5.5 Installing home systems previous
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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:

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:

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:
  3. 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.
  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:

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:

The indicator design given in this chapter is a compromise between the two:

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:


9 Literature
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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.
LM 3914 Dot/Bar Display Driver (technical data on the LM3914 device, sorry, no further data)
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 Normalisatie Instituut.
RODRIGUES, Enrique, 1991
Rural electrification based on 12 V batteries. In: Hydronet no 2 vol. 1991.
published by University of the Philippines (no further data available).
Wisselstroom 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., Amerongen, Netherlands.
De Banki waterturbine; sterkteberekeningen van de schoep (in Dutch). Eindhoven University of Technology, report no WOP-WET 85.007.
Blade calculations for water turbines of the Banki type. Eindhoven University of Technology, dept. of Mechanical Engineering, report no WPS3-83.03.R351.

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