My truck is stock with a 70 amp alternator....the amplifier has an 80 amp draw max ...How do you tell how big of a capacitor to get?
Replies (10)
swez on 01/18/2006 08:34:02
Forget the Cap and buy a 900 CCA rated Battery and do the Big 3 wiring upgrade. That should help much more than any CAP.
Swez
MrBrownstone on 01/18/2006 13:47:10
the good news is that your amplifier draw is 10-25% of the max draw, as the duty cycle of your amplifier is only 10-25%. Your real need is 20Amps, so don't worry about it.
Caps....
http://p205.ezboard.com/fcaraudioknowledgefrm7.showMessage?topicID=33.topic
swez on 01/18/2006 17:10:00
Mr. B.,
Do you have any links or sites we can look at regarding power consumptions and duty cycles of any given audio device? I have heard this statement from you, many times and would like to learn more about this topic.
In fact, I am almost certain the duty cycles for Class A/B (Linear audio amps) and PWM Class D amplifiers are considerably higher then 25%. The information below has proven to my satisfaction, that Class A/B and Class D amps do draw notable power, even when there is no input signal present. The biasing voltage of transistors is always present at Vcc. However, the power rails that provide actual audio output voltages, are cycled between on and off by transistor switching rates, established by the power supply oscillation frequency and sampling rates.
Basically, I believe that duty cycles are actually much higher than 25%, even when there is no audio input signal present. Class A/B (Linear power) amps have a constant need for bias currents to provide effective slew rates at the transistors Vcc source. When an audio signal is introduced to the transistor (switched on and off in complimentary pairs), the voltage rails are already primed with ready voltages. This limits lag time between no signal and full signal voltage ramping rates. (Slew rate)
If there is little or no priming voltage on the output rails and at Vcc, the time lag and distortion values created by switching rates of the transistors would be horrible and so would audio output quality of that circuit.
In Class D amps, mosfets and switching power supplies are indeed more efficient that Class A/B circuits. However, they too need a "ready state" reference rail voltage available., Switch mode power supply is sampling rates are commonly set at 1.0MHz or higher. Here, it is common practice to employ a 50% bias current to the Mosfets, even when there is no audio signal present.
Granted, I am NOT an Audio Design Engineer! However, after a few years of Tech School and some exposure to several types of amplification topologies, it was clear to me that duty cycles of this range (25% or lower) are not possible in linear amp designs. After some research, I am finding that even Class D topology needs at least 50% bias ready voltages to produce accurate and efficient transient power and response curves.
If any wish to learn more about small Class D, high efficiency amplification circuits, do a google search. (85% efficiencies or higher are possible with battery powered audio devices) That is amazing.
FYI: Many Class D audio power amplifiers employ complementary output MOSFETs that use pulse-width modulation power supplies (PWM). The "duty cycles" that form the bases of all output waveforms from this ampllifier topology, are about 50% with zero input signal applied. To maintain acceptable efficiencies, the MOSFETs should use a high impedance load at the given switching frequency that are employed. Meaning, with a given load (resistive speaker) is connected directly across the outputs, the amplifier output stages will conduct almost 100% of their cycle times. This is true, without regard to changes in the actual duty cycle.
Disclaimer: The above "noted" FYI information was "derived" from Class D amplification notes per Dallas Semiconductor tech briefs. It is not verbatum, but is a compilation of information, gleened from textual notes from MIP, Inc.
It is not my purpose to copy/paste information and call it my own work. However, the general theme is from MIP, Inc. But rather in words of my own choosing. Hopefully, this is not an infringment on MIP's information sharing policies. It is only intended for clarification on how PWM, Class D circuits work and the typical duty cycles used in their designs. For those who wish to read more on this topic, do a google search with key words like Class D amplifiers, Duty Cycles and PWM power supplies.
I believe we can safely say "Myth Busted" ! THINK
The Bottom Line: Linear amps have constant current draw at all times. Even when no input signal is present. They draw additional power when activated by input signal sources. The same concept applies to Class D amp designs as well. The duty cycle is about 50% with no input signals applied and no output signals presented to the load. (speaker)
Swez
Harvester on 01/18/2006 17:35:04
and whats big 3?...
MrBrownstone on 01/18/2006 19:13:03
Easy answer. If your amplifier was at a 100% duty cycle, the car would literally shut off every time a bass note cycled through your system.
