Installing home systems is not difficult. The nastiest job
might come when the system already works: Measuring how many
meters of cable, how many switches, lamps etc. have been used and
calculating the costs of these. But there are things that need
- To protect against the risc of a short circuit causing a
cable to overheat and start a fire, a 16 A fuse must be
installed as close to the battery pole as possible. The
battery poles themselves should be insulated with
electrical tape or covered by a piece of plywood that
forms the top of the battery case (see below).
This fuse is always connected to the battery so it should
also stand the charging current of up to 12 A. So at
least a 16 A fuse is needed to prevent that it will blow
during charging. Preferably car type fuses (flat ones or
round ones), with their proper fuse holder, should be
used. Glass fuses (the ones in electrical appliances)
with the corresponding fuse holder can also be used but
these might blow already at too low a current because
they tend to overheat more easily.
- For easy connection of a battery to the battery cable
going to the charge indicator, there should be a
connector between these. Of course the battery cable of
the switchboard will have the same type of connector so
that the battery can be connected to the charger just as
easily. It is important that this connector fits in only
one way so that the battery can be connected only with
the right polarity. Electronic devices like the
indicator, 12 V ballasts of fluorescent lamps, stabilised
voltage supplies etc. do not function when connected with
the wrong polarity and some of these might even be
destroyed by it. And if a battery would be connected to
the charger with wrong polarity, at least a fuse will
blow but it might be that alternator diodes are destroyed
even before the fuse goes.
In par. 4.9.6, using two different types of single-wire
connectors was advised: A flat, 6.3 mm wide one for the `-'
wire and a round, 5 mm diameter one for the `+' wire.
Then the isolated, female ones should be fitted to the
battery so that blank parts can not touch and cause a
short circuit. Short-circuiting either the home system or
the charger without a battery being connected does no
- The battery should be placed somewhere safely, preferably
out of reach of children. However, it should not be
placed so high that it is difficult to get when it needs
recharging. To increase battery life span, it should be
kept cool and especially temperature changes should be
kept to a minimum. So it should be placed somewhere in
the shade, a kind of basement would be ideal.
- For an accurate functioning of the indicator, the wiring
between battery poles and indicator connections must have
a specified, low resistance. This is discussed in more
detail below and in annex D.
Apart from fitting a connector and fuse, some other things
have to be done before a battery is ready for use. New batteries
have to be filled with acid. They are stored in `dry charged'
condition. In this way, they can be stored for years without
needing periodic recharging or other care.
Normally, a battery is filled with acid by the shop once it is
sold. Most firefly batteries will not be used immediately after
they have been bought (they have to be transported, the home
system has to be installed first, maybe someone ordered one but
has changed his/her mind). Therefor it might be better to ask for
batteries to be delivered in dry charged condition (not filled,
but the acid solution delivered separately in plastic bottles) so
that they can be stored easily. A problem with this are the
plastic bottles: Sometimes they leak so they can not be carried
in such a way that leaking acid can pose danger or destroy
clothes etc. (if you tie them to both ends of a long stick, you
can carry them safely).
When filling batteries, mind the following:
- Battery acid is dangerous: Work safely,
keep children away. Acid splashing around could at worst
destroy your eyes so try to get safety glasses and use
- The acid solution should not come into contact with metal
objects or anything that is dirty (see annex C3.4:
Poisoning). Only glass and plastic are safe. So don't use
a metal funnel, use a plastic one or cut the top of an
empty plastic bottle and use this.
- Batteries have to be filled up to a special mark below
the plug, or up to 1 cm above the plates if there is no
mark. The first half an hour after filling, little
bubbles develop and once they have gone, the acid level
might have dropped again, so check again after a few
- Rinse the bottles with water after use so that no traces
of acid are left. Then they could be used for other
purposes and pose no danger for playing children.
- To avoid damage to the battery and riscs to people when a
battery is accidentally dropped and its casing cracks, it
is worthwhile to build a wooden case around the battery.
The bottom part could be a wooden board while for the
sides and the top, plywood will be enough. It is no
problem if the case itself would be damaged if the
battery is dropped, as long as the material absorbs so
much of the impact that the battery casing itself remains
in one piece. So no one gets hurt by acid splashing
around and the battery itself is not lost.
- Batteries can be made easier to carry by fitting belts to
it, so that it can be carried like a backpack and people
will have their hands free when carrying it. For this, it
is best to look how local people carry their loads and
design something similar. It is quite likely that women
carry their loads in another way than men. So if one
would look only at the way men carry things and adapt the
belts to that, the result will look like it is ment to be
handled only by men.
