it up to max (3A) the PSU supplies the full 3A. At this point the the voltage from the PSU is about 6.9V and the voltage across a single load resistor is about 7.5V. After approx 70 seconds in this condition the PSU suddenly switches back to 12V and 660mA and the convertor output jumps back to 8.05V per resistor.

Does that give any clue as to what is going on with these modules? I haven't tried connecting to 12V lead acid battery (which was what I'd hoped to do) because I suspect that the convertor would suck up too much startup current and self-destruct, as Les found.

Robin.

Edited By Robin Graham on 04/02/2023 23:38:19

Edited By Robin Graham on 05/02/2023 00:02:58

Edited By Robin Graham on 05/02/2023 00:47:30

Just a note:

The non-dimmable power supplies are on offer again: **LINK**

https://www.ebay.co.uk/itm/195351986113

MichaelG.

Thanks for the link Michael, I''ve just ordered two.

Ian P

Probably drifting a little off-topic, but I started the thread so what the heck

I visited Chester Cathedral today, and admired these Gurney Patent heaters:

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Inspiration for a ‘heatsink’ perhaps.

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Incidentally: They were decommissioned when trendy underfloor heating was installed

… with the result that the stacking wooden chairs in that area had to be scrapped, because they warped !!

MichaelG.

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Ref. __  https://www.gracesguide.co.uk/Gurney%27s_Patent

Edited By Michael Gilligan on 07/02/2023 21:38:44

A truly wonderful device ! Bolted to a semiconductor how many 100/ 1000s of As can be disipated ? I 'll be back ! Noel.

Footnote:

I have not yet found a downloadable copy of the patent for Gurney’s Stove, but one page is included here:

**LINK**

http://www.hevac-heritage.org/victorian_engineers/gurney/gurney.htm

[ not that it’s particularly relevant … it’s just admirable ]

MichaelG.