Can you replace a capacitor with a lower uf?

Capacitors are one of the most commonly used components in electronic and electrical circuits.

They are very similar to a battery, as they store electrical energy in the form of an electrical field.

Capacitors come in a variety of shapes, sizes and materials (used for the dielectric) which can include Mica, Ceramic, Mylar, Teflon and even air.

Another thing that varies between capacitors is their capacity (how much charge they can hold), also known as capacitance.

Farad is the derived unit of electrical capacitance. It can be defined as the ability of a capacitor or body to store electrical charge.

But, can you replace a capacitor with a lower uf capacitor? Replacing a capacitor with a lower uf one depends on the circuit that the capacitor is being used in. In general the value of the capacitor has been chosen specifically to meet a certain function in the circuit. Replacing a capacitor with a lower uf might affect the circuit in unwanted ways.

I shall cover this in a bit more detail in this article.

What is the capacitor uf?

Let’s take a closer look at the capacitance of capacitors.

As mentioned earlier, Farads is the unit that determines a capacitors storage potential or capacitance.

A capacitor that is 1 Farad, is said to have the ability to store one coulomb of charge at 1 volt, where 1 coulomb equals 6.25 x 10¹⁸ electrons.

A 1 Farad capacitor would require a pretty big packaging to be able to store that amount of charge.

Capacitors come in smaller Farad values that include milli-farad (mF), micro-farad (uF), nano-farad (nF) and pico-farad (pF).

As the capacitance of the capacitor decreases, so does the size of the capacitor and its Farad value and vice versa.

Applications of a capacitor

The capacitor has many uses in a circuit apart from just storing charge which can include;

Eliminating ripples
Blocking DC voltage
Smoothing output of power supplies
Tuning of frequencies in resonant circuits
Stabilizing voltage and power flow in electric power transmission
Coupling
Decoupling
Motor Starters
Energy Storage
Power Factor correction
High-pass and Low-pass filters
Noise Filters and snubbers

Can you replace a capacitor with a lower uf?

If you are wanting to replace a capacitor with a lower uf one, there are many things to consider before doing so.

Different capacitor values will have different functions in each of the applications mentioned above.

So, lowering the uf value might cause the circuit to not function correctly or even stop working altogether.

Below are some effects lowering the uf of a capacitor can have on different circuits.

Resonant circuit – you will most likely change the resonant frequency thereby rendering the system useless.

Timer circuit – lowering the uf of the capacitor will affect the timing intervals which could be good or bad depending on the needs of the application

Motor or light dimming circuit – Depending on how much you lower the capacitance, the results can vary

Feedback loop (Amplifier circuit) – This again would affect the workings of the circuit considerably, as the values of the capacitor are chosen specifically.

The rule of thumb is if the capacitor value plays a part in things like tuning or timing of a circuit, it is best to not lower the capacitance.

Sure, lowering the uf by a little might not have considerable effects but, these small changes will add up in the end.

Other considerations when replacing a capacitor with a lower uf 00

There are some other factors to be mindful of when replacing a capacitor with a lower uf.

These include the Voltage and Type of Capacitor.

Capacitor voltage

Other than having a capacitance rating (Farads), capacitors have a voltage rating as well.

This rating specifies the maximum voltage a capacitor can handle before failure (which can sometimes be a mini explosion).

When designing a circuit, capacitors are chosen with voltage ratings that match or are little larger than the voltages expected in the circuit.

The rule of thumb is to select capacitors with voltage ratings higher than those expected in the circuit as a buffer.

So, if you decide to replace a capacitor with a lower uf one, make sure that the new capacitor has the same voltage rating of the one you are replacing or is larger.

Types of capacitor

The main construction of a capacitor involves two electrical conductors (plates), separated by an insulating material known as a Dielectric.

The metal plates can range from thin metal films, aluminium foil, or disks.

The dielectric can be any insulating material which ranges from glass, ceramic, plastic film, air, paper, mica etc.

Also, other than the materials used, capacitors vary in how they are constructed which include;

Wrap and Fill (Oval and Round)
Epoxy case (Rectangular and Round)
Metal Hermetically Sealed (Rectangular and Round)
Radial Lead type
Axial Lead type

Below are the different types of capacitors available varying in construction and materials used

Ceramic
Electrolytic
- Aluminium Electrolytic or Tantalum Electrolytic
Mica
Polarized
Non-Polarized
Polyester
Polypropylene
Polystyrene

As you can see there are many varieties of capacitors available for use.

However, each type of capacitor behaves differently when used in different circuits.

So, when you are deciding to replace a capacitor with a lower uf one, you will have to make sure that the capacitor type can be suitable in the circuit.

Below are some common rules for different types of capacitors that will help you when you are replacing a capacitor:

Foil wound capacitors will have more series inductance than ceramic capacitors
Tantalum capacitors are more sensitive to inrush currents, so avoid replacing an aluminium electrolytic capacitor with a tantalum capacitor
Cannot use a polarised capacitor in AC applications

Another note to make is whether the capacitor you are replacing is polarised or not.

If it is polarised, you will need to make sure the replacement capacitor is polarised as well.