18 October 2006
Back after only a few days.
This is just a short Newsletter telling you that I will be bringing in BMW motorbike parts within the next few days.
So if you need parts for your Boney contact me now.
What has always amazed me that a particular model of cars always comes in droves.
Sometimes we have 3 Nissan v6’s in the yard and in this case 2 Corollas.
What is good news, is that the MileMarker shipment has just landed.
These Hydraulic Winches fascinate me, not only because they do not break but also because they do not have much chance of damaging your vehicle’s electronics.
Please read it up on my Website.
The following article should explain to you the fickle nature of vehicle electronics.
From March '04 issue of TPR magazine, by Klaus Almendinger
Recently a spate of new products have come to market that improve ‘grounding’ in cars. Sometimes the claims of what these products do are fairly broad. The usual claims of horsepower improvements and lowering fuel consumption are pretty standard for all automotive aftermarket products, including seat-covers, floor-mats and cup-holders.
Let’s look at the issue these products try to adress. Every electrical system in the car (excl. alternator) uses electrical power. Electrical power is defined as voltage (the ‘pressure’ in the line) times current (the flow volume of electrons in electrons/second). Electricity flows from the plus side of the battery through the device back to the negative side of the battery. The negative side of the battery is also connected to the chassis or frame. This is called ‘ground’. In a lot of cars the negative side of a device is connected just to the nearest hunk of metal in contact with the frame. This can cause problems under some circumstances. Here’s why:
Ever been under a nice hot shower while somebody else in the house flushes a toilet? The nice warm water stream suddenly changes to scalding hot? The reason for that is easily explained and the same principle applies to grounding issues. When water flows through a pipe there is a certain pressure loss along the pipe. The pipe creates a resistance to the water flow. The smaller the pipe, the larger the resistance. This resistance lowers the pressure at the end of the pipe (shower head) from the original pressure where the water main enters the house. If another outlet on the same water pipe also uses water, the flow in the pipe to both increases and more pressure loss results. So now your nice balance of hot and cold water is upset because less pressure is available on the cold water side of the shower valve.
In electrical systems it works the same way. Anything that conducts electricity has a certain resistance to the electrical flow. The electrical flow is measured in Amperes (A) or Amps. 1/1000th of an Ampere is a milliAmp (mA). In electrical formulas the symbol for current is I. The electrical pressure (equivalent to water pressure in a plumbing system) is measured in Volts (V). Resistance is measured in Ohms (formula symbol R) The bigger the resistance of a supply wire, the more voltage builds up along that wire (V = R*I). But because there is only a fixed supply voltage available from the battery, the resulting voltage available for the electrical device is less. Bigger wires have lower resistance and therefore lower losses.
If multiple devices share the same electrical return path (for example the frame), the currents of all the devices add up on the way to the battery and there is less voltage available for each, depending on the total current between the ground point and the battery.
Returning to our plumbing example above: If we would run a separate pipe from the water main to each water faucet in the house, there would be no scalding in the shower because the pressure losses from any faucet would only affect that faucet. Of course the other solution would be to run 3” pipes all through the house to minimize pressure losses. This of course would be much more expensive than running only pipes as necessary. It also only minimizes the shared loss effect, but does not eliminate it, like separate pipes would. The grounding systems on the market are the equivalent to that 3” pipe.
In wiring the electrical system in a car the best way is to run separate ground wires from each system to a common ground point. The common ground point should NOT be just a bolt where lugs from each device are stacked in top of each other. The contact patches between the lugs create their own resistance and ground problems. The very best way is to bolt a short piece of copper bar near the battery to the frame. Connect the copper bar to the battery with a heavy duty ground strap. Drill and tap the bar for each ground return. The heaviest current user in a car is the starter. It can take up to 800 Amps of current. So it should have its own ground strap directly to the battery. So should the alternator. Its wires carry the second most current after the starter.
