index page


Picture: The first time the prototype charger was running at the site in pilot village Cambulo, Banaue, Ifugao prov., Philippines.


1 Introduction
1.1 How did it all start: The Cambulo project
1.2 Plan for introducing the firefly concept in other areas
1.3 Set-up of the book
2 Key characteristics of the firefly system
2.1 Micro Hydro systems in general
2.2 The firefly system itself
2.3 The user group
2.4 Battery is the most important component
2.5 The firefly compared to other lighting systems
3 Local conditions
3.1 Availability of year-round water
3.2 Need for electric light
3.3 Possibilities for local production
3.4 Social and economic aspects
4 The charger
4.1 Standard charger design
4.2 The alternator
4.3 The runner
4.3.1 Making the blades
4.3.2 Making the side disks
4.3.3 Soldering it together
4.4 Fixing the runner on the shaft and aligning it
4.5 Seal around the shaft
4.6 The nozzle
4.7 The frame
4.8 The covers and shield
4.9 The switchboard
4.9.1 Functions of the switchboard
4.9.2 Field current control
4.9.3 The indicator
4.9.4 Adjustment of the voltage regulator
4.9.5 Charging characteristic Introduction The relation between charging current and battery voltage When is a battery charged enough Voltage and current as a function of charging time Effects of battery type on charging characteristic Effects of the charger on charging characteristic
4.9.6 Building the switchboard
4.10 Installing the charger
4.10.1 Introduction
4.10.2 Linking in with irrigation technology
4.10.3 Designing an inlet
4.10.4 Designing the canal
4.10.5 A site for the charger
4.10.6 Linking the parts together
4.10.7 The forebay tank and screen
4.10.8 The penstock pipe
4.11 Testing and troubleshooting
4.11.1 Introduction
4.11.2 Final check
4.11.3 Trying it out
4.11.4 Measuring its performance
4.11.5 Troubleshooting
4.11.6 Checking diodes of an alternator
5 The home system
5.1 The battery
5.2 Lamps, switches and cables
5.3 Minor uses for electricity
5.4 The charge indicator
5.4.1 Introduction
5.4.2 How to avoid deep discharge of batteries
5.4.3 Buying components
5.4.4 Building the indicators Electronic circuit and parts list Print lay-out and making the PCB Fitting the components
5.4.5 Testing and troubleshooting
5.4.6 Calibrating indicators
5.5 Installing home systems
9 Literature
Please note:
The 1995, paper version of this manual was intended to be a draft version only. There was a plan for more chapters and annexes. I already made cross references to these and I listed them in the contents section.
As things look now, it is unlikely that I will ever write these missing paragraphs and annexes. To stay close to the 1995 version, I didn't remove these 'ghost' paragraph- and annex headings from the contents section and all cross references to these. Cross references to existing paragraphs are links now while cross references to ghost paragraphs and annexes are just text.
6 Using the system
6.1 Manual for users
6.2 Manual for operators
6.3 Maintenance and repair
6.4 Possible financial arrangements
7 What is needed for a demo project
7.1 Materials
7.2 Tools
7.3 Technical skills
7.4 Technical support from outside
7.5 Money
8 Organisational aspects of a demo project
annex 0 Formulas and reference data
annex A More about alternators
annex B Adapting the charger design
B.1 Matching charger capacity with user needs
B.2 Designing the turbine part
B.2.1 Firefly turbine differs from normal crossflow design
B.2.2 Principles behind design calculations
B.2.3 Energy calculations
B.2.4 Runner diameter and alternator speed
B.2.5 Head, runner width and dimensions of nozzle
B.3 Design for a large capacity - low head charger
B.4 A switchboard for charging more batteries in one go
annex C More about batteries
C.1 General characteristics of lead-acid batteries
C.2 Chemical reactions
C.3 What makes batteries wear out
C.3.1 Corrosion of grid in positive plate
C.3.2 Active material falling out of positive plate
C.3.3 Sulphatising
C.3.4 Poisoning by dirt or unpure water
C.3.5 Mechanical damages
C.4 Open cirquit voltages
C.5 Internal resistance
C.6 Gassing voltage
C.7 Testing batteries
annex D More about charge indicators
D.1 Strategy to prevent deep discharge of batteries
D.2 Demands to charge indicator design
D.3 Electrical characteristics of indicator design
D.3.1 Open circuit voltages
D.3.2 Current compensation
D.3.3 The way the indicator works
D.4 Electronic cirquit of charge indicator
D.4.1 The electronic cirquit itself
D.4.2 Switch S
D.4.3 Supply voltage
D.4.4 The current shunt
D.4.5 The LM 3914 `display driver' chip
D.4.6 The voltage at the `sig in' input
D.4.7 The reference voltages and the reference current
D.4.8 Temperature stability
D.5 Checking components
D.6 Making PCB's
annex E Building your own testing and calibrating equipment
E.1 A stabilised voltage supply
E.2 A speed counter / diode tester
E.3 A small electrical drill
annex F Direct connections instead of batteries
annex G Environmental aspects
annex H Social and economical aspects
annex I Report on Cambulo pilot project
annex J Selecting a site
annex K Alternatives for the home system


