Model Railway Forum

Hi, this is for carriage lights running of a 3.7v 650mah battery & 3v regulator to a 3v led strip & would like to dim them. Is there a better way to do this. Now, i assume if i put a lager resister in the lights will dim. But will i drain the battery quicker? Or would a Potentiometer be better or just the same. I am getting a good 8 hours run time & would like to keep as much as possible. Any suggestions.

Increasing the resistor will reduce the current flow and therefor lengthen the battery life in addition to dimming the leds. A pot will do the same but cost more than a fixed value resistor.

Hi, thanks for the reply. The led strip has built in resistors. So what sort of size Potentiometer do you think would be ok. I am looking as a similar one to below as i can drill a small hole in the carriage roof & the brass adjuster will look like part of the carriage. I can also balance the lights on the 6 carriages better.

Think I’d add resistors rather then drill a hole in the carriage.

What the problem is, some carriages are different sizes & some strips are longer than others & didn't want to keep experimenting with single resistors to get the same brightness in each carriage. So, in this case the adjustable one would be more flexible. These are the ones they sell.

Why not just try adding a fixed version first, say a 20k or 33k shold be about right to dim them right down. If still too bright try a 50k or even 100k.

When using the pot, connect the center and one outside pins only, again in series with the strip. You can add it to either side of the supply though convention is the positive. If the leds dim when turning the pot in the "wrong" direction, swap over the outside pin to the other side, keeping the center pin connected.

Edit: Oooops posted before your last one, try the 100k one.

LEDs brightness is difficult to judge by eye.

My approach would be to connect the LEDs to a pot , judge the required brightness, then measure the resistance of the pot, then use a resistance as near to the measured values.

Rgds

Chuffchuff wrote: ↑Thu Feb 10, 2022 8:14 am LEDs brightness is difficult to judge by eye.

My approach would be to connect the LEDs to a pot , judge the required brightness, then measure the resistance of the pot, then use a resistance as near to the measured values.

Rgds

Now, there's a less work alternative. My carriage's are getting complicated, but good fun & enjoyable work. Fortunately i am on ON30 & have a little extra room than HO/00.

Seems a fun build !

Just wondering if you have sourced latching reed magnets at a sensible price ?

I have taken a look on the net and they seem to be in short supply and / or expensive £25 on one source on eBay. ( I accept that eBay proving can be seen as a money laundering exercise for a number of Wilkinson stores based items)

Rgds

Hi, i got my ones athttps://www.layouts4u.net/electrical-it ... eed-switch & was a far better price. Just remember you switch them on/off using north/south poles. Not just a magnet.