The battery case and carrying belts are not essential and will
probably not be seen as a priority by users. But in the long run
they could be worthwhile.
The only difficult thing in wiring up a home circuit is to
connect the indicator properly. The electrical circuit of fig. 5.3
shows how it is wired up in principle. Then there are some points
that deserve special attention:
- The indicator should measure the total current that flows
through lamps that are switched on. So the `-' wires of
all lamps should be connected to the `L-' connection on
the indicator. No lamps can be connected somewhere along
the battery cable.
- To make sure that users will notice whether their battery
needs recharging, the indicator should be placed very
near to the switch of a lamp that is often used: The lamp
in the main room. The `L+' connection of the indicator
should be connected behind this switch. Then with the
push-button switch on the indicator in the rest position,
the indicator is connected in parallel to this lamp and
it will light up when this lamp is switched on, see fig.
5.3. When this lamp is switched on, the indicator will
draw the attention in several ways:
- One of the LED's light up.
- It doesn't immediately show its final reading,
but `walks' to a final reading in a few tenths of
a second. So it is as if the burning LED moves.
- The `moving' LED changes in color: The first 2
are red, the next 3 are yellow and maybe the
reading reaches one of the 5 green ones.
- The resistance of the battery cable should be 0.042 Ohm
at most. This means that if a 2.5 mm˛ cable is used, it
should be no longer than 3 m, a 2.08 mm˛ cable (no 14 in
American classification) should be no longer than 2.5 m
etc., see annex 0.
This means an additional demand to where the battery
should be placed: Within 3 m cable length from a logical
place for the switch in the main room. Or one has to use
a heavier type of cable: With a 4 mm˛ cable, the battery
cable could be 4.8 m long.
- The resistances of the battery fuse and connectors should
be low and constant. This means that all contact surfaces
of fuse, fuse holder and connector should be free of
oxidation and dirt. With a little grease, oxidation can
be prevented. Also the connectors should fit tightly. And
finally, all connections between the battery poles and
indicator connections should be made carefully so that
there are no extra resistances created there. The
connections to the fuse holder can best be soldered.
- Users should be informed that they can take more reliable
readings by using the push-button switch while all lamps
are off and have been off for some time. They could take
such a reading in the morning, when they have to decide
whether to bring the battery to be recharged or to use it
one more night.
It is best to connect the battery cable directly to the
connector block on the indicator (to `B-' and `B+' respectively)
and use this connector block also as a start for the other wiring:
- The `+' wire to all switches to `B+', so together with
the `+' wire of the battery cable in one unit of the
- The `-' wire of all lamps to `L-'.
- A separate wire from the switch in the main room to `L+'.
Installing the remaining lamps, switches and cables needs less
care. Cable thickness should be chosen such that the voltage drop
remains less than 0.6 V (5 % of 12 V), see par. 5.2. If connector
blocks are considered too expensive, connections can be made by
just twisting wires together and insulating them with electrical
tape. Try to lead cables as much as possible along a safe path,
even if this would mean that a slightly longer cable is needed.
This means that preferably cables should be drawn high along a
wall or on the ceiling. A stretch of cable crossing open air
invites for hanging all kinds of things over it so this should be
To understand why the indicator should be connected this way,
one needs to know a bit more about how it works. In designing the
indicator, there is a dilemma:
- From a technical point of view, it is best to have the
indicator measure the open circuit voltage.
This is the voltage across battery poles when no current
is being drawn from it, or only a very small current like
that consumed by the indicator itself. This open circuit
voltage is directly related to the state of charge of the
battery, see fig. 5.9. Designing the indicator this way
means that it can only produce a reliable reading when
all lamps are off and have been off for at least 10
The indicator could either be connected permanently with
the battery so that it lights up as long as the battery
is connected, or have its own switch. In case it it
connected permanently, the small current drawn by the
indicator itself could become a problem if the battery is
not being recharged regularly because it is not being
used. If it has its own switch, users might easily forget
to check state of charge of their battery regularly.
- From the point of view of usefullness, it is best to have
the indicator measure the actual voltage,
with one or more lamps being switched on. This actual
voltage is lower than the open circuit voltage because of
voltage drops over the battery fuse, connectors, battery
cable and the internal resistance of the battery itself.
To estimate the open circuit voltage based on the
measured actual voltage, there is the current
compensation feature: The indicator measures the
current I drawn by all lamps that are switched on, adds 0.2
x I to the actual voltage and uses this as the estimated
open circuit voltage.
