Can A Capacitor Charge A Battery?

Here is the answer to the question Can A Capacitor Charge A Battery? Yes, a charged capacitor may charge a battery without a doubt if its voltage ratings are appropriate, but the time it takes to charge is determined by the capacitor’s capacitance.

A capacitor can be considered a miniature battery, except those typical batteries have a higher energy density. I.e., it can store a lot of charges but has a low power density, which means it can’t fast deliver all of that charge to the load, whereas a capacitor can provide all of its energy in seconds.

Can A Capacitor Charge A Battery?

Yes, and sophisticated Battery Management Systems with active Cell Balancing experience this. A capacitor is linked to a cell with a higher voltage, is charged, and then is connected to a cell with a lower voltage, where it is discharged, effectively charging the cell and thus balancing the battery.

Certainly, let’s have a look at an example. We’ll need a large super-capacitor, so let’s use one rated at 500F 2.7V because they’re widely accessible. Let’s say we wish to utilize this to charge a battery that requires a USB charger, such as a phone battery.

In this situation, the battery charging circuitry is built into the phone, so you won’t have to bother about it. We need to offer a consistent 5V supply at a reasonable current via a USB port. To accomplish this, we’ll need a boost converter, which will boost the capacitor’s voltage output to 5V.

Because the capacitor voltage drops as it discharges, we need to ensure that our boost converter can withstand a changing input voltage down to a low level. Practical converters can work with input voltages as low as 0.5V. Connect one to our charged capacitor, set up a USB socket for the 5V output, then plug in our phone using a USB cable, and we’re ready to start.

So, how much will we be charged under this arrangement? Because capacitors have a changeable output voltage, talking about charge in mAh is pointless because mAh is only appropriate for a relatively fixed voltage, such as a battery. On the other hand, it is a measure of stored energy that humans can use.

A single watt-hour is equivalent to 3600 joules. We’ll need the formula for energy stored in a capacitor to figure out how much we can pull out of our capacitor.

E=12CV2E=12CV2

As a result, our super-capacitor can store the following information:

E=125002.72=1820 joules E=125002.72=1820 joules E=125002.72=1820 joule

E=125002.72=1820 joules E=125002.72=1820 joules E=125002.72=1820 joule

Which is approximately 0.5 WH? Although there is a little complexity in that we can only pull this out by discharging the capacitor to 0 volts, this isn’t a major problem because most of the energy is released at higher voltages. Because our boost converter discharges to 0.5 V, the following energy is left unused:

E=125000.52=63 joules E=125000.52

E=125000.52=63 joules E=125000.52

We can get roughly 1760 joules (0.49 WH) out of our capacitor.

Typical phone batteries, on the other hand, have a capacity of roughly 10 WH (which is 2700 mAh for a nominal 3.7 V Lithium-ion battery). We’ll also lose some energy owing to inefficiencies during the charging process – approximately 20%. So the percentage charge we’ll get from our fully charged super capacitor in practice is around:

3.9 percent = 0.490.810

3.9 percent = 0.490.810

That isn’t a significant charge. Super-capacitors up to 3000F are available, but they are expensive. So we’ll need a few 500F capacitors wired together to make a practical and affordable power bank out of super-capacitors. We’ll get a 47 percent charge from a dozen. When writing (March 2019), you can import 12 of these from China via eBay for around £40.

Because typical 500F super-capacitors are cylinders with a diameter of 35mm and a length of 60mm, arranging them in a single layer yields a power bank with dimensions of 220mm x 130mm x 40mm. If you want to get close to a full charge, make it 24 capacitors and 80mm thick, depending on the size of your phone battery.

You’ll also need a way to charge the capacitors, which is usually another DC to DC converter with a current-limited output and an appropriate power source. You’ll also need protection and cutoff circuitry to verify that all capacitors are completely charged and none exceed their 2.7 V rating. Naturally, this has been done before, so you won’t have to start from scratch. Look up super capacitor power banks on the internet.

Conclusion

To sum up all about Can A Capacitor Charge A Battery? A capacitor can provide some charge to a battery, but it is impossible to charge it fully. Even super-capacitors have a poor energy capacity compared to most rechargeable batteries; their low breakdown voltage is a major limiting factor.

They’re best used in situations where you need to store and harvest little amounts of energy regularly. I initially saw them as non-volatile memory backups. So, it’s not going to happen in the actual world.

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