Overspeeding a 2 pole 3600 RPM gen head?

[BioHazard]

I'm building my own little "APU" for my pickup based on the Harbor Freight 800w 2 cycle generator. With the gas tank and plastic panels removed, it is remarkably small. I am going to make a custom water jacket for the head and exhaust to preheat my engine coolant. The generator itself will power an onboard 12v charger as well as block heaters or air conditioning depending on the season. Still figuring out some kind of electric starter for it, but want to retain the pull start.

I understand that 2 stroke engines usually spin a lot faster than 3600 RPM. I'm pretty sure the only reason this one does is to make 60hz @ 120v with the 2 pole generator head. How is the gen head going to respond if I bump the engine up to 5000-7200 RPM? Obviously the frequency would go nuts but would the voltage and wattage output increase? Would it be possible to double the speed and generate 240v?  Or would I just let out the magic smoke?

I understand this would decrease engine life but at less than $100 per generator I can afford to experiment. I love this little thing. I am seriously considering odering a container load of them from China. But I think it can do more than 800w....

[mobile_bob]

there is a thing called the "cube law" it goes something like this
doubling the speed produces 8 times the stress ( X * X* X= ?)
( i might be wrong here, perhaps a ME can elaborate, however if not the cube law, there is some equation that could be
used to explain the non linear relationship of rpm vs stress)

what i am unsure of is what safety factors the rotor is setup or could be expected to handle
the rotor might well be thrown apart from a dramatically increased centrifugal forces?

if you can keep the thing from flying apart, yes it will produce 240vac at 7200rpm, or something close to that
provided you alter the excitation capacitor so that it works at that frequency, which will of course be twice what
it was at 3600rpm.

theoretically the stator could handle the same amperage at 240 that it does at 120 so the end effect would be twice the wattage
capability at twice the speed, however in practice it will likely need to be derated just a bit. perhaps 1400watts at 240 vac might be a good
number.

you might want to put the little bugger into some sort of containment as it might well work for a while and then unexpectantly and violently explode?

might be an interesting project

one question, what do you plan on powering at 240vac 120hz?

bob g

[BioHazard]

one question, what do you plan on powering at 240vac 120hz?

LOL, I'm not exactly sure yet. It could be a heating element. I am installing pad heaters on everything with liquid in it to pre heat and thin out the fluids. (got about 3 gallons of 75w90 gear oil to heat up not counting the engine and it's oil/coolant) I'm also working on some sort of custom electric air conditioning, my truck originally came with A/C in 1973 but someone took out the compressor and other parts. All I have is an evaporator. I haven't decided how yet but I want electric A/C.

Also at 800w, I can only power about a 45A 12v "motor home converter", maybe I could get a higher amperage 240v converter that doesn't care about the Hz? Also want to power some serious flood lights, they shouldn't care about Hz.

I may end up with two of these things under the hood with pull starters coming out of the grille. LOL

[vdubnut62]

   RING_DA_DING DING DING BOOM
Ron

[rl71459]

Clack... Clunk! Screach!

[BioHazard]

Clack... Clunk! Screach!

That was the sound the first one made when it broke, at 3600 RPM. Thank god I have the warranty. 

[vdubnut62]

BioHazard  I'll bet that everyone of 'em will sling the windings plum out. Much smoke and shrapnel, Grasshopper.
What the hell, I'll bet you had a lot of fun trying anyway.
Ron

[wiebe]

Here they are 220 volts 600/800 watts ,so there must be some wire,s to be changed .
Ore wil they put a diverent gen head on it ,i dont think that.

[Horsepoor]

Have you considered a cheap 5,000 BTU portatble 120 V airconditioner? I buy them on sale usually this time of the year for just over $70, must look for sales.

http://www.google.com/products/catalog?hl=en&wrapid=tlif129628749702110&q=5000+btu+air+conditioner&um=1&ie=UTF-8&cid=6307869222181177395&ei=CMdDTeXwAsGp8Abch_iTAg&sa=X&oi=product_catalog_result&ct=result&resnum=3&ved=0CDgQ8wIwAg#

This link is not a good price but illustrates the product.

Living in hurricane prone south Florida, I own three window shakers as a quick and low power replacement for central air conditioners. Runs on 500 watts, easily starts with little two stroke generator. In 2005, I made a simple duct system to channel the cool air. I used a Home Depot dryer rectangular manafold which fit very nicely over the cold air exhaust port when duct taped which I ran into 4 in flexible dryer line used to direct cold air into a (clean) horse trailer with cot used for emergency shelter.

I know it sounds redneck, putting a 800 Watt two stroke generator in the bed of your pickup truck along side a window shaker air conditioner, then ducting the cold air into the passenger compartment. But its no more redneck that camping out in a horse trailer doing the same thing. I was UNBUG BITTEN and slept comfortably for several nights. I wonder if there is an application here to cool your pickup truck cab?

[BioHazard]

LOL, yeah, I've thought about the little window A/C units. I bought a 5000 BTU unit last year that only draws 400-something watts. I've considered ripping one apart installing the compressor and condensor under the hood, and then use the stock truck A/C evaporator. Not sure how well that would work though. I know they make specialized 12v A/C compressors that would work, but we're talking big $$$$.

That's exactly what I want to do though, be able to sit in my truck with heat, A/C, lights, and music, without the engine idling. My 350 V8 burns at least 1.5 gallons/hour at idle while this little generator can run 5 hours on that much! I plan on installing four batteries to go along with my little APU and an extra 3kw inverter.

I may in fact just remove the 2 pole gen head and use a standard car alternator to get a few more amps. I figure this little engine is good for at least 3-4hp with a speed increase. A car alternator is smaller anyway....

Wish I could get ahold of one of those 3hp Changfas...