This current compensation feature introduces an error: If
total resistance of fuse, connectors, battery cable and
internal resistance of the battery deviates from 0.2 Ohm,
the open circuit voltage will be over- or underestimated.
And the bigger the total current I, the bigger this error
Having the indicator measure actual voltage means that
the indicator can be connected in parallel with a lamp
that is often used, so that it will draw the attention of
users when they switch on the lamp.
The indicator design given in this chapter is a compromise
between the two:
- With the push-button switch on the indicator in the rest
position, it is connected in parallel with the lamp in
the main room and measures actual voltage.
This way, it draws the attention of users, but its
reading won't be too accurate because of the error
introduced by the current compensation feature.
- When the push-button switch is activated, the indicator
is connected to the battery directly. It still measures
actual voltage, but when no lamps are on,
current I is practically zero so the error introduced by
the current compensation feature is zero: Actual voltage
is equal to open circuit voltage.
This way a reliable reading can be taken, but only if all
lamps are off and have been off for at least 10 minutes.
It can be used in the morning to decide whether to bring
the battery for recharging that day, or use it for one
See annex D for more information on how the charge indicator
works and why it was designed that way.
After a home system has been installed, users should be
informed on how it could be used best. The most important things
- Do not discharge batteries too deep. Car
batteries can be used until the charge indicator reading
changes from green to yellow (then the battery is
discharged until 50 % state of charge, see fig. 5.9).
Solar batteries can be used until the charge indicator
reading changes from yellow to red (then the battery is
discharged until 20 % state of charge). So one type of
indicator can be used for both types of batteries, only
the reading at which recharging is necessary, differs.
Neither type of battery can stand being repeatedly
discharged until it is completely empty and the lamps
themselves start burning less bright.
- Have batteries recharged as soon as possible.
Batteries wear out when left in discharged condition.
When users are short of cash, they should still bring in
their battery for recharging. Then they could collect it
when they have money to pay the charging fee.
- Beware of battery acid. There is no need
to open the plugs on top of the battery and children
should not be allowed to play with it. When carrying a
battery, take care not to drop it so that its case might
crack and acid splash all over the place. Batteries
should be placed and carried in upright position only.
Users should know what to do if someone gets acid in his
or her eyes: Flush with plenty of water for several
minutes. Acid on an open wound is also painful and can be
treated in the same way.
- ARTER, Alex and MEIER, Ueli, 1990
- Hydraulics Engineering
Manual. SKAT, St. Gallen, Switserland (vol. 2 from serie
`Harnessing water power on a small scale').
- DERRICK et al, 1989
- Solar photovoltaic products; A guide for
development workers. Intermediate Technology Publications, London.
- HARVEY, Adam, with Andy Brown, Priyantha Hettiariachi and
Allen Inversin, 1993
- Micro-Hydro design manual; a guide to small-scale
water power schemes. Intermediate Technology Publishers, London.
- LOUINEAU, Jean-Paul, et al, 1994
- Rural lighting, a guide for
development workers, Intermediate Technology Publications, London.
- NATIONAL SEMICONDUCTOR CORPORATION, 19..
- LM 3914 Dot/Bar
Display Driver (technical data on the LM3914 device, sorry, no
- NEN 2063, 1988
- Arc welding fatigue loaded structures;
calculation of welded joints in unalloyed and low-alloy steel up
to and including Fe 510 (Fe52) (in Dutch). Nederlands
- RODRIGUES, Enrique, 1991
- Rural electrification based on 12 V
batteries. In: Hydronet no 2 vol. 1991.
- SOLAR ENERGY COURSE BOOK
- published by University of the
Philippines (no further data available).
- VAM EDUCATIEVE EN TECHNISCHE BOEKEN, 1989
dynamo's (in Dutch). ISBN 90 405 5604 0 (first printing: 1984,
sorry no further data)
VAN DER MEER, ing J.C.F, 1990
- Technische leergang
startbatterijen (in Dutch). Published by: Delta press b.v.,
- VAN DER VELDEN, H.H.P.M., 1985
- De Banki waterturbine;
sterkteberekeningen van de schoep (in Dutch). Eindhoven
University of Technology, report no WOP-WET 85.007.
- VERHAART, P, 1983
- Blade calculations for water turbines of
the Banki type. Eindhoven University of Technology, dept. of
Mechanical Engineering, report no WPS3-83.03.R351.
Sorry, there is no `next': Remaining
chapters and annexes have never been
written, see preface to internet version.