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Topic Review (Newest First)
07-28-2010 11:41 AM
Re: Electrical System Explained

awesome info & a good little read
03-13-2010 03:10 PM
Re: Electrical System Explained

good info thanks!
01-10-2010 09:48 AM
Re: Electrical System Explained

Can someone tell me how the Ah rating on a battery is useful, or how can I tell how many Ah I need for my system.
12-03-2009 09:27 PM
Re: Electrical System Explained

Originally Posted by indrek View Post
If we are talking about the real electricity flow, not the conventional flow, then the flow is from - to +. But why are the fuses placed in the start of the positive wire? It's really bugging me
Really, electricity is electrons moving doing work as they move through the circuit. Electrons are negative.

The sign convention used is just backwards you could say. Because if it wasn't, that would mean I could just plug my system into the ground and get free power. (Because the earth is always marked as negative.)
12-03-2009 03:33 PM
Re: Electrical System Explained

If we are talking about the real electricity flow, not the conventional flow, then the flow is from - to +. But why are the fuses placed in the start of the positive wire? It's really bugging me
07-10-2009 11:29 AM
Originally Posted by thechris View Post
I'm pretty sure alternators are actaully alternators, and not statically excited generators as shown on bcae1.

edit -- seems i had the wrong definition for alternator. I was thinking all alternators were of the brushless variety.
Considering they need 12volt to power the coils to make an electromagnet that allows the generation of electricity, It is correct. I always wondered why you couldn't just have an alternator make energy while spinning; why it needed a 12volt power source. But not that I understand that they have no permanent magnets, it makes all the sense in the world.
09-20-2007 10:08 AM
shaz So the fact my volt meter reads just under 12V across the battery terminals while the car is on...but idleing is something i gota worry about????????????????
09-20-2007 10:02 AM
kensaudio99 17 volt is the highest electrical you car can have, but it can be dangerous to toward the car computer system.
03-04-2007 05:21 PM
thechris I'm pretty sure alternators are actaully alternators, and not statically excited generators as shown on bcae1.

edit -- seems i had the wrong definition for alternator. I was thinking all alternators were of the brushless variety.
02-21-2007 04:31 PM
Gebrochen I posted it in the "electrical systems explained" sticky.
02-21-2007 04:04 PM
momentarylapse7 Sticky, please. I'd like to be able to refer to this in tha future.
02-21-2007 03:56 PM
Gebrochen Battery isolators, alternators and battery bank configurations:

Diode battery isolators work on the principle that a diode semiconductor will only conduct electricity in one direction. This means that components such as amps connected to your second battery will not drain power from your starting battery. This type of isolator is the simplest and most reliable. You don't have to worry about your amps draining from your cranking power. The problem with diode isolators is that you lose 0.7V of battery power. However, most amps have internally regulated power supplies and this isn't a problem if you have a daily driver with enough alternator current to keep the voltage stable.

Relay battery isolators use a solenoid to engage a switch which directly connects your front and back batteries when the charging system is active (engine running) or manually by a driver-operated switch. This kind of isolator removes the 0.7V voltage drop but adds a bit of complexity because you have to decide how you're going to configure the method which the relay engages or wire a kit according to instructions.

No isolators is a configuration chosen by some. The benefit is that your batteries are always engaged together with minimal electrical contact resistance between them and less points of failure to worry about. It is argued here whether mismatched batteries will cause electrical system problems from one battery draining the other. I've typically hooked my systems up like this and have never had a problem as long as I cranked my car every 2-3 days, but I won't say you may not experience issues with weakened batteries. Consider this a "use at your own risk" option if you really know what you're doing or you just don't care.

Second alternator running in parallel, directly connected to your first. This allows you to combine the power of 2 or more high output alternators if you have the room.

16-18V Second alternator completely separate from your car's electrical system to supply a bank of 16 or 18 volt batteries. The stock 12v alternator charges your starting battery and the 16-18v second alternator charges the stereo system.

Independently charged banks of 16 or 18V batteries not connected to an alternator are only useful for competition classes where the engine must be turned off. They are charged either with a special charger or a DC-to-DC converter capable of stepping up 12V to 16-18. (Running your system on a 12-to18V DC converter isn't practical due to the cost of these converters for that much amperage and the power that would be wasted during the conversion).

Fuses are not covered here. All of these options require proper fusing to prevent your car from turning into a pile of cinders in case of battery cables grounding to frame-connected metal.

