I have had some long conversations between my audio tech & my mechanic after installing the power amp in the trunk and the conclusion was that 2 batteries requires the alternator to continually run trying to charge both of them with inadequate capability. Upgrading the alternator to run 2 batteries would solve the problem but cost lots of $$. The quick & dirty answer to my problems, using my trickly charger once a week to keep my regular battery at full capacity and that seems to be really helping.
1993 MX6 4 cyl Silver & Blue Pearl
NGK wires, K&N Cold Air Intake,U R pulley, Magnaflow Cat-back/rocket tip,header raps,J-spec Cams,16/7 AR Cromes/Donlops,slotted rotors,Lowered on Eibachs & KYB set/ractive Strut Bars, Sway bar
Grilled/tinted/covered//pillar gauges int,pedaled,500Watt Alpine V-12amp & Diamond Audios all around!
It never ceases to amaze me just how little most audio guys know about how an alternator and battery system works, lol. As far as the alternator is concerned, two batteries in parallel looks like one big battery with slightly lower internal resistance. In no way does this make the alternator work any harder. All the second battery does is provide a larger buffer between the alternator/"main" battery than a cap would. As I've said before, if you listen to it cranked ALL the time, the second battery will eventually give out. But for "normal" listening, where there are periods of time where the car is driven without the stereo causing permanent hearing loss, the backup has a chance to recover and everything catches up.
Rewiring or upgrading the alternator is ABSOLUTELY the best way to go. If you can't afford an alt - and they're getting cheaper all the time - a second battery is a better option than a cap is.
Car audio guy and resident domestic 4 banger advocate
a large cap can be deep cycled for a very long time though. Even the best batteries hate deep cycles.
You have a maximum amperage that the system is capable of producing from the alternator. If ever the current draw exceeds the charging capability of the alternator, OR exceeds the current output of the voltage regulator, you have a problem. This is usually noted by a drop in the supply voltage, causing the customary dip in teh lights on bass hits.
Capacitor is very good if you exceed the current draw ONLY on bass hits. This would mean matching your car's capabilities. If you exceed them ridiculously, then nothing short of an alternator capable of keeping up with the system current draw will help.
By the way, one of my university lecturers has a patent on the super cap. Capacitor the size of a grape rated to about 5~10V with a capacitance of 55 farad (That is NOT a typo). So if people are making smaller capacitors, believe me its possible. I do however believe that many shops would sell a "Capacitor" without actually rating it, which is a rip. Caveat Emptor (Latin, means buyer beware)
As for class D, they are very kewl amps, run off nice big power mosfets. The only thing i would say about it due to the amplification technique, they're sound quality and faithful reproduction is sacrificed in order to achieve good amplification. Push pull amps (AB) are much cleaner, but as you mentioned are only usually 50% efficient. (Theoretical maximum is 75%). Class A are even more faithful again, but then they have a max efficiency of something like 25%. Class D are what is used in broadcast stations nowadays, any new radio trasnmitters are usually class D.
To be honest, if you bought some 0 Gauge wire, and wired up where the cap SHOULD go, walk into the hifi shop, and say, lemme plug it in, if my lights stop dimming, i'll buy the capacitor. That would be my advice to anyone with an unintentional light show! Whats a bit of wire gonna cost you? really?
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!! Coming soon - Subwoofer enclosure types and their best applications. Stay tuned!!
i agree just remember 4 every 500watts you need 1 farait from a capacitor now days they come all the way up to 5 farait's that's 2,500 watts......nice job mxmissle..it was worth reading....
Capacitors help by creating a buffer between the charging system and your audio system. They are able to dipense a large amount of current very quickly, to feed your amps the energy they require, without stressing the rest of your electrical system out with each hit of the bass.
Last edited by ChilliConCarnag : 9-22-05 at 10:05.
"Spolier size is inversely proportional to wee-wee size"
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.
Hmmm....
Car audio guy and resident domestic 4 banger advocate
Thanks for all the info from everyone - VERY informative... however I was wondering if anyone could help me actually find a more powerful alternator - recommended sites or stores would be awesome. Thanks again for all the help and info from everyone!
Hey guys,
as a bettery tech I would recomend against running 2 batteries paralleled together but by all means go to a 4WD shop and get a quote on a dual battery system. They should be about $200au but this will let you monitor both batteries and you can isolate them as well. Why isolate them? If you stereo battery dies or goes flat you can still start your engine. Once your engine has started you can then switch to charge your secondary battery. On the off chance both batteries are as low as about 20% there is a button you push while cranking your engine and this will parallel both batteries together so you can get home. The duel battery system will automatically charge your primary battery 1st then your secondary. These are great systems and worth the $.
On anouther note if your system seems fine, and everything tests ok, have a look at your harmonic ballancer. I didn't realise that on most cars these are 2 pieces joined by a rubber spacer. When the spacer perishes your ballancer will spin inside you crank pulley. I have recently welded mine while I waite for a replacement and my head lights are brighter, power windows go up faster, and the power steering is lighter. The ballancer is really easy to get to from the drivers (for right hand drive) wheel arch. just take off the splash gard and there it is. Get a good hold of it and try wobble it. If it moves take it off (it's only 6 bolts) and inspct the rubber, Preferably from the engine side as this side will perish faster. I can't give you a price yet as most of the shops in townsville here say " What the hell is an MX-6" or "don't you mean MX-5". But we are educating them slowly.
As for altinators have a look at running 2. 1 for each circuit, but realistically go the DBS, it's smaller, possiblycheaper and I know it works.
Hope this helps.
I usually go with a fuse equal to the alternators max output, rounded up. Like an 85 amp alt, I would use a 100 amp ANL fuse at each end. Again, these fuses are really just to provide short circuit protection for the two batteries, so I opt for a larger one to minimize both resistance and the chance of it blowing for any reason other than a dead short!
Thanx for the Q, hope this helped!
Just checking for my own knowledge, if your Alt puts out 85 amps, and lets say you have several amplifiers that pull a total of 85 amps.
If I put in a 100 amp fuse then it will take 100 amps of power drawn from the Alt/Battery to blow the fuse. If this is the case then wouldnt it be overworking the Alternator?
If I were going to use a 100 amp fuse, then I would suggest a 100 amp Alternator.
Personaly I would use a 90 amp fuse and a 100 amp Alt to supply power to a multi-amplified system that pulls 85 amps. This way the batteries wont get excesively drained, and any capacitors installed could keep up with out much trouble, and it wouldnt be constantly working the Alternator.
The section you quoted applied to a dual battery setup with a 2nd battery in back. The amplifiers will pull what they will pull, regardless of fuses and alternator output. Any shortfall in the alt's output is made up for by the battery(ies) - when this happens, you get the dimnming lights and whatnot that brought this discussion about, becuase overall system voltage drops.
The individual amplifiers should be individually fused for their rated output. The fuses mentioned in that paragraph are at either end of the power wire connecting the rear battery to the front one, and are fused just above the alternators output for that reason. the voltage demands of the amps will be fed by the rear battery first, basically.
Car audio guy and resident domestic 4 banger advocate
You can always upgrade to a Millenia Alt, the 110 amp ones. An auto electric shop said they could do my Alt from 90 to 160 amps for about $160. That seems very reasaonable
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