Electronics notes/Volts, amps, energy, power

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This is for beginners and very much by a beginner / hobbyist.

It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book.


Some basics and reference: Volts, amps, energy, power · batteries · resistors · transistors · fuses · diodes · capacitors · inductors · ground

Slightly less basic: amplifier notes · varistors · changing voltage · transformers · baluns · frequency generation · Transmission lines · skin effect


And some more applied stuff:

IO: Input and output pins · wired local IO · wired local-ish IO · ·  Various wireless · 802.11 (WiFi) · cell phone

Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes

Actuators: General actuator notes, circuit protection · Motors and servos · Solenoids

Noise stuff: Stray signals and noise · sound-related noise names · electronic non-coupled noise names · electronic coupled noise · ground loop · strategies to avoid coupled noise · Sampling, reproduction, and transmission distortions

Audio notes: See avnotes


Platform specific

Arduino and AVR notes · (Ethernet)
Microcontroller and computer platforms ·
ESP series notes
STM32 series notes


Less sorted: Ground · device voltage and impedance, audio and otherwise · electricity and humans · power supply considerations · Common terms, useful basics, soldering · PLL · pulse modulation · signal reflection · resource metering · SDR · Project boxes · vacuum tubes · Unsorted stuff

Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · JY-MCU · DMX · Thermal printer ·

See also Category:Electronics.


Contents

Some theory

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)


Nature of energy, charge, voltage, current

On analogies

Best means of transfer?

Speed of electricity (trivia, mostly)

Power

Current capacity

Voltage and current as related properties

Series and parallel, and a little resistance; Ohm's law, Kirchoff's laws

Real and ideal electrical sources

Ideal voltage source

Ideal current source

Real voltage sources

Some basic volt/amp/resistance circuits and related analysis

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Voltage divider

Current divider

Some practice

Is AC the peak voltage or RMS figure?

Conventionally, AC figures are the RMS value.

Deviations from that should and typically will be mentioned.



Multimeters on AC setting try to show the RMS value - but the cheap ones assuming the waveform is sinusoidal.

Only the fairly expensive actually sample values quickly enough to be able to integrate. Since the waveform is broadly sinusoidal but never perfectly (and use and even wiring can influence this), this can matter a little.



One reason for the 'AC is RMS' convention seems to be that the power delivered through the same voltage VDC and VACrms is roughly the same, which is pretty convenient.

Also comes with footnotes - there is a difference between the root mean square and the average (of the absolute) voltage - see form factor, which for a sine wave is approximately factor 1.1 (and approx factor 1.5 for half-wave rectified output), which also seems to be the source of figures like 110V, 120V as they typically come from AC generators(verify).



Powering your projects

From-the-wall power

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Adapters

Unregulated adapters

  • cheap
  • voltage lowers with more draw (in the cheapest, most basic designs)
  • are fine for smaller draws (e.g. microcontrollers without much load, and since boards often have regulators, regulating twice is pointless)
  • Price for approx ~200mA-2A: EUR/USD 5-10? (verify)

Regulated adapters

  • usually meaning the above plus a linear regulator (linear regulator generate heat, but voltage is stable)
  • slightly more expensive than unregulated
  • Price for approx ~200mA-2A: EUR/USD 8-15? (verify)
  • Price for combinations up to ~100W: on the order of EUR/USD 100? (verify)

Switch-mode power supplies

  • more power-efficient but also more expensive
  • In a few cases the fast switching may interfere with high frequency (E.g. RF) components, produce a hum in audio, and such. Products design that away, as can you in DIY, but it's more work.
  • Price for approx ~200mA-2A: EUR/USD 10-40? (verify)
  • Price for combinations up to ~100W: on the order of EUR/USD ~100? (verify)


Variable / lab supplies

  • can be exactly controlled (voltage limit and current limit), which can be very useful to figure out behaviour
  • bigger, expensive.
  • The simplest start at maybe EUR/USD 70
  • serious versions easily 200-300, more depending on power, precision and ripple reduction, etc.

