Grounding Your Electronics
#1
10-24-2017, 08:11 PM
Grounding Your Electronics
Rather than derail another thread more than it already has been I thought I'd post some info on grounding for contemplation. The concepts can be gleaned from many sources but I'm borrowing one that is very straight-forward. It's a bit of a read but worthwhile if you want some perspective on grounding locations.
Battery path current can be hundreds of amperes during starting, and battery path current is easily 25 amperes or more when charging the battery. Additionally, the alternator supplies all running current for all accessories, with the battery supplying current when an alternator cannot "keep up" with load. With high currents like that, the battery post should be exclusively dedicated to the battery-to-block ground lead, and the battery negative always must have a good solid connection to the vehicle chassis.
Sharing the negative battery lead to engine bolt with anything else or connecting directly to the battery negative post with anything except the block and chassis grounds is a terrible idea. (Connecting electrical devices or hardware directly to a battery negative post is a bad idea unless the negative connection is 100% ground isolated at the electrical device.) When an electrical device is directly connected to the negative post, if the negative post to block or chassis connection opens up or develops excessive resistance, the battery negative post will divert alternator or starter current through whatever is attached to the negative post. This can be hundreds of amperes! Very few devices and wiring will suffer a fault like this without permanent damage. It is also a fire risk.
Grounding directly to the negative post is a fire hazard at worse, and an unnecessary risk to your equipment at best. Battery post connections also increase likelihood of ground loops and ground conducted noise.
The only proper and safe way to connect accessories of any type (this includes ignition and stereo systems) to the negative post is via a path through the vehicle chassis. This is not only the safest path, the chassis is the lowest noise ground path. This is why every vehicle manufacturer has a lead from negative post to chassis, and all devices other than engine block mounted devices obtain negative via the chassis or a designated ground lug referenced to chassis. This is the only safe way to do things, unless the equipment supplier and installer can 100% guarantee there will never be a negative to chassis path through the equipment.
Ground Currents and Ground Loops
All of the vehicle's normal running currents, which include ignition, radio, lights, wipers, horn, and computer systems, flow from the alternator through the engine block to the vehicle's chassis ground, or from the battery to vehicle chassis when the alternator is below battery voltage. As alternator voltage falls below 13.8 volts, the battery picks up an increasing share of load current.
Horns and lights ground to the body shell, while dashboard electronics typically ground to the firewall or the solidly welded or bolted dashboard bracing. Critical sensors and pickups normally float from ground everywhere, grounding only to the computer's internal negative bus system. The computer negative bus then grounds to the firewall or body shell. This grounding method prevents ground loops. Ground loops introduce unwanted electrical noise and/or sensor voltage errors.
A smaller very short lead from the battery negative terminal, as well as ground leads from the engine block, go directly to the body shell. These leads, primarily the heavy short battery ground lead, power all of the vehicle's grounded electronics negative terminals. The body shell, not the battery negative post, is the safest and best common ground point for sensitive electronics.
The unique ground routing for different systems is for very specific reasons. The body shell serves as a giant low dc resistance and lowest impedance high frequency and radio frequency ground point. The vehicle chassis becomes the common point for reducing or eliminating noise in sensitive audio systems, as well as eliminating noise or voltage errors in sensors and/or trigger systems. The vehicle chassis is the common point for optimum RFI and noise suppression, not the battery negative post. The goal is to keep high currents with noise out of the wiring.
Example of ground path resistance:
The resistivity of steel is about 15 ohms per 10-6 cm. The resistivity of copper is 1.7 ohms per 10-6 cm. We can reasonably assume steel has about 15/1.7 = 8.8 times the resistance of copper for the same length and same cross sectional area. While the body shell has higher resistivity material, the body also has much greater cross sectional area.
This means a one foot wide length of steel body shell, if that shell is only .06 inches thick, has about 10% less resistance than an equal path length through out copper wire. It's easy to see why a ground path through the car body, which likely is several feet wide and much thicker in many areas, is a small fraction of the resistance of a copper wire.
