|02-26-2010, 03:45 PM||#1 (permalink)|
DIY - Understanding Voltage Drop (Headlight Dimming)
Lately, I’ve had a lot of people asking me questions about voltage drop, headlight dimming, stiffening capacitors, and other related stuff... so I figured I’d post this DIY, to compliment the one I wrote on upgrading big three wiring. - Enjoy.
What is voltage drop, and why do I have problems with my headlights dimming after installing a powerful audio system in my car?
How Electricity Works:
To understand this, you first need to understand how electricity works. For this DIY, we’ll focus on three main electrical principles – Voltage (Volts), Current (Amps), and Resistance (Ohms). The easiest way to describe the functions of electricity is to compare it to water. Voltage is analogous to pressure. Picture sticking your hand in a moving stream. The force that you would feel trying to push your hand downstream is the voltage. The more pressure you feel, the higher the voltage. Current (or amperage) can be thought of as the flow rate of the stream. How wide and how fast the stream is flowing, and how much water is passing by you at any given time. The wider and deeper the stream, and the faster that the water is moving, the more water you have passing by you at any given time. More water means higher current. Resistance (ohms) would be like a dam in the stream slowing down the flow, and not letting as much water pass by. The greater the resistance, the less water the dam lets through.
Now that you have a basic understanding of how the three main parts of electricity work individually, you need to understand how they work together. To explain this, we’ll refer to “Ohm’s Law”. Ohm's law states that Current (I) is equal to Voltage (V) divided by Resistance (R), or I=V/R . The three elements are bound to one another, so that a change in any one results in a change in at least one other as well. This is commonly expressed graphically with “Ohm’s Triangle” – an easy way to calculate how a change in one variable will effect the others.
Different Ways Electrical Devices Behave:
Different devices handle electricity in different ways. A light bulb, for example, responds to the electricity being applied to it in a very simple manner. If you connect a given light bulb to 12V battery, it will produce a certain amount of light and glow a certain brightness. If you were to keep it hooked up, as the battery loses charge and the voltage begins to drop, it will simply produce less light and be less bright, until the battery is completely dead, at which point the bulb would go out. Most people have experienced this firsthand while using a flashlight. Pretty straightforward, right?
Well complex electronic equipment doesn’t process electricity the same way as a light bulb does. By design, audio amplifiers try to make a certain amount of power to send to a speaker, regardless of fluctuations in input voltage. That means that whether they are getting 14V from the battery, or 10V, the amplifier is still going to try to send approximately the same amount of power to the speaker. This is where our problems with voltage drop begin.
In order for our amplifier to be able to make the power needed to move the speaker and make sound, it needs to be supplied with power itself. This power comes from the alternator and battery of the car. Just like your car needs gas in the tank to run, the amplifier needs power from the battery to move the speaker. The more power your amplifier is trying to send to the speakers (its output rating in WATTS RMS), the more power it needs to pull from the battery to make that power.
The problem is that the battery itself must adhere to Ohm’s Law as well. A given size of battery can only supply so much power at a specific voltage. If your battery is rated to put out 50 amps of continuous current at 12V, and your amplifier is asking for 100 amps to power the speaker, obviously things aren’t going to work out very well.
When this happens, the battery tries its best to supply the needed current that the amplifier is asking for, but it has to give something up in order to do so. In order to provide the 100 amps that the amplifier wants, the battery lowers its voltage, in an attempt to use all its available energy to send amperage to the amplifier. (In reality, this isn’t exactly how this works, but I’m keeping things simple for the sake of this DIY).
The problem is that the amplifier doesn’t just want 100 Amps at any old voltage. It wants 100 Amps AT 12V. So even though it’s getting the current that its asking for, the amp still isn’t happy. It sees the 100 amps coming in at 10V and says, “well if you’re only gonna send me 10V, now I need more than 100Amps… I need 120 Amps” (The whole Ohm’s Law triangle deal… remember, if one changes, at least one other must change as well.).