02-12-2007 09:29 PM
aznboi3644 This is still all copied and pasted from
05-28-2006 03:59 PM
Garrett Powered who makes gel cell batteries? I know the old AC Delco Pros were called "gell cells" but they were actually AGMs or absorbed glass mat like the Lifeline batteries. these two are totally different in construction from the optimas which have six spiral cells. lifelines and the late 7 year AC pros use lead grids with fiberglass matting in between. way more lead is used too, I had a lifeline RV battery that weighed like over 50 lbs. it was an amazing battery.
05-28-2006 03:59 PM
Garrett Powered who makes gel cell batteries? I know the old AC Delco Pros were called "gell cells" but they were actually AGMs or absorbed glass mat like the Lifeline batteries. these two are totally different in construction from the optimas which have six spiral cells. lifelines and the late 7 year AC pros use lead grids with fiberglass matting in between. way more lead is used too, I had a lifeline RV battery that weighed like over 50 lbs. it was an amazing battery.
05-16-2006 10:24 PM
txcyko yes very usefull info......
04-06-2006 08:07 PM
Saynkuck123 Good info.
10-11-2005 05:04 PM
Electrical System Explained

Charging System Basics:
The electrical system in an automobile is said to be a 12 volt system, but this is slightly misleading. The charging system in most cars will generally produce a voltage between 13.5 and 14.4 volts while the engine is running. It has to generate more voltage than the battery's rated voltage to overcome the internal resistance of the battery. This may seem strange, but the current needed to recharge the battery would not flow at all if the charging system's output voltage was the same as the battery voltage. A greater difference of potential (voltage) between the battery's voltage and the alternator's output voltage will provide a faster charging rate.

As long as the engine is running, all of the power for the accessories is delivered by the alternator. The battery is actually a load on the charging system. The only time that the battery would supply power with the engine running is when the current capacity of the alternator is exceeded or when engine is at a very low idle.


Alternator Basics

A basic alternator has 2 main electrical components. The rotor and the stator. The rotor is the part of the alternator that is spun by the drive belt. There are a group of electrical field coils mounted on the rotor. The stator is the group of stationary coils that line the perimeter of the inside of the alternator case. When current (supplied by the voltage regulator - to be explained later) is flowing in the rotor's coils, they induce current flow in the stationary coils. The induced current (and voltage) is an AC current. To convert this to DC, the current is passed through a bridge rectifier.

Stator and Rotor in Action:
In the following diagram, you can see three crudely drawn sets of rotors and stators. In the leftmost diagram (marked 'A'), you can see the rotor's coil approaching the stator coil. As the rotor coil approaches the stator coil, it induces current flow in the stator coils. This causes an increase in output voltage. As it approaches the position where the coils' centers are aligned ('B'), there is no induced current. When the coils move away from each other ('C') the induced current flows in the opposite direction and the generated voltage is negative.


You should have noticed that the generated voltage was AC. You already know that a vehicle's charging system needs to produce DC to recharge the battery. This is done with diodes. The following diagram shows a simple transformer and a bridge rectifier. The transformer is driven with a sine wave (similar to that produced in each stator coil). Since the transformer is driven with a sine wave, the output of the transformer is a sine wave (similar to the one shown). The sine wave is driven into the bridge rectifier and the output is a pulsed DC waveform.

Bridge rectifier:
You should also realize that there are 3 different groups of stator coils in an alternator (not shown in diagrams). The rectification is much like the simple transformer shown above but in the place of a single transformer winding there are 3 windings. It also uses 6 diodes instead of 4.

3 Phase:
The following diagram shows the 3 different phases from the 3 groups of stator windings. The three phases of AC are shown in three different colors. The next set of lines shows the rectified waveforms overlapped. The bottom waveform (white line) is what the rectified voltage would actually look like if viewed on an oscilloscope. Connecting the battery to the alternator will smooth the white line even more.


Alternator Schematic:
The following is a generic schematic showing the stator windings and the bridge rectifier. You also see a diode trio. the diode trio takes part of the output and sends it to the voltage regulator. The output diodes are the rectifiers that rectify the AC and supply power to your electrical accessories.


Brushes and Slip Rings:
For an alternator to produce electrical current, there needs to be some excitation current flowing in the rotor windings. Since the rotor is spinning, you can't just connect a couple of wires to it (cause they'd just be twisted off Smile. To make the electrical connection, slip rings and brushes are used. The slip rings are fixed to the shaft of the rotor. The brushes are fixed to the stationary part of the alternator. The brushes, which are generally made of carbon, are spring loaded to keep constant pressure on the slip rings as the brushes wear down. The following diagram shows the general location of the rotor and the associated parts.


Voltage Reguation:
As you already know from the 'wire' page, all wire has resistance. You also know that when you have current flow through a resistive element (wire), there will be a voltage loss. If the current draw from the charging system was constant, there would be no need for a voltage regulator. If there was no loss, the design engineer would simply design the alternator to produce a given voltage. This won't work with a car audio system because the current draw is anything but constant. This means that the alternator needs a compensating voltage regulator. The voltage regulator controls the flow of current in the rotor's windings. The voltage regulator's output current will typically be between 0 amps (with little or no current draw) and 5 amps (at maximum current draw). The regulator can vary the current flow infinitely to keep the voltage precisely at the target voltage. Generally the regulator is built into the alternator. There are some high current/special use alternators which may have external regulators. Some of the external regulators are adjustable via a potentiometer.


Current demand and flow:
If you have an alternator that can produce 120 amps of current (max) and the the total current demand from the electrical accessories (including the battery) is only 20 amps, the alternator will only produce the necessary current (20 amps) to maintain the target voltage (which is determined by the alternator's internal voltage regulator). Remember that the alternator monitors the electrical system's voltage. If the voltage starts to fall below the target voltage (approximately 13.8 volts depending on the alternator's design), the alternator produces more current to keep the voltage up. When the demand for current is low, the full current capacity of the alternator is not used/produced (a 120 amp alternator does not continuously produce 120 amps unless there is a sufficient current draw).