Repurposing an ATX power supply

See e.g.:


This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Power and cables

Wire gauge, current limits

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Wire gauge markings is often seen as one or more of (all convertible, but tables exist mainly for the common ones):

  • AWG, American Wire gauge (also sometimes Brown & Sharpe, B&S)
  • diameter (inch or metric)
  • cross-section area (inch or metric)
  • SWG, Standard Wire gauge. Imperial as in British. Seen less often. Same order of magnitude as AWG, but a little different - see e.g. http://www.clag.org.uk/swg.html)

There's some others, like Birmingham Wire Gauge, but these tend to be more specific.


The current ratings are approximate because beyond cross-sectional area, the main and obvious variable, it also varies with things like

  • Material
the below is for copper, because it's by far the most common for wiring
  • Solid versus stranded wire
braided has maybe 15% less material for the same outer diameter, so current rating will be accordingly lower
AWG (and probably others) is the total cross sectional area, though, so braided wire of the samw AWG will just be a slightly thicker(verify)
  • Enclosed, or free in air
these figures are for in-air cables
enclosed cables warm up more with the same heat input, so should carry less if it's going to be sustained current
If you like large safety margins, you could say a third.
  • insulation temperature rating
you can safely get away with running wires one or two dozen degrees hotter if it's in better insulation, which can be a good factor 1.5 in terms of amps
  • duty cycle
power transmission assumes constant use
things that are always intermittent can get away with factors more current - at least in heat terms (it's still lossy)
  • frequency, also because braided has more skin effect than solid, and surface matters more than diameter
assume these figures are for DC, mains AC or other low-frequency AC
you can find some tables with "solid will be fully used for frequenies up to X Hz" figures
  • installation
coiled wire heats more. Don't do that on anything that carries a bunch of power. Also a thing on spooled extension cords.
  • safety margin
case in point: the below current figures are moderately conservative, people reading these charts may not about any of the above. In well-considered cases you can safely get away with more.


These and other reasons mean the figures vary between different resources

Not thoroughly checked - Don't stake your life or home on chances there's no typo in here.


AWG Diameter
(Inch)
Diameter
(mm)
SWG (approx) Cross section area (mm²) Ohm/km or mOhm/m (for copper) Approximate current limit
(Amp, for solid copper)
Big footnotes, see above
Notes
40 0.0031 0.08 ~44 0.005 3440 0.05
38 0.0063 0.10 ~42 0.008 2160 0.07 approximately a single strand from (mid-20 AWG range, by size) stranded wire
36 0.0050 0.13 ~39 0.013 1360 0.10 Probably the thinnest you can easily find/buy
34 0.0040 0.16 ~38 0.020 850 0.13
32 0.008 0.20 ~36 0.03 530 0.32
30 0.010 0.26 ~33 0.05 330 0.52
28 0.013 0.32 ~30 0.08 210 0.83 computer ribbon cables for signaling (PATA, SCSI, Floppy, USB port connectors, and such) seem to often be 26, 28, or 30AWG (verify)
26 0.016 0.40 ~27 0.13 130 1.3
24 0.020 0.51 ~25 0.20 84 2.1 Seen e.g. in Cat5 network cable
23 0.023 0.57 ~24 0.26 thickness of various office staples
22 0.025 0.64 ~23 0.33 53 5.0 Seen e.g. in computer power distribution
20 0.032 0.81 21 0.50 33 7.5
18 0.040 1.02 19 0.82 21 10 Seen e.g. in computer power distribution
AWG Diameter
(Inch)
Diameter
(mm)
SGW (approx) Cross section area (mm²) Ohm/km or mOhm/m (for copper) Approximate current limit
(Amp, for solid copper)
Big footnotes, see above
Notes
17 0.045 1.15 ~19 1.04 17 11 roughly equivalent to 1.0mm² copper


16 0.051 1.29 ~18 1.3 13 13
15 0.058 1.45 17 1.5 10.5 15 roughly equivalent to 1.5mm² copper
14 0.064 1.63 16 2.0 8.3 17
13 0.072 1.83 15 2.6 6.6 20 roughly equivalent to 2.5mm² copper
12 0.081 2.05 14 3.3 5.2 23
11 0.091 2.31 13 4.2 4.1 27 roughly equivalent to 4mm² copper
10 0.102 2.6 ~12 5.2 4 32
9 0.114 2.91 11 6.6 2.6 38 roughly equivalent to 6mm² copper
8 0.128 3.26 10 8.2 2.1 45
7 0.144 3.67 ~9 10.6 1.6 52 roughly equivalent to 10mm² copper