And so the amp sends a new signal back to the battery, this time asking for 120 Amps instead of 100. And what does the battery do? The only thing it can. It tries to send the amp the 120 Amps that it is asking for, except that the only way it can do that is to lower voltage even more. And so the two go back and forth, the amp keeps asking for more current, and the battery keeps dropping voltage trying to meet the demands of the amp.
Now, remember what we said earlier about how light bulbs handle electricity. Your headlights are light bulbs, and connected to your battery. So when the battery is at 12V and you turn them on, they glow a certain brightness. Now as the voltage at the battery drops (because its trying to send more current than it is rated for to the amplifier), the headlights get dimmer and less bright. And thus you have the root of your headlight dimming. It comes from the drop in system voltage.
As you can see, there is no way to fix the problem without either a more powerful battery, or a less powerful amplifier. Aside from the annoyance of your headlights dimming, the drop in voltage causes much more significant problems. The amplifier and the battery are going to continue fighting with one another until something either breaks, or turns itself off due to a safety device. This fighting between the battery and amplifier is very hard on both components and produces a lot of heat from the excess amperage that is being put into the system.
Think of trying to lift weights or run 5 miles when you haven’t eaten in five days. You would be working very hard and not able to get much done because you don’t have the energy you need to do the work. This is what the amp is going through. Now think of being healthy and fed, but someone sticking twice what you can bench press on a weight bar, and you trying to keep it from coming down and crushing your chest. This is what is happening to the battery, its struggling to provide more power to the amplifier than it can safely produce. Obviously, neither is good at all.
OK, so I know now that in order to provide the amplifier with the energy it wants, I have to use powerful enough batteries to do so. But how do I figure out how many batteries I need and what size they should be?
First, you need to understand what the rating numbers on the battery mean. Batteries are rated in different ways, but the numbers you are probably most familiar with are a "burst power" type rating, meaning the maximum power the battery can supply for a few seconds at a time. This is not the amount of current the battery can supply for sustained periods. This means that just because your battery is rated at 800 CCA (Cold Cranking Amps), that doesn't mean it can support 800 amps of current draw from audio amplifiers. The amount of current draw that the battery can support for extended use is the AH (Amp Hour) rating of the battery. And that is what you are concerned with when choosing batteries to power high power audio equipment.
Use the following formula to determining the amount of battery power (in Amp Hours) necessary for your amplifiers:
First take the combined RMS wattage of the amplifiers you are using, and divide that figure by 0.7 (to account for losses - we are assuming 70% efficiency in this case). This gives you the amount of wattage the amplifiers need to produce the rated RMS power output. Then take that figure and divide by 13 (we are using 13V as an average system voltage). This gives you the approximate amperage required by the amplifiers in the system.
1000W RMS / 0.7 = 1428.571W
1428.571W / 13V = 109.89A
Meaning that to power a system producing 1000W RMS, you
need approx. 110 amps of current.
Next, you need to determine how much power your alternator is producing. Most stock alternators make around 60 Amps, and you assume that 20-30 amps are normally used to run the car (depending on what electrical devices you have running... obviously, if you have the heater, headlights, and wipers all on at the same time, it uses more current than if you are just driving around with nothing on). But as an average, figure 30-40 amps available to power your audio equipment.
Finally, subtract the 30-40 amps produced by the alternator from the amperage needed to power the amplifiers. This will give you the necessary additional amperage that will be required from the batteries.
In this case:
109.89A - 35 amps (average available from alternator) = 74.89A
This means that you will need an additional 75 Amps of battery power to power your amplifiers.
Now like I said earlier, batteries use different rating systems. The only number you are concerned with is the Amp Hour rating (AH). This is the figure you use to calculate the continuous load that the battery can support. So in our above example, for a system making 1000W RMS, you need to use a battery (or batteries) that have a combined AH rating of at least 75 Amps. Using less battery than this will lead to voltage drop, especially during extended use of the system.
