Parallel Or Series Circuits Guide

This guide will look at Series and Parallel Circuits and the benefits and downsides associated with each. By wiring your circuit in either one or other of these configurations you can fundamentally change how it operates, so it's important to understand the differences to ensure your system works as intended. 

Series Circuits

A circuit wired in series is often used when you want to 'daisy chain' items. This type of circuit is sometimes referred to as 'current-coupled' because the total current will pass through every component in the circuit. This type of circuit only has one path, the result of which is that by switching off the first component you will switch off power to any components after that in the circuit. A very familiar example of these circuits is old-fashioned Christmas tree lights. When a bulb blew in the string of lights the circuit was broken, meaning the whole cluster would not work unit the blown bulb was changed and the current could pass through the bulb again. 

In series circuits the current stays the same, however, the voltage across the loads is divided in the same proportions as the resistance of the loads. This means that if three identical components (with identical resistances) are connected in series, the supply voltage is divided equally across them. 

Parallel Circuits 

Parallel circuits often use more cable than series circuits, but allow current to be shared between components which mean that, should one fail, the remaining components will still be able to function. Using our Christmas tree example again, this is similar to modern lights where an LED bulb can fail but the remaining lights still function.  

In Parallel circuits the total current is shared between components before combining again before it goes back to the supply. The voltage across the components will stay the same for each component.

In both the series and parallel configurations shown above, the brightness of the bulbs would be the same, since the power consumed is the same (4V x 0.3A = 1.2W for series  & 12V x 0.1A = 1.2W for parallel).

Wiring up LED Lights

So, now we understand Parallel & Series circuits let's put it into practice. With our LED lights you will need to connect them in parallel, but why? Our LED lights need to be wired in parallel because LEDs are polarity-sensitive (meaning they only work when positive and negative are connected the correct way around), so you are unable to simply feed the current through the positive and out of the negative to the positive on the next light. Instead, all our LED lights will require the positive to go to a positive connection and the negative to a negative, i.e. they must be wired in parallel.

Older-style incandescent bulbs with a metal filament aren't polarity-sensitive and will work with the positive and negative both ways around (the filament works with current flowing either way through it), so can be wired in series.

Connecting Batteries

When creating a battery bank you can again use series or parallel connections, depending on how you want the battery bank to perform.

Connecting batteries in series allow us to increase the voltage of the total battery bank, but the overall energy storage capacity of the bank in Amp-hours (Ah) remains the same.

12V 100Ah + 12V 100Ah = 24V 100Ah

This is ideal if you have longer cable runs as the higher voltage reduces problems caused by voltage drop. It can also be useful if your starter battery bank is 24V and you want to match your leisure battery voltage.

Connecting batteries in parallel increases the overall energy storage capacity but the voltage remains the same. This is helpful because components designed to run at 12V are widely available and the increase in energy storage capacity allows you to run your components for longer before needing to re-charge.

12V 100Ah +12V 100Ah = 12V 200Ah

Solar Panels

The general recommendation is to connect solar panels in series which would increase the voltage and keep the current the same. This is because MPPT solar charge controllers need your panel voltage to be higher than your battery voltage to provide a charging current. An MPPT must have panels that are at least 5V higher than the battery's nominal voltage or it simply will not activate, and the higher the voltage, the more efficient the operation of the MPPT will be. Having them in series also prevents reverse current through the panels which could cause damage over time and, if they are attached in parallel, it is best to install a diode to prevent this from happening.

Conclusion

There are many ways in which Series or Parallel circuits can be used to help in your project and we hope this guide has provided some answers on this topic. If you have further questions, please do not hesitate to get in touch.