In this new series of articles about electronics, I will try to transfer my experience in electronics. Hopefully you’ll like it.
For now, let’s start with some basics – volts amps watts and ohms (grammar Nazi’s – I know it’s volts, amps, watts and ohms but muh SEO o.O).
Volts, the potential to power the world
Volts are a measure of potential difference with respect to something else. For example, if we take a 9V battery, its positive lead will be 9V with respect to its negative terminal. Think of it like a glass of water 9cm above another glass sitting on the table. If you connected a straw in the middle, water could flow from the glass with higher potential downwards to the glass with the low potential – the one that’s sitting on our table.
For negative voltages, it’s also useful to know that volts are really just a measure of potential difference and that you can assign anything as a ground. So if you were to use 2 9V batteries and connect the first battery’s negative terminal to the other battery’s positive terminal and assign ground potential to it, then the first battery’s positive terminal would be +9V while the second battery’s negative terminal would be -9V respectively. Very useful for inverters, audio amplifiers, and whatnot.
In the thought experiment with our glasses of water, this would be like attaching a second straw to our glass on the table, to another one somewhere underneath. For example, one that’s sitting on the chair. Water wants to flow from the top glass to the second one, into the bottom one. Since the glass is underneath the one on the table, its potential will appear to be negative.
I’d also like to mention that this is why in mains AC the current keeps on switching directions. When the wave is at +230V (or +120V if you’re in the US), current will want to flow from the live wire (which holds our wave) into the neutral wire (which is 0V), because 230V is higher than 0V. When the wave is at -230V, current will want to flow from neutral into live, because -230V is smaller than 0V.
In other words, the pushing and pulling between live and neutral causes the current to switch directions.. the direction of the pull, if you will.
WARNING: Please do not try to dabble with mains AC at home if you’re not experienced in electronics, it can be lethal!!! Use a transformer to step the voltage down to safe levels and wear safety gloves!!
Amps, the speed of the electronics race track
Current which is measured in Amperes or amps, is created when different electrical potentials are connected to one another, only limited by the resistance of the stuff in between (which I’ll cover later). You can think of this as the amount of water that can flow through the straw in our water glass thought experiment. The wider the straw is, the more water can flow at a given time. Similarly, a smaller straw will allow less water to flow through. For our electronics circuit we can think of it as the wires that are used to connect everything together.
The current that is being fed through a circuit is determined by the load. This is why you could buy a 4A charger for your phone, but if the phone only asks for 1A, the charging speed wouldn’t increase – it would just stay 1A. But you could at least rest assured that the 4A power supply is more than beefy enough to supply your phone with the power it needs.
Ohms, the bumps in the road
Resistance which is measured in Ohms, tries to limit the amount of electrons that can pass at a given time. In our thought experiment, we can think of this as squeezing on the straw. The straw’s width hasn’t changed, but the squeezing onto it will limit the amount of water that can pass through it. In electronics circuits, resistors are used like this to limit the current going from positive to negative or live to neutral to safe levels. After all, if we were to just connect them with a wire, we’d essentially be short-circuiting them – only limited by the very small resistance of our wire, and with it trip a breaker or make the battery explode. Resistors on the other hand can handle this job of current-limiting really well.
To calculate the current that a resistor will pass through, we can use Ohm’s law (V=I*R) where V=voltage in volts, I=current in amps, and R=resistance in ohms.
We can also rearrange this equation to derive different values.
To calculate V: V=I*R
To calculate I: I=V/R
To calculate R: R=V/I
Let’s put that into context with some examples.
If we have a 9V battery and want to calculate the resistance required to make it pass 50mA or 0.05A, we can plug in these values – 9/0.05 – and see that we need a 180 ohm resistor to achieve this.
If we have a 9V battery and want to calculate the current that we’ll get when we use a 1k resistor, we can plug in these values – 9/1000 – and see that this would pass 0.009A, or 9mA of current.
If we have a resistor of 200 ohms and we want to send 25mA (0.025A) through it, we can calculate the voltage required to do that by with this equation – 200*0.025 – and see that we need 5V to do this.
Watts, the power to run everything
So now that we’ve got a definition of volts and amps, let’s discuss watts. The watt is the product of volts and amps, and is described by the letter W, though since the formula to derive watts is V*A you’ll also sometimes see it being described as VA. It enables you to measure power consumption regardless of the voltage and current. By using watts, we can find that a 5 volt device consuming 1 amp uses the same amount of power as a 2.5 volt device that consumes 2 amps – both consume 5 watts of power.
Watts are also used to describe efficiency. If you want to know the efficiency of a power supply, you’d measure how much voltage and current goes in (let’s say 100VDC at 1A) and it spits out 10VDC at 8A. This would translate to 100W on the input, and 80W on the output. Therefore our supply’s efficiency would be 80% – which is not too bad. Ideally we’d want our efficiency to be as high as possible though, and watts can help us determine what would be the best design to achieve that.
Conclusion
Phew, that sure was a mouthful. If you’re still with me at this point, congratulations! You should now have a good understanding of volts, amps and ohms and how they relate. I hope that you enjoyed the article. Next up, we’ll discuss LED’s and Kirchoff’s voltage law. Stay tuned!