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Old 12th January 2005, 07:09 AM   #1
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Default Capacitor Question

Hey, I just bought two audiobahn 12" subs and a 1600W amp. The system i have now causes my lights to dim so a buddy of mine gave me a cap he had lying around. We doesnt know where it came from and we were wondering if anyone could decifer what exactly it is. It says the following on it:

Northern Electric co. (no longer exists so im guessing its old)
NSQ4104L2
Electrolytic Capacitor
20000UF
60VDC
DE 4-73

Just wondering if this will do the trick or not. I was planning on buying one anyways so its no big deal if this isnt what im looking for.
Thanks for the help!
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Old 12th January 2005, 11:37 AM   #2
quasi is offline quasi  Australia
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Default Save your money and enjoy the lights or;

Upgrade your cars alternator and add a couple of extra batteries in the boot (trunk).

This capacitor you have will not make any difference and the 1 Farad car capacitors won't help your lights either (unless maybe you had a boot full.

The reason kids put a 1 Farad capacitor on their amp is to hold the voltage up at the amplifier end, not at the battery / alternator end which is what your lights are wired to.

Sorry If I'm blunt, spend your money on some nice tweeters.

Cheers
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Old 12th January 2005, 02:59 PM   #3
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To be a little less blunt...

Lights that dim for a moment or right when the bass notes hit can be helped by a capacitor, provided that the electrical system catches up right afterwards and the lights brighten up again. The capacitor keeps the voltage up for that peak demand time, allowing it to draw a more average current from the system.

This is treating a symptom, not the problem. The problem is that you're drawing an awful lot of power from the elecrical system. 1600W is a lot of power, more than most alternators are capable of in total. Include the rest of the car's systems (heater fan, lights, ignition, etc) into the mix, and your alternator can be hopelessly overloaded. Even more batteries are just a patch at that level. An alternator capable pf providing enoug current to supply all of the demands of the car plus the audio system is what's required.

Fortunately, you probably don't need to supply the full demand of the audio system all of the time. Most people will listen to the stereo at a "reasonable" volume most of the time, and crank it up only some of the time.

I'd also guess that your 1600W amp is 1600W MAX power, and not RMS. Assuming that's an honest power rating, that's 800W RMS, which is still a lot. Without the amp make and model, that's still just a guess.

The capacitor in question is probably not enough to really provide much help. 5 to 10 of them in parallel might make a signifigant difference.
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Old 12th January 2005, 09:57 PM   #4
Stocker is offline Stocker  United States
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The short answer is it might help but you are very likely not to notice it.

Use this capacitor in a DIY amplifier power supply. For your car, buy some regular car stereo capacitors... For that kind of power, I would say maybe 3 Farads' worth. You would need a freakishly large charging system to push that much current for extended periods... but I have heard several stories of successfully eliminating the dimming lights with capacitors near the amplifiers.

Turning it down is, I assume, out of the question.
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Old 13th January 2005, 08:18 PM   #5
maylar is offline maylar  United States
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As the others have said, caps are considered a bandaid for a weak electrical system. It's rare that they do any good, and the one you have is about 100 times too small anyway.

First recommendation is to upgrade the wiring in your charging system. Replace the wire from alternator to battery and from battery to the car body with fatter ones. This can have a significant effect. If that doesn't do it then your alternator is too small.
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Old 13th January 2005, 08:57 PM   #6
Stocker is offline Stocker  United States
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Capacitors are perhaps a bandaid...


But a small cut only needs a bandaid...


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Old 14th January 2005, 05:16 AM   #7
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Agreed. The 1.2f stiffening cap in my system is just enough to cover large transient demands, but then I'm not running 1600W. Where I used to (just) be able to watch the bass line on my dashboard voltmeter, I can't now, but even before the headlights would not dim. We're talking about a droop from 14.4V to 14.0V where the battery is still charging. The capacitor wouldn't help against more than that.

A stiffening cap does not really help an inadequate electrical system. It does help your amplifier overcome parasitic losses in long cable runs when your battery is under the hood and your amplifiers are in the trunk. The right tool for the right job... A pair of pliers can be used to drive in a nail, but that doesn't make it a substitute for a hammer.
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Old 14th January 2005, 03:33 PM   #8
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Thanks for the help guys. I think i will get a new cap, and then if my lights still dim then i will get a new altenator. (dont really want to spend the cash on that) The amp is 1600W max! See the following.

