stock battery question

[mobomelter]

i'm just wondering if my stock battery can stand up to the abuse of having an amp and subs run off it. tia.

 

[ZoomVT]

mine does. granted i did kill it after having the music going for about 4 hours (i was working on other stuff and left the music going) without runnin gthe car

 

[goldwing2000]

If you're going to run a lot of bass, I would stick some caps in the system but otherwise you should be fine. As long as the engine is running, you'll be operating off the alternator. If you're planning on a lot of operation with the engine off, I would stick an Optima Yellow-top in there somewhere. Car batteries aren't meant for deep-cycle use.

 

[mobomelter]

i'll probably have a 980w amp. i don't plan on running it without the car on.

 

[tsunami]

i have 3 300watt amps and have had no issues with the stock battery....

 

[BrianG]

A little off-topic (sort of), but does anyone know of an aftermarket high output alternator that will fit? I recently removed the small amplifiers (30wx4 & 250wx1) I had installed a while back and am re-doing the entire setup using a 400W amp and a 600w amp (both rms ratings). That's 106 amps @ 14.4volts (assuming 65% amplifier efficiency). That's a little more than the alternator will provide - not to mention it has to supply power to the rest of the car.

 

[tsunami]

not sure, but i doubt it... get a high level battery and hope for the best until a ho alt comes out....

 

[goldwing2000]

Short answer: No. There are no after-market alternators.

However... how do you figure 106 amps? (400+600)/14.4 is less than 70 amps. Besides, you're not going to be running the system at full power 100% of the time. The alternator is rated for 90A at 12V or 1080W. With capacitors in the system, it should be able to keep up just fine. Worst case, add a second battery (which is really just a big capacitor, anyway).

 

[BrianG]

...
However... how do you figure 106 amps? (400+600)/14.4 is less than 70 amps. Besides, you're not going to be running the system at full power 100% of the time. The alternator is rated for 90A at 12V or 1080W. With capacitors in the system, it should be able to keep up just fine. Worst case, add a second battery (which is really just a big capacitor, anyway).

Add amp wattage: 400w + 600w = 1000w
Figure in typical amp efficiency of approx 65%: 1000w / .65 = 1538w
Calculate amperage: 1538 / 14.4 = 106.8 amps

How do you know I won't be running the amps at full tilt all the time? Seriously, I know the amps will not pull that current all the time, but I like to figure for worst case scenario, especially since speaker impedances can drop quite a bit below rated specs drawing more power for short periods.

Yes, caps will help with current transients - they supply a quick burst of current when needed, but then need to be recharged. The net effect will simply be a more steady draw of current from the alt/battery. I will be adding a cap though, but just because I hate flickering lights.

Adding a second battery will only help power the system longer with the car off. More batteries simply create more load for the alternator to charge and only supply power if the alternator voltage drops below the battery voltage (typically ~13.8v).

Even if the amps do "only" draw 80-90 amps, what's left over to power the rest of the car - lights, heater/AC motors, etc? Running anything, an alternator included, close to or exceeding it's rating, will shorten its life considerably.

I've had several cars with high power systems and have had to replace the alternator eventually - even when running 2 batteries.

 

[tsunami]

Add amp wattage: 400w + 600w = 1000w
Figure in typical amp efficiency of approx 65%: 1000w / .65 = 1538w
Calculate amperage: 1538 / 14.4 = 106.8 amps

How do you know I won't be running the amps at full tilt all the time? Seriously, I know the amps will not pull that current all the time, but I like to figure for worst case scenario, especially since speaker impedances can drop quite a bit below rated specs drawing more power for short periods.

Yes, caps will help with current transients - they supply a quick burst of current when needed, but then need to be recharged. The net effect will simply be a more steady draw of current from the alt/battery. I will be adding a cap though, but just because I hate flickering lights.

Adding a second battery will only help power the system longer with the car off. More batteries simply create more load for the alternator to charge and only supply power if the alternator voltage drops below the battery voltage (typically ~13.8v).

Even if the amps do "only" draw 80-90 amps, what's left over to power the rest of the car - lights, heater/AC motors, etc? Running anything, an alternator included, close to or exceeding it's rating, will shorten its life considerably.

I've had several cars with high power systems and have had to replace the alternator eventually - even when running 2 batteries.

i believe the ac is belt driven with an engagement clutch... lights don't draw that much power... a bigger alt would be a better route to go but as of now, and prob for a long while there won't be one... caps do help a lil bit, but like you said transient mostly and they still need to be recharged afterwards... this is going to seem like a dumb Q but why did you add in the amp efficiency into the equation? i understand the equation but am at a loss when that part gets added in... the math makes sense...wouldn't the amp makers calc that into their system draw/output ???

 

[BrianG]

i believe the ac is belt driven with an engagement clutch... lights don't draw that much power... a bigger alt would be a better route to go but as of now, and prob for a long while there won't be one... caps do help a lil bit, but like you said transient mostly and they still need to be recharged afterwards... this is going to seem like a dumb Q but why did you add in the amp efficiency into the equation? i understand the equation but am at a loss when that part gets added in... the math makes sense...wouldn't the amp makers calc that into their system draw/output ???

The A/C compressor is belt driven, but the air blower motors are 12v driven.

Headlights can be as much as 50ish watts a piece, high beams a little more. Tail/brake/parking lights are probably around 5watts each.

Then, the battery requires charging. I'm not sure exactly what the charging current is, and it is dependent on the condition of the battery, but it's gotta be at least 5-10 amps.

Not to mention fuel pump, computer, dash lights, ignition, etc, etc.

Add all that up and I wouldn't be surprised if the total current draw is on the order of 30-50 amps total at night. Daytime current draw will be less of course.

