Do I need to buy a capacitor for the system in my car? - Page 2 - diyAudio
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Old 18th November 2011, 05:33 PM   #11
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Update:

Your alternator is capable of supplying 105 amps MAX. It's not wonder that your lights are dimming... You will need a more powerful alternator if you want to supply enough electricity while running a 500 watt amplifier.

Remember that for most of the time your alternator will be generating less than 105 amps.

Here is what I recommend... Upgrade to an alternator that is 140 amps or greater, then make sure to use adequately thick electrical wires. I doubt that rewiring your subwoofer will change things dramatically unless you only use one channel (250 watts of power).

Good luck.
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Old 18th November 2011, 06:09 PM   #12
Francec is offline Francec  Australia
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I would save up for some good hearing aids. You will need them shortly if you don'tbleed fromthe ears first. No, I'm not joking.
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Old 18th November 2011, 06:30 PM   #13
18Hurts is offline 18Hurts  United States
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I'm guessing the dual 2 ohm voice coil is wired in parallel for a one ohm load The Class AB amp is bridged so each channel "sees" a half-ohm so the amp is running an impedance twice as low as it should. This will cause current flow to more than double as the amp attempts to produce 1,000 watts.

When he wires the two 2-ohm voice coils in series for 4 ohms...that should cut his power consumption at least 60% and solve the problem. If he upgrades his alternator or battery--it will provide enough juice to blow the output transistors on his amplifier much faster.

If you want maximum output without destroying your car's electrical system, run two subwoofers that are the most efficient available and use a digital "Class D" amplifier that are around 88 to 92% efficient. Class A/B amps are pigs--that is why they are so large, have huge heatsinks and generate a ton of heat. Figure efficiency of around 57% and it gets worse the lower the impedance it is driving. At very low impedance levels (under 2 ohms) they will convert half the power drawn into heat.

To get an idea--this would just be an example--battery voltage assumed to be 12.5V.

Class A/B (57%) at 4 ohms and 500 watts 70 amps
Class D at 4 ohms (92%) and 500 watts 43.5 amps
Class A/B (50%) at 1 ohm and 500 watts 80 amps
Class D at 1 ohm (88%) and 500 watts 45.5 amps

A car battery can provide "surge" current to make up for music peaks that are not constant. The larger your battery, the more current is available so voltage drop will be less but the alternator will have to keep it charged. Most vehicles can handle a Class D digital 300 to 500 watt monoblock amplifier as long as it has a decent battery/wiring and is not run to constant clipping.

The 300 to 500 watt recommendation only applies to car audio systems used for musical purposes--test tones and bass head hair trick stuff require alternator/battery upgrades etc. As I mentioned in a previous post, my buddy wanted more output with the same 400 watt amp--more woofers and a bigger box caused the glass to be blown out of his car. At least the electrical system didn't have any issues.
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Old 18th November 2011, 10:38 PM   #14
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Quote:
Originally Posted by techbiker View Post
Good electrical wiring is a given, however you won't get anywhere unless you find out what your alternator is rated at. If it's only producing 90 amps, then no capacitor will solve your real issue. I believe that when you upgrade your car, it's important to do it correctly. Adding a second battery just masks the root problem... which is likely a weak alternator.

For safety sake I will try to find out what your alternator is rated at before you do something foolish. Electricity close to fuel in a closed environment is no joke. One spark could be disasterous.
My alternator is 100 AMPs
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Old 19th November 2011, 04:32 AM   #15
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You should just buy another battery...regular one will do the job...and put it in the trunk or if you got space under your hood...put it there. That's what I did in my skylark. Although my alternator is a 220 amp. I use it anyways...I don't have any light dimming what so ever. =D
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Old 19th November 2011, 05:07 AM   #16
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Quote:
Originally Posted by carshateme View Post
You should just buy another battery...regular one will do the job...and put it in the trunk or if you got space under your hood...put it there. That's what I did in my skylark. Although my alternator is a 220 amp. I use it anyways...I don't have any light dimming what so ever. =D
I don't recommend putting a car battery in your cabin because these batteries vent toxic fumes. You can purchase a sealed lead acid battery if you would like to put another in the trunk.

But another battery will act like a capacitor. It will just provide more capacity for spikes in energy usage. It will not fix the power supply issue.
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Old 19th November 2011, 06:03 AM   #17
Jokener is offline Jokener  Germany
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If the alternator is rated at 100 amps, it will never supply those when idling.
If you have the engine idling in a parking lot, the amp only delivers very little power.
And in a regular car that is all okay, because it only has to feed the headlights and a couple watts for all the toys in the car like ECU and audio.
Modern cars, like say a Mercedes E-class (or anything similarly expensive), will turn comfort systems off when idling, just because the alternator can't produce the necessary juice.
(Ever wonder why heated seats don't get hot as fast when you turn on the engine, the headlights and all the other toys? Thats the EMS delaying the seats because you don't have enough juice available and other stuff like ECU is more important...)

