Workshop Handout Web

8/18/2019 Workshop Handout Web

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Electricity Basics

We’re not going to dig too deeply into definitions and equations here but to get to grips with the nature of electricity, we need to learn a little bit about what an atom is. All elements, such as copper and gold, aremade up of atoms. Atoms in turn are made up of particles: protons (p), neutrons and electrons (e).

Protons & ElectronsIn the simplest terms electrons are the smallest units of electricity. Protons & electrons have equal andopposite charges; electrons being negative and protons being positive. Like charges repel each other, unlikecharges attract each other. The visual representation of the attraction between protons & electrons is similar to that of magnets clicking together when we hold the opposite poles toward each other. While protons arefairly static, electrons like to move about. A good example of this is lightning which is when electrons travelbetween the clouds and the ground.

Moving the Electron

We’ve learned that electrons like to get about, but in order for them to be able to move from one place to

another, they need a medium and this is where conductors come in. Just like we use bikes to get from A to B,

electrons use electrical conductors. Conductors, such as copper and aluminium wire, allow electrons to

move about within their structures when a charge difference is created across two parts of the material. If

there is no difference between two points in the circuit then there will be no current.

Charge (Q), measured in coulombs, is the number of electrons that can be found in whatever metal we'redealing with. The flow rate (just like you'd find in a river) of this charge is what we call electrical current (I),

which is measured in amperes or amps i.e. 1 amp exists in a circuit when one coulomb of charge is passing

a point every second.

Voltage or Potential

In the earlier section we mentioned charge difference, meaning a force that will push electrons from one

place to another. This force is called voltage and it is measured in volts (V). If we use a water system as an

analogy, then if we increase the pressure in the system then more water will flow through our pipe per

minute. The same thing happens in our electrical circuit, the higher the voltage then the greater the current inthe wires.

The Essential Mix


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Resistance

Resistance is the opposition to a current and is measured in ohms. Resistance always results in the

conversion of electrical energy into heat. All conductors, have some kind of resistance, and represents a

waste of energy or a loss to the system. Resistance in a wire depends upon the type of metal, length of thewire and the diameter of the wire.

Currents that you may come across

- DC (Direct current) is a simpler type of electricity and is unidirectional flow of electric charge. Insimplified terms in a DC circuit, the current flows at a specific, constant voltage. This type of

electricity can be produced by batteries, solar cells and dynamo type machine such as bike power

generator. When we’re using a torch, pocket radio, portable CD player or virtually any other type of

portable or battery-powered device, we’re using direct current.

- AC Alternating current) is type of current whose direction reverses in cycles. The back-and-forthmotion occurs between 50 and 60 times per second, depending on the electrical system of the

country. Due to this cyclical motion, the voltage in AC current alternates. AC is the type of current

that is delivered to our homes and businesses and we use it to power all of our appliances.

Know your revolutions

Revolutions per minute (rpm, RPM, r/min, or r·min 1) is a unit of frequency. It simply means the number of full rotations completed in one minute around a fixed axis. It is most commonly used as a measure of

rotational speed of some mechanical component, in our case the bicycle wheel.

For more information check out these books:

Off The Grid, Managing independent renewable electrical systems – Duncan Kerridge,CAT Publications, ISBN: 978-1-902175-56-0

Advanced Electrical Installations – C Shelton, Addison Welsey Longman, ISBN: 0-582-24618-0


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Building a Single Bike Generator

SYSTEM DESIGN

Designing any off-grid system is a question of matching up your supply of energy with the amount of power you will need. A single bicycle generator's capacity for energy production is dependent on the power produced by the cyclist and the condition of the bicycle itself. There are many ways to put together a bikegenerator, from cheap to super expensive, from cheap to more complicated. All of them have pros and consand so the choice is really up to you. The generator itself is not the whole story so we have to look at thebigger picture.

