Capacitor Questions

[Brian617]

I've read a bit on the forum and have a couple of questions I'd love an answer to. The first question deals with a video found on this site showing a 1 F capacitor helping dynamic output while a much larger (30 F?) one makes little improvement. The second is one I've had for years seeing 16v and 20v rated capacitors when shopping. I've always been told get the 20v, they're "better", which makes sense from a more is better perspective. But if my thinking is correct, the higher rated capacitor doesn't reach it's full potential until charged to its rated voltage, while the lesser rated capacitor would reach it's full energy storage at a lower voltage.

1) I wonder if the apparent success of the 1 F capacitor tested over the larger one is due to the charging cycle needed after discharge? Is there any rule of thumb on how long it takes to charge from 13.4v to 14.4v per unit of capacitance with a stock alternator? It seems an upper capacitance limit may be practical for a system.

2) Is the measure of capacitance dependent on voltage? If a 20v 1 F capacitor is charged to 14.4v, does it hold the same energy as a 16v 1 F capacitor charged to 14.4v?

[Wicks]

"Bigger" capacitors are not always better.

Capacitors need to be specified for their specific application to do their job properly.

Look inside an amplifier, there are MANY different sized caps, all doing different functions. If one cap was best then every cap in the product would be the same.

The voltage rating on a capacitor is simply a safety rating and states the maximum voltage that a cap can be charged to.

16V caps could be completely fine in a system that doesn't reach or go over 16V.

Of course its always better to have plenty of headroom with voltage ratings.

The RC time constant, also called tau, the time constant (in seconds) of an RC circuit, is equal to the product of the circuit resistance(in ohms) and the circuit capacitance (in farads), i.e. = R * C.

It is the time required to charge or discharge the capacitor, through the resistor, by ≈ 63.2 percent of the difference between the initial value and final value.

It takes 5 "time constants" to fully charge or discharge a cap.

Energy in a capacitor= 0.5CV^2.

Therefore yes a 20V cap and 16V contain the same energy when charged to 14.4V.

The 20V cap just has the capacity to hold more energy, but if you never charge that high then both caps are similar.

The 20V cap just gives you more headroom since you NEVER want to over-voltage an electrolytic cap!

They can vent out gases and electrolyte and in some cases explode apart.

Seeing as though alternators can produce voltage spikes and most voltmeters used in car audio only measure RMS, then you never see those voltage spikes.

Therefore personally I'd lean towards the 20V cap.

It's common in electrical designs to over rate your needed capacitor voltage rating by 2x.

So if you're circuit operates at 12V, a 25V cap would be great for reliability.

[1two3]

What he said lol

[bassman619]

I've read a bit on the forum and have a couple of questions I'd love an answer to. The first question deals with a video found on this site showing a 1 F capacitor helping dynamic output while a much larger (30 F?) one makes little improvement. The second is one I've had for years seeing 16v and 20v rated capacitors when shopping. I've always been told get the 20v, they're "better", which makes sense from a more is better perspective. But if my thinking is correct, the higher rated capacitor doesn't reach it's full potential until charged to its rated voltage, while the lesser rated capacitor would reach it's full energy storage at a lower voltage.

1) I wonder if the apparent success of the 1 F capacitor tested over the larger one is due to the charging cycle needed after discharge? Is there any rule of thumb on how long it takes to charge from 13.4v to 14.4v per unit of capacitance with a stock alternator? It seems an upper capacitance limit may be practical for a system.

2) Is the measure of capacitance dependent on voltage? If a 20v 1 F capacitor is charged to 14.4v, does it hold the same energy as a 16v 1 F capacitor charged to 14.4v?

yes u are right..the voltage is just a cap tha the u dont want to go above at all..if theyre both charged at the he same rate and volts then the theyll both be the same..but then the farads really in my opinion tell u how fast itll discharge and recharge. For example a 10 farad cap would discharge quicker than a 1 farad cap. But the brand comes in to play too. Cheap brands do the same with capacitor farad ratings as they do with amp watts.. they advertise peak not constant to fool the nube..some people will tell never to get a cap. And just to upgrade the alternator and install extra agm batteries. But the way I see it ..what can it hurt? I like caps and feel they help provide more voltage stability to my amp when hitting hard bass notes playing loud. Keep in mind you will get voltage drops when playing loud but as long as it doesnt dip low like 10v or less then ur alright. But just dont use a cap to keep from upgrading electrical.if u have enough watts you will need tk upgrade alternator and battery choices..