Try revving the engine and see if the lights still go dim.
(And don't rev a cold engine. Also, don't rev it to the redline. Idle x 2 or idle x 3 should make a difference.)

And the first thing to replace would definitely be the battery.
It is a reasonably priced part that can be improved by buying a high-quality product.
Just check reviews for the battery size (physical dimensions) that your car can take.
What you are looking for is (obviously) a high peak current draw.
Aftermarket alternators are mostly **** because they don't match the rest of the car.
You end up charging the battery all the time (destroying it), increasing your fuel consumption (noticeably) and, if its a modern car, confusing the on-board energy management.

If the battery doesn't help, I would replace the amp and woofer next.
Because even a large and good cap (read: none of that stuff that is marketed to car hi-fi people) doesn't necessarily solve the problem.
A better, more efficient, amplifier should be able to do wonders.
The woofer would only be replaced in case its a particularly juice-sucking type.
And if all that doesn't help... then you may go ahead and use a good cap to help out.
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Last edited by Jokener; 19th November 2011 at 06:06 AM.
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Old 19th November 2011, 06:27 AM   #18
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Quote:
Originally Posted by Jokener View Post
If the alternator is rated at 100 amps, it will never supply those when idling.
If you have the engine idling in a parking lot, the amp only delivers very little power.
And in a regular car that is all okay, because it only has to feed the headlights and a couple watts for all the toys in the car like ECU and audio.
Modern cars, like say a Mercedes E-class (or anything similarly expensive), will turn comfort systems off when idling, just because the alternator can't produce the necessary juice.
(Ever wonder why heated seats don't get hot as fast when you turn on the engine, the headlights and all the other toys? Thats the EMS delaying the seats because you don't have enough juice available and other stuff like ECU is more important...)

Try revving the engine and see if the lights still go dim.
(And don't rev a cold engine. Also, don't rev it to the redline. Idle x 2 or idle x 3 should make a difference.)

And the first thing to replace would definitely be the battery.
It is a reasonably priced part that can be improved by buying a high-quality product.
Just check reviews for the battery size (physical dimensions) that your car can take.
What you are looking for is (obviously) a high peak current draw.
Aftermarket alternators are mostly **** because they don't match the rest of the car.
You end up charging the battery all the time (destroying it), increasing your fuel consumption (noticeably) and, if its a modern car, confusing the on-board energy management.

If the battery doesn't help, I would replace the amp and woofer next.
Because even a large and good cap (read: none of that stuff that is marketed to car hi-fi people) doesn't necessarily solve the problem.
A better, more efficient, amplifier should be able to do wonders.
The woofer would only be replaced in case its a particularly juice-sucking type.
And if all that doesn't help... then you may go ahead and use a good cap to help out.
This is similar in my Buick. I have a 220 amp alternator. When I put it in park, the lights dim and brighten a little, but when I push the gas just a tiny bit.. the lights brighten and don't dim at all. But I've gone through several master mechanics. One says I need another battery, One says I need to wire my ground from the alternator to a better ground, preferably the battery ground. and the last one says that I have a bad alternator, although I've ran multiple tests and the voltage...and amps output is perfectly normal. The last opinion was that all my ground on my lights are bad....I haven't checked them yet, but I will have to do so very soon, for three of my light bulbs have blown out....lol...probably the voltage...bulbs can't handle it...or somewhat... Although I probably got scammed on the alternator.. I think it's a 160amp..and not a 220amp...considering the small size of the alternator...basically the same size of my stock, just a small pulley.


~About a capacitor, I've heard SO many bad things about them...they hurt your system more than they help...so it's more recommended for a Kinetic battery or something similar...Noted among...one that doesn't give off fumes lol.
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Last edited by carshateme; 19th November 2011 at 06:32 AM.
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Old 19th November 2011, 08:57 AM   #19
Jokener is offline Jokener  Germany
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Having the alternator exchanged at a place that does not do a full "development" of it is an almost universally horrible idea.
Just popping a "larger" unit in a car can have all sorts of unwanted side effects, including (but not limited to ^^) slowly frying the battery, frying or causing unwanted operation of the regulator (unit that turns alternator-AC into on-board-DC) and frying and/or popping the fuses on all sorts of electrical neatness in the car, causing short lifespans in light-bulbs (!!!).

There ARE uses for stronger alternators. I am not doubting that.
But replacing it should be done at a place that knows its stuff and its NOT going to be cheap.
And if they tell you the regulator can be re-used, ask for the exact regulator-schematics and why it is supposed to be capable of handling the new alternator.
If they can't produce both at a minutes notice and explain to a noob most of the details: run!

Regards,
Jokener
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Old 19th November 2011, 02:09 PM   #20
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I think messed up my calculations I think the amp actually does peak @ 1000w bridged to 2ohms can someone check for me, just to be sure. all the info on my amp at the link below.

Kenwood KAC-7204 (kac7204) 1000W 2-Channel Car Amplifier
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