Wattage and Power System

[Phoenixcolt]

I been reading a lot of capacitor war threads on the phorum. I do not want another war in this thread, just wanted to reach out for some quick thoughts on my simple power system.

I will only be running 500-600 watts...but I will want to build in support for a more powerful amp upgrade in case I ever do go for that down the road. I believe my stock alternator puts out a max of 90 amps which is better than my alternators of old at least...

I thought I was going to do stock battery and alternator, 4 gauge power wire, and a capacitor(1 to 2 farads) for my 500-600 watts. Just looking for clean and plentiful power.

But after reading some threads, I am thinking more like stock battery and alternator, and just 2 gauge power wire, No Cap...and would be willing to upgrade the battery if needed.

For the 500-600 watts I am talking, shouldn't the second option be fine?

[Pillow]

IMO Get a 1 farad plain capacitor and run it in line with a 4 gauge supply wire. If you plan on going heavy in the future run a 2 gauge to the cap... I am not a fan of big wire as I think it is overkill, I am a remodeler and home wiring requires much bigger draws without such redunkulous wire sizes. I run all 4 in case anyone was wondering.

I like the idea that the cap smooths out the power from the alternator. And provides a little cushion for the musical bumps where the amp needs a quick power draw.

The general rule is 1 farad per 1000 watts... But I think that is BS. I go for 1 farad for any system and then after that you need to look at the "big three" and a bigger alternator.

Just my opinion, YMMV (your millage may vary)

[Bfowler]

^well home runs on a 110v system, not a 12v. far less amperage. typical home fuses are 15amp, while seeing 60+ is normal in a car. and over 150amp isn't uncommon.

that said....i would just run 4awg for now, and then a second run of 4awg if you need it later.

as far as caps go...i personally believe that using them as a power reservoir does nothing for your system. using them to smooth out AC ripples in your power IS worth a cap.

[Pillow]

One day I need to sit down and do the math on these things... But a 14 gauge wire will run 15A (residential code) which off the top of my head will support roughly 1500 watts.

12 gauge = 20A

I will fill in the rest tomorrow...

But here is my ? are we more worried about watts or amps to support the amplifiers?

As a practical matter, unless the power feed wire is getting "warm"/hot then the cable is adequate. That is the reasoning behind residential wiring at least is to elliminate hot wires that will cause a fire... With that said, the code is probably overkill for the wire itself. But the breakers keep the system honest.

... In car audio the weak point is the connection points. And the largest power constraint the fuses themselves! Lets say I have a 0 gauge wire running into a tinny weany fuse, no matter how much you "push" from the supply side the same amount of power is getting through! That is why I think many people go a little too crazy on power supply systems. Design for the weakest link.

Sorry it is late... I will review tomorrow and make it sound better.

[Bfowler]

^nice post.

one thing to think about in car vs home is voltage drop. a home is much less discriminating about the performance aspect.

a particular size of cable may be SAFE (as far as heat goes) but a undersize cable will create voltage drop which can lead to a decrease in performance and depending on the amp...failure

[ttocs]

if you are going to run 4 awg, then be sure to upgrade your factory power wires with 4 awg. The normally run a smaller 8 awg wire for the ground between the battery and chassis, the chassis and the block, and the power wire from the alt to the battery. You could run 0 awg to the amps but if your return ground wires are still 8 awg, how much current will be drawn? Only what the 8 awg will allow.

I would recomend upgrading these big 3 wires before you add a cap and see if you "think" you need it but I would save my money until you know.

[dwnrodeo]

One day I need to sit down and do the math on these things... But a 14 gauge wire will run 15A (residential code) which off the top of my head will support roughly 1500 watts.

12 gauge = 20A

I will fill in the rest tomorrow...

But here is my ? are we more worried about watts or amps to support the amplifiers?

As a practical matter, unless the power feed wire is getting "warm"/hot then the cable is adequate. That is the reasoning behind residential wiring at least is to elliminate hot wires that will cause a fire... With that said, the code is probably overkill for the wire itself. But the breakers keep the system honest.

... In car audio the weak point is the connection points. And the largest power constraint the fuses themselves! Lets say I have a 0 gauge wire running into a tinny weany fuse, no matter how much you "push" from the supply side the same amount of power is getting through! That is why I think many people go a little too crazy on power supply systems. Design for the weakest link.

Sorry it is late... I will review tomorrow and make it sound better.

You have to take into consideration the formula for Power (watts)

P=V*I where V = voltage and I = current

Say you want to supply 1500 watts of power. (P=1500 watts)

For a home you have ~110v. Given P=V*I then I=P/V

1500 watts/110 volts = 13.67 amps needed

For a car you have ~12v.

