Anyone up for this project?

by swez
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Less/Mr. B. and/or others:

We know the importance of having an adequate power supply for our gear. However, what is the best way to calculate the needs of the vehicle VS how much is left over for Audio and AUX items we tend to add later? (Before the electrical system goes into discharge mode?)

I am of the opinion that a given vehicle needs between 40-65% ALT/BAT power for the critical electrical components in a vehicle. The remaining power a system can deliver, is at the discretion of the user. Here's a short list of critical items a vehicle needs: (Feel free to add more as you see fit)

1. ABS systems
2. HVAC and blower
3. Headlights, brake lamps, side markers and dash lamps
4. ECM/BCM computers & devices they control
5. Airbags
6. Battery charging circuits

The rest of the systems in a vehicle are not used much of the time and therefore, we usually have a surplus from which to borrow some ALT/BAT power for our gear. Such as:

a. Wipers
b. Power seats, windows and door locks
c. High beams and fog lamps
d. Rear window defogger
e. Interior lighting (map lights and courtesy lamps etc.)
f. Amplifiers and AUX devices

Any key primary or secondaries missed? (Please add)

Now, we know that Audio gear is very dynamic in power consumption. The larger our systems, the more power they consume, depending on how we use them right?

OK, we also have to factor in the efficiency and duty cycles of the amplifiers used. Class D (Sub) amps are ~80% efficient. Class A/B (Full range) amps are ~60% efficient and lose the rest to heat. But, since music is very dynamic, the actual power consumption of a given amp is constantly changing, based on the signals they reproduce and the amplitude (SPL) we demand from them. (Today's amps use high powered Mosfets and PWM power supplies with internal storage Caps)

We generally know that test tones are very powerful signals that demand the most from any given amplifier. Here, the duty cycle is very high, but does not last very long in duration. This is our worst case scenario for power consumption of any type amp we are using/testing.

On the other hand, music is not as intense and tends not to push our power consumption as high as test tones do. That means, our amps are not working as hard and pulling as much power as when using test tones. What would be a good range to consider as a duty cycle for an amp under normal listening conditions VS test tones that are practically 100% duty cycle, but short in duration???

Example:

Say we have a Class D sub amp, 1000 watts RMS rated. We also have a 4 channel full range amp to power mids and highs. For a number, this amp nets 100 x 4 watts RMS. Now, how much power demand would we anticipate under the following conditions?

1. Test tones @ ~100% duty cycle, full power from each amplifier
2. Music signals that peak out near full power of each amplifier
3. Music signals that are at above normal listening levels (say ~105 dB for full range and 130 dB for Sub)
4. Music signals that are at normal listening levels (say ~95 dB for full range and 110 dB for Sub)

Basically, say we have 13.5 volts to work with as a base line. How much "net current draw" will be required from the vehicles' electricals under the conditions noted above? (Before we overload the charging system?)

I realize this is a multi-facetted scenario. But, if one had an ammeter and could observe current load changes under the noted conditions, what could we reasonably expect in current draw/power consuption, before key vehicle devices are impaired or starved for power? (Ie: light dimming, severe voltage drops in the entire system)

Got all that? I'm all ears!
swez COFFEE



Replies (11)
lessismorespl on 09/15/2006 22:55:16
On an average, everyday driver system, w/ a factory alternator, there is usually not enough to supply the system as needed. The more the alt. peaks, the more stress we place on the alt., therefore we are also stressing the charging system. We can keep the voltage drops down w/ the Big 3 upgrade and a deep cycle battery, however it does not stop the alt. from working @ peak to keep everything charged, hence placing just as much work on the alt.

An alternator has diodes, these wear out over time, but the harder we work it, the faster they wear down, and eventually burnout. It will still charge w/ several diodes burnt, but at a lower rate. I suggest an alternator upgrade for any system over 1000 wRMS, be it Class D, Class A/B, etc... On average, anyone running 2 amps is somewhere around 800-1000 wRMS, which is anywhere from 50-70 amps. Most factory alts. are 90(at best) amps....but this is peak, which means 40-50 amps at 1000 RPM's, the average fehicles idle. The electrical system of most vehicle, this is a fully loaded power everything, ABS, etc... takes the minimum amperes to operate on idle, which is usually the alts output on idle. So lets say we have 105 peak alt......this would be apprx. 50 amps on idle, this is what it takes to operate everything in the car.

