Can someone with an electronics background help me? I am installing a battery power R/C system and I would like to swap out the existing headlamps with 12V 25mA units from Radio Shack. I am using a 14.8V battery pack with a 2.6A continuous discharge current. How do I step down the power so I don’t burn out the lamps? Can you recommend a resistor I can get from radio shack?
Thanks for your help
Resistors limit current, not voltage. A diode will give a small voltage drop , but best would be a 12V regulator chip. The lamps will probably handle the 14.8V directly, but might be too bright and burn our prematurely.
What sort of loco are you working on? 2.6 amps constant current seems like an awfully heavy drain.
Are they incandescent bulbs or LED’s?
Tony, it is an early generation Bachmann Climax and I would like to use 12V incandescent bulbs. The battery is a Tenergy Lithion Ion 14.8V 2600mah.
OK.
If we cannot convince you to use a 12volt regulator then why not simply replace the anaemic orange LED’s with warm white LED’s. A suitable dropping resistor is already in the wiring.
Actually, I am fine using a 12V regulator. I’ve never worked with one before (Frankly, I don’t know a resistor from a capacitor or a diode) Radio Shack carries a 12V 1A version. Says it is rated up to 35V input. Has three prongs. I guess there is a +input, a +output, and a -ground. It appears to be configured for a PC board but I suppose it could be “free floating” as long as it is protected and the prongs are insulated with heat shrink.
I’ll take a look at the LEDs also. Never worked with them either.
It’s good to learn new stuff!
By the way, the lamps in the Climax glow a weird blueish color. I could probably live with them if they were orange, but blue is just too strange.
I would work with LED’s. Much easier to use.
Until a few years ago most white LED’s have a bluish hue. Replace them with what is called Warm White.
If the original loco wiring is in place there is a dropping resistor already there.
If you are rewiring the loco then put a 470R - 1000R value 1/2 watt resistor in series with one leg of each LED. They are polarised and the long lead goes to voltage +.
You haven’t said which brand of R/C ESC you are using but generally the lighting controls switch the short (-) lead.
I doubt very much the Climax will draw any more than 1 amp.
Tony, I can find 1/2 watt resistors but they state resistence in ohms (for example, 470 ohms). Is that the same as your 470R?
Thanks.
Yes it is.
Not a very clear image, but here is how they are wired.
(http://www.rcs-rc.com/app/webroot/store/image/2013-ESC/Wiring-Pics/OMEGA-3-QS.jpg)
Tony:
That’s great! Thanks so much for the information.
Joe
LEDs are easier to use but in my opinion the light they produce looks to modern compared to an incadesent lamp.
I typically use 14.8v LiIon batteries so if i’m putting lamps in a ‘modern’ steamer I use a 16v lamp so the lamp is bright. If i’m putting lights in an ‘older’ steamer like a climax or shay I use an 18v lamp so they will be dimmer. Remember that a 14.8v LiIon battery has an actual voltage of 16.8 volts when fully charged.
I’ve had the same lamps in my climax for 6 years now with no burnout. Also the current draw is very minimal. If i leave the light on the whole time it may change my run time by 5 minutes if that.
Terry
This website is a great tool for basic understanding of what we railroaders use in electronics…
I use it when I need to remember my rememberer.