[Wicks]

I've read a bit on the forum and have a couple of questions I'd love an answer to. The first question deals with a video found on this site showing a 1 F capacitor helping dynamic output while a much larger (30 F?) one makes little improvement. The second is one I've had for years seeing 16v and 20v rated capacitors when shopping. I've always been told get the 20v, they're "better", which makes sense from a more is better perspective. But if my thinking is correct, the higher rated capacitor doesn't reach it's full potential until charged to its rated voltage, while the lesser rated capacitor would reach it's full energy storage at a lower voltage.

1) I wonder if the apparent success of the 1 F capacitor tested over the larger one is due to the charging cycle needed after discharge? Is there any rule of thumb on how long it takes to charge from 13.4v to 14.4v per unit of capacitance with a stock alternator? It seems an upper capacitance limit may be practical for a system.

2) Is the measure of capacitance dependent on voltage? If a 20v 1 F capacitor is charged to 14.4v, does it hold the same energy as a 16v 1 F capacitor charged to 14.4v?

yes u are right..the voltage is just a cap tha the u dont want to go above at all..if theyre both charged at the he same rate and volts then the theyll both be the same..but then the farads really in my opinion tell u how fast itll discharge and recharge. For example a 10 farad cap would discharge quicker than a 1 farad cap. But the brand comes in to play too. Cheap brands do the same with capacitor farad ratings as they do with amp watts.. they advertise peak not constant to fool the nube..some people will tell never to get a cap. And just to upgrade the alternator and install extra agm batteries. But the way I see it ..what can it hurt? I like caps and feel they help provide more voltage stability to my amp when hitting hard bass notes playing loud. Keep in mind you will get voltage drops when playing loud but as long as it doesnt dip low like 10v or less then ur alright. But just dont use a cap to keep from upgrading electrical.if u have enough watts you will need tk upgrade alternator and battery choices..

I quoted the capacitor time constant in my above post.

t=RC

The time of charge/discharge is directly proportional to the capacitance.

Therefore the higher the capacitance, the higher the charge/discharge time.

A 10F cap will take longer to charge/discharge then a 1F cap.

A 10F cap holds more energy then a 1F cap so it makes sense that it would take longer to charge.

Electrolytic caps are rated at a certain capacitance with a usual 20% tolerance.

Cheaper caps will sit lower in that spec.

Higher quality caps will be higher in the spec'd range.

[Krakin]

I quoted the capacitor time constant in my above post.

t=RC

The time of charge/discharge is directly proportional to the capacitance.

Therefore the higher the capacitance, the higher the charge/discharge time.

A 10F cap will take longer to charge/discharge then a 1F cap.

A 10F cap holds more energy then a 1F cap so it makes sense that it would take longer to charge.

Electrolytic caps are rated at a certain capacitance with a usual 20% tolerance.

Cheaper caps will sit lower in that spec.

Higher quality caps will be higher in the spec'd range.

Are there any pros or cons in running a 1F cap over two two 500μF in parallel or two 2F in series?

Edit: For the comparison lets say it is already parallel from battery to amp, so the amount of terminations will stay constant.

[Wicks]

I quoted the capacitor time constant in my above post.

t=RC

The time of charge/discharge is directly proportional to the capacitance.

Therefore the higher the capacitance, the higher the charge/discharge time.

A 10F cap will take longer to charge/discharge then a 1F cap.

A 10F cap holds more energy then a 1F cap so it makes sense that it would take longer to charge.

Electrolytic caps are rated at a certain capacitance with a usual 20% tolerance.

Cheaper caps will sit lower in that spec.

Higher quality caps will be higher in the spec'd range.

Are there any pros or cons in running a 1F cap over two two 500μF in parallel or two 2F in series?

Edit: For the comparison lets say it is already parallel from battery to amp, so the amount of terminations will stay constant.