AWG Diameter
(Inch)
Diameter
(mm)
SWG (approx) Cross section area (mm²) Ohm/km or mOhm/m (for copper) Approximate current limit
(Amp, for solid copper)
Big footnotes, see above
Notes
6 0.162 4.12 ~8 13.3 1.3 60
4 0.204 5.19 ~5 21 0.81 80
2 0.258 6.54 ~3 33 0.51 100
1 0.289 7.35 ~1 42 0.40 125
0 (also 1/0) 0.325 8.25 1/0 53 0.32 150
00 (also 2/0) 0.365 9.27 67 0.26 175
000 (also 3/0) 0.410 10.4 85 0.20 200
0000 (also 4/0) 0.460 11.68 ~6/0 107 0.16 230
AWG Diameter
(Inch)
Diameter
(mm)
SWG (approx) Cross section area (mm²) Ohm/km or mOhm/m (for copper) Approximate current limit
(Amp, for solid copper)
Big footnotes, see above
Notes


Labeling

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Loose-strand cable tends to list voltage and gauge.


Ready-made power cords are often labeled with 'Designation code for harmonized cables' -- see HD 361,   DIN VDE 0281 / DIN VDE 0282 / DIN VDE 0292 (verify)

Example labeling:

  • H07RN-F
  • H05VV-F
  • H05VV-F 2x1.00
  • H07RN-F
  • H05VV-F3G1,5
  • H05VV-F5G2.5


This conists of...

  • A character indicating
    • H: Harmonized standards (usually)
    • A: Nationally authorized/recognized standards (meaning?)
  • Two digits indicating nominal voltage
    • 01: 100V
    • 03: 300V / 300V
    • 05: 300V / 500V
    • 07: 450V / 750V
  • A character: Isolation material (see merged material list below)
  • (optional) additional structural elements
  • A character: mantle material (see merged material list below)
  • Dash-character, indicating the wire core type:
    • -F: fine wired, for flexible cords
    • -K: fine wired, for fixed installations
    • -H: very fine wired (for flexible cords)
    • -U: single rigid round core
    • -R: standed rigid round cores
    • -Y: Tinsel
    • -D and E: Flexible conductor for use in arc welding cables


Optionally, there is a trailing:

  • Number of (independent) cores
  • earthing details(verify), one of:
    • G - a green/yellow core(verify)
    • X - no green/yellow(verify)
    • Y - tinsel conductor with no cross-section specified(verify)
  • all conductor's (nominal) cross section in mm2, often something like 1.5, 2.5, 0.75 or so


The material list used for isolation and mantle materials - which can be the same, of course (a merged list; either type can only pick a subset of these):

  • V: PVC
  • V2: PVC, heat-resistant
  • V3: PVC, low-temperature
  • V4: PVC, cross-linked
  • Q: Polyurethane
  • R: Rubber (natural or synthetic)
  • B: ethylene-propylene rubber (Synthetic rubber)
  • G: Ethylene-vinyl-(co)acetate
  • S: Silicone rubber
  • N: Chloroprene
  • N2: Chloroprene
  • N4: Chloroprene
  • J: glass figre braid
  • T: Textile braid
  • T: Textile braid, heat resistant


So, for example, a H05VV-F3G1,5 is a 300/500V cable with three fine-wired 1.5mm2leads that uses PVC for both mantle and isolation.


For the implication of the wire cross-section, see e.g. AWG


http://www.eland.co.uk/cable-genius/1/an-introduction-to-harmonised-cables.html

Wire colors

May vary per country. May also have seen a standard change so that houses may be wired old-style.



Outdoor power

In terms of requirements, this comes in roughly three types:

  • Movable cables (on lamps, power points and such that are made to be basically weather resistant)
  • Fixed underground cabling - e.g. to support serious lighting
  • Fixed overground cabling - e.g. to wire up a shed


Electricity and protection

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)


  • IP rating[1]
  • IEC/ISO 60529 (previously IEC/ISO 529)
  • DIN 40050
  • NEMA rating [2]


IP rating (objects and water)

IP code (International Protection Marking, IEC 60529) is two separate numbers. Roughly,


The first digit describes protection against solids, such as fingers, screwdrivers, and dust