Ok, according to the formula, I have enough battery power for my amplifiers. But my headlights are STILL dimming. Now what’s the problem?
Unfortunately, just having a big enough battery to power your amp is not enough. You also have to have an easy way for that power to get between the battery and your amplifier. This pathway connecting the two is of course, your power wiring.
Going back to the water comparisons from the beginning, think of power wiring as a water pipe. Remember that Current (Amps) is the volume of water that is flowing past you in the stream. And that is what the amplifiers are asking for from the battery – amperage. Obviously, you can only move so much water through a given size pipe at one time. Think of a funnel. The bigger you make the hole at the bottom, the more water can get through without backing up. This is the same idea for AWG sizing in power wire. The more Current (Amps) you need to send to a device from the battery, the larger the wire has to be. Pretty straightforward, right?
Remember that we also talked about Resistance (the dam in the river, impeding flow). The smaller the cable, and the longer the distance it spans, the more resistance to flow it will provide. The larger the cable and the shorter the distance , the less resistance it provides. (This is why its very important to use large gauge cables on longer runs, and less important on shorter ones).
Other things effect resistance, like temperature (the hotter it is, the more resistance. As it gets colder, resistance decreases), and the material of the wire (pure copper wire offers much less resistance for a given size than aluminum wire, for instance.) In the case of wiring, resistance is bad.
Keep in mind that electricity flows in a circular pattern, so this information applies not only to the power wire, but also to the ground wire as well. There is no sense putting a huge pipe coming in and a tiny pipe going out. For this reason, the resistance in your ground wire has to be as low as the resistance in your power wire, or you aren’t accomplishing anything.
At any rate, just like using a battery that is not powerful enough, the resistance created within a wire will also lead to voltage drop. This means that while you may have 12V going into one end of the wire, by the time you get to the other end, you might only have 10V coming out. As stated earlier, the way to avoid this is to use wire that is conductive enough and of a large enough size to handle the current draw. The longer the run of wire, and the more current being drawn through it, the greater the voltage drop will be. Just like the battery formula we used earlier, this can easily be calculated if you know a few numbers. Ideally, you want to keep voltage drop below 2% over the run of the wire. Realistically, anything over 4% is a definite issue and should be addressed.
Assuming the same 1000W RMS system we used earlier, we know that we are drawing around 110 Amps. We will also need to know the system voltage (12V in our case), the type of system (DC or AC - in our case DC), length of the wire run (in feet), what material the wire is made out of (copper or aluminum), the gauge of the wire (AWG), the temperature in which it will be operating (in Degrees Celsius - the standard rating are derived at 75C, which is fine for our case), what kind of conduit the wire is enclosed in (in our case none, its out in free air), and the number of cable runs (one, two, three, etc… how ever many runs you are using for your given situation)
Using those figures, you can easily calculate voltage drop in your wiring using the following calculator:
Voltage Drop Calculator
From this, we can see that with our 110 amp draw, assuming a 20ft. run from the front battery to the trunk, if we were to use 4 AWG for our main power wire, voltage drop would be approx. 11.3%, which is way above the acceptable range. This means that if we were to put 12V into the wire, we would have approx. 10.64V by the time we got to the end of it. Were we to use aluminum wire things would be even worse, at 18.6% drop. With aluminum wire, our 12V in would drop to about 9.77V at the end of the wire - no good at all.
So obviously we need to use larger wire. Running the same calculations with 1/0 AWG wiring, we see that the voltage drop for copper is 4.5%. Still above the accepted range, but at least functional, losing around a half a volt over the run, finishing at 11.46V. Again, aluminum is worse, with a 7.4% drop over the cable run - almost a full volt, to finish at 11.11V.
Finally, run the numbers using double runs of 1/0 AWG copper. We’re down to 2.2% voltage drop. Even this is not technically within the desired range for operation, but you have to be reasonable. Your system isn’t going to be drawing that much current all the time, and there is a limit to how much wire you can run in a vehicle that is driven daily. (But this is why you see SPL competitors with 50 runs of 1/0 AWG power wire in their competition vehicles).
