Warning: This tutorial deals with an do-it-yourself project. Everybody following this guide must be aware, that his/her devices could be damaged. We can not be laible for possible damages and explicity advise you. Because parts of this guide include electricity we demand caution from our readers during building and usage!

Tutorial-structure: 1. Battery-pack for mobile power-supply 1.0 Introduction 1.1 Basics   1.1.1 Conception 1.1.2 Preparation 1.2 Assembley (Steps 1 to 5) 1.3 Functional-tests 1.4 Supplement

1. Guide – Battery-pack for mobile power-supply

1.0 Introduction

The battery-pack is intended to grant everyone a certain mobility, who want to use their laptops for watching television outside in their gardens or in the trailer. Although a lot of TV-boxes are pretending to deliver mobility they are still dependend on an external power-connexion, that isn't always at hand or can be used. This tutorial is for all of these people.
For the extreme DXers it can be used to do a short trip including laptop, TV-box and satellite-dish into the next or better beam-area of a satellite, that isn't fully or limited receivable at home. This jestingly remark was realy said by our agnized DXer DXBerlin.

1.1 Basics

1.1.1 Conception

Dimensioning the battery - How long does the battery run?
Capacitance of a battery is specified as ampere-hour (Ah). If you have a battery with 2 Ah for example it means, that the battery will deliver an amperage of 1 A for two hours. To get the operation periode for the used device, you have to simply devide "2 Ah through the amperage of the device".

Examplel:
2 Ah/1.5 A = 1.33 Hours

The choice of the battery was done regarding an television operation periode of 2 hours. It is oriented on an avarage running time for movies of 90 minutes and a laptop running time of almost 2 hours. This should be enough for watching an entire movie and using one laptop battery.
The chosen lead-gel battery has an capacitance of 7.2Ah and provides a running time of 5.5 hours of operation periode for an ampereage of 1.3A. The needed ampereage of the device is normally printed on the power supply unit.

Choosing the diode
The diode should be chosen according to the consumer load: It should at least resist the voltage of the battery (e.g. 12V and maximal ampereage of the consumer. This data is printed on the type-sign. For example our diode "1 N 4001" can be used up to an amperegae of 1A. Above this the diode "1 N 5400" is recommendated (up to 3A).

1.1.2 Preparation

Battery-pack
Needed Werkzeuge: Needed Material: Bill: Costs: 25,43€ www.Reichelt.de T1 Soldering-iron T2 Tin-solder and insulating tape T3 Side cutter T4 flat nose plier T5 Jointing clamp T6 Cable strippers (optional side cutter) T7 Soldering-help (optional) M1 12V-Lead-Gel-Battery M2 Charger for Lead-Gel-Battery M3 Twin strand(ca. 1 Meter) M4 Diode* 1N4001 M5 Voltage-regulator* 78S12 M6 Coaxial power connector (often: Øi= 2,1 mm Øa=5,5 mm, Shaft= 14 mm) M7 Flat connexion *Diode or Festspannungsregler need to be chosen according to the max. ampereage of the consumer load. If the consumer generates an ampereage of 1500 mA, a diode and a voltage regulator are needed, that resist at least 1.5 A. This guide corresponds to positive voltage regulators.

1.2 Assembley

Step 1: Soldering the diode

Firstly a cable of ca. 10 cm of the twin strand is cutted with the side cutter. Afterwards both conducts are splitted, the end of the red conduct is dismantled and the wire-end is twisted. Now the wire-end of the diode is shortend and the remaining wire is solered onto the red conduct in that way, that the ring of the diode is pointing outside.

Installing the diode: The diode needs to be soldered in that direction, that the marker-ring is pointing to the negative-pole. So it is in conducting direction. Does the ring point to the positive-pole however, the diode is installed in reverse-biasing and the current can't be conducted. The diode is used for safety and locks the conction direction in case of interchanging the pole sof the battery. The diode works as an endless resistor in case of wrong polarity and locks the conduct so that no faulty operation or damage to the follwoing electronic somponents can be occur.

Step 2: Soldering the voltage-regulator

Now the previous soldered diode is soldered with the other end to the input pin of the voltage regulator (left pin). The left over black cable (netagive) from step 1 is soldered to the middle pin (ground) with dismantled end.

Then both ends of a ca. 1 meter twin strand are dismantled, and the red cable is soldered to the output pin (right pin) and the black cable is also soldered to the middle pin (Ground or abrev. "Gnd").

