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Old 10-18-2002, 08:04 PM   #1
AmIGrand
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Dimming lights/low voltage question's....

Since the question keeps coming up in threads, and Steve and myself, and numerous others with whom I am regretably less familiar keep replying to them as the questions arise, I am starting this thread as a reference for people who somehow haven't read the FAQ's or found the answers they seek in a search. Feel free to reply, but this wasn't meant to start a discussion, only provide information.

Any guru's please feel free to back me up so that others know this is accurate and credible, or to expound on any part of it if, in your expertise, you find any part of it lacking.

Not to be nasty, but if there be any individual who should feel compelled to disagree with this info based on what their "friend who knows a lot about this stuff" told them, I would ask said individuals to refrain from posting here without doing some heavy duty homework. This post is meant to clear things up for people who have heard different things from different sources and need help, not add to their confusion on the issue. That said -

The most frequently recomended step to help with a low voltage situation is to add a capacitor of one sort or another. This advice is given even by seasoned professionals in the industry. Unfortunately, it is more often than not the wrong advice.

Capacitors (caps) are a good thing - if they're used correctly. When added to an electrical system that can keep up, they provide the extra on-demand power a big amplifier craves. However, if the electrical system is already lagging, a cap helps until it's discharged, then it becomes one more thing for the already overworked charging system to keep up with. Once drained, a capacitor becomes a point of resistance in the system untill it is able to regain a voltage equal to or greater than that demanded "down stream", as it were. Since caps drain very quickly, and the demand that drained them in the first place will draw the current it wants with or without the cap, they do not recharge until the demand drops. So -

Make sure the alternator is in good shape. Then check the existing battery. If either of the above is wanting, replace it. If both are good, then add a second battery to reduce the load on the front end of the charging system. Upgrade the alternator if you are hard on your system to the point where even the 2nd battery is running behind. Once all this is in place, and your voltage no longer drops at the front, add capacitors as you see fit to bolster the amplifiers supply voltage. This is proper use of a cap.

Note that not all situations will call for the additional battery and/or upgraded alternator. If the power shortage is slight, as with a moderately sized amplifier added to a stock charging system in good condition and not overtaxed, a cap MAY be helpful. For most imports, that would be a sub amp fused at less than 40 amps, with few or no other additional components drawing significant power. There are no "exceptions" per se, but there are borderline situations where a cap may be benificial, and the preceeding was a VERY GENERALIZED example of such a situation.

As to what to add if you do in fact need to beef up the electrical system's foundation, here are some Cliff's Notes on what to do when.

When adding a second battery, try to mount it as close to amplifiers as possible. Avoid standard lead-acid batteries - for both safety and practicality. Gel Cell batteries (most popularly the Optima brand Red or Yellow Top units) are good, and will do the job. Redtops work best as a PRIMARY battery REPLACEMENT, Yelows are better as a second, dedicated battery. Drycell batteries (I prefer the Stinger brand, there are other very good ones out there) are better. They have a lower internal resistance, recharge faster, can discharge more current on demand, and are more durable.

Any time a second battery is added, the power wire connecting the two MUST be fused within 18 inches of BOTH batteries positive posts. A dual battery isolator or relay is not NECESSARY, but is a very good idea. It is OK to ground the 2nd battery to the frame if you'd rather not run two wires through the car, but all system components should be grounded to the system batteries negative post (this is usually more convenient install-wise anyway). It is not in fact necessary to have both batteries be of the same type - they will be wired in paralell, so the resistance will therefor average out as far as the alternator is concerned, although the battery with the lower internal resistance will charge faster.

Upgrading the alternator can be done two ways, by having your unit rewound to a higher amperage, or by replacing it altogether with a high output type unit. The former is less expensive, but typicaly less reliable, the latter usually more reliable - but MUCH more expensive. I am not going into adding additional alternators here, it is VERY seldom necessary, and if you need it, you need more help than would be useful here.