The chassis ground, outside of very short runs, is a good system. The system is planned to prevent unavoidable voltage drops in the ground system from upsetting computer sensor voltages. It keeps heavy charging and starting currents out of sensitive electronics, and it ensures a steady supply of clean low-noise direct current to vehicle electrical devices. It also has consideration of safety in the event some ground connection or ground conductor fails. If a battery terminal comes loose, for example, the only damage is a loss of starting or operating voltage. Electronics typically does not suffer catastrophic damage from poor connections, while noise typically does not get into stereo and computer systems.
Connecting negative leads to battery posts, and long negative leads, are almost always a mistake.
To most of us, what goes on inside the little boxes we install seems completely foreign. Most of the world thinks the heavy black power lead is the negative power, and that all negative power exclusively flows through that black lead. Only a few understand power negative is not exclusively via the negative lead in almost equipment, and that anything metal on the device enclosure, and everything exiting the enclosure like wire leads or signal terminals, usually share some of the negative supply current.
There are only two conditions where direct power connections to the battery negative are acceptable, anything else is risky:
when the device's internal circuitry fully isolates the negative power lead from the cabinet and all other external ports or leads exiting the device
when the device's external connections completely and reliably float from ground, and any connections leaving the device are "fused" or current limited at a safe level for that lead
In all cases where the negative lead has a direct current path through internal circuitry to any external conductors, which would include cabinet screws, enclosures, jacks, connectors, and wire leads, grounding the device negative lead to the negative battery or supply terminal can create hazardous conditions.
Battery path current can be hundreds of amperes during starting, and battery path current is easily 25 amperes or more when charging the battery. Additionally, the alternator supplies all running current for all accessories, with the battery supplying current when an alternator cannot "keep up" with load. With high currents like that, the battery post should be exclusively dedicated to the battery-to-block ground lead, and the battery negative always must have a good solid connection to the vehicle chassis.
Sharing the negative battery lead to engine bolt with anything else or connecting directly to the battery negative post with anything except the block and chassis grounds is a terrible idea. (Connecting electrical devices or hardware directly to a battery negative post is a bad idea unless the negative connection is 100% ground isolated at the electrical device.) When an electrical device is directly connected to the negative post, if the negative post to block or chassis connection opens up or develops excessive resistance, the battery negative post will divert alternator or starter current through whatever is attached to the negative post. This can be hundreds of amperes! Very few devices and wiring will suffer a fault like this without permanent damage. It is also a fire risk.
Grounding directly to the negative post is a fire hazard at worse, and an unnecessary risk to your equipment at best. Battery post connections also increase likelihood of ground loops and ground conducted noise.
The only proper and safe way to connect accessories of any type (this includes ignition and stereo systems) to the negative post is via a path through the vehicle chassis. This is not only the safest path, the chassis is the lowest noise ground path. This is why every vehicle manufacturer has a lead from negative post to chassis, and all devices other than engine block mounted devices obtain negative via the chassis or a designated ground lug referenced to chassis. This is the only safe way to do things, unless the equipment supplier and installer can 100% guarantee there will never be a negative to chassis path through the equipment.
Ground Currents and Ground Loops
All of the vehicle's normal running currents, which include ignition, radio, lights, wipers, horn, and computer systems, flow from the alternator through the engine block to the vehicle's chassis ground, or from the battery to vehicle chassis when the alternator is below battery voltage. As alternator voltage falls below 13.8 volts, the battery picks up an increasing share of load current.
Horns and lights ground to the body shell, while dashboard electronics typically ground to the firewall or the solidly welded or bolted dashboard bracing. Critical sensors and pickups normally float from ground everywhere, grounding only to the computer's internal negative bus system. The computer negative bus then grounds to the firewall or body shell. This grounding method prevents ground loops. Ground loops introduce unwanted electrical noise and/or sensor voltage errors.
A smaller very short lead from the battery negative terminal, as well as ground leads from the engine block, go directly to the body shell. These leads, primarily the heavy short battery ground lead, power all of the vehicle's grounded electronics negative terminals. The body shell, not the battery negative post, is the safest and best common ground point for sensitive electronics.