1500 watts/12 volts = 125 amps needed

This is the reason why the wires needed for 12 volt car audio need to be substantially larger than the wiring in home applications.

As for the fuse being the weakest link, you have to take into consideration the length of the fuse. Being that the fuse is such a short length, the smaller diameter of the fuse does not obstruct the current flowing through the fuse a substantial amount. That is why you have a power wire chart that is not only based on the amount of power needed to supply, but the length of wire needed. This is the same practice that is applied to water distribution systems. It is common practice to have a 20" water transmission main metered by a 6" meter. Since the 6" meter is only 2' or 3' long, the minor losses are negligible in such a short run of pipe compared to the several miles of 20" pipe. Sorry, I'm an engineer and have to relate it somehow.

[Phoenixcolt]

Hey ttocs,

What does it do to your power system if you leave the factory power and grounds and just run a 4 awg power and ground for the amp? Does it start to disperse power unevenly because the 4 awg can pull off more power than the factory 8?

Do you think upgrading factory power and ground could start blowing factory fuses and causing other problems?

[stipud]

For a car you have ~12v.

1500 watts/12 volts = 125 amps needed

This is the reason why the wires needed for 12 volt car audio need to be substantially larger than the wiring in home applications.

And don't forget an A/B car audio amp is, at best, 60% efficient. So assuming a 1500 watt A/B car amp like the Ti1200.1...

(1500/0.6)/12 = 208 amps needed.

Check out PG's requirements chart, no doubt you will think this is crazy, but it's absolutely the correct way to do it:

[Eric D]

You don't need the same gauge cable running from the battery to the rear of the car as you do from the battery to chassis, or alternator to chassis. This is because the cable's resistance is based on size and length. An 8ga wire 2 ft long from the battery to ground under the hood is capable of more power with less loss than a 4ga wire from the battery all the way back to the amplifier. Keep in mind the amp in the back still needs ground, but it is getting it from that 2ft 8ga, and the chassis. The chassis is capable of very high current, well beyond the 4ga cable or a 2ga cable for that matter.

A lot of people don't believe this, but if it were not true, then fuses would not work. Since a fuse is typically a 1/16in thick or wide chunk of metal, it would be the limiting factor in your stereo and would present a huge voltage drop, but it does not.

However, even though I completely believe the above paragraphs I posted, I still recommend 100% you replace the battery ground and maybe even the alternator ground. The factory ones are often corroded in older vehicles and getting ready to corrode in newer vehicles. Plus the terminals on them are often crappier. Replacing them with a good 4ga or larger cable, with some nice sealed rings like those made by Streetwires, then heat shrunk on the ends will get you a reliable cable which will last the life of the car.

I often use larger ground cables than the power cables. The ground is there not only to complete the circuit so an amplifier or stereo in general works, it is also there to disperse energy in the cases of amp failure, or shorting a large capacitor from improper installation, etc. Too small a ground and you have a greater chance a large jolt of energy will seek out alternative grounds such as the RCA shield, which will kill decks and other signal processors.

[Eric D]

In the case of caps, I often suggest people use them. They work great for smaller or more typical stereos. Something like a 4-channel amp on the highs and a 2-channel amp bridged for the subs. These installations often benefit from caps in the form of less headlight dimming, less cutting out on major bass tracks, and less stress on the amp's power supply from voltage drop at the inputs.

Caps are not always helpful though. For SPL guys they are pretty much useless. Maybe a very large bank of caps would help them, but batteries are more what they are after.

The cap argument is always a big one and there are plenty of people ready to jump into that debate. Some facts I think everyone would always agree on though are...

-Caps discharge faster than batteries

-Caps don't hold very much charge compared to batteries

-Caps are expensive, but can be less expensive than a larger power wire

If your amplifier needs a burst of instant current, it will get it from a cap before it gets it from a battery, regardless of the size of the power wire. But if the cap drains too far and does not provide enough charge to complete the demand, was it worth it? Plus, you then need to refill the cap and keep the amplifier fed with current. These are all the trade offs you make with caps.

Now I am sure someone will disagree with me on this, but I have NEVER seen a cap HURT an installation. I have seen caps not help at all, but they never make things worse.

[ttocs]

In the case of caps, I often suggest people use them. They work great for smaller or more typical stereos. Something like a 4-channel amp on the highs and a 2-channel amp bridged for the subs. These installations often benefit from caps in the form of less headlight dimming, less cutting out on major bass tracks, and less stress on the amp's power supply from voltage drop at the inputs.

