If we take some time to sit down and do a bit of pre-install planning, then we can save ourselves a lot of post-install time and money. We can design our system around the car (cheap and easy) rather than re-designing our car to fit around the system (a lot more difficult and expensive).By this I mean in particular how much power we choose, or think we need when we pick our amplifiers.Don’t be fooled by almost biblical power handling claims by speaker manufacturers, in particular those for subwoofers, the peak power handling of any bass speaker is generally a long way below its claimed rating,but as the music we listen to isn’t comprised of pure test tones, the average will be a long way below the peak.As the average car’s charging system can only supply enough for about 400 watts of audio power,then if we aren’t going to (or can’t) uprate it,then it really is waste of time and money putting anything more powerful in.
Actually it’s probably unfair to say it’s a complete waste as the bigger amps will still have more headroom to play with than the smaller ones, leading ultimately to better sound quality and longer amplifier and speaker life than from the smaller amps with the levels turned up to near maximum.
SO HOW MUCH POWER CAN WE ACTUALLY GET?
- 90 AMP ALTERNATOR …….As fitted to the majority of mk.4 Golfs/Boras will leave us about 60 amps to “play” with to run our accessories after the important tasks of running the car have been taken care of.
- If we use the commonest class B amps that are about 50% efficient,we will have (Power= current X voltage or P=I X V) 60 X 14.4 = 864 watts INPUT, but as half of this will be wasted as heat,we will only get 432 watts of audio output power.
- If we use class D amplifiers with a much higher efficiency figure (90%),we get will get more useable output power (and a lot less heat as well to get rid of), in this case in the region of 778 watts.
Don’t forget that these are average figures and the peaks could well be lot higher than this.
- 70 AMP ALTERNATOR…….As Fitted to 1.4 litre petrol engined and some other lower spec cars.
- Class B amps……..45 (amps) X 14.4 X 50% = 324 watts
- Class D amps……..45 (amps) X 14.4 X 90% = 583 watts
Actually “charging system” is a misnomer as charging the battery is only a very small part of the work the electrical system in our cars have to do. There are a lot of misconceptions about how the electrical generating system in our cars work, some that can lead to wrongly diagnosing any problems we may have, and also that may lead to causing those problems in the first place. The points raised here are based on the laws of physics and established scientific principles, rather than those of urban myths and backyard science fiction. First of all what is power? It is the ability to do work, the more work we want to do, the more power we need, whether it’s to boil water, to get our cars moving, or to make a subwoofer move. In our case power is a product of voltage and current (P = V X I), so to get more power we need to be able to supply more of either (or both), it’s easy to generate more voltage, but it’s lot more difficult to provide more current. Voltage is “pushed” down a wire (by the power source which could be the battery or the alternator), connecting a 1 volt light bulb to a 12 volt power supply will cause it to it instantly burn out. Current on the other hand has to be “drawn” from the power supply, if there is no load, then no current will flow. If we connect a 12 volt light bulb that normally draws about ½ amp for it to light at full brightness to a source that can provide thousands of amps (e.g. the batteries in a fork lift truck wired for 12 volts), then it will still only take ½ amp and light at normal brightness. Voltage will need the same size wire if it’s 1 or 1000 volts, which if we use the analogy of water in a pipe is how fast the water is flowing, but current needs a corresponding increase in the diameter of the wire if more flow is needed, the same with water in a pipe, if we need to get more water through in the same time, then we need a larger diameter pipe. Because the amplifiers we use can only make a small voltage bigger, how much you can get out of them is only limited by how much you can put in. We don’t have an unlimited amount of power to put in (this is limited by our car’s electrical generating system),so we will never get an unlimited amount out as some people seem to expect. If we play our sound system loud at night and we can see the headlights dim every time a bass note hits, then something is obviously not right. If they just dim slightly and then recover and stay bright, this could just be a sign that the regulator can’t adjust things quick enough to keep up with bass sounds such as kick drums (it isn’t designed to respond this quick when doing just the job it’s designed to so there isn’t anything actually wrong with it).
If it dims as soon as a long bass note hits and stays dim, then this is a sign that the alternator has reached its limits, and if we carry on like this the alternator output voltage will drop below that of the battery, which will now start to supply everything in the car, including the sound system. At this point the alternator will no longer be charging the battery, and in extreme cases the engine will eventually stop when there is no power left anywhere to keep it going. As our charging system is fixed at a nominal 12 volts (ok it’s actually about 14.4 volts) ,if we want more power from our sound system then we need to be able to provide more current……
……but where will that extra current come from?
It can come from one of two places……………..
