There have been some recent interest in things electrical, and in fact some threads on a somewhat mysterious subject known as Grounding. Actually the broader subject is Power and Grounding, the study and art of how to distribute electrical power within your bikes electrical system and then get it back to the source from where it started. Current return is what completes the circuit which is a basic requirement for electricity. Electricity runs in circuits or circular paths.
http://www.thegsresources.com/_forum/showthread.php?139115-Ground-Loops
http://www.thegsresources.com/_forum/showthread.php?140109-High-Performance-Power-and-Grounding
I have posted at length about this over at the GS Resources, but I figured I would create a condensed version here for the members of XS650. Anybody interested in electrical stuff, might want to read through those threads. For those that are just interested in having a properly running XS650, I will just summarize the basics here in a new thread and only focus on Grounding.
1st Principles of Grounds: Current Returns to the source
The source of power in your bike actually comes from two sources. Both a battery and the Alternator. Whether the alternator is a Permanent Magnet Alternator or a Field Controlled Alternator, this power source is in parallel to the battery and so depending upon the loads and RPM of the engine, the alternator may or may not be sufficient to provide the power needs. When it doesn't, the battery picks up the slack. When the engine is not running there is no power coming from the alternator and so the battery is generating all of the current.
Your bike is already well designed to deal with the first thing that happens (i.e. cranking the starter). There is a large ground strap that provides a direct current path to the battery for any current that is supplied to the starter. OK that is easy, but what about after the bike has started and there is alternator output?
Recall the 1st principle; "Current Returns to the source". So when the alternator is outputting current (normally on a heavy red lead) and is powering whatever lights, coils or other electrical components on the bike(including charging the battery), all of that current must return to the alternator to complete the circuit. If your electrical component is powered rest assured the current is getting back to the source. The main thing to worry about is whether your components are getting the full voltage.
You see if the current return paths are indirect, or more specifically have excessive resistance, then there will be voltage drops across the ground returns. It is as simple as V=I*R (or Ohm's Law). I is current and a typical XS650 load is 10 amps. So even a very small 0.1 ohms resistance will result in a full 1 volt drop in voltage. Losing 1 volt on a dash light might not be the end of the world, but having a 1 volt error in the charging systems sensing voltage can be disastrous. I'll repeat , 0.1 ohms is a pretty small value. Most people ohm meters have a minimum resolution of just 0.1 ohms. So many times this is not something that you can really even measure with an ohm meter. You need to measure voltage drops when operating at full load when maximum current is flowing. You can then see the voltage drops.
For a PMA, you typically want the voltage drops between the R/R and the battery to be less than 0.25 (this is actually borderline and not recommended) if not less than 0.1 volts. At 10 amps 0.1 volts corresponds to 0.01 ohms which is way below the capabilities of most people's ohm meters
So what is the solution? The solution is simple and it is really based on two fundamental principles.
1.) Make the return current path for any device as "direct" as possible.
2.) Avoid "sharing" return currents on fundamentally different loads.
OK that sounds simple enough to understand, but how do I do that?
This is where the philosophy for a "Single Point Ground (SPG)" comes to play.
The notion is that all currents from the alternator (or more specifically R/R(+) ) must return to R/R(-) and as such it is best to collect up through the most direct paths practically all current return sources into a common point. This point is called SPG. After collecting all the currents, they then are routed to the R/R(-).
The main benefit is that when doing this , you have a much more clear idea of how the currents are returning, and the voltages of each device are only being reduced by their own loads.
The only place that return currents are sharing the same path is the single wire between the SPG and the R/R(-). Obviously keeping this wire fairly large (14 awg) and short are best.
A simple schematic for a typical PMA is shown here. The R/R has multiple wires for double R/R(+) and a sense wire, but ignoring that the grounds shown follow the SPG philosophy described above.
The SPG is located someplace that is electrically close to the R/R(-) return and it is the collection point for three current sources:
1.) The harness "backbone" ground if there is one.
2.) The battery for the return of and battery charging currents.
3.) The frame grounds for anything that is grounded to the frame and not through a common backbone.
I sell something called a Solid State Power Box that is designed to optimize the power distribution following the analogous techniques for power distribution (i.e. getting the power out as effectively as possible). With those systems I make a small SPG harness. The SPG harness has usually has 4 wires attached to it.
three coming into the SPG
1.) Harness ground - 16 awg
2.) Frame ground - 16 awg
3.) Battery ground(-) - 16 awg
and the last
4) wire is to return this current to the R/R(-) 14 awg
I construct the SPG harness so that all of the wires are joined into a single ring lug called the SPG. You mount it somewhere but in fact it doesn't even need to be bolted to anything if all the wires are joined(crimped and soldered). You should be able to identify the SPG and all the connections mentioned in the simplified schematic.