Caps are not always helpful though. For SPL guys they are pretty much useless. Maybe a very large bank of caps would help them, but batteries are more what they are after.

The cap argument is always a big one and there are plenty of people ready to jump into that debate. Some facts I think everyone would always agree on though are...

-Caps discharge faster than batteries

-Caps don't hold very much charge compared to batteries

-Caps are expensive, but can be less expensive than a larger power wire

If your amplifier needs a burst of instant current, it will get it from a cap before it gets it from a battery, regardless of the size of the power wire. But if the cap drains too far and does not provide enough charge to complete the demand, was it worth it? Plus, you then need to refill the cap and keep the amplifier fed with current. These are all the trade offs you make with caps.

Now I am sure someone will disagree with me on this, but I have NEVER seen a cap HURT an installation. I have seen caps not help at all, but they never make things worse.

I have to corect you on one point in this. You said that an amp will get its current from the cap before the battery. I think technically this would be difficult as a cap is a voltage storage device, not a current storing device. Your amps are current driven, not voltage driven so the amount of "amperage" that a cap supplies compaired to what the amp is requiring is minimal. It will keep the 12v a little smoother but it does
NOTHING for the current as far as I am aware, I could be wrong.

I have also been hearing of some mysterious power problems that pop up in cars months after a large cap is installed. After alot of troubleshooting, replacing some parts they could not explain why the problems went away when removing the cap. I think they confuse some modern charging systems or computer......

Now for the short factory ground wire argument I really do not agree either. The voltage loss or current limiting ability of a short wire is certainly less then with a long wire, but why would you want to keep the limiting device in there? A fuse can drop .1-.2 volts but is needed for safety, the grounds not being upgraded are just limiting your system and choking it and probably causing those wires to generate some heat. By not doing it you might open yourself up to bigger problems and possibly a safety issue. We are not giving people advice on how to install their sony stuff, we all know what a strong PG amp can pull for current........

Caps are really just band-aids for the bigger problem of current demands. I always recomend that people first upgrade their power wires, get the biggest/best CCA battery they can and then if they are still having power dips to do the right thing and upgrade the alt and if everything is done right you will have NO issues. This solution will answer all the questions regarding "what size cap do I need" and correctly address the problem.

[Eric D]

A cap stores charge. Not voltage, and not current. Charge flowing is current. An amp will get its charge from the cap before the battery, as the battery takes too long to discharge.

My explaniation is not without its flaws, but the overall concept is sound.

In the case of the wire, if you have more loss on a 4ga wire to the back than the 8ga wire under the hood, the 8ga wire is not the limiting device, the 4ga wire is. Upgrading the 8ga wire to 4ga will not improve anything if the limit is the 4ga wire.

If what you were getting at is true, then the ultra thin traces within an amplifier would be a limit, and they are not.

The further you go, the bigger the wire you need. It really is that simple.

[ttocs]

stores a charge??

yer kidding right?

[brenzbmr@sb]

pops orville redenbocker in micro wave and patiently waits.

[Eric D]

stores a charge??

yer kidding right?

I don't know what you are getting at, if you are joking or what.

Electricity is based on electrons and electron flow. Electrons are flying around the outside of atoms and when they move from one atom to another you can start doing things with them.

Electrons are known as charge, and a capacitor stores electrons, thus it stores charge.

http://en.wikipedia.org/wiki/Electron_charge

http://en.wikipedia.org/wiki/Capacitor

Read some of that and you will find they don't store gnomes or magic pixie dust.

[ttocs]

I have a technical degree in electronics and worked in electronics for over 15yrs and have never heard anyone refer to electrons as a "charge" in a technical conversation. Is that reffering to current, or voltage? to be honest even reading wikipedia definitions that you supplied confuses me. I will put the pipe down and try reading them later, and stop crapping on this post.

one final qustion, do you not agree that a high output alt should be considered in EVERY high power system sooner or later(after the stock one dies)? What you and I might consider to be high powered would obviously be different but bottom line, if you have power problems a cap does not create a charge/voltage/whatever, it can only store what has been already produced. You can't store what you don't have...........

I just don't see the need to waste money on a cap.

[stipud]

I just don't see the need to waste money on a cap.

Capacitors work extremely well as an A/C ripple filter, by cleaning up your amplfier's D/C power input. The rectifier diode on an alternator is far from perfect, so you end up with lots of A/C artifacts. If you peek at your D/C signal under an oscilloscope you can see lots of dips and peaks. While a capacitor certainly doesn't contain enough charge to power your amp while playing a bass hit, it has more than enough (and reacts fast enough) to smooth the imperfections in D/C.

