how important is it to have cap for you amplifier. if your lights aren't dimming when the bass is booming do you even need one?

 

Nope... most systems don't really need caps... particularly systems with amps that use regulated power supplies (which covers most of the higher-end market).

-Alt

 

It is not a nessesary upgrade but will extend the life of your alternator.

 

How does that work ortiz? It's not like the alternator turns off once it has generated enough power. It just spins along spitting out volts as long as the engine is running.

 

What happens is that the Amp draws XX power to run itself. At high volumes (big base) the amplifier has to draw more power from the battery (a power spike). The power draw from an amplifier is never constant.

The alternator has a built in power regulator to insure that it doesn't burn out anything on your car (ei. Battery). That power regulator has to work extra hard to regulate the spiking power that the amp is drawing. Our car has an unusually powerful alternator/ with a good regulator.

A capacitor will draw a constant power while providing the power that the amp needs. By storing energy (enough power to supplement the power spikes), it relieves stress from the power regulator in the amp.

I used to go through a lot of alternators. So I started doing research on how to alleviate the stress on the alternator without adding a second one.

So, yes I would recommend that any TSX owner with a HIGH power amp(s), might want to invest in a capacitor.

BTW, when an alternator goes out usually it is because the power regulator goes out.

 

Hey ortiz, im going to be putting in a Hifonics Brutus 1500x running at 4ohms 500 watts rms.. do you think I should run a cap with it?

 

To be safe, anything that peaks above 1000 watts should have a cap. When desiding on Cap or no cap you look at the peak power not the RMS.

RMS just gives you an average output of an amplifier running under normal circumstances. Peak lets you know how much power the amp will draw at peak bass with peak volume.

 

Not sure what the peak would be (checked their site) but lets say since it can run 1500 RMS at 1ohm, having it peak near 800-900 on a 500rms load is not unreasonable. That being said how manay farads do i need?

 

From prior research I have gathered that you should have 1 farad of capacitance for every 1000 watts.

 

Agreed, but their are some small caps that are useless. Make sure that it says it is rated for 1000 watts.

 

ok your all wrong!
first off a capacitor will only slightly help to maintain a constant voltage. when you use a cap in a system it uses less than 1 of the 5 time constants in it's duty cycle. in fact the electrical system is only fluctuating between 14.2 volts (alternator output) and 13.8 volts (static voltage of the battery)

what is hard on the alternator is not the voltage regulater but the diodes in the alternator that turn the AC output of an Alternator to the pulsed DC output is the weak link in the alternator.

adding a cap will help with the power surges of a system with a lot of current draw but any energy that comes out of the cap from such a current draw has to be replaced after its been used. this means the alternator works just as hard its just that it is doing it at a more constant level rather than in surges.

also a regulated amplifier will draw far more current than an unregulated amp because a regulated amplifier with try to maintain the voltage at the output stage by drawing additional current from the battery. unregulated amps draw less current because the design of the amp will allow the output voltage fluctuate with the voltage present at the power input side of the amp.
you can tell an amp is unregulated is its specs say it is for example 150 watts @ 12 volts and 175 watts @14.4 volts in order to get more watts the output stage has to increase in voltage if impeadance is held constant.

also RMS stands for Root Mean Squared it has nothing to do with peaks or spikes or anything of the sort. it is in fact another way to rate the wattage of an amp or any sinusoidal waveform.
is it exactly .707 of peak in other words a 100 watt Peak amp is equal to 70.7 watts RMS
RMS is the DC equivelent in an AC circuit. since AC changes in amplitude and direction it is not on constantly so you cant express the wattage the same as a DC circuit.
since a DC circuit has a constant output you can calculate watts or (heat) pretty easy. since AC is on and off the Duty cycle is different. this is why you have to multiply the value of an AC curcuit by .707 to get the equivelent Wattage of a constant DC signal.
RMS is ther more accurate way to express the output of an amp. manufacturers found a loop hole in expressing the output of their equipment to the unsuspecting public by advertising watts as peak because the numbers look better. this adds an assumed value to their product and in car audio this is unregulated in the 12 volt industry. in home audio it's against the law to missrepresent wattages in any value other than RMS
also you will see wattages expressed by Alpine in a rating called EIAJ this is a japaneese rating scale that is different and again looks better on paper. it's like Farenheit and Celsius or standard and metric measurements.
i dont know the relation between EIAJ and RMS but i know the ratio is almost 2 to 1. a 100 watt RMS amp is the same as a 200 watt EIAJ rated one.

