Model Railway Forum

I was pondering the next project and using LEDs, so was taking a look through suppliers.

I found a pack of 50 LEDs and was about to take the plunge and I saw a warning that they were 3v AC ,

Wondering if the generic term LED, might cause a few problems in the future ?

Or even the term light emitting diode still applies ?

Rgds

LEDs in White will need around 3 to 4volts to operate. They should still be feed via a suitable series resistor to limit the current.
The "AC" comment has stumped me really, as LEDs work best on DC. While they will light on AC its considered poor practice to run them on AC without either a series diode or inverse diode plus the series resistor. Of course it is possible they have an inverse diode fitted internally already?

Can you supply a link to the LEDs, as it may become clearer?

AC LEDs are two LEDs reverse biased so in each sinusoidal cycle one LED will emit light in the upper curve and the other in the lower curve. I have never used any but can see no reason why they could not be used in a DC circuit as it would not matter which way round they were connected only one of the LEDs would be lit.

Richard

I agree and have seen AC LEDs sold - Rapid sell a few white versions and in Red too. Its exactly the same as an inverse diode, but uses an inverse LED instead, thus providing continuous illumination rather than flickering at the AC frequency (In the UK 50Hz) Though TBH you can not normally see the flickering. Cost from memory was considerably more than over that of a conventional LEDs The ones I saw were around £0.80p each but there may now be cheaper alternatives?

It must be remembered to always use a series resistor to limit forward current whether on AC or DC unless the LED is rated at the supply volts e.g. 12volt rated etc in which case a resistor is factory fitted internally.

IMO LEDs should be feed from a regulated stable DC supply.

The link is

https://www.rapidonline.com/truopto-osw ... 0--56-2312

The description states they should not be used with a rectifier.

Took a while to find them again, all I was find was Christmas lights !

Rgds

Those are indeed AC LEDs but still would need a series resistor. Why are AC LEDs needed?

Seriously consider using standard white LEDs and a suitable series resistor, all feed from perhaps a 12 volt regulated power supply.

Chuffchuff wrote: ↑Mon Nov 01, 2021 9:01 pm The link is

https://www.rapidonline.com/truopto-osw ... 0--56-2312

The description states they should not be used with a rectifier.

Took a while to find them again, all I was find was Christmas lights !

Rgds

That comment in the description seems odd, there is no mention in the data sheet except to say it is an AC LED which internally is two similar LEDs reverse biased as expected. The only possible reason for the rectifier comment is neither of the two LEDs can withstand a continuous current as in a DC circuit and need the ON/OFF of the sinusoidal AC, but I would expect that would be in the data sheet which is the document that circuit designers would refer to rather than Rapids description.

The bottom line as Brian has said, it is an expensive LED to use where a cheaper standard LED will do.

Richard

The data sheet does confirm there are twin leds.