The Firefly Micro Hydro system

by Greenstep NGO

The following construction is based on Jan Portegijs Firefly Micro Hydro system, ac-cording to an internet version from January 2003.Explanations and measurements for runner, nozzle and frame can be checked in this manual and will not be explained again.

The complete construction of the turbine was done in Cameroon. Therefore, all of the fol-lowing working steps as well as manufactured parts reflect the conditions of a workshop of a developing country.

1 Stator

In the picture below, there can be seen three self-winded coils with inner iron cores. They are placed in a form of coated wood.The number of windings for each coil is x. The diameter of copper cable is 1,6 mm. The coils are arranged in a 120 degree radius.The iron cores are made of pieces of packaging tie which is usually used for fixing heavy loads on pallets. Iron cores and the magnets on the rotor should have the same size. They should be placed in the finished generator on top of each other. The magnets cover an area of 25x50 mm, so the iron cores are 25x50 mm as well. The iron cores are not necessary for the functioning of the generator. However, they will increase the resistance of the generator. That means the power output will be higher com-pared to the same generator without iron cores running at the same rpm. The form of coated wood together with the coils will be filled with resin later. The coils are placed on a piece of glass fibre which gives the finished stator a stronger surface. The OD of the stator/ ID of the casting form is 210 mm.Beginnings and endings of each coil must be marked and remain outside of the casting area.The surface of the casting form must be covered with candle wax to ensure easy removal of the stator.

Fig. 1 Self-winded coils in casting form

Before filling the form with resin, it must be ensured that each coil has the same distance to the middle. Furthermore, all coils should have the same distance to each other (Fig. 2).

Fig. 2 Placing the coils next to each other

To ensure that the iron core properly functions, all cores inside the coils have to be con-nected to each other. To accomplish this, we formed a ring of the same material as the cores of the coils, and with a diameter which allows the iron ring and iron cores to have the most possible contact with each other.

To get a homogenous magnetic field inside the generator it is very important that all lay-ers of the complete iron core are shown in the same direction, and also in the direction of the magnetic field of the copper windings (Fig. 3)!

Fig. 3 Placing missing part of iron core

Before filling the casting form with resin, the coils and the iron ring should be fixed, e.g. with a wooden bar (Fig. 4).

There are different kinds of resins. Some of them consist of two components: resin and hardener. Other types need three components: resin, hardener and accelerator. We used the type with three components.

Using gloves is important (glasses too!), as is keeping the exact mixing ratio of the differ-ent components!

Fig. 4 Fixing the parts of the stator before filling with resin

After filling the form with resin some glass fibre was added again to get a strong surface (Fig. 5). The stator should be removed of the form before becoming completely hard!

Fig. 5 Casting form after filling with resin

Fig. 6 shows front and backside of the finished stator.

Fig. 6 Finished stator

2 Rotor

For the rotor, a steel disc with a thickness of 5 mm and a diameter of 160 mm was choosen. To make sure that the magnets cannot leave the disc during rotation, a flat bar around the disc was welded (Fig. 7).

The finished rotor will be a quite heavy load. To enjoy the turbine (bearings, shaft etc.) as long as possible it is important to ensure a smooth rotation.More specifically, this means paying attention to manufacture the disc as “round” as pos-sible. In addition, the hole in the middle for mounting with the shaft should be drilled as precisely as possible!

Fig. 7 Rotor disc with welded flat bar and attached magnet

Unfortunately, further pictures of the shown rotor in fig. 7 are missing. So the following steps are documented in pictures of a former rotor which was manufactured in the same way like that shown in Fig. 7.

Four permanent magnets were mounted on the steel disc. The magnets have an area of 25x50 mm.

Pay attention to attach the magnets in the correct order! If this step is done incorrectly, the finished generator will not work!

The magnetic poles will alternate north-south-north around the circle (Fig. 8). Therefore each block must be the right way up. Each time a magnet block is placed, hold it above its neighbour just previously placed. It should be repelled. If it is attracted, then turn it over and try again. If it is repelled then

place it without turning it over again. This will ensure that it has a different polarity than the previous block.

Fig. 8 Attaching the magnets in the right order

The distance of the centre of each magnet to the middle of the disc must be the same, just like the centre of the coils to the middle of the stator. That means the centre of the magnet and the centre of the coil should be on top of each other in future generators!Moreover, the distance of the magnets to each other should also be the same.

In Fig. 9 the finished rotor is shown. A piece of pipe was used as an inner border for the resin (removed after casting). Because of the flat bar outside, a casting form was not ne-cessary.

Fibre glass was not used to avoid unbalance. To protect the magnets. they were covered with resin. The level of resin is ca. 0,5 mm more than the thickness of the magnets.

Fig. 9 Finished rotor (mounted to the shaft)

3 Frame

The outer dimension of the frame is constructed according to the manual written by J. Portegijs. The inside is constructed to hold the shaft (Fig. 10).

Fig. 10 Modified frame of the turbine

4 Shaft and bearings

In former times the rod in Fig. 11 was a part of a shock absorber from a car. In the fol-lowing steps it will be modified for the shaft of the turbine.

Fig. 11 Rod from a car shock absorber

Bearings which fit very well to the rod are ball bearings number 6205 and 5200. In Fig. 12 the chosen bearings are mounted on the rod.The thread over the small bearing will hold runner and throw-off ring (for runner and throw-off ring see J.P.).