As to your amplifier efficiency question; manufacturers rate amplifier output power, not the power required on the 12v input. All that heat on the heatsink is power coming into the amp, but not making it to the speakers. Class D (pulse modulated output) amps are more efficient in how they work, so they will use more power more efficiently. Typical class AB amps (covering the vast majority out there) are typically only about 65% efficient (the explanation for this is a bit involved). This means for every watt of speaker output power, there is about 1.5 watts required in 12v power. That extra 1/2 watt is lost as heat on the heatsink.

So, to answer your question, you have to take the efficiency into account when calculating current draw, because it will be more than simply the output wattage divided by 14.4v. Don't forget, as Goldwig2000 said, amps will not require this amount of power all the time since music is dynamic, but it is always best (IMO) to err on the side of caution.

(Sorry for the thread hi-jack mobomelter.)

 

[djltoronto]

Funny... all this talk about our cars electrical devices and their respective current draw and nobody mentioned our power steering pump!
It is the single largest electrical load on our cars (factory equiped). It is fused at 80 amps (probabaly draws around 50-60 amps when in use).


mobomelter, Just curious, but what is the model of the 980 watt amp you are planning to use?

 

[djltoronto]

Funny... all this talk about our cars electrical devices and their respective current draw and nobody mentioned our power steering pump!
It is the single largest electrical load on our cars (factory equiped). It is fused at 80 amps (probabaly draws around 50-60 amps when in use).


mobomelter, Just curious, but what is the model of the 980 watt amp you are planning to use?

Just wanted to correct myself here....
The starter motor is probbaly the largest load of all the factory equiped electrical devices. But the steering pump would be the largest load while the car is running! The load is only really there while turning, but it is a substantial load.

Anyone know approx how much current the steering pump would draw when it just idling (going straight)?

 

[tsunami]

The A/C compressor is belt driven, but the air blower motors are 12v driven.

that makes sense... kinda figured they ran the blowers off of something else..

Headlights can be as much as 50ish watts a piece, high beams a little more. Tail/brake/parking lights are probably around 5watts each.

50 wow, i thought it was more like 15-25 for some reason

Then, the battery requires charging. I'm not sure exactly what the charging current is, and it is dependent on the condition of the battery, but it's gotta be at least 5-10 amps.

Not to mention fuel pump, computer, dash lights, ignition, etc, etc.

Add all that up and I wouldn't be surprised if the total current draw is on the order of 30-50 amps total at night. Daytime current draw will be less of course.

alright i can agree with the low end in that imo... 50amps seems a bit high, but after reading bout the power steering pump, i can see where in instances it could reach 50-60amp draw...

As to your amplifier efficiency question; manufacturers rate amplifier output power, not the power required on the 12v input. All that heat on the heatsink is power coming into the amp, but not making it to the speakers. Class D (pulse modulated output) amps are more efficient in how they work, so they will use more power more efficiently. Typical class AB amps (covering the vast majority out there) are typically only about 65% efficient (the explanation for this is a bit involved). This means for every watt of speaker output power, there is about 1.5 watts required in 12v power. That extra 1/2 watt is lost as heat on the heatsink.

i knew most of that allready... the 1.5-1 is interesting... so a class D is more efficient, but class D amps are sub amps mainly (possibly only) so the 1.5-1 is class AB only do you know what the class D is, just since i am learnin and all... (thumb)

So, to answer your question, you have to take the efficiency into account when calculating current draw, because it will be more than simply the output wattage divided by 14.4v. Don't forget, as Goldwig2000 said, amps will not require this amount of power all the time since music is dynamic, but it is always best (IMO) to err on the side of caution.

makes more sense now, thanks for the explanation... and nicely done to boot..

 

[mobomelter]

i was going to use a power acoustiks amp. but i decided to buy a nitro r/c car instead since i can't do anything until my mazda warranty is up. (70k miles left)

 

[tsunami]

that thing must fly..... you deff could have done the stereo work with out really voiding anything on your warranty as long as it was fused and set up properly the only things you could hurt would be your amp(s) and speakers....

 

[mobomelter]

wasn't worried about warranty. just decided that getting the nitro car would let me do something with my hands without worrying about a warranty.

 

[BrianG]

...i knew most of that allready... the 1.5-1 is interesting... so a class D is more efficient, but class D amps are sub amps mainly (possibly only) so the 1.5-1 is class AB only do you know what the class D is, just since i am learnin and all...

The 65% (or 1.5:1, or .65 ratios) are typical class AB specs. Some are higher, some lower. It depends on how the amp is made. Some people even suggest using a 50% efficiency rating in calculations. However, generally speaking, 65% seems to be the norm from what I've measured.

Class D usually reaches around 90% efficiency, give or take a few %. This is due to the fact that the output devices are either on with current flow, or off with no current flow. Since there is very little voltage dropped across the output devices (transistors, FETs) while current is flowing, there is very little heat. The only losses are usually created during the output device switching times, and maybe some power supply losses. The audio output is basically a high frequency square wave, with varying duty cycle (the ratio of "on" vs "off" time) proportional to the audio signal, which is then "filtered" by the subs coil and some amp components to create the audio signal (whew, that was a mouthful). As you can imagine, the quality of the filtering is somewhat dependant on the sub's coil impedance. Class D full range amps use much higher output switching, almost to the point of RF transmission!

 

[BrianG]

that thing must fly..... you deff could have done the stereo work with out really voiding anything on your warranty as long as it was fused and set up properly the only things you could hurt would be your amp(s) and speakers....

Nitro R/C cars rock. I have a Traxxas Revo and it'll do about 40-45 out of the box, while doing wheelies in 4WD.

And BTW, "Nitro" is short for NitroMethane, not nitrous (I imagine that's what you were thinking ).

 

[mobomelter]

and nitromethane = $25 or more a gallon. you think paying 3 bucks sucks...