Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Not sure I have an answer to your post Don, I have used both LED & incandescent bulbs and both have their strengths , LED's take much less power, but pulse greatly at lower speeds but are brighter, incandescent bulbs light (somewhat) at lower Rpm's to very bright...until you blow the bulb, I've never blown out an LED bulb.

The problems are total load versus on-off sensitivity.

An ordinary incandescent bulb is a resistive load, no different than a brake applied to a wheel. Hit the binders on a train, and things get mighty hot before slowly stopping the train.  Just like our brake, it gets hot and can stay lit momentarily, even as the generator is on the low end of its output.  That resistance helps a bulb smooth out lumpy low speed generator power. But yes, run them slow enough, even old car headlights dimmed at idle.

An LED is a different kind of light. It comes on and goes out instantaneously, with very little resistance, heat, or delay.  As our generator drops to minimum speed, it effectively flutters the LED as supplied voltage wavers around the minimum required by the circuit.

Selecting usable LEDs is another matter. Just as with bulbs, ratings matter.  Those designed to run at very low voltage may light bunches of lights, but may pop at high voltage if the circuit is overdriven.  I’ve popped LEDs using a battery pack to check a string.  The LED furthest away popped like a shotgun primer, startled me. Lol.  Incandescent bulbs will blow, but give warning as they get very bright when overdriven.

The key when designing a circuit is either matching output to load, a tricky proposition when generator speed and output  varies a lot, (and why we use alternators in cars nowadays), or adding a regulator. I get bogged down with circuit math, but in essence, you have to match load to output. Either govern the generator speed or use a regulator of some kind.  I’d google the circuit diagram and parts list for a simple low power battery charging circuit with a regulator.  Otherwise, youll pop a string of LEDs like fireworks while trying to entertain folks with your clever steamer, or you’ll cook the wiring trying to drive too many bulbs.

There are tons of different LEDs and bulbs out there. Thankfully there are circuit diagrams as well.  I used to once know the numbers, but not these days.  I learned after I used an unregulated output from an (AC STATOR) outboard motor to run lights. Worked great until I opened the throttle and popped the bulbs, leaving us out on the water, at night, in total darkness.

Hey guys, to help with the pulsing of LED's at low speeds, try connecting a capacitor into your wiring. Assuming you are using a dc generator (very important) you can put a capacitor across from the generator's + and - and it will function as a very short life battery to cover the power needs of your lights while the generator magnet makes another lap. This is a bit of a balance because if the LED circuit needs more power than your generator is producing at low speeds then you will still have pulsing. I have also employed a step down converter to step from 12v to 5v to drive LED's. With a capacitor in parallel with the generator before the converter, the generator is able to run even slower without pulsing because the converter is limiting the amount of power flowing out to the LED's. The other benefit of using a dcdc converter is that it will keep your LED's at a constant light level regardless of generator speed.  So going back to the original question, I totally think you should do LED's but understand it will take a bit of extra effort to make it work for you!

Wow, these step down converters look pretty neat. I had no idea they were so cheap and available.

How can one find out if the generators we are using are producing AC or DC?

for the sake of aesthetics never use LED.

Using a Multimeter in DC mode if it reads anything but 0v constantly then it is probably AC. If using the multimeter in AC mode, if it reads 0v, it is probably DC. It's important that the speed of the generator be pretty constant when you try to measure this. Hooking it up to a motor or drill while you measure is probably the best bet. I have a generator hooked up to a Jensen 25 that I have never actually attempting to read, might make a video when I do that.