 There is a law of physics that states that “Power always flows from the point of highest potential”.This means that when the engine isn’t running power for everything comes from the battery (technically a “chassis” battery),but it’s main purpose that it has to excel at is to give a very large hit of current for no more than a few seconds at a time to spin the starter motor (as much as 150 amps) ,with a few minor functions such as central locking, alarm and radio memory backup. This ability to provide hundreds of amps for short periods means that with the engine off we can actually get more current to our amplifiers than when it’s running, hence more output power and higher SPL’s.
It can make this much current because it has a large number of thin plates that have more surface area ,but must always be kept topped up with a trickle charge to avoid permanent damage, whereas deep cycle leisure batteries have fewer thick plates (less surface area), and can be deep cycled (or allowed to go flat) a large number of times without any sort of damage occurring, but because of the smaller plate area they can’t give as much current, which is ok for their intended purpose of running TV’s, fridge’s ,lighting etc all of which have very modest continuous current demands.The diagram below shows how power flows before you start the engine. 
 The diagram below shows how power flows when the engine is running.As the alternator will always be at a higher potential than the battery (it has to be to overcome the high internal of resistance of any battery to charge it),the alternator via the fusebox will now be the only source of power in the car. Any power that we need to run the car will flow through the alternator fuse with a small amount being taken by the battery as a trickle charge, the rest of it going into the car to the secondary fusebox and relay rack where it is sent to do various jobs around the car such as to power the ECU, ignition coils fuel pump, lights, heater/air con etc.
There is always an amount of safety headroom built into how much an alternator can safely supply, I normally reckon that everyday driving will only take about a third at the most of it’s total output, but quite a lot more during short winter journies in the dark, maybe as much as three quarters of it’s total available output. 
NONE OF THE FOLLOWING WILL:-
- POWER CAPS (or stiffening caps if you prefer).These are only storage devices, and if we’ve run out of power for everything else, then we won’t have any left over to keep our over sized capacitor(s) charged up, and in most cases will only make matters worse, don’t forget that we only get out what we put it, but a lot quicker. So if our supply voltage has dropped down to 10 volts, then we will only ever be able to get 10 volts out again.
This is not to say that they are a bad thing as they are the basis of ALL power supply design, but only in properly designed power supplies that have enough headroom for the job they have to do, this is very rarely the case with in-car sound systems.
- HEAVY DUTY BATTERIES……All these will do is to give us more current when we crank the engine over, but will actually draw more current when being charged, so as with power caps could make things worse.
- DEEP CYCLE LEISURE BATTERIES…….(Yellow tops) These must NOT be used to start the engine as damage to the battery will eventually occur.
Used as part of a split charge system with a leisure battery in the boot, they will only give extended engine off listening time without flattening the chassis battery. As before it will be another load on the already over-worked alternator to try and keep charged, meaning less to run our sound system, exactly the opposite of what we are need to achieve.
- THICKER POWER CABLE……..Changing our 4 gauge main power cable that will handle 150 amps continuously for 0 gauge that will handle over 300 amps is pointless when connecting it to an alternator capable of sourcing no more than 120 amps, remember also that this will go through a 150 amp (maximum) fuse as well as the big fuse we put in the cable to power our amps, therefore if this fuse has never blown then we have never drawn as much as the rating of the fuse from it.
All the thicker power cable will do is reduce the voltage drop which in itself is a good thing, as less supply voltage will mean the amps will try to draw even more current to compensate for this, as long as we have designed the system properly in the first place and already have thick enough power cable, there is nothing to be gained from increasing it’s surface area.
- A LARGER MAIN FUSE…..Yes I do get asked a lot of times if putting a higher amperage main fuse in will let the amplifiers make more power? It’s surprising how many people don’t understand the principle of how a fuse works.
No of course this can’t give more current, neither will any other forms of black magic or voodoo.
- MORE POWERFUL AMPS……If our amps are showing the symptoms of underpowering whatever they’re driving, then putting a higher powered one in won’t and can’t give us any more power, in fact changing to lower powered amps could be an advantage in cars that have a limited amount of current on tap.
SO HOW DO WE BUILD THE ULTIMATE POWER SUPPLY?
As we have now determined that the car’s alternator will be at the start of our power supply chain, then we might as well start with it. The highest output from any stock alternator will be 120 amps as first fitted to VR6’s,and now to the R32/4Motion and Anniversary cars although only 30 amps more then the more common 90 amp ones that are normally fitted, every little helps as they say.
If you need even more than this, and don’t want to or can’t do the extra work needed to fit an aftermarket alternator and want one that will still be plug and play, then it is possible to have it rewound. At the very best we can expect about a 20% increase in output by doing this, which would take us to about 140 amps. The link below is to a company that can do custom alternator rewinds, and also any other related repair work that you need doing.http://www.qxcomponents.co.uk/index.php If you don’t mind doing a lot more work, then we can buy alternators that put out over 200 amps that are designed for lorries and trucks, Toyota and Mercedes seem to be the most common, and can normally be found for a reasonable price on e-bay.
