Model Railway Forum

Hi Brian and Richard - thanks for all the information.

The beacons did come from Kytes Lights - they came with two resistors for using with a 12v supply, and a battery box for two AAA batteries giving a 3v. supply.

Initially, with just the beacons wired into the 3v supply (though the voltage regulator) they worked fine - straight off the bus, no resistors - I then cheated and wired the taxi lights to the bus, and everything started flashing. I disconnected the taxi's, and removed the voltage regulator - so the bus was now 9v (only had a 9v psu), I wired in the two resistors to the negative wires on the beacons (one each) - the instructions said to wire the resistor into the negative wire - with this done the beacons came on but didn't flash - so I assume need 12v? Although Brian says 9v should power fifty LED's - but as I said, with 9v the beacons don't flash.

The voltage regulator came pre-wired, with a pair of wires for power in, and a pair for power out. No resistors, and no mention of using them.

Using the link Steve M posted, I think I need 330 ohms resistors. Barry

330 Ohm is very low! I would opt for a minimum of 1000 (1K) and perhaps even 1500 (1K5) on 9 volts DC.
I feel 680R is about the lowest you should consider on 9 volts DC!
I suspect and without seeing the regulator, it contains built in resistors and an IC to reduce volts.

Thanks Brian - I have ordered some 1k resistors. With a 12v PSU how many amps should it be for the likes of powering LED's - they seem to be 1 or 2amps or sometimes a bit higher. Barry

If you're needing more than 2.0Amps at 12 volts then you're seriously onto mega power!
1.0A to 2.0Amps for LED feeding will be fine. Some will go for a 4.0 or 5.0Amp 12v PSU and then sub divide the output in four or five separate Sub feeds and protect each of these subs with a 1.0Amp fuse or self resetting Circuit Breaker.
But unless you're in need of such, just go for a single output PSU of 2.0Amp maximum.
I have listed some PSU and connectors in this post here...https://www.modelrailwayforum.co.uk/vie ... f=9&t=3215 See my post #6.

My "Rule of thumb" for 'Standard' LEDs. when looking at LED current is to allow on a 12v DC supply with each LED having a series 1K resistor 0.01Amp (10 milliamp) per lit LED. So a 1.0 Amp power supply can technically feed 100 lit LEDs, but in practice you would not load the supply to its maximum allowing it to reach only around roughly 80%-85% max loading. So then the total LEDs lit are around 80 on a 1.0A and around 160 on a 2.0Amp supply.
Increase the resistors Ohm value and you reduce the current draw of that LED and reduce its brightness. But go too far with the resistors Ohm rating (Say over 10K) and eventually the LED wont light or will become very dim! There are now low current LEDs that only need a two or three milliamps to illuminate brightly.

Thanks Brian - that is very helpful. Barry

If the resistor can be connected to either +/-, why on the belisha beacons from Kytes Lights would it say the resistor (supplied) has to be attached to the negative lead? Whereas the lamp posts it says resistor can be attached to either +/-? Something to do with the flashing?

I'm assuming that the Kytes BB has some sort of circuit board? If so, I guess that the resistor then has to be in one specific lead. But TBH I can see no real reason for this without a circuit diagram of how the BB works.
For any ordinary LED it matters not a jot which of its leads the resistor is inserted into.

The BB's just came as BB's - no external pcb, with two wires (blue and red) to be attached, via the resistor (blue wire) to a 12v power supply.

bulleidboy wrote: ↑Tue Oct 20, 2020 10:44 pm The BB's just came as BB's - no external pcb, with two wires (blue and red) to be attached, via the resistor (blue wire) to a 12v power supply.

So Im now more convinced they are basically just a flashing LED and each is acting as the beacon.

Brian - I'll report back when 12v supply and appropriate resistors are fitted - thanks for all your help. BB