The point is, hopefully you can see the importance of using large gauge, high quality power cable in low voltage DC systems, and making the cable runs as short as possible.
The “Big Three” Wiring:
I’ll also touch on the big three wiring. While not the focus of this DIY, knowing what you now know about voltage drop in wiring, obviously the wires connecting your battery to your alternator should be treated in the same way as your wires connecting your battery to your amplifier. These wires are casually referred to as "The Big Three", becuase they are the three main underhood wires on the charging circuit. You can use the same calculations as you did for the amp wiring, just adjust the length of the wires and use the output of the alternator (in amps) instead of the current draw from the amplifiers. For more information on Big Three wiring, see my step by step DIY on the Big Three, Here:
But What About Stiffening Capacitors? Aren't They Supposed To Stop Headlight Dimming?
What a Capacitor Is:
A capacitor is simply a storage container for electrical energy (Think - "Bucket Of Water"), much the same way a battery is. However, unlike a battery, a capacitor does not release energy slowly over time. Instead, it dumps all of its current at once, like a gunshot. This constant "all or nothing" dumping of current makes them less than desireable for supplying input power to electrical devices like your audio amplifiers.
Whats Wrong With Them? Why Are They So Bad?
For certain applications, nothing. In fact, the circuitry inside most amplifiers uses small capacitors to supply parts of the amplifier with power. However, when you try to use large capacitors in place of a battery (which we now know they are not), they become an additional load on the charging system. Think of it this way: Since the capacitor is designed to dump all of its charge at once, very quickly, every time voltage drops in the system, the capacitor releases all of its energy to try to make up the difference (think - pouring out the entire water bucket in one shot). The problem is, now the capacitor is empty. How is it going to get filled up again? The energy needed to refill the capacitor needs to come from the alternator and the battery. If you recall, this is the same place that power for the amplifier comes from. So now, not only are your battery and alternator being asked to supply the power needed to run the amlifiers, they are also being asked to refill the capacitor. So the charging system now has to work harder - it only has so much energy to give out, and any energy spent refilling the capacitor is not going to your amplfier. It should be obvious that this is not what you want. You want all available system power going to your amplifiers, not being used to refill stiffening capacitors. While they might reduce headlight dimming, they are merely a band-aid fix to the underlying issue, and ARE NOT helping your electrical problems any.
It all comes down to physics. There is no way to cheat with electricity. Adding junk like capacitors and other nonsense to your electrical system does nothing but waste your money. If a capacitor could do the job of a battery, then auto makers would all be using stiffening capacitors to start and power their vehicles. If you aren't convinced, try replacing your battery with a stiffening capacitor and see how well it works.
Stabilizing voltage in an electrical circuit is a factor of using adequate battery power and the correct gauge wiring for the current demands, pure and simple.
Last edited by HsOffRoad; 03-31-2010 at 05:53 PM.
|04-01-2010, 05:20 PM||#9 (permalink)|
Hans speaks the truth. Sticky anyone?
i had a local shop build me a quick amp rack and i asked if they could do the big 3 while they were working on it. of course they never heard of it. and when i described it to them they told me that it wouldnt help because the wire wouldnt create any current to aid my battery. supposedly this guy has been competing in sq competitions for 10yrs now. and also has never heard of CDT. he reminds me of the honda dealers who compliment me on my nice si.......i drive an ex btw
|04-01-2010, 11:38 PM||#12 (permalink)|
Join Date: Apr 2009
Location: Devon, Alberta
iTrader: 2 reviews
|04-01-2010, 11:49 PM||#13 (permalink)|
The guys over at Mising Link Audio (Missing Link Audio) have been working on this problem for quite some time now.
At the moment, the easiest way around the LRC issue is to run a seperate domestic alternator and stand alone regulator in a dual alternator setup.
