# using reactive components to build a battery??

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#### Learner

##### Full Member level 2
Dear friends,
I am poundering on the idea to use reactive components such as inductors and capacitors to build a temporary power storage medium such as a battery but I an not quite sure if this is possible, can anyone give me any advise and guidance to see if this is possible??

My aim is to build a high current storage battery, thank you for all your help!

#### IanP

##### Advanced Member level 5
If you compare both characterisitics you can easily find out that while discharging a battery the voltage remains more or less constant for the most of discharging time and then drops ..
In opposition to this, while discharging a capacitor the voltage starts to drop down immediately ..
After all, capacitors are very good at storing charge for short time periods, and they can be charged and recharged very quickly. In applications, however, where it's more convenient to have a slow-but-steady flow of charge batteries are used ..

In conclusion, I wouldn't spend much time on this issue ..

Regards,
IanP

### Learner

Points: 2

#### echo47

##### Advanced Member level 5
Sure, high-farad capacitors are sometimes used in lieu of a battery. Memory backup, hybrid vehicle power, even flashlights.

But first, give us some idea of how much voltage, current, and total energy you need.

For example, see the EPCOS ultracapacitor family. You can buy them at DigiKey. Beware, expensive!
https://www.epcos.com/

A Google search finds many interesting starting places such as this:

I have not heard of anyone doing long-term storage of energy in an inductor, except maybe superconductor research.

### Learner

Points: 2

#### Learner

##### Full Member level 2
Hi guys,
Thank you so much for your participation in the discussion, I truly appreciate your help!!

To clarify the situation further, what I am looking to do is to build a power storage buffer.

For example I have a windmill turning the generator to generate power, the AC voltage is then rectified to DC. I would then like to store the DC somewhere first for later use, this is what I am trying to do.

I am looking to get like 24V and as much current output as possible, eg 10 amps or more.

Thanks again my dear friends.

##### Full Member level 3
You failed to give the last piece of information needed to give you an answer. The amount of time you need this power for. That is perhaps the most important one. 24 volts at 10 amps for a couple seconds is possible using high value multi layer or carbon aerogel capacitors but anything more than a couple seconds would get prohivitivly costly and impossibly large. Why don't you just use a simple battery bank? Two marine grade batteries in series will likley cost you less than a system that can backup 24 volt power for a few seconds and the real batteries will provide the power for minutes or hours at lower currents.

### Learner

Points: 2

#### Learner

##### Full Member level 2
Thank you for raising the point, I am looking for something that can buffer the power and hold it for a long period of time meanwhile has a high current output ability to provide torque for driving motors.

I was thinking of using caps to hold the charge and connect the load to discharge it when needed, any thoughts on this idea???

##### Full Member level 3
Learner,
This is your third post without defining the hold up time required. You need to specify with no if's, and's, or but's three things. The voltage you need to maintain (a maximum and minimum allowable value) the current being drawn, and thirdly and most important the time you need to draw that power over. "A long period of time" is not an exceptable value in electronics =) Number of seconds would be much better. 24 volts (20-30 volts) at 10 amps you will at BEST be able to get a couple of seconds (1-3) and that's with a capacitor bank more expensive than a battery bank able to do the same thing over at least a half hour or better..

#### IanP

##### Advanced Member level 5
I still think that for applications like yours (windmill) batteries are much better option than capacitors, even, if you need energy just for a "short" period of time (how short???) ..

Here are examples:
A 1F (1,000,000µF) 12V capacitor will light a bulb for about 15 whole SECONDS!!!
(not mentioning the physical size of 1Farad capacitor) ..
A 4700µF would likely discharge so quickly that it would barely cause the light to flicker ..

Reards,
IanP

#### Learner

##### Full Member level 2
Learner,
This is your third post without defining the hold up time required. You need to specify with no if's, and's, or but's three things. The voltage you need to maintain (a maximum and minimum allowable value) the current being drawn, and thirdly and most important the time you need to draw that power over. "A long period of time" is not an exceptable value in electronics =) Number of seconds would be much better. 24 volts (20-30 volts) at 10 amps you will at BEST be able to get a couple of seconds (1-3) and that's with a capacitor bank more expensive than a battery bank able to do the same thing over at least a half hour or better..

I have yet to set a specification for the project because the specs would highly depends on the storage medium that is available on the market given that I have a space and weight limitation, at the moment my objective is to determine what would be the most appropriate device for my purpose.

What I would like to do is to store the energy generated by the windmill and hold it indefinitely until it is required, this means the medium needs to be able to hold a large amount of charge because the windmill could be generating power for days non stop.

Based on the advise received so far it looks like capacitor is definitely out of the question since the size vs the amount of energy it can store does not satisfy what I am looking to do, so I guess I would be looking at rechargebale batteries that is light weight, compact and capable of storing a big amount of energy.

Can anyone suggest if such type of battery exist ?

Specs would be 10Amps min and 20Amps(max for 10 mins), the load is a motor.

The only reason that I am converting the mechanical force(windmill) to electricity then back to mechnical force(motor) again, is so that the motor can be used only when needed and the energy stored has the ability to drive the motor with very hi torque for a short period of time(10min @ 20Amps).

Added after 2 minutes:

IanP said:
I still think that for applications like yours (windmill) batteries are much better option than capacitors, even, if you need energy just for a "short" period of time (how short???) ..

Here are examples:
A 1F (1,000,000µF) 12V capacitor will light a bulb for about 15 whole SECONDS!!!
(not mentioning the physical size of 1Farad capacitor) ..
A 4700µF would likely discharge so quickly that it would barely cause the light to flicker ..

Reards,
IanP

Thanks for the insight!!! It has been extremely helpful!!

#### IanP

##### Advanced Member level 5
If you take into account several types of batteries, the sealed lead-acid seem to be the best choice ..
And the main reasons are:
- The internal resistance of lead-acid batteries is very low. The battery responds well to short current bursts ..
- It only self-discharges 5% per month ..
In this publication:
you will find capacity curves (Fig.3) from which you can select the most suitable (Amp-Hour rating) battery for 20A over 20min scenario ..

Regards,
IanP

#### echo47

##### Advanced Member level 5
You guys must have slept through the ED capacitor revolution.

Let's build a hypothetical capactitor bank using EPCOS ultracapacitors. The B49410B2506Q000 is 5000 farads at 2.5 volts, or 15.6 kilojoules. ESR is negligible. It's about the size of a tall can of beer.
Datasheet: **broken link removed**

We could put ten of them in series to get 25 volts and 156 kilojoules. You'll need a DC-to-DC converter to regulate the discharging capacitor voltage, and it will have some inefficiency, so let's guess that you can transfer 100 kilojoules to your load. That much energy will run your 24V 10A load for about 7 minutes. Maximum available current is scary high, so be careful, don't wear any metal jewelry!

#### GonzoEngineer

##### Newbie level 5
Well...This is Gonzo,........ but try this.

Sell the power back to the grid when the windmill is running, and buy
it back when you need it.

I admit that this is Utopian, but the power grid is still the best battery you can find.

No need for storage, just let the power company decide how to use it. handle it.

In the United States, the most efficient way to use renewable energy is to make the power company buy it when you have it, and sell it back to you when you need it. Preferably at the same price, which is what we are making laws to do.

The key is to pass laws that recognize renewable energy and its value. Let the government make the power companies comply with it.

Now that is Gonzo!

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