  • 0: none
  • 1: Protection against objects thicker than 50mm
  • 2: Protection against objects thicker than 12mm
  • 3: Protection against objects thicker than 2.5mm (fingers, many tools)
  • 4: Protection against objects thicker than 1mm (most tools)
  • 5: Protection against large amounts of dust
  • 6: Protection against all dust
  • X: no information


We often care more about the second digit, the way it deals with liquids (water and other inert stuff)

  • 0: No (added) protection
  • 1: Protection against vertically falling drips
  • 2: Protection against falling drips up to 15 degrees (tipped device / slanted falling)
  • 3: Protection against falling drips up to 60 degrees (most rain), and atomized water (condensation?)
  • 4: Protection against drips and sprays from all directions (e.g. good idea around pools - to protect this added object, and if it is fixed to something)
  • 5: Protection against a stream from all directions (you can e.g. clean it with a garden hose)
  • 6: Protection against strong jets, situations on sea (like 5, but can deal with more force)
  • 6K: jets of very high pressure. Rarely used.
  • 7: Protection against submersion (...under given conditions of time and pressure/depth)
  • 8: Protection against constant submersion (...under given conditions of pressure/depth)
  • 9, also 9K(verify): introduced later[3], basically for high-pressure, high-temperature washing, and implies 69. Separate standard[4].
  • X: no information


X is often deliberate, often because it doesn't quite make sense to test or specify in the first place.

You can often assume or estimate what rating something might have.

For example,

  • wallsockets would typically rate IP2X
  • Even cheap bathroom lights are probably IP3X, and probably approximately IP33 in that you'ld have to intentionally spray it before it has trouble.
  • many things rated IPX7 are waterproof enough that you can often assume it's IP57 or IP67 (...there's just no tested guarantee).

...assuming that checks out with common sense, e.g. that there are no big moving parts, access ports, or whatnot.


"Can I leave this outdoor" depends on use. For example:

  • IP67 usually means 'entirely closed', but you don't always need that
  • "Takes a bit of splashing" does not necessarily mean "good to leave where a deep puddle may form"
  • Outdoor speakers that you place in the garden would be nice if they were X4,
...yet X1 may be enough if you put them under a patio, since the worst they'll deal with is moist air.


See also:

  • NEMA enclosure ratings[5] (tests different things, so no direct conversions to IP ratings)

Cable connector types

See Common_plugs_and_connectors#Power_-_wire-to-wire_connectors


Measuring your house's power use

See Electronics project notes/DIY home resource metering

Solar panels

ElectroVoltaic (EV) panels, that is -- solar panels can also refer to water heaters.


Yield and planning

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

You'll want to look at:

  • panel peak rating
  • how much sun you'll get (per year, in the darkest part of year, etc.)
  • (if necessary) how you're going to bridge the times you have no direct sun, or only diffuse overcast sunlight



A solar panel will only give anywhere near its given current in direct sunlight, and so the figure for a panel is often in Wp - Watt-peak[6], the highest Watt output the panel gives, with the panel at 25°C and the sun delivering around 1000W/m2 (its approximate peak, which varies with place on earth, pollution, weather, and more).

Of that rating, you will often see less:

  • up to the rating for ideal situations
  • perhaps 70% for a decent but not ideal day and/or setup
  • perhaps 30-50% in good sun but when badly oriented, on overcast-yet-still-brightish days, behind reflective glass (e.g. phone charger in the windowsill), etc.
  • perhaps 15-30% in dreary overcast weather, or shadows

(verify)


When you look at insolation maps and such, you'll often see figures in peak sun hours per day. It looks like most places can count on at least two hours for a yearly average, but relatively few more than five.

For example, in the Netherlands we get around 1000 peak sun hours per year, which is ~2.7 per day, and that's an average - a long-term graph will look roughly like a sine wave with a period of a year, with perhaps 1 in the darkest months (...and that's still an average; seeing a week with less isn't crazy).


If you're powering some electronics on a solar cell and a battery, you want to consider some of the worst cases:

  • if you're going to power your device 24 hours per day with perhaps 1 to 2 hours of peak power (and a little more current than that from diffuse or indirect light), that means the panel current should be perhaps eight to twenty times the average current your device uses.
  • using the power is lossy. For example:
    • inverters (perhaps 80-90% efficient(verify))
    • regulators (loss depends on voltage drop and regulator type, but again, ~80-90% with some consideration(verify)).
  • consider losses in battery charging (often involves regulation), although matching panel and battery voltages means this doesn't have to be serious.
  • consider short-term variation - you may want a large enough rechargeable battery so that you can deal with perhaps a week of nasty overcast weather and little charging.