Dimming lights:
When you play your system at very high volumes and the lights on your vehicle dim slightly, it generally means that your alternator can not supply enough current for all of your electrical accessories (including your amplifiers). If you play a long bass note/tone and the lights get dim and stay dim until the note is over, your alternator clearly can not keep up with the current demand. If, on a long bass note, the lights dim just for a fraction of a second but return to their original brightness while the note/tone is still playing, the alternator's regulator may just be a little slow in reacting to the voltage drop. Since the lights return to their original brightness during the bass note, the alternator is able to supply the current needed by your power your amplifiers and other electrical accessories.



Some people tell you that you can check your alternator by disconnecting it from the battery to see if the alternator can produce enough current to keep the engine running. BAD IDEA! Disconnecting the battery will subject the voltage regulator (and computer and audio equipment...) to significant voltage spikes which may cause an otherwise good alternator to fail. Even if there were no damaging spikes, this test would not indicate whether or not the alternator was good because the engine will easily run with a weak or failing alternator.

Simple Test:
If you want to see if your alternator is producing current, turn on your headlights when you're parked and the engine idling with the headlights shining on a wall (at night). Notice how bright they are. Then turn the engine off. The lights should get dimmer when you turn the engine off. If the lights get brighter when you kill the engine, the alternator was not charging sufficiently. When doing this test, the lights should be the only load (turn the stereo, a/c and other accessories off). With a heavy load, an otherwise good alternator may not be able to produce sufficient amounts of current at idle.


Basic Battery Information

Battery Construction:
A standard 12 volt cranking battery has 6 individual cells. Each cell is designed to produce ~2.1 volts. The cells are connected in series for a total of about 12.5 volts. Each cell basically consists of 1 set of lead plates and 1 set of lead plates coated with lead dioxide submerged in a sulfuric acid electrolytic solution.

Electrolyte Levels:
The level of the electrolyte should be about 1/8" below the bottom of the filling wells. If the electrolyte is above the bottom of the well, it may be forced out when the battery is charged. If the electrolyte is allowed to fall to below the top of the plates, the battery will be damaged. If the level of the electrolyte is low, refill it with distilled water only. Regular tap water has minerals which may coat the plates and reduce the battery's capacity.

Distilled Water:
Distilled water is water that's been heated to cause it to evaporate into water vapor. The water vapor is then condensed back into liquid water. The distilled water is free of all impurities including minerals that would coat the plates of the battery and therefore reduce its capacity to produce electrical current.

Cranking Amps:
Cranking amps is the spec that tells you how much current a battery can produce for 30 seconds at a temperature of 32° F and not have the voltage on any of the individual cells drop below 1.2 volts (7.2 volts for a 6 cell automotive battery). This may also be known as MCA or marine cranking amps.

Cold Cranking Amps:
This is the same test as cranking amps but is done at 0° F. The CCA spec is especially important if you live in a really cold climate. Since the chemical reaction that produces electrical current in the battery slows down as the temperature drops, the battery can produce less current at colder temperatures (especially below freezing). When comparing the current capacity of batteries, make sure that you have some standards to qualify the current ratings. If you see the current rating without CA or CCA, you don't know how the battery was tested and the current rating is virtually useless.

Reserve Capacity:
The reserve capacity is the time that a battery can produce 25 amps at 80° F before the individual cell voltage drops below 1.75 volts (10.5 volts for a 6 cell automotive battery).

Deep Cycle vs Standard Battery:
A normal lead-acid battery will be damaged if it is completely drained (even if it's only one time).
A deep cycle battery is designed to survive being drained multiple times.
Deep cycle batteries have more reserve capacity but have less cranking amps for a given size.
A standard battery would have more total surface area on its plates when compared to a deep cycle battery of equal size. This extra surface area provides more area for the chemical reaction to take place and therefore produce a higher output current.
The electrolyte in a deep cycle will be a slightly more concentrated sulfuric acid than a standard battery.

Gel-cell Batteries:
Gel-cell batteries use a thickened (gelled) electrolyte that will not leak out like a liquid electrolyte. Many of them can be mounted in virtually any position. These batteries may be suitable for some applications but for engine starting, other batteries should be used. Gel-cell batteries can not produce as much current for long periods of time as standard liquid electrolye batteries.

Recombinant Gas Batteries:
RG batteries have only 2 long thin plates per cell. They are constructed much like an electrolytic capacitor. The plates are separated by a fiberglass mat material designed to hold the electrolyte. These long thin plates have significant amounts of surface area (compared to standard batteries). This extra surface area allows the battery to produce significantly more current than standard batteries of similar physical size. OptimaŽ is one manufacturer of RG batteries. If you're going to add batteries to your system and the batteries will be in the vehicle's trunk or passenger compartment, RG batteries won't vent flammable hydrogen gas or corrosive gasses into the vehicle.

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