Voltage Drop For DIY Mechanics

When I first tried to learn about voltage drop, I’d keep running into the same problem.

I would open a web page, start reading, but I couldn’t really grasp the concept.

Most articles had too many buzzwords and equations. They would jump straight to Ohms and Kirchoff’s laws. I just wanted someone to explain it to me like I’m 8 years old- and how it related to my motorcycle- maybe throw in a few stick figures or a simple video!

So that’s the goal for today, drop the academic fluff, and explain what voltage drop is and why the concept is useful to understand. 

What is Voltage Drop in Simple Terms?

A voltage drop is simply a decrease in the voltage between two points in a circuit. The drop occurs when the electrical current interfaces with some form of resistance. This resistance could due to the presence of a load (eg. a light bulb), a resistor, or even a failure in the wires. 

Wherever there’s a voltage drop, I like the think “work” is being done there. That work could be lighting up a lightbulb, moving through a resistor, or even escaping in the form of heat in a damaged wire.

Technically, you could argue that my definition of work is not comprehensive.

If I directly connected two battery terminals together on a 9V battery, I would still have the voltage drop between two battery terminals of 9V.

In this case, there are no lightbulbs, no resistors, and no “work” is being done.

That goes back to the broader definition of ‘electric potential’. Because there is a 9V electric potential between the two terminals of my battery, I can still have a voltage drop of 9V.

A Simple Voltage Drop Example

You can see here in the example provided, we have one 12V battery and one lightbulb rated at 12V.

In electronics, the total voltage drop for the entire circuit going to equal the value of the supply voltage. Here our Voltage supply is a 12V battery.

So how does the voltage drop occur in this example?

Between points A and B we have our light bulb. Work is being done by at the point to the lightbulb transforming 12V of electrical energy into light and heat. 

Remember, whenever “work” is being done, there is an increase in resistance which results in a voltage drop.

What is Voltage Rise? 

The voltage rise relates to the power source in an electrical circuit. For example, a battery produces a rise in electric potential from 0V to 12V. It’s important to understand that there’s always a balance of forces in electricity – for every voltage drop in a circuit, there’s a voltage rise.  

How to Measure Voltage Drop? 

In an electrical circuit, the best way to measure voltage drop is with a digital multimeter or a voltmeter. I shot a video explaining how to use a multimeter to measure voltage.

Does Voltage Drop Increase Current? 

No, the voltage drop does not cause an increased current. Once you put together a circuit - connect your wires battery and lightbulb, the current circuit does not change. 

In my opinion, It’s not a good question to ask because the question itself is a bit confusing.

Sure, if I take two identical circuits, and add an extra resistor to one of them, then technically I have introduced “more” voltage drop, however, that results in an overall decrease in current. 

To explain further, let’s introduce the concept of Ohms law.

When it comes to current, Ohm’s law states that current can only be increased by decreasing resistance or increasing voltage.  

I = V * R

For example, let’s take two circuits:

Circuit A (lower resistance)

V = I * R
12 = I * 2
I = 6A

Lower resistance results in a higher current. 

Circuit B (higher resistance)

V = I * R
12 = I * 4
I = 3A

Higher resistance results in a lower current.

It’s easy to get confused by this because it is true that current behaves differently between a series and parallel circuit, and the reading can be slightly different in places in a parallel circuit.

I would strongly recommend watching this video here if you are confused by series and parallel circuits.

Voltage Drop In Parallel Circuits

In the case that devices are connected in parallel, that is, all the positive terminals and all the negative terminals are connected at the same two junctions, the voltage drop across all the appliances is the same. 

For example, If a 12 V battery is connected to two light bulbs in parallel, the voltage drop across each bulb is still going to be 12V.

This happens purely because potential is defined for each and every point on the circuit, and since the appliances are between the same points, they all receive the same voltage drop.

How Does Kirchhoff’s Laws Relate to Voltage Drop?

It turns out a pretty smart guy named Gustav Robert Kirchhoff figured out this voltage behavior a long time ago. Put simply, In his second law, also known as the “loop law”, he states that the sum of all the voltage drops in a circuit, must equal the total output voltage of the supply. 

There is a drop in voltage at every subsequent device, corresponding to the resistance of the appliance. Since the supply voltage is constant and the amount of energy in the current is constant, the magnitude of voltage drop will be equal to the supply voltage. 

That means if a certain number of appliances are connected in series, that is, their positive terminals are connected to the previous terminal’s negative terminal, the supply voltage is “distributed equally” amongst the appliances.

Final Thoughts

Voltage drop is what makes most of our electrical appliances function, from electric bulbs, which use their resistance to convert electrical energy to light energy, to water heaters that use their resistance to convert electricity to heat. 

Voltage drop might seem like a counterintuitive idea to most. But is just like friction between your foot and the ground which enables us to walk, voltage drop allows us to operate anything that uses electricity. 

I hope you have learned a thing or two today. If you like it, why not give it a share.

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Written By Tim M

I’m on a journey to learn all I can about electronics - and I’m sharing everything. If you like my content, check out my Honda CX500 Restoration Project

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