first time question, and not much of an electrical guy. so please be patient.
My dad however, is an electrical engineer, who loves little goofy gadgets as most engineers do.
For Christmas I want to get him a stirling engine, something similar to this; http://www.amazon.com/gp/product/B00DS1NLXQ/ref=s9_simh_gw_p21_d0_i5?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-3&pf_rd_r=0MB6C0MFFEPQB5NAPB9P&pf_rd_t=101&pf_rd_p=1688200422&pf_rd_i=507846 ,
however I want to use the flywheel mounted pulley to run a small generator to charge a cell phone. I know its not practical but he would enjoy it.
my question is, is there any other options besides the bike generators devices available that can help keep this package "small". the charger is rated 5v @ 2.1 amps.
another thing I wonder about is the 5volt constant, if so I cannot know for sure if the engine is capable of holding a steady rpm being an engine that rely on temperature changes to work. is there a way to use capacitors to store the power so that the charger always gets what it needs.
wow, I guess in my head this was a lot easier. if anyone can help push me in the right direction that would be great. even if the best option is to come up with a different gift idea haha.
thanks in advance guys, and take care.
Best Answer
The first question is, can the engine produce the amount of power required?
5V @ 2.1 Amps = 10.5 Watts. We know your sterling engine can light a small LED, but that is probably only a fraction of a Watt. A typical bike dynamo produces around 3~4W at 20kph, but needs 10~12W of mechanical power to do it. So your sterling engine would have to produce about 20W to get sufficient power from a bike dynamo.
I don't know how much power that engine can develop, but I doubt it is even close to 20W. However the phone charger might still work with a more limited supply, so what kind of generator is required to get any power at 5V?
The engine is supposed to run at 1300~1500rpm. If we assume the lower figure under load then the generator needs to produce 1V for every 260rpm (260rpm/Volt). However you could use a belt drive with different sized pulleys to increase generator rpm and then the rpm/V would be higher, eg. at 1:4 it would be 1040rpm/V. This is similar to the Kv of small brushless motors that are used in model aircraft.
You could use a small brushless outrunner motor like this as an alternator, coupled to the engine via a 1:5 pulley set (20% extra rpm to account for electrical losses). The motor wires would be connected to a 3 phase rectifier (using Schottky diodes for low voltage drop) with a large electrolytic capacitor across the output to keep the voltage smooth. To regulate the output voltage you could use a 5V LDO linear regulator. The circuit might look something like this:-