Ironically, most of the time, an amplifier is listening 3/4 of the time, and talking 1/4 of the time. If us men could get that much in talking to women, the world would be a better place.
I'll research a little more. **HINT** Richard Clark
MrBrownstone on 01/19/2006 04:20:02
Swez
I reread my post, and yours. after further review (actually, I'm not at work and can review it a little more @ length) I misquoted the post.
The MUSIC demands a duty cycle of ~25% maximum. You are correct, the amplifier is far different than the demand from the source.
In a nutshell, it's highly unlikely the INFORMATION will require a Duty Cycle higher than 25%.
MrBrownstone on 01/19/2006 04:42:45
forwarding the text of the 'post' as the original one is archived and unavailable.
4 docs, and a pDF of the test.
swez on 01/20/2006 05:54:50
If we want to test power draw of an amplifier, we can use a ammeter. There are 2 common types I have used.
One is an inline (series) version that is inserted between the power line and the device we are powering. If we anticipate high current, may need a decade load resistance of the proper value, to get an accurate reading.
The other type employs an inductive loop type clamp. We simply opwn the jaws of the clamp, encircle the wire to be measured and use the proper scale for the anticipated readings of current draw. Many of the new digital versions out there, can measure AC and DC current as well. The better ones have an "Autorange" function as well. We don't have to mess with external load resistors.
Here's what a clamp on Ammeter looks like:
http://www.electrical-contractor.net/The_Store/EX/MA100_120.htm
Swez
PS The duty cycle of music programming is indeed short. Am not debating that issue. However, the amplifier circuits used in audio devices, require a constant bias voltage/current, even during the "quienscent" period. (the time when no signal information is being amplified)
The power rail voltages also have to be maintained as well. It's just a matter of switching the controller transistors on and off to send the rail voltages up or down the AC scale. This is where paired transistors are used. One controls the + voltage rail. The other controls the - voltage rail. Hope that helps...
PSS Mr. B and I go way back. These "little fits and snits" are just verbal sparring matches to keep us on our toes.
PSSS The Big 3 post is probably buried a few pages down again. You can look and when found, bump it back to the main page. Tks!
Victor on 01/20/2006 14:16:18
Ps... Pss...Psss.... hehe
swez on 01/20/2006 15:45:19
Psst...Pssssttt.....Psssssttt.... I gotta go! I gotta Pee
Replies (10)
swez on 01/18/2006 08:34:02
Forget the Cap and buy a 900 CCA rated Battery and do the Big 3 wiring upgrade. That should help much more than any CAP.
Swez
MrBrownstone on 01/18/2006 13:47:10
the good news is that your amplifier draw is 10-25% of the max draw, as the duty cycle of your amplifier is only 10-25%. Your real need is 20Amps, so don't worry about it.
Caps....
http://p205.ezboard.com/fcaraudioknowledgefrm7.showMessage?topicID=33.topic
swez on 01/18/2006 17:10:00
Mr. B.,
Do you have any links or sites we can look at regarding power consumptions and duty cycles of any given audio device? I have heard this statement from you, many times and would like to learn more about this topic.
In fact, I am almost certain the duty cycles for Class A/B (Linear audio amps) and PWM Class D amplifiers are considerably higher then 25%. The information below has proven to my satisfaction, that Class A/B and Class D amps do draw notable power, even when there is no input signal present. The biasing voltage of transistors is always present at Vcc. However, the power rails that provide actual audio output voltages, are cycled between on and off by transistor switching rates, established by the power supply oscillation frequency and sampling rates.
Basically, I believe that duty cycles are actually much higher than 25%, even when there is no audio input signal present. Class A/B (Linear power) amps have a constant need for bias currents to provide effective slew rates at the transistors Vcc source. When an audio signal is introduced to the transistor (switched on and off in complimentary pairs), the voltage rails are already primed with ready voltages. This limits lag time between no signal and full signal voltage ramping rates. (Slew rate)
If there is little or no priming voltage on the output rails and at Vcc, the time lag and distortion values created by switching rates of the transistors would be horrible and so would audio output quality of that circuit.
In Class D amps, mosfets and switching power supplies are indeed more efficient that Class A/B circuits. However, they too need a "ready state" reference rail voltage available., Switch mode power supply is sampling rates are commonly set at 1.0MHz or higher. Here, it is common practice to employ a 50% bias current to the Mosfets, even when there is no audio signal present.
