Replacing LEDs in strip lights...

[Commander Kinsey]

I use this sort of thing: https://www.ebay.co.uk/itm/163956674647
When they eventually fail, it\'s the LEDs that have gone.
Isn\'t it possible to buy a strip of LEDs to slide into it instead of buying a new power supply and chassis aswell?
Uneconomical and wasteful of resources.

 

[Rich S]

On Monday, July 27, 2020 at 4:47:43 PM UTC, Commander Kinsey wrote:

I use this sort of thing: https://www.ebay.co.uk/itm/163956674647
When they eventually fail, it\'s the LEDs that have gone.
Isn\'t it possible to buy a strip of LEDs to slide into it instead of buying a new power supply and chassis aswell?
Uneconomical and wasteful of resources.

Sure you can buy LED strips. I\'ve used this vendor:
www.superbrightleds.com
But you have to know what you need: physical size, voltage (12 or 24VDC), etc.

 

[Commander Kinsey]

On Mon, 27 Jul 2020 20:07:05 +0100, Rich S <richsulinengineer@gmail.com> wrote:

On Monday, July 27, 2020 at 4:47:43 PM UTC, Commander Kinsey wrote:
I use this sort of thing: https://www.ebay.co.uk/itm/163956674647
When they eventually fail, it\'s the LEDs that have gone.
Isn\'t it possible to buy a strip of LEDs to slide into it instead of buying a new power supply and chassis aswell?
Uneconomical and wasteful of resources.

Sure you can buy LED strips. I\'ve used this vendor:
www.superbrightleds.com
But you have to know what you need: physical size, voltage (12 or 24VDC), etc.

Most commercial tubes (which I was trying to replace the LEDs in) run at 75V, powered by a constant current supply. I need a strip of LEDs with no resistors in it, with about 24 LEDs in series, and blocks of those 24 in parallel with each other.

 

[whit3rd]

On Monday, July 27, 2020 at 3:02:23 PM UTC-7, Commander Kinsey wrote:

On Mon, 27 Jul 2020 20:07:05 +0100, Rich S <richsulinengineer@gmail.com> wrote:

On Monday, July 27, 2020 at 4:47:43 PM UTC, Commander Kinsey wrote:
I use this sort of thing: https://www.ebay.co.uk/itm/163956674647
When they eventually fail, it\'s the LEDs that have gone.
....

> Most commercial tubes (which I was trying to replace the LEDs in) run at 75V, powered by a constant current supply. I need a strip of LEDs with no resistors in it, with about 24 LEDs in series, and blocks of those 24 in parallel with each other.

That\'s a problem. Firstly, the large-number-of-LEDs-in-series design keeps wiring simple, BUT
you can\'t usefully repair by replacing ONE LED, because matching matters. It\'s used because it can
work with fluorescent ballasts in old installations. Second, the \'current source\' supply
with blocks in parallel means your parallel blocks must match (a shorted LED ruins the
match of the whole parallel block). Third, the use of fluorescent-compatible design
introduces time-dependent current; even if the flicker doesn\'t bother you, it
can drive optical sensors of all sorts completely crazy (or radiate RF). But, you wouldn\'t
ever depend on a remote control to work, right?

The many-in-series current drive is inflexible, which is why the constant-voltage
drive into resistor-equipped short strings is so popular. There are long strips
of such paralleled short strings, easily available, and can be used with a variety
of the familiar 12V regulated DC supplies we all have a dusty box of...

 

[Commander Kinsey]

On Mon, 27 Jul 2020 23:26:10 +0100, whit3rd <whit3rd@gmail.com> wrote:

On Monday, July 27, 2020 at 3:02:23 PM UTC-7, Commander Kinsey wrote:
On Mon, 27 Jul 2020 20:07:05 +0100, Rich S <richsulinengineer@gmail.com> wrote:

On Monday, July 27, 2020 at 4:47:43 PM UTC, Commander Kinsey wrote:
I use this sort of thing: https://www.ebay.co.uk/itm/163956674647
When they eventually fail, it\'s the LEDs that have gone.
...

Most commercial tubes (which I was trying to replace the LEDs in) run at 75V, powered by a constant current supply. I need a strip of LEDs with no resistors in it, with about 24 LEDs in series, and blocks of those 24 in parallel with each other.

That\'s a problem. Firstly, the large-number-of-LEDs-in-series design keeps wiring simple, BUT
you can\'t usefully repair by replacing ONE LED, because matching matters.

Actually it doesn\'t. I\'ve replaced single ones many a time. As long as the current is fairly similar, they work. If the voltage is different, the PSU adjusts.

It\'s used because it can
work with fluorescent ballasts in old installations.

Not always, the ones I\'m referring to, most of the ones in my house, are not retro fit. They are their own unit.

Second, the \'current source\' supply
with blocks in parallel means your parallel blocks must match (a shorted LED ruins the
match of the whole parallel block).

Yeah that happened with one light I had. I assume a few failed in one series strip, and that strip\'s remaining LEDs got more and more current until they all blew. The light continued to function with the other half for years, which is surprising, since they should have got double the current. Either the PSU hit a voltage limit, or the dead strip was consuming current.

But most of my lights are actually groups of 2 LEDs in parallel, then all the groups put in series. So when one fails short circuit, that pair go off, but the rest get the same current from the supply, which adjusts the voltage to retain the correct current.

It\'s just as well these LEDs always fail short circuit, or the lights would have a very short life. I remember early LED lights, before the individual LEDs were so powerful, the LEDs used to fail open circuit. Traffic lights aswell - you\'d see them with a third of the circle of LEDs off.

> Third, the use of fluorescent-compatible design introduces time-dependent current

Why?

even if the flicker doesn\'t bother you, it
can drive optical sensors of all sorts completely crazy (or radiate RF). But, you wouldn\'t
ever depend on a remote control to work, right?

I\'ve never had a problem.

The many-in-series current drive is inflexible, which is why the constant-voltage
drive into resistor-equipped short strings is so popular.

Resistors waste power. I\'ve only seen them in the low voltage strips used for cars, not in the mains powered ones, those all have constant current supplies. not sure why they aren\'t in the car ones, probably because people like to just connect different lengths up, and you can cut the strips to length. I used some to repair an old insect zapper, as I couldn\'t find mains UV LED strips.

There are long strips
of such paralleled short strings, easily available, and can be used with a variety
of the familiar 12V regulated DC supplies we all have a dusty box of...