Function of voltage-regulators:
Most of electronic circuits need a certain, constant operation-voltage. So sometimes there is to regulate a differing and/or oszilating voltage to a fix parameter, so that the circuitry can function. batteroes and accumulators provides a voltage higher then the displayed 12 Volts, e.g. 14 Volt, directly after a complete charge-up and it decreases, when it is discharging. To handle this problem there are so called voltage regulators. These are certain components provided with this uncontrolled, oszilating voltage and transforming it to the wanted, constant voltage and reducing overvoltage.

A controller is a comparator and it compares the output-values of the voltage with internal reference parameters. When the measured output-voltage is too low, a transistor that leads the output-current will be more energized, so that more current can be conducted until the demanded voltage is achieved.

When the aotput-voltage rises too much, the current is reduced by the transistor until the voltage stabilized again and the demanded output-voltage is reached. The transistor works as a kind of variable resistor that can controll the "excessive" voltage-difference between input and demanded output-voltage can be lead out through ground and all thout independently from the conducted current.

A bad efficiency and a big dissipation loss are disadvantages of this linear voltage-regulation. The not demanded output but feeded voltage falls in the transistor and is transformed into heat. Dependent on the current-level it can generate intensive heat of the controller, so that radiators are needed for the controller which often have mounting parts for it and additional costs are generated. In our case no radiators are needed. But because of the transformation into heat and caused power loss the operating time is reduced by the regulator when connected to an accumulator or a battery.

The parameter for voltage on that it is controlled is noted on the typsign of the controller. In our case we are using a 78S12 (78Sxx) and the llast two digits represent the parameter for voltage of 12V.

Step 3: Assembling the flat-connexion

After all pinsof the voltage-regulator are correspondingly connected the ends of the short piece of cable that is soldered to the voltage regulator is cutted on both ends to the same length and both are dismantled and twisted. Now the flat-connxions are attached and clamped with a jointing clamp (alternatively done with a normal clamp or tongs.

Step 4: Assembling the coaxial power connector

The ends of the long cable are dismantled and twisted now. After screwing the coaxial power connector the casing is slided over the cable and the red cable is soldered to the shorter cable and the black cable is soldered to the longer pin of the coaxial power connector. Afterwards the casing is screwed back on. The flat liers could be handy to squeeze the soldering points (Keep an eye on not causing a short-circuit!). Now the positive pol is on the inner pin of the connector and the negative pole is the outer ring. Depending on the device the polarity has to be switched (see type-signs).

Step 5: Checking and insulating

At the very end the flat-connexions are connected to the battery and the voltage is measured at the coaxial connector, if there is a voltage and if the polarity is right, if a volt-meter is available. If everything is okay, the soldering points are insulated with tape to avoid short circuits.

1.3 Operational-test

The complete battery-pack is tested and provides enough power, so that the computer recognized the TV-box. During operation of a HD-channel broadcasted via DVB-S2 the battery ran provided power to the TechnoTrend S2-3650 for about 9 hours at 1.3 A (projected for 5.5 hours) and to the TechniSat SkyStar USB plus for almost 8 hours at 1.7A (projected for 4.2 hours). The maximal values are very like just used for short periodes, e.g. initialising of the device, and afterwards the power-need is reduced. That's why the battery has a longer operational time then calculated.
The battery provides a sufficient time for television and the task and function of the battery-pack is fullfilled.

Improvements

There are some small parts, that could be improved, but wasn't realized for this project because of cost reasons. But they should be concidered for reproduction.
Ends of cables could be "glued" together with a small drop of tin-solder insted of being twisted. The liquied tin-solder is dragged inside by capillary-effects and connects the end-wires, so that these can not fray out anymore.
For soldering the relevant parts can be pre-heated, so that shocklike expansion is avoided when the tin-solder has contact to them and hindering a temperature-difference between the components. On the one side the tin-solder can not cool down at too cold surfaces and not causing stress and it can gain a higher strength an ddurability. On the other side it can spread wider, because it stays liquide for a longer time.
The soldering-help should be clamped to those areas, where excessive heat can transmit into and through the clamps away from heat-sensitive components. So the heat can't reacht those components, because it is tapped. Such a heat sensitive component is our used voltage regulator.
Instead of insultaint tape a heat shrink tube can be used. because it doesn't loose its adhasive abilities in contrast to the tape and so it doesn't fall off, and it looks better. The contacts underneath should be separatly insulated in the gaps, which is not possible with heat shrink tubes.

1.4 Supplement

1.4.1 Needed Software:

Software:

• TinyCAD (OpenSource)