Floating Ground?

[Gunni]

I'm switching out my fuel gauge (VDO euro ohms) for a WEMA/KUS sender and Faria gauge with American ohm range. Can I just use the existing installed wiring (signal wire and ground) that are attached to the VDO sender or do I have to separately ground the sender and the gauge. There is mention of using a "floating ground" in the Faria instructions. What is that?

 

[FastOlson]

Wish I could be of more help, but we did wire in a new Wema diesel tank gauge a few years ago. I ran the two-wire cable from the alum. tank to my 12 volt ground terminal strip, along with the tank ground wire.
BTW, we really Like the new fuel level gauge!

 

[Gunni]

I don't have a ground buss anywhere close to the tank, so I would like to just use the existing ground wire attached to the VDO sender flange and get my ground at the helm instrument panel. I may be overthinking this thing, I have a ground lug and a sender lug on the gauge and two wires coming off the WEMA / KUS sender.

 

[Bill Roosa]

Well ground is ground. If the sender has a ground wire and the gauge has a ground terminal/wire then I'd recommend connecting them and connecting the wire to the ships ground also (corrosion avoidance). If either one does not have a ground wire/terminal then it is grounded through its housing and that may or may not be grounded to the ships ground. A plastic helm/nav station panel would need the housing to be connected to ships ground. Wires are wires and don't care so reuse as possible.

 

[walt]

I dont know anything about your setup.. so this is somewhat of a guess..
The floating ground may refer to a reference line between two devices that need to communicate with each other. Ie, you would just connect the floating ground of one device to the floating ground of the second device but NOT connect this to the system ground. The reason for this is that the system ground may have noise on it caused by supplying current to devices. You would have better signal to noise (and more reliable communications) with a reference that was "floating" from the main ground with possibly very little current flowing through it.

 

[Brian D]

A floating ground is a ground that is not attached to any physical earth or water ground. An example.

You have a laptop that is running on battery power. It is connected to a device such as GPS receiver that is also running on battery power. The ground between to two is considered floating. There is no physical connection to earth (to include water).

Now, if that laptop is being powered by the vessel's battery bank, then the negative return is considered grounded because it is connected to the negative terminal of the battery. That in turn could be connected to a thru-hull that is submerged. Now that is a real ground.

When dealing with grounds, it is possible to create a ground loop. Very dangerous to the equipment and possibly to the human who interacts with that equipment. If you touch something metal on the boat and get a shock, that might be the results of a ground loop. A ground loop is two different grounds at different potentials. Thus, current is flowing.

I believe in your case Gunni, Euro and American are just relating to wire size and current handling. A wire size regardless if Euro or American will carry the amount of current determined by its diameter.

This is all my opinion, of course.

 

[Brian D]

Another thing...

The Euro ohms vs the American ohms might have to do with the total resistance in the sender and the wire. The sender could be an internal resistor with a float. When the float moves the resistance changes and thus you see a change in fuel level. If you use different wire size for the given length, you may have to re calibrate your sender. There may be two calibration points: full and empty. This is info I remember when in Afghanistan a generator I was using ran out of fuel. But the gauge said it was full. The float had to be adjusted. It was too long and hit something. That is why I was getting a full reading.

Now on the ground point. Vessels are usually grounded to the water via something. Could be thru-hull as mentioned before, or it could be an outboard motor that needs a battery to start. Maybe the engine via the shaft and prop.

 

[Gunni]

If you touch something metal on the boat and get a shock, that might be the results of a ground loop.

See, that is what confounds me about electricity, you can't see it and it will kill you.

In this case the fuel gauge appears to be working as an ohm gauge-reading a variable resistance from the sender that is turned into a fuel level reading. So I don't think there is any significant current running through the wires. The difference between euro and American fuel gauges is the ohm range. Euro is 10-180 ohm and American is 33-144 ohm (empty to full). The gauge and the sender have to matched or you get incorrect readings. I understand the technology it is just the low volt DC stuff that confuses me.

Thanks for your help guys. I'm going in, wish me luck!

 

[Daveinet]

Well ground is ground.