I REALLY hope there won't be many questions remaining after this, I tried to make it easy to grasp. Sorry it was so long, I hope it will be worth it!!
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Old 10-19-2002, 11:37 PM   #2
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What about upgrading the stock batt/alt wiring to a bigger size? Doesnt this have any benefit?
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Old 10-19-2002, 11:40 PM   #3
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Ah - he finds the part I left out. Sorry about that!

Yes. Upgrading the factory power wire and ground straps is very effective, even without a big audio system or other draw. Voltage gains of .5 volts are usually realized simply by replacing the alternator wire and the alt and batt ground wires with quality 4 ga.

Good call!!
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Old 10-19-2002, 11:57 PM   #4
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Any tips, tricks to offer on how to do this properly? I remember a post stating that you shouldnt "replace" the alternator wires, but to add another...
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Old 10-20-2002, 10:41 AM   #5
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There was an individual who wasn't sure where to take the wire. He was concerned about going to the fuse box first and then the battery, or battery and then fusebox. In all reality, it doesn't matter, they're in a parallel circuit. He finaly left the stock wires in place, and added an additional wire (4 ga) straight to the battery. Nothing wrong with that, but nothing wrong with replacing the stock wires, eiher (well, warranty issues, if they wanna be jerks about it).
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Old 10-20-2002, 10:47 AM   #6
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Quote:
Originally posted by AmIGrand
There was an individual who wasn't sure where to take the wire. He was concerned about going to the fuse box first and then the battery, or battery and then fusebox. In all reality, it doesn't matter, they're in a parallel circuit. He finaly left the stock wires in place, and added an additional wire (4 ga) straight to the battery. Nothing wrong with that, but nothing wrong with replacing the stock wires, eiher (well, warranty issues, if they wanna be jerks about it).
It is involved and really really difficult to replace the stock alternator -> fusebox wire, because of the way it travels, and it enters a connector on the underside of the fusebox that you will never get a thicker cable into. Easier to re-run from the battery right to the alternator.

You can also re-run the small cable that goes from the battery to the + supply on the underhood fusebox with 4ga, I did that, it takes about 2 seconds.
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Old 10-24-2002, 11:24 AM   #7
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Quote:
Originally posted by iceman


It is involved and really really difficult to replace the stock alternator -> fusebox wire, because of the way it travels, and it enters a connector on the underside of the fusebox that you will never get a thicker cable into. Easier to re-run from the battery right to the alternator.

You can also re-run the small cable that goes from the battery to the + supply on the underhood fusebox with 4ga, I did that, it takes about 2 seconds.
Are you saying that running a 4 ga wire from the battery to the + terminal on the engine fuse box is just as good as running a 4 ga wire from the alternator to the fusebox?
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Old 10-24-2002, 11:45 AM   #8
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Well I'm saying that you are not going to be able to replace the wire that goes from the fusebox to the alternator with 4ga, it's impossible. You can, however, re-run fron the alternator to the battery, and also re-run the battery-fusebox connection.

There really are 2 distinct different wires... You could go from the alternator to the fusebox if you wanted, but you still have the "small pipe" to the battery.
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Old 10-24-2002, 01:18 PM   #9
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I think it would be a good idea for someone to post a how to on this...it would def. clear alot up...
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Old 11-19-2002, 11:46 PM   #10
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Slight drain?

What would a slight drain be classed as?

My lights dim quite a bit (like 30-35%) on a thump; but do not if I rev up to 1500rpm or so. My battery voltage seems to wonder with the weather but thatís it, it always seem to return. This seems like it might be a slight drain, but I'm running nearly 800 watts?! Thatís a lot of drain. I mean I know the equipment is crap but... would a capacitor help me? How big? Should it be wired on the other side of a diode to prevent flash back if it ever burns?

