|
Already provided with a nice assortment of resistors? Now it's the turn of the capacitors. After all, after the resistors, these are the parts that you use the most in daily practice. Here, too, you can make very economical use of a Chinese assortment. |
Which capacitors do you need?
Three technologies
In practice, you need capacitors from 10 pF to 4,700 μF. That's such a wide range that you can never cover it with just one assortment. What's more, you can never fill in all these values with one type of capacitor. You need three different technologies:
- Capacitors up to 100 pF: ceramic.
- Capacitors from 100 pF to 1 μF: polyester film.
- Capacitors from 1 μF: electrolytic.
This article is about polyester film capacitors, because values from 100 pF to 1 μF are what you will need most often in daily practice.
Polyester film capacitors
Polyester film capacitors are parts that use a dielectric of the thermoplastic polymer material Polyethylene Terephthalate (PET), well known from the PET bottles in which today all soft drinks are delivered. A very thin PET film is coated with an evaporated metal layer. Two such films are rolled up or strips of film are stacked as a kind of sandwich. These two films or the strips form the two electrodes of the capacitor. The polyester film absorbs very little moisture and is therefore suitable for the production of 'naked' capacitors which do not have a protective coating on the outside. This leads to the production of the cheap, mass-produced capacitors that are often used in the very cheap modern mass electronics: 'non-encapsulated polyester film capacitors'.
However, polyester capacitors are also offered with a coating, so that the capacitance is not affected by pollution.
The characteristics of PET capacitors
Polyester film capacitors have relatively small dimensions with relatively high capacitance values. PET capacitors are mainly used in semi-critical circuits with maximum operating temperatures up to 125 °C. The capacitance of polyester film capacitors is relatively dependent on the temperature of the capacitor, variations of ±5 % over the whole temperature range are no exception. The frequency dependence of these parts is about 3 % in the range of 100 Hz to 100 kHz.
PET capacitors have a very special property: they are 'self-healing'. If you accidentally connect such a polyester capacitor to a high voltage for a short time, the component will not break down permanently. If the high voltage causes a breakdown in the dielectric film, the metal layer on the polyester film around the hole evaporates. This prevents the formation of a permanent short circuit.
What values do you need?
Polyester film capacitors are made with tolerances of ±10 % and ±5 %. If you buy capacitors with a tolerance of ±5 %, you should in fact use the E24 range to get a nice consecutive set of values. However, for capacitors, the E12 range is used almost exclusively, with one decade being covered by twelve different values.
278 capacitors for € 6.50
Various capacitors assortments available
Of course you can find various assortments with polyester film capacitors on the internet. We selected a six-and-a-half euro package from Banggood (see sponsor-ad at the end of this article), in which you will find 278 polyester film capacitors with thirty different values from 470 pF to 470 nF. For most values ten are supplied, for some large values only five are supplied. With such a range, you can start working in your hobby laboratory!
The price per capacitor
Capacitors are of course not all equally expensive, the price depends on the value. It is therefore not possible to calculate a standard unit price and compare it with other suppliers. On the average you pay only € 0.023 per capacitor. Exactly the same capacitors cost between € 0.15 and € 0.25 each at a Dutch mail order company (MARTOParts). No need to comment!
The delivery
The package was ordered on 17-04-2019 and received by postnl on 16-05-2019. A delivery time of one month is not unusual for this kind of deliveries from China. As usual, hardly any attention is paid to the packaging. In order to save as much shipping volume as possible, the 278 capacitors are crammed together in a far too small plastic bag.
 |
| The capacitors are crammed together in a far too small bag. (© 2019 Jos Verstraten) |
This one bag contains thirty small plastic bags, each of which should contain ten or five capacitors. We write should, because in our package there were several bags that contained eight, nine, eleven or twelve capacitors instead of the promised ten. Moreover, the five of 470 nF were missing. Instead, two 100 nF bags with a total of sixteen capacitors were delivered.
 |
| The different values are packed in separate plastic bags. (© Banggood) |
The capacitors look good and are all protected by a solid green coloured coating. The tolerance is ±5 %. To give you an impression of the dimensions, in the picture below we have compared the dimensions of a few values with a centimeter scale. The largest capacitor (330 nF) has a grid size of 10.0 mm, the smallest value (470 pF) of 4.0 mm.
 |
| The dimensions of the capacitors. (© 2019 Jos Verstraten) |
As already written, you get thirty different values in this assortment. All delivered values fit in the E12 series. In the table below we have summarized the four decades in which the values fall. From 1.0 nF to 82 nF all E12 values are supplied. It is a pity that not all E12 values are delivered in the four decades. This would have been possible for a few euros extra.
 |
| The delivered values. (© 2019 Jos Verstraten) |
The value of the capacitors is printed with silver ink on the green lacquer layer and is not easy to read. The capacitors are coded with 2AxxxJ, in which:
- 2A stands for the type of capacitor.
- xxx stands for the value.
- J stands for the tolerance of ±5 %.
The value can be found in the three digits xxx. The first two digits give the value in pF, the third digit defines the number of zeros after this value. A few examples:
- 2A471J: 47 pF + one zero = 470 pF
- 2A222J: 22 pF + two zeros = 2,200 pF = 2.2 nF
- 2A334J: 33 pF + four zeros = 330,000 pF = 330 nF
The specifications
The supplier does not reveal many specifications of the capacitors supplied. Three important parameters are:
- Maximum DC voltage across the capacitors: 100 V
- Maximum deviation: ±5 %.
- Operating temperature: -40 °C ~ +105 °C
The capacitors tested
The accuracy
We have selected six values from the total range and measured all supplied capacitors with an accurate RLC meter. We first calibrated this meter with a series of capacitors with a tolerance of ±1 %. In the table below we have summarized both the maximum deviation measured and the average deviation. From these measurement results you can deduce that in each tested value there was at least one specimen that deviated more than the specified ±5 %, but that the average deviation in most cases is within the specifications.
 |
| An overview of the maximum and average deviations. (© 2019 Jos Verstraten) |
Our conclusion about this capacitors assortment
If you start tinkering with electronics and still have to buy everything, this assortment of capacitors is an excellent first purchase. For less than ten euros you will get enough capacitors to get started. Buy some small ceramic values and some large electrolytic values and you are fully covered!
278 Pcs Polyester Film Capacitors
