Discussion in 'Car Audio / Security / Electronic Accessories' started by wrx-killer- Sti eater, Jul 18, 2006.

1. ### wrx-killer- Sti eaterJunior Member

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I see that there is not to much info on this subject here. This should be useful to everyone here.

Determining the current capabilities of your vehicle.

Before installing a power amplifier in your system you should take into consideration the vehicleâ€™s ability to provide adequate current to the amplifier. In most vehicles, the alternator is only capable of supplying a little over the requirements for the standard electrical system (i.e. headlights, air conditioning, etc.).

How you play your system will determine the amount of current you will need. For example if you listen to your system at low listening levels, then youâ€™ll probably use less than one-third the rated current draw. If you play your system loud, then you will use most of the rated current of the amplifier.

Most alternators have about a 40 percent reserve capability. In order to determine how many in amperes of current you will have for your system; you will need to find out alternator rating. If youâ€™re not sure of the total amperage of your alternator, a good place to look is on the alternator itself. Most alternators have a metal tag stating the total average available. If you canâ€™t find the tag, check with the manufacture to find out the rated amperage. Once rated current of the alternator is determined, you need to multiply this number by .40 in order to determine the reserve current available for use with your power amplifier.

For Example:

Alternator = 80 Amps 80 x .40 = 32 Amps

Please keep in mind this is an estimate only and not exact science. It is best to get your electrical system tested by a professional to determine the electrical system's true capabilities.

Calculating Amplifier Current Demands

By using the fuse value of the amplifier you can get a rough idea of the amount of current draw that will be used under full output power. Although the full output rating is good to determine the total amperage draw in the system, it does not represent the true continuous or averaged amperage draw in the system. Listed below is a simple way to determine the approximate continuous current draw of your amplifier.

1.) Determine fuse value of the amplifier.

2.) Divide the RMS power Rating by the Peak power rating.

Example:

50Watts RMS Divided by 100 Watts Peak Power = .50 (50%)

Once you figure the percentage of RMS vs. Peak power, you multiply the fuse value of the amplifier by the RMS percentage.

Example:

If the amplifiers fuse value was 30A, then 30A multiplied by 50% would be 15A of continuous current draw.

Depending on systems current requirements vs. your electrical systemss capabilities, you may need to upgrade your electrical system. For example, if you find that your headlights dim when you have your system cranked up at night, this is a sign you should upgrade your electrical system.

There are several different ways to accomplish this. One way is to upgrade the alternator so that it has higher amperage output. Another way is to purchase a Capacitor. We recommend that you consult your Car Audio Retailer to determine what is best for your system.

2. ### TurboMirageYEEAAAHHHVIP

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good stuff!

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This is seriously flawed. Where did you get it from?

4. ### wrx-killer- Sti eaterJunior Member

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were do you see a flaw?

5. ### TommyTheCatGonzo Scientist

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"It is best to get your electrical system tested by a professional to determine the electrical system's true capabilities."

This is funny. I hope you dont mean, go to Autozone and have them "test" your alternator's output. Most car stores do not test the electrical system properly and get very wrong results. I would only trust an alternator rebuilder that knows whats going on (aka doesn't tell you an alt cant be rewound and the like).

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The rated RMS vs peak power stats on the amplifier have NO direct bearing on how much of the fuse's current capacity you're going to draw. None. It's just a general indicator.

To be truly safe, you should prep the car for current draw equal to the rating of all your amplifier fuses all added up. To get a TRUE idea, you need to find out what continuous wattage your amplifier is really rated at, then divide that by 12 or 14.4 (however you want to run the system) to find the true current draw. Almost all decent amplifiers come with a "birth certificate" that tells you what kind of power it made on the bench, and usually at what voltage and current draw too. You have to keep in mind that the true RMS output of an amplifier is not going to give you how many watts is actually consumes to make that power either, because no amplifier is 100% efficient. Take whatever current draw you need, then add some padding to make things safe.

7. ### wrx-killer- Sti eaterJunior Member

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I gave a easy way to figure it out. If you read the post it says a rough Ideal, If you want to find out the true you need to take it to a shop. thIs post will get you into the ball park. The fuses are overated on your amps anyways, You are 100% correct in your post.

"By using the fuse value of the amplifier you can get a rough idea of the amount of current draw that will be used under full output power. Although the full output rating is good to determine the total amperage draw in the system, it does not represent the true continuous or averaged amperage draw in the system. Listed below is a simple way to determine the approximate continuous current draw of your amplifier."

Notice its say-approximate -^

Mr cat, I don't mean autozone,lol. I would not trust them to change a battery in a pager.

This post was to help people in general, I been installing for 14 years and I own my own shop. I not just posting up some b.s.

Last edited: Jul 18, 2006

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Ok, good. I just don't want people to read this and think this is gospel- and I don't want people to read this and then say "look at those tards on HondaSwap that think they know how to spec out amps" or variations of that.

9. ### wrx-killer- Sti eaterJunior Member

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I cee, I should of made the topic diffrent, This will get you in the right direction. Its good for noobs and more, I didn't want to post the hard way or more advance method. Most don't have the tools to do it.

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Eh, I think it's easy enough to do the math on the RMS rating divided by the running voltage level of the car.

11. ### MikeBergyBlah blah blah....

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And fuses are NOT overrated from the factory bro. I've popped several fuses rated for the amplifier in my car (40A). The fuse is deisgned to keep the electrical equipment from frying. If it weren't for the limiting set by the fuse, I would have overdriven my amp and done some damage.

