Electrical puzzle

[ttmott]

There is also a phenomena called inductive loading where if two conductors are run parallel for a distance potential will be transferred between the two due to the magnetic field generated by flowing current. Possibly the sender wire is routed next to one of the AC wires and a voltage potential is being imposed on the gauge.

 

[Bt Doctur]

The tank is connected to the ships negative side thru the engine block ground witch is connected to the neg battery post

 

[M99]

There is also a phenomena called inductive loading where if two conductors are run parallel for a distance potential will be transferred between the two due to the magnetic field generated by flowing current. Possibly the sender wire is routed next to one of the AC wires and a voltage potential is being imposed on the gauge.

Now that is an interesting concept that could possibly be occurring. I hadn't considered inductive coupling because its a low voltage DC system, but of course it could be picking up some AC in some manner. I'll just have to run a jumper form the sender to the gauge directly, and if that solves it Since I can't easily access the full run of that Pink ground sensing wire, I'll pull a new wire to replace it instead if that's the solution. Thanks.

 

[M99]

Finally figured it out. It was a bad bonding wire to the fuel tank. On my boat, it was very difficult to even find where the bonding wire attached to the tank, and impossible to get to the other end of it without taking half the boat apart. I had checked the tank to ground several times previously, and it did show a ground connection. But apparently, there is some corrosion at one end of that bonding wire so it reads ground with a VOM, but there is some small resistance. So I tried jumping the tank directly to a good earth ground and everything worked. Once I figured that out, I just added a second bonding wire from an existing bracket on the tank to a good earth ground and the problem was solved. Basically there were two problems to start with. The main connector to the gauge was not making a good connection, and that was solved with Stabilent 22. Once that was fixed, the sender was getting a sneaky partial ground through the Shore Power connection as well as a partial ground through the existing Tank bonding wire. That's why I was getting intermittent and inaccurate readings. Now both gauges read the same. 30 minute fix after weeks of trying to figure out what the fix was.

 

[Lazy Daze]

Cool, I'm glad you got if figured it out. You know, 9 times out of 10 (may be an exaggeration, but it certainly seems like that) electrical problems seem to come back to dirty connections/grounds.

 

[M99]

Cool, I'm glad you got if figured it out. You know, 9 times out of 10 (may be an exaggeration, but it certainly seems like that) electrical problems seem to come back to dirty connections/grounds.

True, and I'm usually pretty good with electrical stuff. But this had me stumped because using a VOM it always read as a decent ground to the tank. It was only after I put the VOM on 1 x ohm that I started to see an anomaly. Since they use very low ohm (34 to 270) I finally realized that even a slight resistance in the ground circuit could cause a significant problem. I wonder why they chose that range. Its 8 to 1, but if they had used say 500 to 4000 ohms. then slight connection problems would not have been significant.