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Old 11-19-2002, 11:54 PM   #11
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It's a matter of current draw. At higher RPM, your alternator turns faster & produces more of it, so your lights don't dim. If the total amperage rating of all your amplifiers is less than 60 amps, you are probably OK with a cap. Less than 30, you shouldn't even need that. Over 60 you want to start considering a second battery or a beefed up main one at least, over 100 a high output alternator would be a good idea in the long run.

A diode would choke power too much. For small applications (under 10 amps or so) they are fine, but not here.... Should the cap fail, the fuses in/on the amplifier will protect it sufficiently.
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Old 12-02-2002, 09:30 AM   #12
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here is a list of questions to any who feel the need to answer

what is the (amperage?) on the stock alternator

for a 90 amperage what would the best route be? im thinking optima red top

ok nevermind class over.
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Old 12-02-2002, 10:56 PM   #13
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Stock alternator is 90 (I think) on the 2.4, and 105 on the 3400.

If the combined rating of amps is 90, and one of them is powering highs, you're OK with the stock setup and maybe a cap. If the 90 amp rating is jsut the sub amp(s), an upgraded or seconf battery would be a good idea.
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Old 12-04-2002, 03:24 PM   #14
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I dont believe a second battery with our stock alternator would work, I don't think it could handle the resistance of the two batteries and would blow out. And upgraded battery would be good, but for a second battery youre going to need an upgraded alternator first.
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Old 12-04-2002, 07:25 PM   #15
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I don't know where this comes from, but this is the second or third time we've been here....

Adding a second battery does not significantly change the load to the alternator.

I have done DOZENS of systems with 2 batteries on the stock chrging system in lots of different cars - including GA's - and NEVER had a problem.
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Old 12-08-2002, 12:52 AM   #16
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As an automotive instructor teaching advanced electrical systems, I would like to put in my 2 cents. When adding a second battery, it is wired in parallel. According to Ohms law, the more circuits you add in parallel, the LOWER the resistance, and your total resistance will be lower than the resistance of your smallest branch. (such as 2 4-ohm speakers in parallel have a total resistance of 2 ohms) Therefore, 2 batteries wired in parallel will have a lower total resistance than 1 battery alone. and before anyone asks the question, if you wired them in series, you would have 24 volts instead of 12
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Old 12-09-2002, 08:56 AM   #17
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Unhappy

Well I just went a dropped most of a pay check on stereo components, I'm still running the same 2x 250 watt (20Amp) amps pushing the same 2X10" bandpass and the same 600 watt (40amp) pushing the same 15, but I added a 24v 1 farad capacitor (as everyone seemed to agree (including the sales man and i doubt he would have passed up the opportunity to sell)) But when I added I rewired from an 10 gauge wire run from the inside the fuse box to a 4/8 gauge from the battery terminal, now my light nearly turn off at an idle. They were like 30% dimming before. My battery voltage still seems to be stable but still this is not good, not after $150 on a capacitor and $250 on wire.
But on the upside when it really hits it hurts.
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Old 12-09-2002, 06:22 PM   #18
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Why are you running two different subwoofer systems?
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Old 12-11-2002, 10:06 AM   #19
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Well the Band pass only hits to about 40 Hz, and the 15 will hit as low as 18hz. The GA trunk only seems to produce one strong antinode at about 52hz so I'm not complaining (I think it sounds great) and there is not detectable node.

But that not the point of my question, the 1100 Watts wasn't dimming to bad before the cap and now I can feel the car shudder like it's going to stall.

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Old 12-11-2002, 07:00 PM   #20
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If it's reacting that badly, you may have a bad cap, or there may be another problem. With the car idling in park and the parking brake on so the DRL's are off, with no other accessories running, test the voltagfe at the battery terminals with the system up loud. If it dips below 12 for more than a second or so, a new and stronger battery is a good idea. Have that cap looked at either way, though. 80 amps of combined current shouldn't drain the car that badly, but that's enough current to justify an upgraded battery in addition to your capacitor.
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