Notes for offgrid power workshop

Safety

Shock risk – up to 60 volts is generally thought to be safe – lower voltages could cause risk if the skin is wet.  If contact points are on the chest, especially if it were wet, there is significant danger at lower voltages, even possibly at 12volt. insulation is important . cover live metal parts with plastic (plastic insulating tape is often used)
Fires (fuses)- Fires occur when a wire, or other piece of metal in a circuit starts to carry more power than it was designed to it heats up to red hot melting the plastic cover and setting fire to things. Fuses are a short piece of wire that is added to a circuit that will melt before wires can get hot enough to start a fire.  It is important to use the right size fuse, considering the size of the wires that are in a circuit.
Sharp tools – cable strippers/shears
Hot tools – soldering iron
Trip hazard
Trailing cables

Circuits

Wire / cables

single strand / multi strand multistrand is easier to shape and maneauver, which aids installation.  Its also used in vehicles/on machinery as single strand wire is prone to breaking under vibration.
Multi core – a number of wires can be bundeled together into a multicore cable – eg. most mains power cables have three cores earth,live and neutral. These are held together by an outer sheath.
Colour/stripe to aid identification of a wire.  Often in DC power cables the positive wire is marked while the negative is not.
Cable size – the cross-sectional area is measured in AWG (American Wire Gauge) or mm²(millimeteres squared)- area of surface of coppper on the cut end of the cable
wire/cable size important- thicker cable can carry more power, need to think about distance, amount of power to be carried and cost
voltage drop calculator – can be used to calculate how much power will be lost on a long cable run.
its possible to double up thin cables to carry more power, but, in the interest of safety, it would require each thinner cable to be individually fused
strain relief – the plastic sheath around the wire is attached and sometimes cushioned to stop copper strands breaking if the wire is repeatedly moved, also to help resist breakage if it is pulled with force.
insulation tape
protection/tidying sheaths (inc. heat shrink)
cable routing  – route to try and cables getting caught/pulled.  Cable clips and cable ties can be used to secure cables.
solid copper bus bars (squashed copper water pipe can be used)
12v systems use 2-core positive + (sometimes red) and negative – (sometimes black)

Fuses

why to use them?
different types of fuse
fuse holders
fuse boxes

Batteries

Different chemistries
amp hour
looking after lead acid – avoid heavy discharge, dont leave discharged for extended periods, fully recharge every couple of weeks.

Power generators

PV Panels about 20% efficient (solar thermal, heating water, is about 80% efficient)
Wind
Water
TEGs – power from heat
petrol/diesel generators

Charge controllers

Stop batteries being overcharged.  Most also offer protection against extremely excessive discharging of the battery

Switches

amp rating – make sure they are designed to handle the power and are not going to melt
on/off/momentary etc.

Lighting

LEDs – only work if wired one way round – although some clusters of LEDs have a electronics which automatically switches the connection so they will work when wired either way round.
Cold cathode
Flourescent tubes
Incandescents

Connections

Crimp connectors
Crimp terminals (spades, rings, fork)
Choc blocks screw connectors
soldering
silicone/dialectric grease for connections (metal to metal when not soldered) to prevent corrosion over – especially if might be exposed to weather. This can happen surprisingly quickly under some conditions. Vaseline not as good, but better than nothing.

Circuits

Parallel
Series

System design

Figure out power loads – how much, where
Spots 6W
LED corn bead chip 1.5W
Increasing intensity – sound,light,heat,motion
AV=W
Minimise loads – appliances selection
Assess charge controllers
specify wire sizes
specify fuse box location

Monitoring the system

Checking wiring
Monitoring battery state

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