Electrical Phase Converter I - Intro

Here's an interesting problem: How do you get a 3-phase 400V induction motor to run on 220V single phase electrical supply?

But first, how is that interesting... Aside from the obvious "square peg-round hole" nature of the question, if you can solve the problem, a host of wonderful industrial machines become available for home use.

In our case, we want to run 4 industrial-sized popcorn machines on our farm. Each machine is fitted with a 1-HP, 3-phase, 400V motor to turn the metal drum where the corn pops. The drum rotates over a line of propane burners. But our farm only has single phase 220V mains electricity.

If you're like me when I approached this problem, you don't even know the difference between 3-phase and single phase power. Basically, AC power oscillates the direction of current. Periodically the current has to stop and turn around. In single phase, the current isn't moving at that moment, and there is no power. In 3 phase, there are three currents and they never stop at the same time, providing continuous power. 3-phase produces a lot of other desirable effects in a motor, particularly that with three phases the electro-magnetic field induced by the currents can impart motion to the rotor. With single phase, the magnetic field simply oscillates and the rotor needs a kick start to get moving. This will be critical in understanding the situation later on. So remember, A SINGLE PHASE MOTOR CANNOT START MOVING WITHOUT HELP (e.g. spinning it up by hand or adding capacitors to another circuit). For more details check out Wikipedia on 3-phase.

In this case, I was able to overcome the lack of 3-phase power by simulating 3-phase power using a 3-phase motor running on single phase (details to come) to generate an electrical potential (voltage) in it's 3rd stator. That is, I hooked up two leads, started the motor, and then found the potential for current in the 3rd lead. Naturally the third lead was out of phase with the others. I then hooked up the popcorn machine's motor to run on the two single phase leads and the third, generated, phase.

Of course, this is all pointless since the input and generated voltages are somewhere around 220V. The popcorn machine requires 400V. The answer here was to reconfigure the stator leads into a delta formation from their original star formation. This is quite simple in practice, but I had no idea if it would work with my particular motor, since most dual voltage motors are marked as such on their name-plates. This one was only marked 400V.

After reconfiguring the motors (both where in star before), and connecting the wires as described, I managed to rotate the popcorn machine. Details pictures etc. to come.

Bamboo Windmill IV - Troubleshooting (Bearing)

The stone bearing has been a miserable failure. It worked previously, but now I can't manage to keep the windmill centred. There was some lateral movement - slipping between the bearing plate and the pointed stone. This was due to some unknown lateral force, which was also rolling the pointed stone out of place.

I decided to upgrade the whole bearing unit to a proper machined bearing. My first inclination was to use a bicycle bearing. As it turns out, the entire hub and axle of a bicycle wheel work quite well.

I extended the axle so as to sink it about 15cm into the centre post. I also used a large washer to spread out the load on the post. I welded two pieces of angle iron to the place where the bicycle spokes are meant to go. This provides the surface for the windmill to rest on.

I changed the grease in the hub before doing the welding. I forgot to account for the tremendous heat generated during the weld, and found the grease a bit liquefied. Hopefully this will not have any ill-effect.

One drawback to this bearing is that I've used the wrong type of bearing. A wheel bearing is a radial bearing (the load is meant to be applied perpendicular to the axis of rotation). In this application, the bearing is functioning as a thrust bearing, in which the load is applied parallel to the axis of rotation. This could cause the bearing to fail instantly under load, though I doubt it. Most likely, this will result in the bearing failing faster than it might under another application (e.g. on a bicycle).

Beehive I - intro

Honey has been a major part of African diets for centuries, predating almost all other modern food sources except fish. Before maize, sorghum, millet, beans, cattle, goats, and chickens were introduced to the diets of Southern African cultures, people here were fishing, hunting game, foraging indigenous fruit, and collecting wild honey. All of these traditional food sources are threatened today primarily by the destruction of indigenous habitats. Over-fishing and pollution plague the lakes and rivers. Wild game and fruit are now found only on protected lands. And honey has become scarce as a result of deforestation.