 

<bows to the mighty bass mechanic>

With what you stated, would you reccomend adding a CAP for the amp setup i listed above?

 

only if the lights were flickering a cap may help but it wont solve the whole lack of power from the alternator problem.
i have only seen a few cars mostly hondas bennifit from a cap. hondas voltage regulators are slow to react to a sudden surge in current. that said a have found a cap to be usefull in helping to allow the voltage regulator to kick in a little smoother with the help of a cap.
i would get a 1 farad and call it a day..

 

Electrical engineer (and power supply designer) here:

1) Yes, the stress for the alternator package is in the rectifying diodes. If you consistently pull more power from them than they were designed for, you can overheat and blow. Either way, you will reduce the MTBF (life) due to the higher operating temperatures.

2) For a sinusoid, the RMS is equivalent to 1/sqrt(2) * peak/amplitude. However, this is only valid for votlage and current, not power. Since power is volts * amps, you have 1/sqrt(2) * volts * 1/sqrt(2) * amps = 1/2 peak power.

3) Difference between regulated and unregulated supplies. Ignoring the fact that one supply could be linear versus a switch-mode, it essentially means you are trying to be as efficient as possible with an unregulated supply. But I wouldn't think there would be too much difference in actual efficiency...maybe 5% at most. In fact, if you draw the same amount of current from your load (speakers), with the higher output voltage, you are drawing more input current (see statement #1).

In a regulated power supply, your duty cycle changes (tweaked) based on load current and input voltage. I think the main difference between the two is from the noise generated by the power switches. WIth an unregulated supply, you have a specific set of frequencies that will be noisy across every unit built and can be corrected for. In a regulated supply these frequencies will vary dynamically as the duty cycle changes.

4) Output capacitance only affects load transients with three caveats. First, the unit will still draw the same average current with or without the cap. Second, you will smooth the transient loading caused by excessive current draw by an oversized sub, etc. Third, you decrease the response rate of the amplifier by adding the cap. Too high of cap will probably make the system sound a bit less crisp for low frequencies.

Overall, a capacitor is essentially a bad solution for most personal systems. If you make sure you have an amp that can handle the peak current loads generated by your speakers you should be fine. Worst case, get a bit oversized one.

 

isnt this pretty much what i already said?

and as for the cap (statement #4 ) we arent talking about caps in the output stage in the amp we are talking about basically a large filter cap installed across the input of the amp. or in parallel with the car battery, adding a cap here wont affect the audio output at all but the theroy is that it will help to prevent the voltage fluctuations for the car when you have an amp that is pulling surges of power when the bass beats hit.

as for regulated power supplies, yes most (if not all) powersupplies in an automotive amp have a switching power supply that generates an AC voltage through the use of a tetroid transformer. they usually step the voltage up to at least +60 and -60 volts and filter it for DC. if you design powersupplies then you know that a regulated one has to lower it's internal resistance to compensate for an excessive load on the +60 and - 60 volt rails if it is to maintain the voltage present to the speakers.
unregulated amps simply run wide open and just allow the output or rail voltage to vary.
this is why regulated power supplied draw more than unregulated. and i agree there is some differences in efficiency also. but generally speaking this is correct isnt it?

as for RMS it's been about 12 years since i had my nose in a book trying to remember thoes formulas but i still say wattage can be expressed as RMS and can be calculated the way i calculated it. watts is directly related to voltage and current so it would be affected in exactly the same way.
if im wrong show me some formula on the net i can read to correct myself. (i know i can't always be right)

 

what about a 600 watt peak amp? should i get a half a farad?

 

i would try it without a cap and if you dont have any light flashing then dont worry about it. you can always add it later if youi need it