Coming from a designer's pov, ALWAYS design your systems for the max capabilities of the system; while your doing that, throw in a factor of safety.

12. ### wrx-killer- Sti eaterJunior Member

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The fuses are rated at peak. If it was not over rated or was at rms. The fuse would pop while normal playing, ie- 40 amp fuse on amp is pertty much peak. Not rms, which you should be running a amp at. If you go over peak the fuse or fuses blow to keep the amp protected.

Edit because of typo and customers.

Last edited: Jul 20, 2006
13. ### MikeBergyBlah blah blah....

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I'll have to disagree with you there. If fuses were installed that allowed the amp to operate above its max power, you'd never pop a fuse, and you would overdrive the amp until it died. I get what you are trying to say. I wouldn't design my system to push any less than what the max rating for the fuses that are being used in the components.

14. ### wrx-killer- Sti eaterJunior Member

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Mike tell me this, When you were playing your system when you blew your fuse, You were playing it at near or full volume. If this was the case you problably got near peak out put of your amp. There could also be many reason why the fuse blew, to high of a input source, clipping, gains to far up, speaker voice coil causing a short. or speaker on its way out. grounding problems. You seem like a guy that knows were he is coming from so I am putting my money on going close to peak.

15. ### MikeBergyBlah blah blah....

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I'm sure that for the songs that the fuse popped, that it exceeded the peak rating. But that is what the fuse is for - to keep the amp from exceeding it's maximum output. If the fuse was rated higher than the max output of the amp, you'd damage your amp. I am not a car stereo guy - I am more at home with studio pa systems, mixer boards, and stage amplification - playing music and recording and what not is my thing. I am just saying that you should design with maximum power requirements in mind, not normal operating requirements. That is basically my point.

16. ### skillz2k5Senior Member

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Caps are junk... for almost the same price you can buy an optima and run an extra battery in the trunk. As far as going to a car audio dealer.. 75% of those guys have no idea what's going on and charge way too much. Mark up in the car audio retail business is usually 50% or more, I'd stick with online purchases and doing it yourself!

17. ### wrx-killer- Sti eaterJunior Member

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Thats good for you. If you ran a stereo shop or had a ideal what we go thru you would know that we make our profit off of labor. Not product. Off of radio's and amps I barley make 15-20%. I could not keep my doors open by selling products alone. I make a lil off of accesorries. It not like most shops are best buy or circuit city that buy bulk product and they can mark the product to full retail and make a killing. You get cheap product off the internet because the have no overhead. How else are we going to pay for our the leases. The only place I would buy from if I was a consumer would be from crutchfield.com. At least they have customer service. and are authorized to carry the products that they sell. Most big companies are going to stop the sale of there products on ebay and limit what products are sold on the net, with price caps coming soon, If you are a vender and went to ces this year you would know that. Look at what mtx is doing.

Not MTX Authorized Online Resellers alot of companies are following suit to protect there stores that sell to the public. There are more walk in sales compare to the net. I Not saying there are store on the net that just want to rip you off. There are good people on there trying to make a living too. Read the scam list.

Now as to your diss on caps, You are going to have to bring some hard evindence to your claim besides that they are junk. On a spl car they have no good use imo. When you are trying to burp 160 db. But for everyday use they do work. Most people use them as a band-aid to fix electric problems that there car is having. Thats what they were intending on use for. But with a proplerly set up system they can work wonders. I stongley dissagree with you on the % of shops out there. I seen some shadey installs but not all shops. I not sure how it is in your area but when have high-end shops out here. And we have low end shops. I say its more like 50-50. You get what you pay for. I consider my self to be more on the high-end. But to my low end customers I give them the same respect and install that I give to my customers that spend over 5-10 gs on there cars.

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And that's how you build a reputation, convert low end customers into high end customers, and bring in more business by word of mouth.

19. ### suspendedHatchaudio/security

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This is fine for only a very small percentage of people. Hell, it's how I got started originally. Unfortunately I deal day in and day out with people that took this route and ended up paying double or more to get it working right than if they just went to a chain store in the first place. And it's not like they're stupid or something. Just with car audio, you don't know what you're doing unless you've been specifically trained and have had time to gain experience in car audio. "Knowing cars", or "knowing electronics" isn't enough. I have fixed plenty of cars from guys that were trained in the military or who are professional electricians.

You buy a product online, you don't know that the seller is selling a bad batch of stuff that was thrown in the trash. It goes bad in a week, and that online seller can just ignore your emails. Maybe they'll send you out another product from that same bad batch. Then when that one doesn't work, it's proof to him that it's your fault. Happened to me before. With a chain store, you pretty much have 30 days to return it regardless. If you buy their \$30 warranty, they're stuck with your ass for 2 years. I've been on both sides of this. It's your gamble.

You go to a chain store, the labor is covered for the amount of time you own the vehicle. That labor charge isn't so bad when you think about it like that. You can get it cheaper from a mom and pop store, or you could have your buddy do it. But when something goes wrong, you come to us. When your buddy scratches or cracks your dash, where are you then? Is he insured for that?

Not trying to discourage anyone. I'm all about DIY. I have an entire site dedicated to DIY. But just know what you're getting into and don't assume you know what you're doing; or that everyone born with a penis should know how to install a stereo and an amp. I started out DIY, but I've learned and continue to learn a lot from my professional experience.

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