Power Distribution in Car Audio Systems – Gotta Get Yourself Connected
I = TP X 2/Vbatt
In a previous blog we wrote about power measurements in a car audio system in an attempt to demystify this often misused and misquoted parameter. In so doing, we touched extremely briefly on the concept of power consumption as opposed to power output. Here we want to expand on this concept in an effort to explain why elements of a car audio system must be powered using cables of a certain gauge.
The equation at the top of this blog is the way power and earth cable sizes are calculated when using Connection cable. Connection make some of the finest cables available and we are happy to take their judgements on face value having worked with the brand for some years now. However, we feel it is useful to know a little of the science of power consumption and the restrictions it can put on the design of your car audio system. This may not be as hard to understand as other technical elements provided there is an up front understanding that a cable that is being asked to carry an electrical current has a finite capacity which is determined by its size and any losses or resistance it may introduce due to the materials used in its construction. The majority of cables in electrical and electronics applications are made from copper as it is easy to work into the required shape and one of the best conductors of electricity known so we will assume that this is the material of choice.
So, back to the equation. I = TP X 2 / Vbatt. In order for this to makes sense, we need to qualify what everything means. I = Current, TP X 2 = Total RMS power of all channels of the amplifier you are wanting to power up and X2 because most modern day amplifiers are 50% efficient. Vbatt is the voltage (Volts) provided in this case by a car battery or charging circuit. Worth noting at this point that although a car battery is rated at 12 Volts, the charging circuit in your car will produce more than this and the typical running voltage of your car is probably more like 14 Volts. OK, let’s throw some specifics at this equation. If we assume a two channel amplifier with a rating of 100 Watts RMS per channel and an operating voltage of 14 Volts, our equation would look like this: I = 200 Watts X 2 / 14. Resolving this further would give us a required current capacity of 28.5714286 Amps (courtesy of pedant watch!). However, there is an important parameter missing and that is the length of the cable run. When it comes to Connection cable ratings, they produce a handy table at the back of their brochure, which tells me that according to my example, I would need to use 8 AWG gauge or 8.4 mm squared for cable for a run of up to 6 meters.
One of the reasons we like to work with a network of specialists is that they all have this knowledge and are so used to selecting the correct cable, they hardly have to think about the science when advising customers. However, when it comes to DIY installs, we have over the years, seen some very poor practice. By under rating the power cable to an amplifier, inexperienced or novice installers can put a driver in extreme danger. If a power cable does not have sufficient capacity for the current it has to carry, the cable will become hot and could eventually catch fire if enough of a mismatch is encountered. We would therefore, always advise anyone wanting to put an amplified system in their car to use the skill, knowledge and experience of a qualified installer.
The rules which apply to the live feed also need to be applied to the earth or ground side of the amplifier power. It is often the case that the vehicle’s own earth connection will need to be beefed up and once again a FOUR MASTER equipped with Connection cables will be able to ensure that everything is done correctly in this regard. The power cables to your amplifier can end up being quite sizeable requiring special attention to be taken when running these. Connection cables are extremely flexible allowing them to closely follow the contours of the vehicle and a professional installer will ensure the cables are secured firmly and are routed away from sensitive on board equipment as well as systems which may generate electro magnetic disturbance which can be picked up by long cable runs and turn up as annoying pops and buzzes in your amplifier. Care also needs to be taken when running power cables through bulkheads between engine bay and passenger compartment and passenger compartment to luggage area. A professional will use a correctly sized grommet which will be sealed after feeding the cable through.
Power wiring is one area of your car audio system where you do not want to take chances! makes sure a professional job is done and that the live feed is correctly and independently fused. In fact, get your FOUR MASTER to do it, you know it makes sense….
Call 0800 652 5125 or visit www.fourmasterscaraudio.co.uk to find your nearest expert.
(Content supplied by Driving Sounds – www.drivingsounds.co.uk)