The areas we need to take into consideration when we are building our system are:

Assessing our loads and the potential for reducing these where possibleStoring power with a battery AC or DC or bothSystem controlDistribution of powerSafety precautions as electricity can be dangerousDeciding upon your budget and thinking about a system that you can afford

In this workshop we’ll follow the above sections in more detail with some examples of different generator setups at the end. Below is a simple diagram to help guide you through the process:

INITIAL ASSESMENT

Existing Situation

What you need to and want to power

Resources available to you

Your budget


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SYSTEM PARTS

Here is a complete list of the components we use to build a single bicycle generator. You may notnecessarily need all of the items listed below (depending on your budget or requirements) but it's good to getan idea of all the bits and pieces that can go into the system.

Bicycle (ideally with slick tyres)Bicycle training standDC permanent magnet motor

Plate or wood for mounting motor Skateboard wheel or roller Multimeter Cable & connectors (30 amp Anderson connectors or mains 3 way connectors)Screws, nuts and boltsRegulator Inverter Capacitor Heat sink

12V connectors x 412V socketsFuses & fuse holdersRCDEarthing systemBatterySystem housing e.g. wood boxTools e.g.Crimp tool

Soldering iron & solder Terminal blocksElectrical tapeEl t i l d i


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If we’re planning to plug in more than one appliance at a time into our system we need to be thinking aboutout total peak consumption, i.e. adding up all the watts, to make sure that our load fits within the capacity of our system.

Look at the load assessment table below (taken from the Off The Grid book) to see how you can assess your DC and AC loads.


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We have to remember that most batteries cannot withstand being completely discharged. Depending on thebattery they should only be discharged to 50% to 80% of their capacity. If you have a battery that is 70 Amp-hours than you really need to see that available power as 50% (leisure battery) to 80% (deep cycle battery)of 70 depending upon the battery. The best batteries to use with bike power are deep cycle batteries as they

are designed to regularly discharged between 30% to 80% of their capacity. Well-treated deep cyclebatteries will last much longer than a leisure battery. When buying a new battery, the more expensive it is thebetter the quality.

Car batteries are not suitable to use with bike power, as they were made for short bursts of high current.They never get discharged much in the short time it takes to start a car and they are recharged immediately.Therefore deeper discharge of car batteries damages them.

We’ve included another excellent page from the Off The Grid book to tell you about the Hazards and care

with regards to batteries and what to look out for when you’re buying second hand batteries.


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Different loads will have different tolerances to inverter characteristic and different inverters will have differenttolerances to load characteristics. This is important to consider when buying an inverter e.g. some inverterscan’t deal well with peaks in sound equipment. Also, all inverters work inefficiently at low loads.

The things to look out for in inverter specifications (example at the back of the hand out):

Power output

Input voltage

Waveform

Efficiency

Standby

Surge abilityInput Voltage

Load sensing

Interference suppression

Protection mechanism

Cost

Recommendations

System Control

Without control mechanisms our electricity would be all over the place. Controls make sure we don’t blowthings, set them on fire and hurt ourselves and/or other people. Controls also get rid of fluctuations within our system. The voltage that person produces on a bicycle is variable and can be as high as 70V and that has tobe kept in check by regulations.

The sorts of controls that we need to know about with bike power are:

R i t t bl ki b hi d ith di d O DC t i t


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3. What gear the bike is in (downhill gears = greater motor RMP)

The disadvantage of the converter is that with the motors we currently use thevoltage can sometimes get a little bit too high if a person jumps on a bike and spins.

If not careful this can blow the board. This can be overcompensated with larger roller or smaller motor. The converter also requires a heat sink attachment to dump excesspower as heat. Running the converter at high loads without a heat sink can blow theboard.

B. Capacitor . A capacitor can be used to smooth the output voltage from the motor and has the added benefit of providing a reservoir of energy for bass notes in soundsystems for the amplifier to use on demand. As a rough estimate every 400W of sound requires 0.5 farad of capacitance.

There are a couple of disadvantages in using a capacitor. The capacitor doesn'tsupply a constant output voltage. Once charged it corresponds to the voltage outputfrom the motor, which (as discussed above) is relative to its RPM. If you are usingan inverter (designed to work between 9 and 14V) or sensitive 12V equipment youwill need to keep an eye on the voltage across the capacitor and adjust your pedalling speed or the gear you are in to keep the voltage steady.