Input capacitance on an amp is usually just enough to make it work, but a 1 farad capacitor does a lot better and can create a very noticeable SQ improvement, assuming you already have adequate power distribution network, and good enough speakers and install to notice the difference. Similarly the rail capacitor bank in your Octane will clean your powersupply's output very nicely, so that your output stage is spic n span. If I were you I would run a 1f cap on your amp as well to clean the powersupply input equal to your rail caps, ensuring clean voltage on both ends.

Charge is a very common term in electronics. The technical unit of measurement is the Coulomb, which is 6.2*10^18 electrons. Amps is the measurement of the RATE of charge transfer (coulombs/second), so 1 amp means 1 coulomb will pass through the wire in 1 second. Finally, a Farad is the number of coulombs that a capacitor will accept, for the potential to change 1 volt. So at 14v a 1 farad capacitor would contain 14 coulombs of electrons, where a 20 farad capacitor would have 280 coulombs at the same voltage.

You may be more familiar with the term mAh used for batteries (milliamp hours). This is just another unit of charge measure, with 1Ah -> 3600 coulombs of charge (3600 seconds in an hour), so 1mAh = 3.6 coulombs. This means a 14v 1 farad capacitor has 14/3.6 = 3.9mAh. This is a hilariously low charge capacity compared to a AAA battery (550 mAh), or especially car batteries that generally have 100Ah or more (360000 Coulombs!). So you can see where the theory of using a capacitor to power your amp during bass hits is a stupid myth. The difference is a capacitor has much lower ESR than a battery, so it smooths out much smaller imperfections than a battery can.

[stipud]

Thought of a good example... let's say you have a 500w amp playing a -0dB bass note for 1 second. For the sake of simplifying the argument, the amp is 50% efficient, so it requires 1000w to produce its rated power. 1000w at 14v is 1000/14=71.42 amps. This means to power the bass note for one second requires 71.42 coulombs of energy. If you were drawing only from a 1 farad capacitor (14 coulombs at 14v), with no external charge, it would be drained completely flat in 14/71.42 =0.196 seconds. Now this is assuming the amplifier would even run below 10v or so. If you assume that the amp turns off when the voltage sags below 10v, then you only have 4 coulombs of power available, which means it would be drained to 10v in 4/71.42 = 0.056 seconds.

So for powering an amp, a capacitor is utterly useless. But for filtering microscopic ripple in D/C there is nothing better.

[kg1961]

and now you know!!!!

[ttocs]

ok, I can understand that. I have not hear coulumb since chemistry days and that was 20 yrs ago. I was wondering if you would measure "a charge" with volts, amps, watts er watt to help explain it.....

But now, once again, do you disagree that a cap is a band-aid and that a HO alt is the real way to fix this? Again the cap and batter can fill up with any electrons if the alt doesn't supply it.

You can dig a hole as big as you want in the desert for a lake, but if it don't rain enough, all you have is a muddy hole and a large storage capacity.

[rscecil007]

and now you know!!!!

AND KNOWING'S HALF THE BATTLE!!!

Thanks Professor Stipud, good info.

[VW337]

Well this was fun.

One thing which was touched on regarding home wiring vs car that really was not fully addressed but has a large bearing on the matter.

Why is it that home wiring uses 110VAC and the big power lines outside are 480VAC or better?

If P = E*I and E/I = R, since Voltage and current are inversely proportionate then by increasing the voltage you can lower the current and thus lower the overall effect that resistance in the line creates, in turn using smaller cable.

If resistance is creating a drop in voltage then at higher voltages it takes far greater amounts of resistance to create the same effective change in P, thus in car audio even minor amounts of resistance in the power cable can result in voltage drops.


The argument will always occur when discussing caps, but know a cap will improve your audio if you use it in the right manner. It will not keep your lights from dimming if you have a crappy alternator, battery and thin power wire. It can reduce voltage drops but the most notable difference at moderate volume is the AC filtering it provides, this you can hear.

[Bfowler]

dammit, i like how i say that in the 3rd post...no one ever listens to Brian!

[ttocs]

The argument will always occur when discussing caps, but know a cap will improve your audio if you use it in the right manner. It will not keep your lights from dimming if you have a crappy alternator, battery and thin power wire. It can reduce voltage drops but the most notable difference at moderate volume is the AC filtering it provides, this you can hear.

agreed..........