No it isn't. Try installing a recording studio in the 38 floor of the Sears Tower (or as it was called then) Hmm, or shall I say HUM. There is no such thing as ground. The higher you went, the greater potential you are from earth ground. Any current flow coming from the rest of the building caused the ground to significantly drift.
The trick with grounding is to find only a SINGLE PATH. If the tank is grounded through another source such as a separate grounding terminal, and the gauge is grounded to another source, such as the meter case, you don't want to connect a signal ground between the two. In that case, you would "float" the signal ground, because there is already a ground connection through the case or terminal. This is the common definition of the term "floating ground". The floating part refers to the signal ground, because it is floating, and depending on the case to actually supply the needed ground connection. So Gunni, if your meter does not have any connection to the case, or your tank has no other terminal for ground, then you would connect the signal ground.

Incidentally term "floating ground" does not mean there is no connection to earth ground. It just means the signal ground is floating, because it is using an alternate source for grounding, such as earth ground. So if you are using a floating ground, that really means the real ground you are using is true earth ground. (not signal wire ground)

 

[walt]

There is mention of using a "floating ground" in the Faria instructions

Yep, "ground" may not be ground when you add in current and frequency. All sort of grounds (analog, digital, signal.. etc) but I wouldnt spend much more time worrying about this until the OP gives way more context to the question above.. And I am curious what that context is?

Ground loops are also usually about noise or corrosion if wire is properly sized. You have to add in current surge way above intended ratings to have any safety issue (like lightning currents).

 

[Daveinet]

Floating ground - well dah, your on a boat. If it ain't floating, you have a lot greater things to worry about than your gauges LOL.

 

[NYSail]

Why don't they just provide a picture on how to hook it up...... make life easy for me.

 

[Brian D]

Not to be contentious, but a floating ground is as I have described it. Please refer to any electrical manual or site. A floating ground is a common ground that is not physically connected to earth or water. My example of a Laptop on internal battery connected to a GPS on internal battery uses a floating ground between the two.

 

[Ron20324]

. A floating ground is a common ground that is not physically connected to earth or water. My example of a Laptop on internal battery connected to a GPS on internal battery uses a floating ground between the two.

Brian, isn't this what we've so often talked about with, say, a Honda 2000I and some line reverse lights come on? Honda has it's OWN, floating ground, not earth ground..

 

[Mark Maulden]

"Ground" is an electrical or electronic term that is the most misused term there is...All it is, is a reference point. Whether it is a return to the planet in primary power systems or a reference to 5V DC on a circuit board..How one treats "grounds" are important. Low amplitude return (ground) paths should not be the ships grounding or bonding system. Run the wire..

 

[Brian D]

 

[Gunni]

From the install instructions:
Ground: Standard ground is the most common having battery negative connected directly to the engine block. Sending units may have one terminal (signal). In a floating ground system the battery negative is not connnected to the engine block so merely threading in the sender does not supply ground. Floating ground sender will have two terminals (signal and ground) . Both sender terminals may be wired to the appropriate gauge terminal or the senders ground may be wired directly to the battery negative. A floating ground sender may be used in a standard ground system but not vice versa.

My new WEMA/KUS sender does have two leads, signal and ground.

My OEM VDO gauge brings the ground from the boat to the gauge where it is shared with the sender ground. So I suppose I have liberty to do it that way with this new sender.

 

[walt]

Since I had wanted to understand that a little better.. my ,02.. You have an analog signal from the sender and will get the lowest noise if you run both sender signal and sender "ground" back to the gauge. You have the option to do this and as someone else said, run the wire..

However, it sounds like that system works just fine if the sender gets its ground from the sender chassis through the tank it contacts to the engine chassis. That would introduce a lot more noise on the sender reference so its apparently not real sensitive to noise in the first place (tank fluid level).

 

[JamesG161]

The Euro ohms vs the American ohms might have to do with the total resistance in the sender and the wire. The sender could be an internal resistor with a float. When the float moves the resistance changes and thus you see a change in fuel level.

spot on target in the DC instrument world.

From WEMA...

• The signal input for our stock gauges are 240-33 ohms, American Standard (when applicable)
• For 0-180 ohms, European Standards

Therefore, if you have a grounded Fuel tank [sender] that is at a Different Ground than your gauge [receiver] you could get an interfering Gound Loop current flow. Classic problem in the 2 wire power/ground DC instrument world.

Since on my boat, my Gauge is DC battery grounded and my Fuel tank is DC grounded... NO GROUND LOOP!

________
American Standard is the BEST.
You will NOTE that 0 and 100 % are called LIVE readings.

Where European 0% level = 0 ohms resistance, which can also be DEAD power.

Jim...

 

[Daveinet]

IS your fuel gauge electronic or is it passive? In other words, does the gauge require battery power to operate?