OK, dumb question time!
Can you put a capacitor with a grain of wheat light bulb so it will stay lit for about 5 seconds while the power is off to reverse engine directions on an analog layout? The bulb will stay on regardless of the loco’s direction, correct?
dragenrider,
I’ve never tried it with a capacitor. I did have a simple circuit for constant intensity, bi-directional lighting for analog (DC) engines that keeps the light full brightness whether the engine is moving full speed or sitting still, as long as there is enough voltage to the rails to light the bulbs (about 3 volts). The neat part about the circuit is that the bulb in the trailing direction is lit dimly, but goes to full brightness as the direction changes. The parts include: 1 - 1 amp, 50 PIV bridge rectifier, 1 - 1N4001 diode, and two (or more) 1.5 volt bulbs. Cost is less than $2.00 plus the cost of the bulbs. It is wired in series with the motor, so it helps slow down the engine a bit.
Works great for DC. DCC has better lighting effects included in many decoders. Not compatible with DCC.
Mark C.
If the lamp is in parallel with the motor the capacitor will be discharged very fast by the low impedance of the motor. Also the capacitor would have to be bi-polar and very large in value and physical size. The lamp would still go out while the polarity changes. You could isolate the lamp from the motor with a diode bridge but the capacitor would still have to be large to light the lamp for any amount of time.
Anyone try this idea with a nicad battery instead of the capacitor? It would still need the bridge rectifier to maintain the polarity.
An electrolytic capacitor of the rating necessary to keep a light bulb glowing for even one second makes it rather large and expensive – and these capacitors are polarized and can explode if you reverse the polarity to them, which is what would happen when you reversed the throttle setting unless you added additional circuitry.
I have used battery backup capacitors like those in a VCR or DVD player that keeps the clock from losing time during a short-duration power failure to prevent flickering of marker lights on the back of a caboose where there was plenty of room for the associated electonics, but it would be hard to find room for one of these in a locomotive.
The caboose circuit required changing the trucks to ones with electrical pickups; a bridge rectifier to keep the voltage at the correct polarity regardless of direction of travel; the capacitor; and resistors to limit the current to the surface-mount LEDs.
The capacitor I used is rated at 4700 Microfarad @ 100 Volts, and costs $2.50 each from All Electronics, Van Nuys, CA. This rating capacitor will keep the LEDs lit for up to 5 minutes after the power is turned off, but it measures 1.39" diameter x 1.64" long. A grain of wheat or grain of rice bulb would probably drain this capacitor in two or three seconds due to their much higher current draw.
The same effect could easily and more cheaply have been obtained by putting a battery inside the caboose instead of all the complicated electronics; but here again, you don’t have that option with a locomotive.
I recomend using a bridge rectifier w/two leads soldered together. Another option is using a lighting kit designed specifically for analogue layouts
Ch
I think I just walked off into the deep end of the pool. Glub, glub!! [D)]
Sorry folks, I understood next to nothing of what you posted. I take it the answer is pretty much “no”.
Maybe we need to ask dragenrider what he is trying to do. My guess is that he has a 12 volt bulb connected to the track pickups and as he slows down the bulb dims. When he slows to change direction, the bulb is essentially off until he gets back up to speed. The rectified lighting circuit I mentioned above stays fully lit until the voltage is below about 3 volts. The engine will be stopped at 3 volts, usually, so he could change the direction switch and not have the lights go totally out. The circuit keeps the trailing bulb dimly lit, just like some diesels, and goes full intensity in the direction of travel, whether standing still (with at least 3 volts power applied) or full throttle. I really think this is what he is trying to fix.
Mark C.
Hey mcouvillcon where did you find the 1 amp, 50 PIV bridge rectifier , rdaio shack, and all electronics on the web did not have it. Was able to find the diode though. Also was trying to follow a arctile from april 1998 model railroader magazine about lighting, was having probelms finding the right capacitors from it also. What i a trying to do myself, is install at lest 2 1.5 grain of wheat bulbs in a dummy engine, and not have them flicker, what is the best way to go go about doing this? looks as if everbody has there own way of doing it, my skills at this are limited to say the lest. any help whould be nice. Thanks.
Gee, I never have that problem with my lights.
Full-intensity, auto-reversing, you can read waybills in the dark and see to couple…
NiCads or NiMH through my throttle…lay a screwdriver across the tracks and it still runs just the same, as do the lights.
RAM makes a high-intensity regulator-controlled constand lighting headlight. I just installed one for a customer in an FA.
3 or 4 V track power and it’s full bright.
Your reverse light should come on when you back up. You can make your headlight “dim” with diode arrays in reverse…
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