Amp and capacitor

 

dumbnewbie
Unregistered guest
I have a capacitor with a digital display and have a few questions bout it (and my amp):

1) The cap display shows anywhere from 14.3-14.87, what is this? The volts from my alt?

2) If my amps say 400 watts rms at 14.25v, but I have a stock alt, what is the percentage of that I'm getting? Am I getting all of the 400 watts since my capacitor reads higher than 14.25?

3) Also, my friend says you don't need a high power alternator if you have a capacitor, I say you need a high power alternator if you have a lot of amps and such, who's right?

4) Last, why do some amps say, for example 400 watts rms at 14v, but reading some threads on this site people say without a high power alternator the same amp won't put out that much power. Is this true?

Any help would help out alot because I'm just starting out and need all the help I can get. And if anyone is wondering, I did buy stuff without knowing about it, just gave money to a friend and trusted them to pick out a decent system for me, but now I want to learn about what I got.
 

Gold Member
Username: Theelfkeeper

Stockbridge, GA USA

Post Number: 1209
Registered: Feb-05
the display ont he cap shows the voltage charge at the cap, which is usually very close to the charge at the battery, which is being charged by the alt. all of which can have a voltage drop inbetween.

the actual output of the amp depends on the efficiency of the amp. class, load, voltage the amp gets...ect...if your giving it the full 14.25 volts and the load at which the amp was rated at for that 400 watt rating, then you should be getting the 400 watts or close to it. do know that some manufactures over rate their stuff, some underrate though.

well, ask your friend where the capacitor gets its power from...the alternator. the alternator is the heart of the system, if it doesn't have the power to handle everything you add to it, nothing will work like it is suppose to. a capacitor just holds a charge, makes everything a little more stable, discharges and reacts faster then most voltage regulators in alternators, and filters out ac ripple.

most amps are rated to give their output at 14.4 volts and at the lowest stable impedance. if you don't have a HO alternator, then you will more then likely have a large voltage drop due to the alt not being able to supply enough current. which causes the amp's output to drop and clip. that also causes damage to the amps and subs.

i'm pretty sure that covers it, although i'm not saying i know everything about the topic. i'm sure you'll get other replies. this has all been discussed before and you may be able to find some of your answers in some older threads.
 

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11306
Registered: Dec-03
1) The cap display shows anywhere from 14.3-14.87, what is this? The volts from my alt?

that's the voltage at the capacitor.

2) If my amps say 400 watts rms at 14.25v, but I have a stock alt, what is the percentage of that I'm getting? Am I getting all of the 400 watts since my capacitor reads higher than 14.25?

If the amps have unregulated power supplies, the wattage is a function of amps*volts, minus loss for efficiency. generally amps should be measured at 12 volts. at 14.4 volts, you get 20% more power, approximately, compared to 12 volts. take 400 watts, divide by 14.25A, and that's how many watts you get at one volt. Take that and multiply by the reading on your voltmter. That's your approx power.

3) Also, my friend says you don't need a high power alternator if you have a capacitor, I say you need a high power alternator if you have a lot of amps and such, who's right?

your friend is wrong.
http://www.glasswolf.net/caraudio/capacitors.html
http://www.glasswolf.net/caraudio/charging.html
http://www.betteraudio.com/geolemon/newmain/battcapalt/
http://www.bcae1.com/charging.htm
http://www.bcae1.com/chargin2.htm
read those.

4) Last, why do some amps say, for example 400 watts rms at 14v, but reading some threads on this site people say without a high power alternator the same amp won't put out that much power. Is this true?

some amps put out the same power within a given voltage range like 10-16VDC. these have regulated power supplies. Some amps with unregulated power supplies put out power based on the voltage they get. see here for more info:
http://www.glasswolf.net/caraudio/amplifiers.html

As for the alternator issue, if the alternator can't supply enough current to feed the amp, voltage rails will sag. wattage is amps*volts, so when volts drop, watts drop. When volts drop, the amplifier also "clips," which causes damage to the speakers. This is why you need a charging system that can keep up with the audio system.
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