Out-Of-Stock Parts? Combine Capacitors And Keep Shipping

Capacitors have been described as “the silent heroes of modern electronics”, and there is plenty of justification for such a characterization. 

The role that capacitors play in storing electrical energy – acting like mini batteries to provide bursts of power and maintain stable voltage – means they are important across a range of functions and applications. 

In the absence of capacitors, many everyday electronic devices would not function properly, or at all. This underscores the crucial contribution made by capacitors to the management of energy flow, the filtering of signals, and the preservation of stable conditions. 

A Lack of Capacitor Parts Isn’t Necessarily An Emergency

A classic scenario is that you may be carrying out or overseeing a repair, DIY project, or electronics build, and you suddenly realise you are short of capacitors. 

It might therefore seem that a major delay to your project is inevitable – but this won’t automatically be the case. 

The reality is that suitable capacitor parts for the job might be easier to obtain than you think, or you may be able to have exact matches backordered. 

There may also be the possibility of combining capacitors, whether in series or parallel, to match the required specifications. 

3 Steps for Handling Out-of-Stock Capacitor Parts 

Below are courses of action you can take to address any deficiency in capacitors you are facing, to help keep your current builds and projects moving, even as you wait on stock. 

We’re generally assuming here that you’re working with common types of capacitors, such as electrolytic, polypropylene, or dual-run AC capacitors. 

1. Check For Direct Replacements or Stock Status 

If you have an old capacitor in relation to your project or application that you can check, you can begin by verifying its exact specifications. 

While certain parts, such as particular Elna or LCR electrolytics, may be discontinued or obsolete, equivalents are likely to be available from reputable online or offline sources. 

Higher voltage ratings, such as 400V instead of 250V, aren’t a great concern, provided that the capacitance matches. You will want to avoid lower voltage ratings, however, to prevent failure. 

In-stock capacitors can be obtained from such major suppliers as RS Components, Farnell, and Rapid Electronics. There are online retailers, large distributors, and specialist shops that all offer dependable stock levels. 

2. Combine Capacitors as A Workaround 

In the event of the exact value that you require not being available, you do also have the option of combining, or “ganging”, capacitors in series or parallel to approximate it. 

If you take this route, it will be crucial to ensure the total voltage and capacitance match or exceed the originals. 

You may be familiar with how resistors can also be combined in series or parallel. If so, you will need to be aware that capacitors add together in a way that is completely the opposite of resistors. 

The placement of capacitors in parallel with one another, for instance, means the total capacitance will be the sum of all capacitances. This is analogous to how resistors add when in series. If, for example, you have three capacitors in parallel with values of 10 μF, 1 μF, and 0.1 μF, the total capacitance will be 10 + 1 + 0.1 = 11.1 μF. 

If capacitors are placed in series, the total capacitance of these will be the inverse of the sum of all inverse capacitances. 

The formula 1/C_total = 1/C₁ + 1/C₂ + 1/C₃ + … can be used, where C_total is the total capacitance, and C₁, C₂, C₃, and so on, are the individual capacitances. 

An online capacitance converter can help with calculations like these, by enabling you to rapidly convert all individual capacitor values to the same unit, such as microfarads (μF). 

3. Keep Shipping Fast, And the Costs Low 

When you are looking to obtain capacitor parts quickly, it helps to seek out suppliers with large UK warehouses to avoid import fees and delays – especially if they offer next-day delivery as well. 

So, you should pay close attention to the delivery policies of the stores you’re considering. 

Keep a lookout, too, for sites that have filters for “in-stock only”, to help minimise waiting time. 

With capacitors tending to be cheap, you might not easily reach your chosen store’s threshold for free delivery. So, it can be a good idea to add other essentials to your order, perhaps bunding with resistors and wire. 

Follow the steps above that apply to you, and you can help ensure your projects involving the use of capacitors keep moving quickly and smoothly – with great end results. 

How Can I Determine The Appropriate Voltage Rating When Selecting Alternative Capacitors?

When selecting an alternative capacitor, it is essential to consider the most important factor: not choosing a replacement with a lower voltage rating than the original. 

In the majority of cases, selecting a capacitor with an equal or higher voltage rating is acceptable and often safer. Why? Well, it helps in providing a larger margin against voltage spikes and extends the component’s lifespan.

And here comes the main part: how would you determine the appropriate voltage rating? Let’s find out! 

Identification Of The Voltage Rating Of The Original Capacitor

Locate the voltage rating printed on the body of the original capacitor. Larger capacitors often have the value explicitly written, such as 10V or 50V. Smaller capacitors may use alphanumeric codes, which can be looked up using a code chart.

Consider The Operating Voltage Of The Circuit

Measure the maximum voltage the capacitor will experience in the circuit under all operating conditions. 

A multimeter can be used for a basic DC measurement. Still, an oscilloscope may be necessary to capture high-frequency AC components or voltage spikes, such as ripple voltage in a power supply.

Determination Of The Required Derating 

Apply a safety margin, also known as derating. Select a replacement capacitor with a voltage rating that matches the original. This should be significantly higher than the circuit’s maximum operating voltage. 

You can apply a common rule of thumb. This can help you to select a capacitor with a rating 1.5 to 2 times higher than the operating voltage to ensure long-term reliability and account for transient voltage spikes. 

or example, for a 12V rail, a 20V or 25V capacitor is a safe choice. Some types, like tantalum, may require a higher derating factor of up to 50%.

Examination Of All The Other Factors 

Beyond the voltage rating, you must consider other factors that influence a capacitor’s performance and lifespan! 

Capacitance value: You have to choose a replacement with the same capacitance. Unless the application is non-critical, such as bulk filtering! Only in such cases is a slightly larger value acceptable.

Capacitor type: Use the same kind of capacitor to ensure compatible performance characteristics. This can be ESR (Equivalent Series Resistance), frequency response, and stability.

Temperature rating: Thirdly, ensure the replacement’s temperature rating is suitable for the circuit’s operating environment. 

For high-power circuits, select a higher-rated component to account for internal heating.

Size and polarity: Verify that the new component will physically fit on the circuit board and that its polarity (for polarized types) is correct

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