1600W max power
500W x 1 RMS into 4 ohms, 20Hz - 100Hz at 0.2% THD
900W x 1 RMS into 2 ohms, 20Hz - 100Hz at 0.6% THD
Class D

I have two new questions for you guys though.

I bought the Audiobahn ALUM12Q "Sound Q" Subs. (2 of them) I have heard them before in a small sealed box (which i have also purchased) and they sound great! My question is how you guys think i should hook them up. They have the following

Size: 12 inch

Sensitivity: 96.4 dB
Frequency Response: 18-500 Hz
Recommended RMS Power: 1000W
Peak Power Handling: 2000W
Impedance: dual 6 ohms

The thing that is throwing me is the dual 6 ohms. I have never hooked up subs with dual voice coils.

Any tips you guys might have would be greatly apreciated. Aparently the subs come with a wiring diagram but i hear that you can hook them up in parallel or in series, and just wondering what would give me the best performance from the subs given the amp i have.

I also just installed all new Infinity Speakers in the car
Perfect Kappa 6.5 component set up front and Kappa 6X9's in the rear. Powered by my old sony 4 channel amp (800w max)

Now that you know everything in my car what Cap would you guys suggest? 1 Farad or 2?

Thanks Alot guys

Later
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Old 14th January 2005, 11:10 PM   #9
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The dual 6 ohm voice coils give you some options.

In parallel (The amp wired the same to each voice coil) they will present a load of 3 ohms. In series they will present a load of 12 ohms.

Wire each sub in series, then put both subs in parallel, and you'll get a final load of 6 ohms. 1/(1/12 + 1/12) If you wire the subs in parallel then put the resultant 3 ohms loads in parallel you get a 1.5 ohm nominal load 1/(1/3 + 1/3), which your amp may or may not handle well. Most amps that can do 2 ohms will take it, but may get excessively hot.

6 ohm DVC subs are usually put into sets of 3. That way you can wire all thee in series, (12 ohms each) then put them all in parallel for a final load of 4 ohms 1/(1/12 + 1/12 + 1/12). This suits the output of most amplifiers better. This allows the amps to run cooler, as well as each sub to run cooler.

Putting 3 6 ohm DVC subs in parallel then putting the whole shooting match in parallel gives a final load of 1 ohm 1/(1/6 + 1/6 + 1/6 + 1/6 + 1/6 + 1/6). Many competition amplifiers work best (for SPL) at this kind of load, putting out maximum power, distributing the power dissipation over 3 separate subs. This works very well in hatchbacks and the like where generally there is room for 3 subs, but not more.

Good luck!

[edit] 1 farad will probably help about as much as a cap will, with just that amp. Class D is very efficient as far as current draw goes, so 600W of class D power probably draws about as much current as my 280W of class A/B. However with caps starting to get cheaper, it's probably easier just to get a 2 farad cap.[/edit]
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Old 15th January 2005, 01:41 AM   #10
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Default ...more info...

Hi,

The cap you quoted is 0.02F, a one farad cap is 50 times bigger...but as the others have stated, it must be electrically really close to the amp to do any good, connected through huge cables, 4 gauge would be a good start. We are talking monstrous currents here, 1600w peak is well over 100amps, even a 50th (0.02) of an ohm in a 'lousy' connection will cost you a couple of volts at the amp terminals.

You might want to check the rating of your alternator before you spend money on equipment that cannot possibly help the situation and may actually damage your cars electrical system...

..I don't know what the rating on your alternator is, but 90amps would not be unrealistic. This corresponds to 1120w peak output, when the engine is spinning at, say, 3500 RPM, you can't get much more by spinning the engine faster because of the internal losses in the device itself. At 800rpm you will be lucky to get 30amps, this is why the lights dim so obviously when you are showing the system at a standstill. Basically your charging system is barely able to keep up with the cars needs, let alone the stereos. As a tip, rather than watching the lights dim, turn them off, you'll have 15+ more amps for the stereo...and you may save yourself a call to AAA.

If you are *really* going to use 800w of power for more than a few minutes, especially at idle, you will smoke your alternator, the diode pack, the regulator or more likely all the above. I have overheated and cooked an alternator in one of my trucks, it seized and took out the accessory belt, I was at home, you may not be so lucky...depending on where you are, you may need a tow. A better alternator will seem cheap right about then. They can be obtained starting at about twice the price of an OEM piece, $200-$300, plus they are rated for their low RPM performance as well. If you plan to keep the car for a while and do a big install in it, it's a very sound investment.

Good luck, Happy thumping

Stuart
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