List of figures
1.1 A real firefly. It's an impressive sight to see thousands of them twinkling in a tree on a moonless night.
1.2 High school students testing the charger they have built. The man listening so attentively is their physics teacher. With thanks to the Gouda firebrigade for lending them a pump.
2.1 Typical layout of an installed firefly charger, schematic drawing.
2.2 The first prototype in the workshop where it was built. There was no drill, holes in the frame had to be cut using an electric arc welding set at full blast. Covers are not fitted yet.
2.3 The Cambulo coop store.
2.4 Ben Nanglihan is preparing a battery for use. Connections are made and it must be filled with acid: A tricky job. He'd better wear safety glasses and have his son playing somewhere else.
3.1 Cambulo, the pilot village of PRRM's Micro Hydro project. To irrigate the rice terraces, there are small irrigation canals and one of them was used for the charger.
3.2 Rosita Bentican signs a loan agreement. Materials for the home system were sold on installment basis. Rosita is a teacher so she needs good light at night and earns enough to afford it.
3.3 The trail to Cambulo: A 12 km hike to the nearest road. It is unlikely that Cambulo will be connected to the national grid in the foreseeable future.
4.1 The standard charger: Not a big thing. The shield around the runner is not fitted yet.
4.2 The charger seen from below. The amount of water coming through it is quite impressive.
4.3 Characteristics of standard charger.
4.4 Making the blades.
4.5 Bending blades with a makeshift press.
4.6 Making side disks.
4.7 Using modified jigsaw sawblades for cutting slots in side disks.<< Nog noemen: Het kan ook met hacksaw sawblades that are grinded off at the side opposite of the teeth.>>
4.8 A modified vernier calliper for marking circles on steel.
4.9 A jigsaw machine adapted for cutting side disks in series.
4.10 A modified jigsaw sawblade for use with a jigsaw machine.
4.11 Soldering a runner.
4.12 The seal and the way to fix the runner on the shaft.
4.13 The separation sheet.
4.14 The other parts of the seal.
4.15 Sides of the nozzle.
4.16 Two possible shapes for a blocking timber.
4.17 Nozzle sides assembled.
4.18 The extension pipe.
4.19 A flanged connection, please note: Not on scale 1:1.
4.20 Parts of the frame.
4.21 The frame assembled.
4.22 A square made out of one piece.
4.23 The frame with the nozzle welded on.
4.24 Covers and shield.
4.25 Electrical circuit of the charger.
4.26 A scale for the indicator.
4.27 Relation between charging current, voltage and state of charge (copied from VAN DER MEER, 1990).
4.28 The charging process as a function of time.
4.29 A complete switchboard.
4.30 The back side of the switchboard front panel, with all components and wiring fitted.
4.31 Modifying a mechanical, 6-wire Japanese voltage regulator.
4.32 An expensive, permanent forebay tank.
5.1 Ruud Portegijs helps Leon Bentican wiring up his house.
5.2a Stabilised voltage supply for 6 V output. For 9 V output, use device `7809' instead of `7806'.
5.2b Stabilised voltage supply for 4.5 V or 3 V.
5.2c Charging NiCd batteries with a series resistor to achieve the right current.
5.2d Constant current device for recharging 1 up to 6 NiCd batteries in one go.
5.2e Circuit for recharging small, 6 V, maintenance-free lead-acid batteries from the main battery. The LM 317 must be mounted on a piece of aluminum for cooling. The part of the circuit with transistor and LED's can be omitted, it only serves to show whether the charger is functioning and whether the battery is charged already.
5.3 Electrical circuit of home system.
5.4 Component layout and copper pattern of the Printed Circuit Board for the indicator.
5.5a Twelve copies of the PCB copper pattern (in mirror image) fitted on standard size PCB board.
Note: For correct dimensions, print this figure at 300 DPI (Dots Per Inch).
5.5b Alternative: Eight copies of PCB design with current shunt.
Note: For correct dimensions, print this figure at 300 DPI (Dots Per Inch).
5.6 An indicator with copper wire switch. This one has an older version of the PCB: A lying trimmer is used and the placing of some components is different. The wound-up wire underneath is the current shunt.
5.7 Cross section through copper wire switch.
5.8 A plexiglass cover.
5.9 Relation between state of charge and open circuit voltage. Treshold voltages and reference voltages of the indicator are also drawn in.