Honey bees are important for more than just food; they help to pollinate some flowers, including plants important to agriculture like okra, sunflower, soya, cotton, beans, pumpkins, and host of vegetables.

Our intention is to build a beehive that is cheap, simple, and effective. There are many local design from which to draw, ranging from an over-turned bucket to the bark of the brachystegia tree. There are also great designs world-wide, that each have their strong points. When it comes to a balance of simplicity and effectiveness, a Langstroth hive with a medium super and brood might be our best option.

The Langstroth hive has been used in America since it was invented in the 1850s. It uses removable frames to hold the honey, which allow the farmer to extract honey without disturbing the wax comb. This increases honey production since the bees don't have to rebuild the comb. It is portable and expandable. And by my estimates it will cost about $45 to build one in Malawi.

What is the potential for honey? Well, it is inexpensive to produce, costing little more than the expense of building the hive. Depending on the environment, the hive may be harvested upwards of 3 times per year. If one hive can produce 10 litres per harvest, the value of the honey would exceed $200/year (against a per capita GDP of $750/year).

In my experience, keeping beehives helps a farmer to suplement his income. But there is potential for honey to make up a significant portion of a farm's production, while also boosting crops through pollenation.

Western style Langstroth hive:

Modern African hive:

Traditional hive made from a log:

Bamboo Windmill III - Construction

I began building pieces of the windmill several weeks ago, as far back as March. But only last week did I finally get to assembling the whole thing. I decided to build this second version around the centre post, still in place from the first attempt. As such, I took a centre-out, top-down approach to the assembly.

First, the centre cage:
It's as simple as it looks: a rectangular box. The diagonals are in place to reduce unwanted play (an artifact of bad joinery). At the bottom of the cage, there is a smaller square that touches the centre post in four places. This keeps the cage vertical even though the balance is not perfect. Otherwise, the cage would tilt until the bottom of the cage touched the centre post - too much tilt.

A close-up of the bottom of the cage:

The bearing plate is also attached to the centre cage. It is a flat stone inside a bamboo frame. The frame is fixed to two bamboos in an X. This whole unit is then placed inside the cage, so that the cage rests on top of the bearing plate unit. The bearing plate rests on a pointed stone embedded into the top of the post. The cage is not tied down in any way (obviously, or it couldn't rotate); it simply rests on the bearing. Here is a close-up of the bearing plate:

After installing the cage, we lifted the top cross pieces into place. We tied the cross pieces to the cage. At this point, I was able to spin the windmill by hand. It seemed fairly free moving, but I had to shave off some of the centre post where the cage touches it at the bottom. The balance was a bit off, and I was beginning to fear some major flexing in the top cross pieces.

A close-up of the top cross piece:
The next post will show the assembly of the windsurfaces, their frames, and the last details. I have completed the windmill, if there was any doubt. It spins nicely, and I'm onto the pump - perhaps this week. Though this week also has a beehive, oil press, and evaporative cooler box on the schedule. HA!

Bamboo Windmill II - Design phase

(note: the pump used in conjunction with the windmill will be the subject of a future guide)

John Drake and the rest of the crew over at Africa Windmill Project designed the first two prototype windmills based on the following parameters:

• Cost: must be affordable for the poorest farmers in the world
• Materials: must be made from local materials so that repairs can be made without ordering spare material
• Simplicity: must be simple enough to be built and maintained by the end-user
• Functionality: must be capable of irrigating a garden of at least 1/4 acre

I've tried my best to keep the spirit of these parameters in my redesigns.

The State of the Art

Bamboo Windmill Prototype 2 plans by Africa Windmill Project

Panemone Windmill: a vertical axis windmill with pivoting wind surfaces. The wind surfaces (sails) face the wind on the downwind stroke, and pivot to run parallel to the wind on the upwind stroke, thereby reducing drag on the upwind stroke (and obviously maximizing force on the downwind stroke). This design was probably invented by the Chinese or the Persians at least 1500 years ago.

