Car audio power

[ke5frf]

wow. thank you both soo much. now how can i find out how much amps my current alternator is producing and (side note, is an alternator an easy replace or will i need a mechanic?) thank you for your advice ke5frf, i assure you i have thought about the costs. the system didnt cost anywhere close to $2000, im a deal hunter lol. i found it on ebay for $150 all brand new. two amps 960 and 750, 4 x 6.5" speakers, 2 x 4" speakers, and a 10" sub.

would a 120 amp alternator suffice for the power needs? i think i have a 70 amp now?

and so your saying no matter what the battery thats not connected to the system will still die? even if i connect the other one directly to the alternator?

I would think 120 amps would be fine, can't be sure about a 70 amp alternator because I have no idea the total power needs of your automobile. It might be fine too, as long as you aren't running the AC, the headlights, applying your brake and turn signals, heating your cigarette lighter, powering a laptop, recharging your cellphone, as well as listening to the stereo etc etc all at the same time.

Second question. If you have two batteries connected to one alternator, they will be (or should be if you did it right) in parallel. It may be hard to see this or imagine it, but two parallel batteries can be considered as one "bigger" battery. They will be working together to provide twice the power. Thus, everything drawing power will be pulling from both batteries...theoretically equally. Unless you isolate them with large diodes or something. But isolating them would be undesireable because having the batteries in parallel working together offers advantages. The only disadvantage to this is that when one battery no longer holds a charge you won't know it and the other battery will be taxed to supply the entire system until it fails too.

 

[tcmtech]

Like everything else you get what you pay for when buying new. If its a low end system I doubt it a 1700 watts RMS at the speakers.
But then again I did buy 2 Audiobahn 8004's and two Audiobahn 2302's for $350 used. They have honest specs sheets and the amplifiers and their power circuitry are huge.

Some of the odd name stuff is just generic versions of the higher end stuff too. But then again some of the high end stuff is just cheap junk with a fancy name and loads of advertising behind it.

To be honest 1700 watts of power is not that expensive now days. I was running around 1000 watts RMS at the speakers back in the early 90's when I was in high school. (I had to custom modify the amplifiers myself though) If I could do it back then on a high school kids budget there is no reason a person cant do it now and with more!

And for some of you guys car audio has came alone way since vacuum tubes you should know!
Yes there is cheap junk out there but then again there are also great finds on the good stuff as well!

 

[mistermatrix24]

These are the Specs for my Amps. they dont seem like they'd draw that much power

Specifications
B4.250.2
• Maximum Power: 750 watts
• Power Rating:
85w x 2 @ 4ohms
125w x 2 @ 2ohms
250w x 1 @ 4ohms
• Input Sensitivity: 150mV - 4V
• High Level Input: 1.5V - 10V
• Signal to Noise Ratio: > 70dBA
• Channel Separation: 50dB
• Crossover: High/Low/All Pass switch
• Crossover Type: Variable 50~500Hz
• Amplifier Fuse Value: 20Amp (2)
• Chassis Size: 2”H x 11.25”W x 11.25”D

B4.320.4
• Maximum Power: 960 watts
• Power Rating:
55w x 4 @ 4ohms
80w x 4 @ 2ohms
160w x 2 @ 4ohms
• Input Sensitivity: 150mV - 4V
• High Level Input: 1.5V - 14V
• Signal to Noise Ratio: > 90dBA
• Channel Separation: 50dB
• Crossover: High/Low/All Pass switch
• Crossover Type: Variable 40~400Hz
• Amplifier Fuse Value: 25Amp (2)
• Chassis Size: 2”H x 11.80”W x 11.25”D

 

[audioguru]

"Maximum" power is usually peak power which is double the amount of real power. Distortion is not mentioned so the volume control was probably turned up too high so the output was powerful but very distorted square-waves.

The "750 Whats" amplifier would dissipate about 600 Watts so its total power should be 1350W. But is is fused for only 20A x 2 x 13.5V= 540 Watts. So this "750 Whats" amplifier is really just a little 432W amplifier when the fuses blow. Maybe it produces 300W at clipping.

The "960 Whats" amplifier might produce 384W at clipping.

The total actual power is 684W which is enough to deafen people.

 

[Ross Craney]

These are the Specs for my Amps. they dont seem like they'd draw that much power

Specifications
B4.250.2
• Maximum Power: 750 watts
• Power Rating:
85w x 2 @ 4ohms
125w x 2 @ 2ohms
250w x 1 @ 4ohms
• Input Sensitivity: 150mV - 4V
• High Level Input: 1.5V - 10V
• Signal to Noise Ratio: > 70dBA
• Channel Separation: 50dB
• Crossover: High/Low/All Pass switch
• Crossover Type: Variable 50~500Hz
• Amplifier Fuse Value: 20Amp (2)
• Chassis Size: 2”H x 11.25”W x 11.25”D

B4.320.4
• Maximum Power: 960 watts
• Power Rating:
55w x 4 @ 4ohms
80w x 4 @ 2ohms
160w x 2 @ 4ohms
• Input Sensitivity: 150mV - 4V
• High Level Input: 1.5V - 14V
• Signal to Noise Ratio: > 90dBA
• Channel Separation: 50dB
• Crossover: High/Low/All Pass switch
• Crossover Type: Variable 40~400Hz
• Amplifier Fuse Value: 25Amp (2)
• Chassis Size: 2”H x 11.80”W x 11.25”D

The perfect example of what Nigel said. You have two amplifiers with a total power consumption of 1700W & you talk as if it is 1700W OUTPUT. To me it looks like your max power o/p will be 250W into one 4 ohm speaker plus 2 x 160W into two 4 ohm speakers. Total 570W. That will be peak so RMS will be about 400W delivered between TWO amplifiers. Now we are getting back to the real world.