Assuming you mean two 500,000uF caps in parallel.

There are definitely pros and cons to using multiple smaller caps rather them one large one.

Design engineers will use multiple caps for reliability purposes. If one fails, the others can take up the slack and keep the circuit working.

Multiple smaller caps may have a lower resulting ESR (equivalent series resistance) which could help reduce power loss and voltage drop.

In some cases a larger cap may have the better ESR. Depends on your needs.

Always a good idea to check the ESR of your cap options before you purchase.

You might use caps in series to increase your resulting voltage capability since caps in series can handle an overall higher voltage applied to them then a single cap. This really comes into play with super caps or ultra caps with voltage ratings of only ~2.7V.

Caps have "ripple current" ratings.

Sometimes your circuit requires a ripple current higher then one cap can handle.

Therefore you use multiple caps to spread out the current between many caps which also increases the life of the caps.

[Brian617]

• I appreciate the replies. I see now that capacitance is not the total amount of charge, but determines the amount of charge per volt. I also see that the rate of charging varies with the ESR of each particular capacitor, which can vary.

[bassman619]

I've read a bit on the forum and have a couple of questions I'd love an answer to. The first question deals with a video found on this site showing a 1 F capacitor helping dynamic output while a much larger (30 F?) one makes little improvement. The second is one I've had for years seeing 16v and 20v rated capacitors when shopping. I've always been told get the 20v, they're "better", which makes sense from a more is better perspective. But if my thinking is correct, the higher rated capacitor doesn't reach it's full potential until charged to its rated voltage, while the lesser rated capacitor would reach it's full energy storage at a lower voltage.

1) I wonder if the apparent success of the 1 F capacitor tested over the larger one is due to the charging cycle needed after discharge? Is there any rule of thumb on how long it takes to charge from 13.4v to 14.4v per unit of capacitance with a stock alternator? It seems an upper capacitance limit may be practical for a system.

2) Is the measure of capacitance dependent on voltage? If a 20v 1 F capacitor is charged to 14.4v, does it hold the same energy as a 16v 1 F capacitor charged to 14.4v?

yes u are right..the voltage is just a cap tha the u dont want to go above at all..if theyre both charged at the he same rate and volts then the theyll both be the same..but then the farads really in my opinion tell u how fast itll discharge and recharge. For example a 10 farad cap would discharge quicker than a 1 farad cap. But the brand comes in to play too. Cheap brands do the same with capacitor farad ratings as they do with amp watts.. they advertise peak not constant to fool the nube..some people will tell never to get a cap. And just to upgrade the alternator and install extra agm batteries. But the way I see it ..what can it hurt? I like caps and feel they help provide more voltage stability to my amp when hitting hard bass notes playing loud. Keep in mind you will get voltage drops when playing loud but as long as it doesnt dip low like 10v or less then ur alright. But just dont use a cap to keep from upgrading electrical.if u have enough watts you will need tk upgrade alternator and battery choices..

I quoted the capacitor time constant in my above post.

t=RC

The time of charge/discharge is directly proportional to the capacitance.

Therefore the higher the capacitance, the higher the charge/discharge time.

A 10F cap will take longer to charge/discharge then a 1F cap.

A 10F cap holds more energy then a 1F cap so it makes sense that it would take longer to charge.

Electrolytic caps are rated at a certain capacitance with a usual 20% tolerance.

Cheaper caps will sit lower in that spec.

Higher quality caps will be higher in the spec'd range.

my bad I should have been more specific...I meant a lager cap will have quicker response once charged and in use...like it can respond to the voltage dips while in use quicker than a smaller one can

[bassman619]

Also if you use a cap be sure to wire it to a distributor block..having multiple wires connected to the terminals on a cap can hinder it..i hate seeing a cap with 3 or 4 power wires coming out of it..you only need 1 power and 1 ground and 1 remote if applicable..unless u use that rockford 10f cap or something similar..cuz it pretty much has a distribution block built in...or if you do multiple caps than multiple wires are understandable..but then when you do multiple caps you probably spend enough money to where you could have just bought an extra battery or two instead..but thats all up to you bud...dnt let anybody tell you not to do something u want to do cuz at the end of the day its yours not theirs ..