Ok, this is an offshoot of the R/C-engine-as-mini-generator thread.
Can someone tell me about R/C engines? What aux components do I need to get one to run beside the engine itself (and the motor)? What should I be considering when building a 50W (perhaps 200W) portable generator?
For starteers, I did a little research. Seems like even a tiny 8-ounce engine can put out 0.5 HP (370 watts) of mechanical power! Are the manufacturer specs legitimate? If they are (meaning it’s 5x more power than I need), can I buy an even tinier one? But would a larger engine be better if I wanted to balance noise and fuel economy?
bear in mind that engines used for RC models usually depend on huge volumes of air moving around them for cooling. considerable power would have to be used to that end.
Hmm, I hadn’t checked on that one yet…
Let’s see. Ebay. Nitro fuel. 3 gallons for $115, incl shipping. Ok, and I thought $5 gas was expensive. 3 gallons of 80% methanol mixture is 7.2 kg is 160MJ is 45kWh. 50 watts for 250 hours (25% efficiency) is 50 cents per hour.
That’s 50¢ for .02kWH or $10/KWH, which is around 1000x as expensive as grid electricity. It’s also 2x as expensive as solar.
Are you sure that having an equal volume (of your generator) of rechargeable batteries isn’t a better idea?
Keep in mind that these engines are really fast revving. The peak power comes at 20-30 thousand rpms. So you’ll need some sort of gearbox to slow the output down before coupling it to an alternator. A gearbox like those RC cars have will probably do.
Progress Aero Works is a manufacturer of r/c diesels. Their smallest models are much smaller than two-stroke methanol/nitro ones. As small as 42g offering .07 hp (!). PAW also claims they don’t need any maintenance:
It also gives formulas for mixing fuel at home. The kerosene is dirt cheap (relative to that nitro/methanol) and available, although the diethyl ether might be a problem to source.
Most RC engines sittilg in one plaqce will be a little on the noisy side.
Where are you going to get the generator or alternator. And what about matching proper RPMs.
If you want an AC output With an 2 pole alternator your speed will have to be around 3600 RPM, a 4 pole 1800 RPM. Or you will also have to electronicly adjust the cycles.
With DC you are going to have to match the generator to the motor and have a way of regulating the exicitation.
I think you will end up needing a special generator or alternator and some way to electronicly modify the output to useable.
A solar panel would be cheaper and smaller with less noise.
Regulation circuits are a given. A high-rpm AC motor (or rather, a brushless DC with its electronics removed) will just get rectified into DC. Then, regulated to the correct ~20V.
Noise seems to be the barrier, but i don’t yet know what can be done about it. The youtube videos don’t seem to use mufflers, I don’t know what kind of effect RPM has, and whether I can somehow sound-isolate the whole thing.
I don’t have first hand experience but a friend of mine was really into this stuff. Whenever he got a brand new engine he would run it on the car without the cover for maybe one hour and then he would do the first rebuild. Later rebuilds were done every 5-6 hours or so. Note that this was back in the late 80s - early 90s. Maybe modern engines are stronger.
How much fuel do modern engines consume? I remember something like a litter per hour back then.
I don’t understand; Many years ago I used to fly RC planes. I’d use those engines for months and months without ever rebuilding them. Has something changed?
It’s certainly doable. Don’t know if it will be the best solution from an economic POV, but it should definitely be functional and be a nice conversation piece.
I don’t think you’ll have much luck with an airplane engine. They rely on tons of air for cooling and even then I don’t know if they wouldn’t overheat at sustained max output.
Instead, I 'd go with a 4-stroke boat engine. Over sized so it can be run at less than max output. I’d then add a closed system water loop with a small heat exchanger (radiator). It would need an electric water pump and a fan so some of the generated power will be lost to run those devices which needs to be taken into account.
To make it more economical you could look into gasoline powered boat engines. Yes they exist.
However, how about a lawn mover engine? Dirt cheap used, 4-stroke, regular unleaded… Probably the cheapest alternative. Also has a built-in cooling fan already. If you limit your output and don’t load it too much it should not overheat.
It seems there are two fundamentally different types of engines – nitro and diesel (glow plug and autoignition). Diesel is the older, simpler design which does not require any cleaning or maintenance. It is also much more fuel efficient. (Though I don’t actually know how efficient… even half of a liter per hour is rather unsustainable.) They’re also quieter, although they do spit oil and smell (when fueling them with castor oil).
Using a real, gasoline, spark-plug, 4-stroke boat/lawnmower/weedwacker engine has many advantages, but it is WAY overpowered. Anything that approaches the size and power of a readily available 1kW generator (and those are fairly compact) defeats the purpose of the exercise.
That is actually very cool. I haven’t investigated peltiers yet. Of course they are known for their inefficiency and expense, but their advantages are equally substantial. I’ll do some research on what it’d take to go to 50W.
Here is a company that makes self-contained commercial units: http://www.globalte.com/index.php?pageId=2&sId=31
Their smallest model (5030) is a 21W unit. It is 14"x14"x18" in size and uses almost a gallon of propane per day. Cost is not specified, but they sell to the military and oil/gas companies, if that gives anyone a clue.
But hell, we can do better, right?
This company is offering individual thermoelectric elements. A 20W unit measures 3"x3". Ok, that’s more like it. Its cost: $200. Err, ok, could be worse. Its advertised efficiency: 4.5%.