 

[Sceadwian]

Nigel I think that's the second time you've mis-stated that. Gotta keep up on the law =) It's older than I am =O

Amplifier Rule CFR 16 Part 432 (39 FR 15387)Amplifier Rule CFR 16 Part 432 (39 FR 15387)
has been in effect since 1974, and was ammended in 98 to apply to desktop speakers with built in amplifiers.

 

[tcmtech]

I have to agree with them. Your no where near 1700 watts in any realistic manor. Being most speakers are still 4 ohm impedance. Good subs can be 2 ohm though and some are even 1 ohm now as so I have been told.


I dont keep up on the car audio so much any more. It just got to be too much of headache dealing with all the brainless golden eared pinheads after while.
What I have found out over the years is that physics and common sense got left behind and are now not part of what makes for good honest ratings and sound quality any more. Its now more about brand recognition and grossly overpriced junk that doesn't have anything to do with the sound itself.

 

[Nigel Goodwin]

Nigel I think that's the second time you've mis-stated that. Gotta keep up on the law =) It's older than I am =O

It's not older than I am

Back in the 70's there was a sudden surge of American audio in the UK, all with vastly inflated specifications. American laws don't affect me over here, but we still see today the vastly over specified amplifers from the USA.

 

[audioguru]

It seems that those amplifiers have 10 channels?????
No.
I think the spec's say the power is 85W x 2 into 4 ohms but forget to say or 125W x 2 into 2 ohms.

55W x 4 into 4 ohms or 80W x 4 into 2 ohms.
They do not say how much distortion so the numbers don't mean anything. Maybe it makes terribly distorted square-waves at the powers listed.

 

[mistermatrix24]

see im not gonna lie. i know hardly nothing about audio systems. so your saying that im probably not even using 700 watts of power, is that still alot.... in that case will a 120amp alternator be powerful enough to power everything?

 

[Sceadwian]

US amplifiers? They're all made in china =P You probably get them from a branding shop straight outta Hong Kong =O

 

[audioguru]

see im not gonna lie. i know hardly nothing about audio systems. so your saying that im probably not even using 700 watts of power, is that still alot.... in that case will a 120amp alternator be powerful enough to power everything?

The fuses add up to 90A. But the amplifiers do not play continuously at full power. The car needs a lot of power so maybe a 120A alternator will work.

 

[Nigel Goodwin]

see im not gonna lie. i know hardly nothing about audio systems. so your saying that im probably not even using 700 watts of power, is that still alot.... in that case will a 120amp alternator be powerful enough to power everything?

Multiply the amps and volts together - 12V x 120A gives you 1440W capacity from the alternator. As AG says, it won't be taking full power all the time anyway - most people wouldn't bother uprating the alternator.

 

[mistermatrix24]

well my battery keeps dying ever since i installed the system so im assuming that the current alternator isnt producing enough

 

[Nigel Goodwin]

well my battery keeps dying ever since i installed the system so im assuming that the current alternator isnt producing enough

By all means upgrade your alternator, but do you ever use it without the engine running?.

 

[tcmtech]

Small cars have small batteries with very little reserve capacity on them. Years ago I had 1984 Mercury Topaz with my big 1000 watt sound system in it. I knocked out the sides of the battery tray and put a severe service duty diesel truck battery in it that was about 2.5 times larger capacity than the original battery size.
I also ran a 110 amp alternator with and over drive pulley as well. The stock alternator was only 61 amps rated.

When the bass hit the idle RPM's would drop by about 100! But I didn't have any battery failure or other problems afterward.

 

[mistermatrix24]

no i don't i don't run the system without the car running or at least i've never had a reason to.

 

[tcmtech]

You could just be getting bad batteries. Some of those cheap $35 ones they sell now are built to just live past their 18 month warranty in good working conditions. Abuse them just a bit and they die right away.

Also have you confirmed that your alternator is in fact working properly? Many times they burn out a diode and will still put out enough power to keep the vehicle working but they are not able to charge the battery any more. Adding more power drain only makes things worse.

Another common problem is that incorrect wiring keeps the system on even when its supposed to be off and its draining the battery down when the key is off. Have you checked to see if there is any power draw when every thing is shut off?
A simple multimeter check of the battery while the key is off would tell you right away if things are still on that shouldn't be. If you see more than a few milliamps of current being drawn off the battery then something is still on that shouldn't be.

 

[mistermatrix24]

this is the battery i have

**broken link removed**

I've already noticed some hesitation when i try to to start and i literally got it last monday. so for now i have disconnected my power wires for the amp in hopes that this will keep this battery from dying

 

[mneary]

Is your amplifier shutting down properly when you turn the ignition off?

If your system is drawing even a little bit of power all the time, it will kill the battery very fast.