Orientation usually means pointing the thing south on the northern hemisphere, and north on the southern hemisphere -- basically, orientation and inclination should point to the place where the sun is while the peak sun hours happen.


Inclination matters mostly to direct sun, and you can choose a good fixed value based on your latitude.

For diffuse light, lying the panel flat seems to work best (since that means you're getting light from all of the sky) - in practice meaning ~15-20 so that rain and wind may wash off fallen leaves.


Tracking (primarily for orientation) is only worth it if you get a lot of sun hours, because only then will a fixed position mean noticeable yield variation within in those hours. Of course, the occasional manual seasonal adjustment can't hurt, particularly if it's easy enough to walk up to them and move them a bit.


Reflectors are not useful for peak sun hours, because solar panels are built for peak sun (~1000W/m2) and more than that will heat the panel, lessening its efficiency (will noticeably lower its voltage). Getting it particularly hot may even shorten its lifespan, and for this reason, using reflectors may void your warranty.

However, reflectors can give you better yield during overcast hours, which can be worth it if you get more overcast hours than peak hours where you live.

You would need to be clever about it, because you want to reflect only diffuse light, and specifically avoid reflecting direct sunlight onto an already directly lit panel.

Note that a reflector setup may take a lot of area - and that filling that same space with more panels may give you more power (assuming of course that you can afford that many panels).




See also:

Panel types

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)
  • polycrystalline (currently the most common)
    • slightly cheaper than the other options
    • ~14-17% conversion rate (efficiency of conversion of sunlight to electricity)
    • ~20% efficiency drop in hot panels
  • monocrystalline
    • ~12-15% conversion
    • ~15% efficiency drop in hot panels
    • a little less W/m2 than polycrystaline
  • amorphous, a.k.a. thin film
    • ~5-7% conversion
    • Noticably less W/m2 of poly/monocrystalline
    • little efficiency drop in hot panels
    • easier to apply in many surfaces (so easier to spend the space you need)
    • combined with a laminate at production, often glass (often plate glass and not tempered(verify))


Watt-Peak per cost (yield efficiency) and cost per area are usually the most interesting figures, but it does depend on your situation.





Wiring

Wiring panels in series adds voltages, wiring panels in parallel adds currents.

In both cases, having some panels shaded is a potential problem:

Glass

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Preferably tempered glass, as it's stronger than regular plate glass, and not so sharp if you manage to break it. Plexiglass is even less likely to break (but a little more likely to cloud).


Anything that reflects considerably, or clouds over time, will reduce your efficiency.

Voltage-related labels

Circuit labels related to voltage

In circuits and specifically on components, you'll see power pins labeled as:

  • VCC (positive) and VEE (negative/ground) are used with BJT circuits (and also more generally).
the name seems to come from "the voltage common to all transistors' collectors" (verify)
  • VDD (positive) and VSS (negative/ground) are used with FET/CMOS circuits

The distinction between these two is blurred in practice. You regularly see VCC in the general meaning of 'positive supply voltage', regardless of component type, and probably see 'Gnd' more than VEE.

VSS and VDD, being newer, have a more marked meaning when they are used.


V+ and V- are also sometimes used, as are VS+ and VS−. These are even more vague.


See also:

Some notes on delivery of electricity

Generation is often on the rough order of 10kV(verify).

Transmission over any distance is done at at higher voltages (increasing over time, long distances currently around 1MV). There are a handful of reasons this, some intertwined, and not all about losses.

City-scale distribution steps it down, often in a few stages. Near your house it's kilovolts again.

In your house it's a few hundred volts tops, whether split-phase or three-phase.



Polyphase power

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)


Various voltages; wye and delta

See also

Unsorted

Some notes on house wiring

Open hot, open neutral, open ground

Putting your safety ground in the dirt

Floating neutral versus bonded neutral

On zapping people

See Electronics notes/Electricity and humans

Power Factor

Power Factor Correction

Power supply considerations

Power conditioning

Is europe 220, 230, or 240V?