Now we add a 500 wRMS Class D amp, and aftermarket H/U, and a 50X4 Class A/B amp. We have to average this out b/c amps all have different current draws, even if they are made by the same manufacturer(if you do not believe this, just look at a MTX Audio spec sheet, or a Kicker Birth Certificate). So lets say on average, a good mid grade 500 Class D amp draws 50 amperes(and this is a low estimate, it is probably more like 70 amperes) and the 4 ch. draws 30 amperes. That is a total, at normal operating level, 70-80 amperes. Now you are basically making the alt. work @ peak, even on idle. Even w/ the Big 3 and a good Deep cycle battery, you are looking at shortening the lifespan of most alts.

I'm not even getting into blowing major fuses, not the cheap ones in the main fuse relay, I'm speaking of the major fuses under the hood. Many of them are Dealer only and are very costly. I personally believe if you are going to run a 2 amp system, or a high powered 1000+ wRMS system for your subs, you make the investment. Almost every decent size city has a shop that will rewind an alt, which works well to a point. But if you shop around, alts are not that exspensive. H/O and Ohio are high b/c of the rep they built in dB Drag, you will pay $300-$600 for a basic 250-300 amp alt. Motorcity Reman, under $200 for a 200 amp alt., Irragi, about $250-$300 for 200-240 amp. I personally like Motorcity b/c they are based in Detroit (Troy I believe) and communicate well via emails and phone calls to make sure everything is right. I have seen their shop and had 2 techs look over the alts I purchased from them, they said the quality of the windingd diodes is far superior over factory and aftermarket rebuilds. That was all I needed.

I just believe in being smart and frugal w/ my money. In my opinion, it is better to drop $200 now on a good high output alt than it is to replace alts @ an avg. of $65-$70 after exchange, every year or so. My 03 Taurus burnt the alt in the first 8 months, I replaced it w/ a Motorcity Reman 200 amp, never replaced since, going on 3 years now. I paid $219, a 105 amp rebuilt cost $68 after exchange, $204 if I replaced them over this same period, not to mention the knuckle breaking hassle of replacing them.....lets face it, it is not a difficult job, just time consuming and very slow.

I dragged this out and got off topic a little, but you get my point right???

less



MrBrownstone on 09/16/2006 00:12:42
Well the good news is that 12V systems have been around for 80 friggin years, so there isn't a lot of mysteries as to how they operate.

To sum it up, it's all comes down to load and supply. 1kW from a Class D subwoofer amplifier requires X amperes of current. A specific alternator provides X amperes of current.

Factor in all the accessories, and the remaining available current, and you know roughly how much current you have left before the voltage dips and you go from a 13.8V system to a 12.5V system (battery providing the additional power).

The good news is that amplifiers aren't using 100% of their maximum power--even when we are playing them at 100% RMS. heck, unless we are 100% clipped, they aren't. Therefore, our loads are pretty easy to determine.

The real challenge is:

1. How much peak load do we have
2. How long is the peak
3. Will the amplifier entirely discharge current before the peak is reached.

Just because the lights dim doesn't mean a system isn't keeping up--it means the amp has discharged the power (ala powered our speakers). Dimming lights is a REACTION to the amp sucking out the power, not the discharge of signal.

In a nutshell, do you really need an upgraded alternator for a 1kW system? Probably not. If a 70A 1989 Toyota Corolla with 185,000 miles didn't, most people won't. Wiring was 2guage all around, so there wasn't much concern other than the alternator and battery..which doesn't really do much until after the alternator fails to keep up.

When DO you need an upgrade? depends upon the load, the expected use, and how long you expect to use the system at full potential.

In most cases, under a kW, it's a wasted upgrade. Between 1kW and 2kW, there's an advantage...provided you are using the amplification devices to their max RMS potential or higher.

Remember, although 1kW may use 50A, that doesn't mean it uses 50A 100% of the time all the time continuously. Only when the amp is pressing full output power.

Concerning how much current accessories use, if you are:

Slamming on the Brakes (ABS)
Skidding out of control (traction control)
Have your high beams on (pointing at a deer)
Blasting the Airconditioning
Using the wipers (for what?)

Sure, 45 to 50% of the current supply is in use. Once you let off the brakes, traction control comes back to you, and you put your beams back to normal, there really isn't much load. The airconditioner uses electricity, but most of it from the fan blowing around air as a separate belt provides it's compressor power.

Amp efficiency

I know what the packages say, but Class Ds are about 70-75% efficient at 100% RMS 1% THD power. They can be 95% efficient at 100% distortion. Same with A/Bs...they are 40-45% efficient at volumes you care to listen to them, but can be nearly 100% efficient when totally clipped!!



swez on 09/16/2006 10:34:21
Thank you fellow participants!