Electronic fuel injection and ignition systems have their own caveats though. Ignition systems create very high current pulses for a very short time. This is especially true for Capacitive Discharge Systems. Those need their own ground wire to the common. EFI systems rely on different sensors in the car. Throttle position sensor, Intake and coolant air temp sensors, Manifold pressure sensors and so on. These sensors typically have 2 or 3 wires. When they have 2 wires, one is typically the signal and the other ground. 3 wire sensors need a 5V supply, signal and ground. DO NOT connect the ground of these sensors to the common ground as described above. The EFI computer, as any electrical device can only see its own ground and references all measurements to that. The EFI computer also switches the injectors on and off. Injectors use relatively high currents, and these currents have to flow back to the battery through the EFI computer’s ground wire. This causes a voltage drop on that ground wire. Were the sensors grounded to the common ground as described above, the ECU would see only the sensor voltage minus the voltage drop of its ground. Instead ground the sensors directly at the EFI computer to its ground. Sensors only take a few mA of current anyway, so the additional drop on the EFI ground caused by them is irrelevant.
Another issue arises with sensors that create a very small signal, like thermocouples for EGT and cyl.-head temperature measurements. In an engine compartment a lot of current pulses from ignition and injection systems flow around. Any electrical current also creates a magnetic field. The two wires from the sensor (signal and ground) create a loop, which acts as antenna to pick up these magnetic fields. To avoid that, either use shielded wire or simply twist the wires together. Each twist creates a smaller loop, which picks up less of that noise, but also adjacent loops pick up a signal that’s inverted from the loop before. This way the induced noise voltages in each loop cancel each other.
Audio systems in cars also need to be connected to this ‘star’ ground. The human ear is the most sensitive organ we have. The difference between the loudest noise (pain threshhold) and the quietest noise we can hear is over 1 million to one. So any electrical noise from inadequate grounding can be amplified by the audio system to hearing level.
Now to the claims of some of the grounding systems regarding 10 times better impedance. We talked about resistance of the wires before. Resistance applies to steady-state current (DC). Steel has about 10 times the specific resistance of copper. So the material must have 10 times the square area of copper to achieve the same resistance. This is not a problem when using the frame as ground.
The material with the lowest resistance known is silver. Followed by copper (a few % higher) High frequency currents (and pulses contain high frequencies) make the wire behave differently. High frequency resistance is called impedance and depends on the frequency of the current. Very high frequency currents tend to flow not evenly in the whole cross-section of the wire, but only on the surface. Therefore multi-stranded wire creates more surface area for the high frequency currents to flow, hence lower impedance. But this effect is only important for VERY high frequencies in the upper radio frequency range. If the electrical system in your car produces high currents with frequencies that high, your car would shut down TV and radio reception for miles around. Frequencies that high are just not normally encountered in a car. The advantage of multi-stranded wire in a car is flexibility and vibration resistance.
As to claims of better performance and lower fuel consumption: The EFI systems injects fuel according to the amount of air drawn into the engine, measured with it’s sensors. More performance can only be had if more air/fuel enters the engine. No electrical system can increase the air-flow, so no more fuel flow either. The only effect a better grounding system can have is if the sensor grounding was so bad before that the EFI computer misread the sensors due to ground offsets. This can be inexpensively remedied by following the grounding guidelines above. Some of the better EFI computers utilize ‘differential’ inputs. They measure both, the signal and the ground of the sensor itself and calculate the difference. This way they become independent of any grounding issues.
As to ignition system grounds, one of the performance parameters in an engine is ignition timing. Timing is derived from sensors on the flywheel or crank. These sensors create reference pulses. A pulse can either be there or not. If not, the car stops. No additional grounding changes that. As to the ignition system itself: as long as there is enough spark energy to light the fire, the engine runs. More ignition energy does NOT increase power, just spark-plug wear. Corresondingly, if the ignition system is adequately grounded no amount of additional grounding will do any good.
That’s it for now.
Please remember There are no stupid questions when you are a buying customer