Granted, I am NOT an Audio Design Engineer! However, after a few years of Tech School and some exposure to several types of amplification topologies, it was clear to me that duty cycles of this range (25% or lower) are not possible in linear amp designs. After some research, I am finding that even Class D topology needs at least 50% bias ready voltages to produce accurate and efficient transient power and response curves.
If any wish to learn more about small Class D, high efficiency amplification circuits, do a google search. (85% efficiencies or higher are possible with battery powered audio devices) That is amazing.
FYI: Many Class D audio power amplifiers employ complementary output MOSFETs that use pulse-width modulation power supplies (PWM). The "duty cycles" that form the bases of all output waveforms from this ampllifier topology, are about 50% with zero input signal applied. To maintain acceptable efficiencies, the MOSFETs should use a high impedance load at the given switching frequency that are employed. Meaning, with a given load (resistive speaker) is connected directly across the outputs, the amplifier output stages will conduct almost 100% of their cycle times. This is true, without regard to changes in the actual duty cycle.
Disclaimer: The above "noted" FYI information was "derived" from Class D amplification notes per Dallas Semiconductor tech briefs. It is not verbatum, but is a compilation of information, gleened from textual notes from MIP, Inc.
It is not my purpose to copy/paste information and call it my own work. However, the general theme is from MIP, Inc. But rather in words of my own choosing. Hopefully, this is not an infringment on MIP's information sharing policies. It is only intended for clarification on how PWM, Class D circuits work and the typical duty cycles used in their designs. For those who wish to read more on this topic, do a google search with key words like Class D amplifiers, Duty Cycles and PWM power supplies.
I believe we can safely say "Myth Busted" ! THINK
The Bottom Line: Linear amps have constant current draw at all times. Even when no input signal is present. They draw additional power when activated by input signal sources. The same concept applies to Class D amp designs as well. The duty cycle is about 50% with no input signals applied and no output signals presented to the load. (speaker)
Swez
Harvester on 01/18/2006 17:35:04
and whats big 3?...
MrBrownstone on 01/18/2006 19:13:03
Easy answer. If your amplifier was at a 100% duty cycle, the car would literally shut off every time a bass note cycled through your system.
Ironically, most of the time, an amplifier is listening 3/4 of the time, and talking 1/4 of the time. If us men could get that much in talking to women, the world would be a better place.
I'll research a little more. **HINT** Richard Clark
MrBrownstone on 01/19/2006 04:20:02
Swez
I reread my post, and yours. after further review (actually, I'm not at work and can review it a little more @ length) I misquoted the post.
The MUSIC demands a duty cycle of ~25% maximum. You are correct, the amplifier is far different than the demand from the source.
In a nutshell, it's highly unlikely the INFORMATION will require a Duty Cycle higher than 25%.
MrBrownstone on 01/19/2006 04:42:45
forwarding the text of the 'post' as the original one is archived and unavailable.
4 docs, and a pDF of the test.
swez on 01/20/2006 05:54:50
If we want to test power draw of an amplifier, we can use a ammeter. There are 2 common types I have used.
One is an inline (series) version that is inserted between the power line and the device we are powering. If we anticipate high current, may need a decade load resistance of the proper value, to get an accurate reading.
The other type employs an inductive loop type clamp. We simply opwn the jaws of the clamp, encircle the wire to be measured and use the proper scale for the anticipated readings of current draw. Many of the new digital versions out there, can measure AC and DC current as well. The better ones have an "Autorange" function as well. We don't have to mess with external load resistors.
Here's what a clamp on Ammeter looks like:
http://www.electrical-contractor.net/The_Store/EX/MA100_120.htm
Swez
PS The duty cycle of music programming is indeed short. Am not debating that issue. However, the amplifier circuits used in audio devices, require a constant bias voltage/current, even during the "quienscent" period. (the time when no signal information is being amplified)
The power rail voltages also have to be maintained as well. It's just a matter of switching the controller transistors on and off to send the rail voltages up or down the AC scale. This is where paired transistors are used. One controls the + voltage rail. The other controls the - voltage rail. Hope that helps...
PSS Mr. B and I go way back. These "little fits and snits" are just verbal sparring matches to keep us on our toes.
PSSS The Big 3 post is probably buried a few pages down again. You can look and when found, bump it back to the main page. Tks!
Victor on 01/20/2006 14:16:18
Ps... Pss...Psss.... hehe
swez on 01/20/2006 15:45:19
Psst...Pssssttt.....Psssssttt.... I gotta go! I gotta Pee
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