List of tables
4.1 Calculated performance of standard charger.
4.2 Connection codes of some suitable types of alternators and regulators.
4.3 Guidelines for choosing the inlet and charger site, and designing the canal.
4.4 Trouble-shooting guide.
5.1 Selection of cable type.
5.2 Parts list for the charge indicator.


List of text boxes
2.1 Hydro power at different scales.
2.2 Privately owned chargers.
4.1 Condition of the alternator.
4.2 Orientation of brushes and direction of rotation.
4.3 Blades with rounded inner sides.
4.4 Bending blades in series.
4.5 Building or buying side disks.
4.6 Using side disks without slots.
4.7 Firefly runner and nozzle design.
4.8 Modifying a vernier calliper for marking circles on steel.
4.9 Making side disks in series.
4.10 Strength problem.
4.11 Machining runners in series.
4.12 A flanged joint.
4.13 Faster construction of the square.
4.14 Changing the setting of a non-adjustable regulator.
4.15 Voltage spikes.


Tips for reading and printing this manual
  1. Some drawings might be wider than your browser window and then a horizontal scrollbar will appear. Such drawings are easier to view when your browser window is as wide as possible. Maybe select a larger screen size in your computer system settings.
    A wide browser window makes that text is printed with very long lines. For reading the text only, a narrower window might be more comfortable. Or you might select a larger font size ("Text size" in "view" menu) to make text better readable.
  2. For viewing pictures: Adjust `brightness' and `contrast' of your monitor such that the full color range is distinguishable ("dark grey" should look different than "black"). Text becomes easier to read when brightness is adjusted very low and contrast so high that the white background is just light enough (then "dark grey" and "black" look the same).
  3. For printing the text: Try out first which font size setting (see above) gives well readable text without using too much paper.
  4. If you use the "print" option of your browser, most likely drawings will not be printed at the right scale. For printing drawings to scale, you need a copy of the image file at your own computer. If you downloaded and unpacked the manual, you can just select the right image file: Its file name starts with its figure number. If you are viewing it on-line: Right-click on the drawing you want and choose option "Save picture as" to download it.
    Open the image file with an imaging or photo processing programme and print it at 150 DPI (Dots Per Inch). If it is not possible to specify a DPI in the `print' option, look for an option like `adjust image size', and then set it to 150 DPI while maintaining file size.
    Please note: Figure 5.5.a and figure 5.5b must be printed at 300 DPI to get them at the right size.
  5. There is no index. For searching on keywords in the downloaded version, you might use the windows "find" tool to get a list of files where a keyword is mentioned. Below, the procedure for Windows NT is given, for other Windows versions, it might be a bit different: For searching in the online version, you might use the "Search" function of mr. Klunne's main micro hydropower page and open only pages in subdir ".../portegijs/firefly_bm"


Preface to 1995 draft, paper version

This book is meant as a manual for building a firefly Micro Hydro system and setting up a firefly demonstration project. It is still a draft version. The chapters on technical issues are reasonably well worked-out by now. The introduction chapter, the ones on the firefly system in general and on local conditions have not been written with that much care. The last two chapters and many of the annexes have not been written yet. In an attempt to keep copying and postage costs within budget, the annexes that are available, are not printed in this book. These can be requested with me. Most of them deal with the considerations behind the technical design and are not relevant for people who just want to build a system. Background information that might be relevant to some readers, has been printed in boxes dispersed through the text. To keep lay-out work simple, these boxes are not printed as separate blocks of text, but only printed in italics and numbered.

For people who have got the previous draft version (of July 1994), an overview of the major changes might be interesting:

To improve this draft version further and turn it into a useable book, I would very much appreciate reactions from readers. So please take time to write me your comments.

Another request to readers: I would like to receive data on firefly systems that have been built and installed. Aspects that are important to me are:

I know that answering these questions in detail would take too much time for most readers. So please write down some basic information rather than to postpone writing until you find time to answer them all. Of course I am willing to give advice to readers who write me about problems they could not solve themselves.