Capacitors can be damaged or may cause damage to those nearby if not treated

with respect. The voltage rating of any capacitor will be written on it. Once thecapacitor is full of charge, if a voltage higher than its rating is supplied to it candamage the capacitor. Some capacitors come with their own built in voltmeter,making monitoring of voltage easier.

C. Battery Charger. This is a slightly more advanced system that still requires theuse of a capacitor in combination with a battery charger charge in diversion modesetting. The capacitor is usually wired after the bikes followed by the battery charger.Every battery charger is different and has different specifications that have to be

followed when deciding about how it will work in the system. This option alsorequires the use of dump loads such as metal coils that heat up in the case of excess power is produced. Using battery chargers can be expensive.


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sorts of cable that you’ll need.


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DC cables will need to be much thicker as the current in a DC system is much higher than 240V AC. Cablesalso need to be thicker because of voltage drop. Voltage drop is the loss of power as the current runs down

the cable. This is due to the resistance in the copper. The loss of power occurs as heat. Voltage drops will beworse for cable stretching long distances. Voltage drop can also possibly damage appliance that aresensitive to the voltage they receive. The most efficient systems will have the smallest voltage drop. Theformula for working out suitable cables is:

Volt drop (V) = 0.04 x cable length (m) x current (amps) / cable cross sectional area (mm 2)

It’s also possible to knock out 25A on a bike for bursts, so our cable should be able to handle those sorts of currents too!

Safety precautions as electricity can be dangerous

Please take all safety precautions mentioned in this hand out such as earths, fuses, RCDs, and more!Read the guidance on working with batteries and be aware that the power coming out of an inverter is240V.

This is not to scare you, but electricity when handled wrong can be deadly. Even though a 12V systemdoesn’t pose an electrocution hazard, there are still other hazards such as electrical fires from too muchcurrent. Keep a fire blanket and a small extinguisher near by if possible. If you’re not sure of anythingask an electrician. If you intend to take you generator to a public event get a certificate from a qualifiedelectrician, which will assure that your installation is safe!

Deciding upon your budget and thinking about a system that you can

afford


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Suppliers of parts

Bicycle (ideally with slick tyres)Local bicycle storeGumtree - www.gumtree.co.ukEbay - www.ebay.co.uk

Bicycle training standCycle Store - www.cyclestore.co.ukCycle Sports UK - www.cyclesportsuk.co.ukOn Your Bike - www.onyourbike.co.uk

Minoura

DC permanent magnet motor Ebay - www.ebay.co.uk - Part no. MY1068Conrad Electronic - www1.conrad-uk.comScience Shareware - http://www.scienceshareware.com/Campaign For Real Events - http://www.c-realevents.demon.co.uk/

Plate or wood for mounting motor

Timber merchantsSteel stockistsDIY store

Skateboard wheel or roller Skate shopMR - www.magnificentrevolution.org

Multimeter

Maplin - www.maplin.co.ukScrewfix - www.screwfix.comDIY store


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RS - uk.rs-online.comOutdoor GB - www.outdoorgb.com12V Shop - www.the12voltshop.co.uk

12V SocketsRS - uk.rs-online.comOutdoor GB - www.outdoorgb.com12V Shop - www.the12voltshop.co.uk

Fuses & FuseholdersMaplin - www.maplin.co.ukHalfords - www.halfords.comOutdoor GB - www.outdoorgb.com

RCDWickes - www.wickes.co.ukRS - uk.rs-online.com

Earthing SystemCanford - www.canford.co.ukScrewfix - www.screwfix.com

BatteryHalfords - www.halfords.comOutdoor GB - www.outdoorgb.com

System housing e.g. wooden boxDIY storeRS - uk.rs-online.com

Cable & connectors

Maplin - www.maplin.co.ukRS - uk.rs-online.com

S t d b lt


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Electronics for Dummies – Gordon McComb & Earl Boysen, Wiley Publishing, ISBN: 0-7645-7660-7

The 12 Volt Bible For Boats – Miner Brotherton, McGraw-Hill, ISBN: 0-07-139233-5


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Documents

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