The unique ground routing for different systems is for very specific reasons. The body shell serves as a giant low dc resistance and lowest impedance high frequency and radio frequency ground point. The vehicle chassis becomes the common point for reducing or eliminating noise in sensitive audio systems, as well as eliminating noise or voltage errors in sensors and/or trigger systems. The vehicle chassis is the common point for optimum RFI and noise suppression, not the battery negative post. The goal is to keep high currents with noise out of the wiring.
Example of ground path resistance:
The resistivity of steel is about 15 ohms per 10-6 cm. The resistivity of copper is 1.7 ohms per 10-6 cm. We can reasonably assume steel has about 15/1.7 = 8.8 times the resistance of copper for the same length and same cross sectional area. While the body shell has higher resistivity material, the body also has much greater cross sectional area.
This means a one foot wide length of steel body shell, if that shell is only .06 inches thick, has about 10% less resistance than an equal path length through out copper wire. It's easy to see why a ground path through the car body, which likely is several feet wide and much thicker in many areas, is a small fraction of the resistance of a copper wire.
The chassis ground, outside of very short runs, is a good system. The system is planned to prevent unavoidable voltage drops in the ground system from upsetting computer sensor voltages. It keeps heavy charging and starting currents out of sensitive electronics, and it ensures a steady supply of clean low-noise direct current to vehicle electrical devices. It also has consideration of safety in the event some ground connection or ground conductor fails. If a battery terminal comes loose, for example, the only damage is a loss of starting or operating voltage. Electronics typically does not suffer catastrophic damage from poor connections, while noise typically does not get into stereo and computer systems.
Connecting negative leads to battery posts, and long negative leads, are almost always a mistake.
To most of us, what goes on inside the little boxes we install seems completely foreign. Most of the world thinks the heavy black power lead is the negative power, and that all negative power exclusively flows through that black lead. Only a few understand power negative is not exclusively via the negative lead in almost equipment, and that anything metal on the device enclosure, and everything exiting the enclosure like wire leads or signal terminals, usually share some of the negative supply current.
There are only two conditions where direct power connections to the battery negative are acceptable, anything else is risky:
when the device's internal circuitry fully isolates the negative power lead from the cabinet and all other external ports or leads exiting the device
when the device's external connections completely and reliably float from ground, and any connections leaving the device are "fused" or current limited at a safe level for that lead
In all cases where the negative lead has a direct current path through internal circuitry to any external conductors, which would include cabinet screws, enclosures, jacks, connectors, and wire leads, grounding the device negative lead to the negative battery or supply terminal can create hazardous conditions.
Last edited by Respect; 10-24-2017 at 08:14 PM.
The following users liked this post:
Gannicus (10-24-2017)
#4
10-24-2017, 08:35 PM
#7
10-24-2017, 09:12 PM
a suggestion for you from the original conversation from the other thread,
run a redundant ground from some point on the main frame of the bike and up into the structural metal of the fairing. this will allow the ground path that you were talking about, but bypass the the area of the neck bearings that becomes the weak link in the ground path due to the issues of grease and roller bearing surfaces being used to pass the juice to ground.
m
run a redundant ground from some point on the main frame of the bike and up into the structural metal of the fairing. this will allow the ground path that you were talking about, but bypass the the area of the neck bearings that becomes the weak link in the ground path due to the issues of grease and roller bearing surfaces being used to pass the juice to ground.
m
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#8
10-24-2017, 10:08 PM
The problem is a motorcycle doesn't have a true chassis ground like a car as there is no ground strap. So if one was to ground the frame or anywhere besides the battery or the ground post, it will be insufficient. Sure we would love to run a very short ground lead like in a car, but that only leads to problems.
#10
10-24-2017, 11:36 PM
Ultimate HDF Member
The problem is a motorcycle doesn't have a true chassis ground like a car as there is no ground strap. So if one was to ground the frame or anywhere besides the battery or the ground post, it will be insufficient. Sure we would love to run a very short ground lead like in a car, but that only leads to problems.
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slyedog (10-25-2017)