See the divergence of opinions, observations and experiences here? That's what I was hoping to draw out and hopefully come to a real concenses on. Basically, how much power draw a given amplifier will actually pull from the electrical system, before we create a negative effect on the electricals of a given vehicle?

Both of you guys make some very good points and for the most part, it all boils down to:

1. How much power does a given amp actually draw under various listening conditions?

2. How long does this condition actually last? (Duty Cycle and eff.)

3. What is the break point where one is best advised to upgrade the ALT, BAT and wiring? (Before we blow expensive ALT's, damage charging circuits, pop expensive fuses ect.)

4. How do we detect that our electricals are being taxed to a point of imminent failure? (For discussion purposes, let's say that threshold is when the voltage/current exceeds ALT's design and begins to pull reserve power from the BAT... <12.5 volts)

Both of you gentlemen have very good points in your replies. However, these points are more from experience and observation and less about the specifics of what is really going on under the hood under a given set of specific conditions. We all seem to agree that amplifier performance varies from brand to brand and Class to Class. But we don't seem to have a "real world" (Measured results) concenses on the actual power demands these amps actually demand in real time working conditions.

If I had the equipment handy, I would run several very fundamental tests and report the findings. But alas, I don't have such tools at hand and cannot perform these tests. Amp makers do publish test results on their products. However, the testing mechanisms are often skewed to show the data they desire to point out. (Not always in step with real world conditions some tend to put them through) They don't really do that, do they? Without independent testing by an unbiased 3rd party to verify the results, sure they can. (And many in fact, do just that!)

The idea here, is to prove in a reasonably scientific and repeatable way, what the end user can actually expect, measure and verify as they set up a given system. Basically, how much "real load" is presented from a given amplifier and how does it actually effect the rest of the electrical systems we are dealing with?

Can anyone come up with a plan to measure and report such findings?

swez COFFEE

PS Am not trying to divide this forum into factions and camps of various beliefs, opinions and observations. However, it seems like a good goal to test a system under specified conditions and determine through hard data, what the end user is likely to encounter as they use their gear.

In a nutshell, is this a worthwhile project or do we stick with various assumtions and observations and leave it up to the user to deside? Or, is it useful to set up a well defined set of parameters, test the theories and put forth some general guidelines to prevent system meltdowns?





Victor on 09/16/2006 16:47:14
fractions.. well CK has never been and never will be into fractions.. we are all here to share our experience and theories.. one always learns by the means of discussion and healthy arguments...

MrBrownstone on 09/16/2006 16:56:39
So what we are looking for is the answer to 1 question, "when do we need to upgrade the alternator?"

Correct?

Victor on 09/16/2006 17:01:31
i guess so....

swez on 09/16/2006 22:22:34
Quote: "So what we are looking for is the answer to 1 question, "when do we need to upgrade the alternator?"

Correct?

Yes, that is the bottom line answer to the main question here. However, the deeper issue is... "How much current draw do amps really need to operate fully w/o stressing a stock electrical system." And how do we verify that we need to upgrade the stock ALT/BAT???

swez

PS I said "factions" Vic... not fractions. LOL "Factions" are divided camps of opinions and beliefs on a topic or subject matter. Opposing camps choose up sides and take a rigid stand on one side or another of a given subject. Factions argue and are divided on the subject, based on feelings and observations, but the facts no longer matter.

It's kinda like what's going on in the Middle East right now. Three main tribes (Sunnis, Shiites and Progressive Moderates) are struggling for power, domination or autonomy in Iraq. Now, that's a real "faction" with dire consequences.... WAR!!!


emoboywyl on 09/17/2006 03:51:32
What about the United Imperialist State of America? Wouldn't we be considered part of the warring factions over there?

MrBrownstone on 09/17/2006 04:22:58
In our case, it'd be:

Viagra (Swez)
Propecia (TTOCS & Mr. B..although I haven't lost any hair)
Desetin (all you diaper rash kids)

:-)


Victor on 09/17/2006 05:53:58
Mr.B.... care to clean up...I just pee'd in my diapers.....GRIN

swez on 09/17/2006 10:00:53
Am beginning to think it is not the right timing for this little project. Instead of making a bunch of noise on the matter, think I'll just gather up the needed tools and a few amps I have lying around and do some testing on what's available from my own toy box.

Viagra? Don't think that's gonna help bud. What good is having plenty of lead in the pencile, if you have noone to write to?

A good muscle relaxor and some Tylenol 3 would be most helpful for the recent flair up of Sciatica I have been contending with for the past 3 weeks. Anyone got any of either to spare?

swez



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