Jibe: when a wind surface crosses the path of the wind and catches thrust on the back side of the surface. Our previous design employed a stop-rope to stop the sail from pivoting past 120 degrees. This jibe created additional wind surface, but caused the sails to abruptly stop pivoting. This abrupt stop caused the windmill to spin unevenly. I would like to use a piece of bent bamboo under tension as a spring to gradually stop the pivot of the sail.

Joinery: Soft metal wire was used to lash the bamboo. Bamboo tends to vary in width across each section, which allowed the joints to slip especially under stress. New joints must be used.

Bearings: Two types were employed on Prototype 2: stone bearing and bottle-cap bearing. Both worked well. The central bearing was of the stone type: One flat stone resting on one pointed stone. The bottle-cap bearing was used for the pivoting sails: a bamboo shaft inserted into a hollow bamboo shaft (about 7cm long) with a bottle-cap at the bottom.

Design Changes

The joinery will be improved by passing the soft wire through holes drilled in the bamboo, thereby preventing it from slipping.

The bent bamboo supers will be replaced by straight pieces to reduce unnecessary stress.

All rectangular structures will have two fixed diagonals to prevent twisting.

The stop-ropes will be replaced with springs (of tensioned bamboo) if possible. Otherwise, the jibe effect will be discarded.

Sketches

As you can see, all lines are straight, doing away with tensioned bamboo. The sketch leaves out some diagonals which I intend to include in the construction. The cage should touch the centre post somewhere at the bottom and at the top by tightening the cage. This helps in balancing the windmill. Bamboo is a decent bearing surface and will eventually make grooves in the centre post.


Diagram 2 shows the theoretical function of the "jibe" (the top sail). Most likely this is impractical, if not inaccurate. I will try to facilitate the jibe by improvising a spring.

A look at the sail. Notice that the left edge is taller than the right. This facilitates clearance at the bottom and top and allows the top of the left edge to pass through a loose square of bamboo to hold it vertical while pivoting on the bearing.

A look at the bearing stone. (Don't use sandstone or other stones that are not hard, obviously). This works surprisingly well. It is greased with some petroleum jelly or old automotive grease, as available. (Actually, any bearing surface can be greased likewise.)

End Notes

I find working with bamboo a blessing and a curse. The blessing is that bamboo is lightweight, strong, and (sort of) straight. The curse is that it is difficult to pre-measure and pre-cut before assembling due to the inconsistencies of the bamboo and the difficulty of making any kind of box joint or end-to-end joint. Pieces must overlap, giving even a simple square 3 dimensions. Therefore, rejoice in a strong, light final product. But, struggle through the construction, measuring and cutting each piece as it is needed in the assembly.

I hope this post and the Africa Windmill Project website have given you a preliminary understanding of what I'm trying to build. You should have the benefit of a step by step guide through the construction phase. But ultimately, with bamboo every structure will be a unique design.

Bamboo Windmill I

I'm kicking this blog off with a project I'm pretty excited about: because it's fun, and potentially useful.

When we were babies, they used to mount mobiles above where we sleep to soothe us. So began our love of things that twirl. At last!, windmills are getting their share of popular attention and media coverage in the Age of Global Warming. (My prefered name for the age, though less widely accepted, is "The Age of Global OMG WE GONNA DIE!!!").

Why have windmills become so popular recently? Our infantile infatuation with things that twirl aside, the reasons are three: technology has made them better, they do not pollute very much, and every Tom, Dick, and Harry can build one. Search "DIY windmill" on YouTube for some inspirational successes, and some hilarious failures.

I recently joined up with the Africa Windmill Project to help build their second prototype windmill (the first prototype was built in Florida, USA). This prototype was constructed from local materials in the Central Region of Malawi, Africa. It cost us less than $60 to build and is capable of irrigating a 1/4 acre or more depending on what is planted.



Unfortunately, it was a prototype, and our construction skills with bamboo left much to be desired, chiefly strong joinery. It fell apart within six weeks, but not before getting our minds turning on the possibilities. After a little thought, I set out to build Prototype 3.

This is the How to Africa - Bamboo Windmill Guide:

• Design phase
• Construction phase
• Troubleshooting phase
• Implementation phase

Keep checking in as I work through the project!