High Speed Connection

[WXYZCIENCE]

I find so many of these small weed wackers at the dump. This week I decided to mate one to my: High Speed Alternator. The first tests worked well until I shut it off. The alternator was turning at 12000 rmp and it sheared the 1/4" shaft.







I went back to the shop and constructed a one way clutch with a torque bearing. This allows the alternator to freewheel when the engine is stopped.






This fixed the problem the unit runs smooth, I was getting 50 watts per coil. Next while, I am going to mount the whole thing on to an aluminum base. The coils pictured in this last frame are mounted into a plastic holder.







I need to find out what the horse power of the weed wacker is to get a better understanding of the maximum power this unit will kick out.
Joseph

[peter vt]

Most weed-wackers are in the range of 3 horsepower, mostly due to the high RPM's. Just speaking from experience, as a former industrial maintenance mech.

[Norm]

Nice, but instead of trying to get the maximum

power I would prefer an alternator that would

be just large enough to handle a fast idle of

the weed wacker....the little critters are just

too noisy and waste too much fuel at high speeds.

   Does look like fun tho'

          ( :>) Norm.

[WXYZCIENCE]

peter vt, thanks I figured the horsepower per pound was very high. Seen guys make small remote aircraft with them.<Joseph>

[WXYZCIENCE]

Norm, I agree the noise is very loud, but 12000 RPM the weed-wacker was just idling. I will be adding my freq. counter to check rpms. At 12000 RPM the alternator can put out 1800 watts.
Joseph.

[Chagrin]

You aren't concerned with shaft breakage due to (inevitable) misalignment?

[stephent]

Most of the weed eaters have a centrifugal? clutch just behind the square drive point.

Any reason to not use it?

And you will be surprised at the actual rpm of the engine when you do measure it.

[WXYZCIENCE]

stephent, this one is called a featherlite, didn't have the centrifugal clutch. Most bigger one have the clutch.
Joseph.

[stephent]

Oh--ok.

Just never ran across one of those without one, my yard is kinda big so I buy the larger ones to use.

Neat Idea using one coupled to the high speed alternator you built.

[WXYZCIENCE]

Chagrin, the coupling has a bearing surface and spins very true. The alignment is very accurate but I don't know if the coupling will be able to take the torque over a long time. I may have use a stronger square stock.
Joseph.

[3rd Charm]

The cheaper ones are direct drive to the line spool.

They run no where near 12,000 rpm, most run no more than 3,600.

It is nothing like a small rc airplane glow engine which are deigned for those speeds.

If a weed wacker engine ran at 12,000 rpm the  line spools would explode, and you could just imagine how dangerous it would be with a brush cutting blade on it, and hitting a rock in the flower garden.

Now, a person could lean out a weed wacker engine and get some extra rpm out of it, but it will only run at that speed for about 2-3 mins before the piston melts and fuses to the cylinder.

Now that's quite a feat getting 1800 watts out of a 19 -23cc weed wacker engine, when my store bought 63 cc 2 stroke genset (which is about 3 hp) only puts out 800 watts ( a little over 6 amps) @115 volts.  (But it runs all day and is very quiet).

[TomW]

WXYZ;

I feel foolish saying this but couldn't you use some method of magnetic coupling in the driveline? Seems that might mitigate both shaft breakage and misalignment?

Not a mechanical sort myself, but just seemed obvious in a group so involved with magnets.

Cheers.

TomW.

[3rd Charm]

WXYZ; If you hooked up a wind vane governer (robbed off an old lawn mower engine) you could probably regulate it to put out a steady usable 2-300 watts @60hz. The clutches are fairly cheap  and consist of an outer hub with an inner slotted iron disc which usually screws on to the crankshaft of the weed wacker engine.  Or maybe you'll get lucky and find a discarded one with one already on it.

[jimjjnn]

A lot of small pumps are magnetically connected. I can't think of any reason that it can't be done with a whacker

[oztules]

Well Joseph,

Your inginuity never ceases to amaze me. Interesting project, and nice "clutch" system.

Simple and it works.

........oztules

[willib]

Nice idea Tom , and the allignment problem is solved because if its a little off it dosnt matter..

its good to see you posting again Joe & Oztules

how about a lever system to bring both halves of the coupler together and apart.

on second thought , joe is probably saying to himself , you guys are killin me here!

with magnetic couplers...i'm just trying to spin this baby up..?

lol

but it might get pretty violent if the alt caused the mags to decouple.

[Warrior]

"Norm, I agree the noise is very loud, but 12000 RPM the weed-wacker was just idling. I will be adding my freq. counter to check rpms. At 12000 RPM the alternator can put out 1800 watts."

Joseph, are you sure about the engines speed? i'd say it idles at 1200 rpm (twelve hundred), and might max out at 12000 rpm, depending on the engines' size, but they seldom go above 10000 rpm.

Warrior