Finally, I would like to thank some of the people who have contributed to my work on the firefly system. First there is engr. Simon Taylor, my successor at PRRM-Ifugao. His letters gave many hints on aspects of the design that weren't worked out properly yet and kept me in touch with what happened in the Cambulo project. Two frends gave valuable comments on the technical design: Willem Steyvers van Orsselen, a marine engineer, and Siem Broersen, an electronic engineer. Then there were the people who took the time to test-built some major parts: Catharien Ternisscha van Scheltinga and Jacobijn van Etten who built the charge indicator, and Fleur de Bruin, Gonnie van Dijk, Joost Kaptein, Eric Schulte, Maurice Simons, Saskia Stolwijk, Dominique van Unen en Josefien Versteeg, the `Gouda Group' high school students who built a charger and Theo van der Geest, their physics teacher. Fa. J. Dignum and sons let me to use their tractor and irrigation pump for testing a charger. Finally I would like to thank the people from `Casa de Pauw' for allowing me to use their workshop and computers, with special thanks to Wim van der Hoek, who kept me going with many cups of coffee, funny remarks and inspiring comments.

There are many more people who have contributed to this project, too many to mention them all here. I won't forget them...

Jan Portegijs, 9 September 1995

Copyright: Jan Portegijs, 1995.
Copying minor parts of this book with literature reference is allowed without prior authorisation. Copying major parts or the whole is allowed if the copies are meant for private use only.


Preface to 2003, internet version

A lot has happened since I finished the draft version in 1995: I went back to the Philippines to support two Philippine organisations with their efforts to introduce the firefly. This trip was paid by Dutch ODA dept. and I started my own little consultancy enterprise to qualify for that funding. My frend Siem Broersen and I developed the 'Humming bird' Electronic Load Controller / Induction Generator Controller and I wrote a building manual on that. Meanwhile, I got to know a lovely, pretty woman. We decided to try our luck and by now, we have two nice kids that need our care. Since this first ODA job, I hardly earned any money with my consultancy work so did odd jobs. Eventually, I ended up in computer work, making industrial automation software. Now I am working for a large company that produces high-tech machines for the computer chips industry.

One thing did not happen: I never wrote the missing chapters and annexes for this manual... And I don't think I ever will so quite likely, this manual will forever remain an incomplete, draft version. There is one obvious reason: I don't want to spend all of my spare time for the next year writing them. But there are some other reasons too:

  1. I am less optimistic about chances that the firefly will 'break through'. From a technical point of view, the batteries are a weak point: Life span is poor when they are discharged too deeply and chances are that the case gets damaged when they are carried around so often.
    Solar energy has similar battery problems and still is much more expensive, but it is more convenient: No carrying of batteries and no troubles about sharing a charger with other users. And above all: There are funding agencies, solar cell suppliers, traders, local technicians who all support it and earn a living from it. So I guess that solar energy will win the race even in areas where suitable water sources are available. Maybe the firefly is too cheap....
  2. I lack the experience about using the firefly in practice and setting up a firefly introduction project. I think these are the most interesting parts, but I can only write down some generalities and common sense about them.
    I could write the technical annexes, but I doubt whether that would make much of a difference. Part of it would be rewriting pieces of technical school books. I guess that most people who want to build a firefly system, will have enough technical knowlegde themselves or can find such information themselves. Then there are specialistic issues about details of the firefly system. These are relevant for readers who would like to adapt the firefly to their own needs. Until now, I did not receive concrete questions about these from readers so I guess there is not a great need for such information either.
  3. The best way to exchange experiences between people and organisations using the firefly, nowadays is via internet.

So this is what I want to do: Build and maintain a web site on firefly projects worldwide, with reports, photo's, contact addresses, links to sites that people have made themselves, see:


If you have something to show or tell, mail it to me and I will see whether it fits in.

Apart from several mistakes that were corrected and a small number of additions, this downloadable version is identical to the printed version of September 1995.

Jan Portegijs,

9 February 2003


Additions and corrections to 1995 draft, paper version

This section is meant for people who have the paper version and would like to update it. In this internet version, these additions and corrections have of course been made already.


Insert at page 4-10 under figure 4.7:

Hacksaw sawblades can be used also.