Fig. 12 Bearings mounted on the rod

After finding well-fitting bearings, the rod was cut (fig. 13). In the future the left part will work as the shaft of the turbine. The right part was supposed to be used to hold the rotor. However, there was a change in construction, and now the right part is not necessary for the following steps.

Fig. 13 Rod after cutting

To protect the shaft from corrosion it was painted with oil paint (there are still some prob-lems with the right use of that kind of colour ).

Because of the small oil drainage in the centre of the shock absorber (hole along axial dir-ection) it was easy to cut a thread for holding the rotor (Fig. 14).

Fig. 14 Painted shaft

Fig. 15 Tapped thread M10

5 Housings of bearings

For holding the bearing 5200 a piece of pipe is used. The ID is nearly the same as the OD of the bearing. To fit it very well the pipe was slotted in axial direction with a metal saw. To increase the ID it was bended. After that it was welded again. The pipe was connected to the metal sheet by welding. The housing is mounted on the frame with two threaded bolts M10.

Fig. 16 Housing for ball bearing 5200

Fig. 17 Assembly of housing and bearing

Bearing 6200 is fixed with two metal plates and 4 screws M6 (fig. 18).

Fig. 18 Housing of ball bearing 6200 from front and back side

6 Sealing

To seal the inside of the turbine a labyrinth sealing is used (for more information see J. P`s. manual).The sealing consists of three parts: a metal sheet, distance sheet and throw-off ring.

The distance sheet is made from a piece of a truck tire (Figs. 19 and 20).

Fig. 19 Piece of truck tire

Fig. 20 Finished distance sheet

Distance sheet and metal sheet are screwed together on the downside of the turbine’s frame (Figs. 21 and 22).

Fig. 21 Distance sheet placed on downside of the frame (bearing 5200 is mounted jet)

Fig. 22 Distance sheet and metal sheet mounted on the frame

Mounting the throw-off-ring will be discussed in the next chapter.

7 Assembling the Turbine

At first, the housing, including ball bearing 5200, is assembled (fig. 23).

Fig. 23 Assembling the housing with bearing 5200

Two legs of the turbine can be mounted now.

Fig. 24 Mounted legs on the turbine

The throw-off ring can be placed in the free space between the metal sheet and frame.

Fig. 25 Placing the throw-off ring

Next, the holder with the bearing 6200, the shaft and the runner can be mounted (fig. 26). The bearings must be positioned exactly to ensure that all parts are turning smoothly and balanced. Runner and throw-off ring should not scratch the frame or the metal sheet. To keep them the right distance away from frame and metal sheet, washers are used. The runner is fixed on the shaft with a nut from the former shock absorber.

Fig. 26 Assembled bearings, shaft and runner from above and below (legs are missing in upper picture)

The rotor is fixed with an M10 screw and a spring washer.

Fig. 27 Mounted rotor

In the next step one part of the turbine’s housing is screwed to the frame. After that the stator is assembled.

Attention: the rotor will attract the stator!

Fig. 28 Stator and a part of the housing are assembled to the turbine

The rotor and stator should be mounted as close as possible to each other. Because of a small wobbling of the rotor the gap between the rotor and stator in this turbine is limited to 3-4 mm (fig. 29).

Fig. 29 Air gap between rotor and stator

The second part of the housing can be attached. To change the alternating current (AC) to direct current (DC) diodes are used. They are mounted on the inside of the housing (fig. 30). To cool them down, a cooling part on the outside is assembled and connected to the diodes with screws.

Fig. 30 Second part of housing together with diodes

At the beginning, the nozzle which was used was exactly the same as described in J. Portegijs. After increasing the middle sheet of the original nozzle (by hand) a higher rpm could be noticed. Hence, a decision was made to form the nozzle as shown in Fig. 31.After connecting the nozzle to the PVC pipes, the gap between the nozzle and runner of-ten changes due to a bended angle bar which is holding the nozzle. To avoid changing the distance between nozzle and runner an extra bar was welded.

Fig. 31 Changed nozzle assembled with turbine

The completed turbine can be seen from front and backside in Fig. 32.

Fig. 32 Complete assembled turbine

The PVC pipe which is connected to the turbine has an inner diameter of 63 mm. The height between the forbay tank and turbine sight is 11 m. After an initial test, the follow-ing data could be measured:

- Produced Voltage disconnected to battery: 38 V - Produced Voltage connected to battery: 13,8 V - Charging current: more than 10 Amperes (exact measuring was limited by

multimeter: U(max) = 10 A)

(A turbine according to J.P’s manual assembled with a car alternator was installed on the same sight a year before. It was producing: Produced Voltage disconnected to battery: 22 V(!); Produced Voltage connected to battery: 12,3 V; Charging current: unfortunately not measured).

At a certain speed the turbine undergoes very rough shaking. The iron core may very well be the reason. All bolts need to be fixed with spring washers!!

Fig. 33 Turbine in action

Attention!!

- This layout of a turbine was not running for long; the vibrations are too strong. It got broken after 2 weeks of running (cracks in stator resin, cut cop-per cables, broken legs, melted connectors of cable)

- proposed solution for short term: increasing the gap between stator and rotor (fig. 29) up to 10 - 20 mm

- proposed solution for long term: new layout of stator and rotor needs to be de-veloped