There are of course many more details and much theory behind this simple explanation, but if you are just trying to get your arms around why it is a bad idea to just ground everything to the frame. This should provide some ideas that you can grasp and grapple with.
Good Luck.
http://www.thegsresources.com/_forum/showthread.php?139115-Ground-Loops
http://www.thegsresources.com/_forum/showthread.php?140109-High-Performance-Power-and-Grounding
I have posted at length about this over at the GS Resources, but I figured I would create a condensed version here for the members of XS650. Anybody interested in electrical stuff, might want to read through those threads. For those that are just interested in having a properly running XS650, I will just summarize the basics here in a new thread and only focus on Grounding.
1st Principles of Grounds: Current Returns to the source
The source of power in your bike actually comes from two sources. Both a battery and the Alternator. Whether the alternator is a Permanent Magnet Alternator or a Field Controlled Alternator, this power source is in parallel to the battery and so depending upon the loads and RPM of the engine, the alternator may or may not be sufficient to provide the power needs. When it doesn't, the battery picks up the slack. When the engine is not running there is no power coming from the alternator and so the battery is generating all of the current.
Your bike is already well designed to deal with the first thing that happens (i.e. cranking the starter). There is a large ground strap that provides a direct current path to the battery for any current that is supplied to the starter. OK that is easy, but what about after the bike has started and there is alternator output?
Recall the 1st principle; "Current Returns to the source". So when the alternator is outputting current (normally on a heavy red lead) and is powering whatever lights, coils or other electrical components on the bike(including charging the battery), all of that current must return to the alternator to complete the circuit. If your electrical component is powered rest assured the current is getting back to the source. The main thing to worry about is whether your components are getting the full voltage.
You see if the current return paths are indirect, or more specifically have excessive resistance, then there will be voltage drops across the ground returns. It is as simple as V=I*R (or Ohm's Law). I is current and a typical XS650 load is 10 amps. So even a very small 0.1 ohms resistance will result in a full 1 volt drop in voltage. Losing 1 volt on a dash light might not be the end of the world, but having a 1 volt error in the charging systems sensing voltage can be disastrous. I'll repeat , 0.1 ohms is a pretty small value. Most people ohm meters have a minimum resolution of just 0.1 ohms. So many times this is not something that you can really even measure with an ohm meter. You need to measure voltage drops when operating at full load when maximum current is flowing. You can then see the voltage drops.
For a PMA, you typically want the voltage drops between the R/R and the battery to be less than 0.25 (this is actually borderline and not recommended) if not less than 0.1 volts. At 10 amps 0.1 volts corresponds to 0.01 ohms which is way below the capabilities of most people's ohm meters
So what is the solution? The solution is simple and it is really based on two fundamental principles.
1.) Make the return current path for any device as "direct" as possible.
2.) Avoid "sharing" return currents on fundamentally different loads.
OK that sounds simple enough to understand, but how do I do that?
This is where the philosophy for a "Single Point Ground (SPG)" comes to play.
The notion is that all currents from the alternator (or more specifically R/R(+) ) must return to R/R(-) and as such it is best to collect up through the most direct paths practically all current return sources into a common point. This point is called SPG. After collecting all the currents, they then are routed to the R/R(-).
The main benefit is that when doing this , you have a much more clear idea of how the currents are returning, and the voltages of each device are only being reduced by their own loads.
The only place that return currents are sharing the same path is the single wire between the SPG and the R/R(-). Obviously keeping this wire fairly large (14 awg) and short are best.
A simple schematic for a typical PMA is shown here. The R/R has multiple wires for double R/R(+) and a sense wire, but ignoring that the grounds shown follow the SPG philosophy described above.
The SPG is located someplace that is electrically close to the R/R(-) return and it is the collection point for three current sources:
1.) The harness "backbone" ground if there is one.
2.) The battery for the return of and battery charging currents.
3.) The frame grounds for anything that is grounded to the frame and not through a common backbone.
I sell something called a Solid State Power Box that is designed to optimize the power distribution following the analogous techniques for power distribution (i.e. getting the power out as effectively as possible). With those systems I make a small SPG harness. The SPG harness has usually has 4 wires attached to it.
three coming into the SPG
1.) Harness ground - 16 awg
2.) Frame ground - 16 awg
3.) Battery ground(-) - 16 awg
and the last
4) wire is to return this current to the R/R(-) 14 awg
I construct the SPG harness so that all of the wires are joined into a single ring lug called the SPG. You mount it somewhere but in fact it doesn't even need to be bolted to anything if all the wires are joined(crimped and soldered). You should be able to identify the SPG and all the connections mentioned in the simplified schematic.
There are of course many more details and much theory behind this simple explanation, but if you are just trying to get your arms around why it is a bad idea to just ground everything to the frame. This should provide some ideas that you can grasp and grapple with.
Good Luck.
