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 special attention:

• 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 harm.
• 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 them.
• 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 hours.
• 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:

1. 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.
2. 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.
3. The resistance of the battery cable should be 0.042 Ohm at most. This means that if a 2.5 mm² cable is used, it should be no longer than 3 m, a 2.08 mm² 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 mm² cable, the battery cable could be 4.8 m long.
4. 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.
5. 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 connector block.
• 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 avoided.

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 minutes.
  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 will be.
  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 more night.

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 are:

• 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.

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