The downside to these will be their physical size and weight, anything up to twice as heavy as a stocker, with a corresponding increase in size, meaning custom brackets would need to be made to support it, or even some of the pipework around that part of the engine might need re-routing as well. They will also need more torque to turn them which wouldn’t normally be noticed on the big diesel engines they were designed to be fitted to, but could well cause a loss of idle speed on smaller petrol or diesel engines, and a corresponding increase in fuel consumption.
If there just isn’t enough room to fit it to the original position, then it can be remotely mounted anywhere in the car and driven hydraulically by a couple of power steering pumps, even in the boot right next to our amplifiers for the ultimate in low loss power transmission.
How about getting one of these babies rewound, imagine what you could do with 240 amps!!!!!
It is at this stage that I would suggest that we now use thicker power cable from the front to the back of the car,0 SWG will allow us to carry the extra current with minimal voltage drop.
As we normally connect our power cable to the positive terminal of the battery, which is connected to the alternator via a length of cable of roughly 8 SWG and a fuse link, it would be pointless trying to get all this extra current through them as they were never designed to carry this much.What we will need to do is connect our shiny new length of 0 gauge cable directly to the output terminal of the alternator, we do of course need to keep the original cable that goes to the battery connected.
Not forgetting our ANL style of fuseholder which is a must if we need to pass a very high amount of continuous current as they are available up to 300 amp rating, please NOT the very poor quality AGU type that take the cylindrical glass fuses.
We will also need to put a thicker earth cable from one of the bolts that hold the alternator onto the engine to somewhere on the car’s chassis, preferably as close as possible to where the alternator is.The earth cable should be kept as short as possible when we’re dealing with this much current, and should be bolted through a section of floor or chassis where we can get a nut on and properly tightened up, and of course grind or sand the paint off so that the ring terminal is bolted onto fresh, clean metal.
If you are running multiple amps, then Power Distribution Blocks (PDBs) are the easiest way to get the power where it needs to go and keep everything neat and tidy for both power and ground cables. It is alright to make the cable run from the PDB’s to the amps using a smaller gauge cable if you want to, as the voltage drop over this shorter distance will be negligable.
- MAKE SURE ALL CONNECTIONS ARE AS TIGHT AS POSSIBLE
In particular where we connect our 0 gauge power cable to the alternator don’t use a crimp connector unless you have the proper tool to do do it with, by this I mean not Molegrips or in a vice, you’ll never be able to get it properly tight. If there’s any movement whatsoever of the wire in the crimp, then we’ll get problems with voltage drop and heat when we start pulling large amounts of continuous current through it.
We can solder if we still need to use the crimp connector, but it will need a lot of localized heat, if we don’t get the joint hot enough then we will end up with more flux inside it which could make a worse connection than not soldering it at all.Apply heat to just the connector and make sure the solder fills it up as much as possible, but doesn’t go back too far up the wire, we can stop this by clamping a heatsink such as Molegrips onto the wire to take the heat away.We can use a gas soldering iron without the tip, a small blowtorch or even one of those old fashioned heat on the fire type of plumbers soldering irons, small electric irons of less than about 100 watts just won’t stay hot for long enough.If you can’t solder or crimp than you can’t do worse than using the compression style of ring terminal, the Autoleads G9-49-0 would be good for this particular application, but make sure you get it properly tight by using two spanners and not just hand tight.
If we have designed our system properly and have a bit of spare headroom to play with, we should now be able add some power supply stiffening.
It has been proven that a larger number of small caps are better than one or two large ones, but we should still work on about 1 Farad /1000 watts as being just enough and not too much.
Either a number of 0.5 Farad caps joined together with busbars, or one of the ready made capacitor banks assembled into an amplifier style case will keep it all cosmetically correct if you’re staying brand loyal.
A very important point to remember is to keep the cables between the caps or cap bank and the amps as short as possible, ideally six inches or less, but don’t worry too much if you can’t get them all quite as short as this.
Something I hadn’t heard of until very recently,but basically a very small battery with the discharge characteristics of a capacitor,so the best of both without the disadvantages of either.
These don’t need a split charge system as you would if you were running a second battery,but are wired directly across the amp’s power terminals,and so effectively always in parallel with the car’s alternator and chassis battery.In fact they are said to be able to supply enough current in short bursts to be able to crank a small engine should your chassis battery not be able to,something a powercap could never do as it would be fully discharged in well under a second.Real world tests have shown them to increase the voltage and current available to power hungry amplifiers,so taking some of the strain off the cars original electrical system. More information about Batcaps can be found here:- http://www.batcap.net/
That’s about it as far this subject is concerned,if anyone wants to question anything I’ve said here please feel free to express your opinions,I’d be interested to hear them.
Chris.
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