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High Speed Connection
By WXYZCIENCE, Section Diaries Posted on Sun Jun 24th, 2007 at 04:03:30 AM MST
Finally a Use For Weed Wackers

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

High Speed Connection | 16 comments (16 topical, 0 editorial)

Re: High Speed Connection (3.00 / 0) (#1)
by peter vt on Sun Jun 24th, 2007 at 06:46:05 AM MST
(User Info)

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.
Power to the people!

Re: High Speed Connection (3.00 / 0) (#3)
by WXYZCIENCE on Sun Jun 24th, 2007 at 09:12:56 AM MST
(User Info)

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

[ Parent ]

Re: High Speed Connection (3.00 / 0) (#14)
by oztules (oztules__at__bigpond.com) on Sun Jun 24th, 2007 at 04:28:26 PM MST
(User Info) http://www.anotherpower.com/gallery/Oztules-toys

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

Simple and it works.

........oztules
Flinders Island Australia
[ Parent ]

Re: High Speed Connection (3.00 / 0) (#2)
by Norm (peppysue@suite224.net) on Sun Jun 24th, 2007 at 08:19:57 AM MST
(User Info)

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.
( :>) Norm

Re: High Speed Connection (3.00 / 0) (#4)
by WXYZCIENCE on Sun Jun 24th, 2007 at 09:30:14 AM MST
(User Info)

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.

[ Parent ]

Re: High Speed Connection (3.00 / 0) (#16)
by Warrior on Mon Jun 25th, 2007 at 12:56:51 PM MST
(User Info)

"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

Warrior__ "Why can't Murphy's Law be used to my advantage??"
[ Parent ]

Re: High Speed Connection (3.00 / 0) (#5)
by Chagrin on Sun Jun 24th, 2007 at 11:52:27 AM MST
(User Info)

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

Re: High Speed Connection (3.00 / 0) (#9)
by WXYZCIENCE on Sun Jun 24th, 2007 at 03:07:53 PM MST
(User Info)

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.

[ Parent ]

Re: High Speed Connection (3.00 / 0) (#6)
by stephent on Sun Jun 24th, 2007 at 12:30:52 PM MST
(User Info)

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.

Re: High Speed Connection (3.00 / 0) (#7)
by WXYZCIENCE on Sun Jun 24th, 2007 at 02:57:20 PM MST
(User Info)

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

[ Parent ]

Re: High Speed Connection (3.00 / 0) (#10)
by 3rd Charm on Sun Jun 24th, 2007 at 03:10:42 PM MST
(User Info)

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).

[ Parent ]

Re: High Speed Connection (3.00 / 0) (#8)
by stephent on Sun Jun 24th, 2007 at 03:06:24 PM MST
(User Info)

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.

Re: High Speed Connection (3.00 / 0) (#12)
by 3rd Charm on Sun Jun 24th, 2007 at 03:30:19 PM MST
(User Info)

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.

[ Parent ]

Re: High Speed Connection (3.00 / 0) (#11)
by TomW on Sun Jun 24th, 2007 at 03:19:59 PM MST
(User Info)

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.

"Education consists mainly of what we have unlearned."--Mark Twain

Re: High Speed Connection (3.00 / 0) (#13)
by jimjjnn (jimjjnn at yahoo dot com) on Sun Jun 24th, 2007 at 03:51:54 PM MST
(User Info)

A lot of small pumps are magnetically connected. I can't think of any reason that it can't be done with a whacker
Jim Denver,CO
[ Parent ]

Re: High Speed Connection (3.00 / 0) (#15)
by willib (willibur at comcast dot net) on Sun Jun 24th, 2007 at 07:58:23 PM MST
(User Info) http://www.njwind.com/webcam.html#

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.
Carpe Ventum (seize the wind)
[ Parent ]

High Speed Connection | 16 comments (16 topical, 0 editorial)

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