In charger building workshops in the Philippines, people used hacksaw sawblades of which about half of the height of the blade was grinded away and probably even more at the side where it touches the outer edge of the slot. With such sawblades fitted in a normal hacksaw, they could cut the slots quite fast. However, the side disks I have seen, had slots with radiuses quite a bit larger than the design value of 14.2 mm and consequently, blades will be less strong. Also the width at the teeth is only 1.0 mm instead of 1.4 mm for jigsaw sawblades. One could try to widen the slot by cutting away material from one of the sides, but this means extra work and a less smooth result. Normally, only 1.0 mm thick blades will fit in (instead of 1.25 mm) and this makes the blades even weaker. If you are interested, see the picture "Joel Cubit cutting a side disk" in:


Insert at page 4-27 between
"Both versions have been tested and worked fine up to free running speed at respectively 12 and 15 m head"
"With a pulley that consists of two halves..."

Anti-splashing ring for seal for pulley in one piece

With the seal type for a pulley in one piece, there was still a leakage problem: Some water comes through and gathers at the bottom of the alternator compartment. It does not pose a real danger as it comes through as a liquid and not as a fine mist of water droplets that can be sucked into the alternator: One could even drill a hole through the separation sheet at its lowest point to get rid of it.

Probably the water can come through because there is a jet of water leaking away between the runner and the nozzle. This jet hits the separation sheet just outside of the pulley and apparently, some water is forced inwards through the narrow gap between the pulley and this sheet. A solution would be to fit an anti-splashing ring of 0.5 mm galvanised iron sheet, inner diameter = 6 mm, outer diameter = 100 mm between the runner and the pulley (see fig. 4.12). This ring should prevent the water jet from splashing against the separation sheet at high speed. I haven’t tested this solution yet, please let me know whether it works.


Insert on page 4-31 below figure 4.16:

Adjustable nozzle.

Instead of fitting a suitably sized blocking timber inside the nozzle, one could also adapt nozzle design such that the flow through it, can be adjusted. This can be done by making part of the inward side hinge towards the bent side. See:"
for a design. Such an adjustable nozzle comes in handy for:

Insert on page 4-44 at the end of par. 4.9.1:

Electronic switchboard.

There is also a design for a fully electronic switchboard, see
It is more user-frendly and it can charge two batteries in one go. But it requires quite some electronics experience to build.


Insert on page 4-62 between:
"When the switchboard is ........... and might make short circuit etc.:
"Box 4.15: Voltage spikes"

Mechanical regulator might work inaccurately

Mechanical regulators might overcharge batteries batteries when used in a firefly switchboard. Once the battery becomes charged and voltage surpasses 14.7 V, the regulator does not reduce field current properly, but continues to provide full field current. Consequenty the battery is charged further and battery voltage rises to well over 15 V. Probably, this is caused by the contacts of the voltage regulator relais sticking together after having sparked a little. In a car, this problem would not occur because:

The extra force needed to pull loose sticking contacts will differ all the time so this problem can not be solved by to readjusting the regulator to a lower voltage: Then on other occasions, it won't charge batteries well enough. It makes sense to check whether the spark extinghuishing diode is functioning properly. If this doesn't help: Look for an electronic regulator.


Change in table 5.2: Parts list for the charge indicator

On page 5-13, the number of red LED's should be 2 pc (instead of 3). The number of green LED's should be 5 pc (instead of 4).

Size of standard PCB board is 160 mm (instead of 150).


On page 5.16, replace "150" by "160" in the following paragraph:


At page 5-17 add "the diode" in paragraph:


On page 5-16, add new figure

Fig. 5.5b: Alternative: Eight copies of PCB design with current shunt.
Click on the link to find this figure, then right-click on the figure and select "save picture as" to copy it to your local computer and print this copy at 300 DPI (Dots Per Inch) using an imaging or photo processing programme.


Insert on page 5-20 between:
"....the `B-' and `L-connection must be short-circuited with a piece of wire."
"As stated in the parts list, the current shunt consists......"

Instead of making a current shunt from copper wire, one could also use the PCB design of fig. 5.5b with an on-board current shunt. With this PCB design, there is a copper strip between `B-' and `L-' that has such a length and width that its resistance is ca. 0.02 Ohm. Of course also thickness of this copper strip plays a role, so it can only be used with PCB material with the usual 0.035 mm copper layer. When in doubt: Check resistance afterwards by having a stable DC current going through it (e.g. from a lamp connected to a battery) and measuring voltage drop over the shunt with a digital tester on mV DC range.


Insert new text in parts list at page 5-12 in column 1 under "Current shunt, 0.02 Ohm"

(or use PCB design with on-board current shunt, see fig. 5.5b)

next (= chapter 1)

More information on hydropower at the microhydro webportal

Last modified on 12 July 2003  since May 2003
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