While not exactly practical for most daily driven vehicles, the dual alternator setup does offer the advantage of being able to run an independent 16V or 18V system for your amplifiers, while retaining 12V operation for other equipment and vehicle functions.
|04-02-2010, 06:19 PM||#15 (permalink)|
Join Date: Oct 2006
iTrader: 4 reviews
I'd like to know for sure about the FlashPro thing as well, as I do remember hearing that too.
Also, I have yet to see any dual alt. setups in an 8th gen so if anyone has any information on one or a thread on any forum, please advise.
|04-02-2010, 09:32 PM||#16 (permalink)|
I don't know about the flashpro situation. They may have figured out a way around the LRC/ELD, but if they did, I am not aware of it.
As for the dual alternator setup, It would require fabrication. To my knowledge, no one sells a dual alternator kit for our vehicles. Since space is usually quite limited on smaller import cars (like our civics), most guys will modify the air conditioning compressor bracket to accept a second alternator. Others fabricate custom bracketry to hold a second alternator and an idler pulley. Like I said, not exaclty the most practical thing for a daily driver.
I've never seen a dual alternator setup in an 8th gen either, but I'm sure someone has done it - the cars have been around for a few years now.
Heck, you see the audio competition guys running like ten alternators in some of the larger soundoff vehicles. I've seen plenty of dual and tripple alternator CRXs, for instance.
Honestly though, for normal, daily use, I wouldn't worry all that much about the LRC. If you have enough battery to support the current draw of your equipment, its really not that big of a deal. I didn't do anything about it in my car, and I'm running close to 4000 watts RMS.
Last edited by HsOffRoad; 04-03-2010 at 12:20 PM.
|09-08-2012, 12:07 PM||#17 (permalink)|
Join Date: Mar 2012
iTrader: 0 reviews
Hey Hans, i have a few questions if you don't mind me asking. I am putting together a system for my 08 sedan. It will consist of two 1500 watt rms mono-blocks and a single 640 watt rms 4 channel amp. I plan on running 0/1 gauge to the trunk for power and it was recommended to me to make a return run of 0/1 back to the battery for the negative instead of using the chassis. What is your opinion on the negative run? would it be better to run a positive and a negative or two positive?? I don't think i can fit more then two runs without modding the car beyond reason.
I am purchasing an alternator from dc power engineering. It is rated at 200 amps at 750 vehicle rpm and 270 amps at 2,600 vehicle rpm.
With this being said obviously i am upgrading the battery. I put my figures into the calculations you gave in this thread and work it through as such:
1500+1500+640 = 3,640 watts rms
3,640/70% efficiency = 5,200 watts
5,200/13 volts = 400 amps needed
My second question is should i be spending a lot of money on an expensive battery such as this one:
Stinger SPP2250 2250 Amp SPP Series Dry Cell Battery w/ Protective Steel Case
Also if i keep my oem battery under the hood and install a second battery in the trunk will this help my voltage drop as the runs from my second battery to my amps would be significantly shorter?? And would a battery such as the one i posted the link to with such high cranking amps kill my starter or hurt the cars electrical system?? I would greatly appreciate any help you can give me.
Will adding a capacitor increase the life of my battery?? I am aware it will not help with voltage drop but my understanding is a battery takes a charge over a period of time and is designed to release it over time. A capacitor charges fast and discharges fast. I don't want to shorten the life of my battery by treating it like a capacitor.
Last edited by civic.junkie; 09-08-2012 at 12:37 PM.
|03-24-2013, 04:41 AM||#19 (permalink)|
Join Date: Mar 2013
iTrader: 0 reviews
I installed a subwoofer (280 watts RMS 2ohms) and two new 6.5” speakers (50watts x 2 at 4 ohms) and my car would stutter at red lights when my bass hit.
Installed the big 3 and no more engine stutter! My car is running like a champ what a great upgrade!
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