Negative Battery Terminal

[boatnamesue]

While volt drop testing fuel gauge using #1 neg battery terminal as ground it returned 11.4v. Using #2 neg battery terminal it returned 12.6v. Using #3 neg battery terminal it returned 12.6v. Batteries 1,2,3 are separate batteries.

The power source did not change during test. The connections I was testing did not change. The wiring is brand new. The battery ground terminals for 2 out of 3 batteries returned 12.6v. The 3rd battery returned 11.4v.  Battery #1 is only few months old. Terminals are clean. What's happening here?

[Capt. Bob]

What's happening here?

Good question.  I'm not sure what you're saying.

Which battery was the power source?
1, 2, or 3?

When was the last time any of the batteries were fully charged?

A little more detail on how they are wired together. Pic?

[boatnamesue]

What's happening here?

Good question.  I'm not sure what you're saying.

Which battery was the power source?
1, 2, or 3?

When was the last time any of the batteries were fully charged?

A little more detail on how they are wired together. Pic?

Batteries are fully charged. 

#2 battery is solely for cranking and powering fuel and tach gauges.

When voltage testing #1 battery it returned 12.6v.  When this #1 battery was powering and grounding a terminal block that the console's rocker switch panel is tied to this panel did not work.  So I removed the ground from the terminal block and grounded the block using the negative terminal for battery #2.  The panel worked.  So the panel was working when being powered by #1, grounded by #2.  The panel would not work when being both powered and grounded by #1 battery.

I then did another test.  Used #3 battery to power terminal block, used #1 battery to ground block.  Panel did not work.  I then removed #1 as the ground for block, using #3 to both power and ground the block.  The panel worked.

So for some reason, despite the #1 battery testing 12.6v, when it's actually providing power and ground there's something wrong.  When this #1 battery is being soley used as a ground source it also does not work. 

Can you recommend some other meter tests to perform on this #1 battery other than testing its voltage?  For example, how would I test its negative terminal to be sure its good?

[Capt. Bob]

Work with us here.

Is there a battery switch in your setup?

Can you describe how your system is wired? Starting battery, house battery and what does the third battery do?

Pics????

Whatever wiring setup you have, you can always remove the #1 battery and have it load tested. If you wish to do this yourself with a volt meter, then make it your starting battery and see if the engine will crank. You can also measure the voltage while cranking (a second set of hands will help) and post what you find. You stated the battery is only a few months old so it must be under warranty. Take it to your place of purchase and have them confirm its condition and function at the terminals. If it tests good then you need to look at your wiring and connections.

Good luck.

[boatnamesue]

Work with us here.

Is there a battery switch in your setup?

Can you describe how your system is wired? Starting battery, house battery and what does the third battery do?

Pics????

Whatever wiring setup you have, you can always remove the #1 battery and have it load tested. If you wish to do this yourself with a volt meter, then make it your starting battery and see if the engine will crank. You can also measure the voltage while cranking (a second set of hands will help) and post what you find. You stated the battery is only a few months old so it must be under warranty. Take it to your place of purchase and have them confirm its condition and function at the terminals. If it tests good then you need to look at your wiring and connections.

Good luck.

This is the best I can do.  Pictures wouldn't help in this scenario.  No battery switch.  So for this diagram below, disregard the numbers I previously assigned to the batteries.  Refer to this diagram as to which # battery is doing what. 

#1 is cranking, #2 and #3 are accessory batteries.  There is a series connection between #2 and #3 to provide the trolling motor with 24v.  10 +/- terminal block indicates a 10-gang block for both positive and negative leads.  #2 battery is this blocks power supply and ground.  For each battery I've indicated what connection is made for each terminal on that battery.  Everything works with this setup on the diagram.   If I were to use #3 battery as the power supply and ground for the terminal block is where I was having issues.  If I disconnected the #3 battery ground source to the terminal block, and then replaced it with ground from #2, everything worked.  So #3 wasn't having a problem with power, it was a grounding issue.  Mind you I was using the same wires to connect the battery #2 and #3 to the terminal block.

[RickK]

Lets look at it a different way


To the left is your trolling motor connections - the bottom is the neg side of batt 3 and the top is the pos side of batt 2.  If you were to put a meter across the pair, with the black lead at the bottom, you'll read +24v.
To the right we introduce a "reference" point in the middle.  This reference point changes what you would read across each battery.  From the reference point (black lead at reference point) if you put the red lead at the top of batt 2 you read +12V.  If you put the red lead at the bottom of batt 3 you now read -12v. So, as you can see, you have to be careful with the reference and where you read across which battery.

Here is another scenario using the left set of batteries. If we leave the reference point at the bottom and you want to feed some terminal block from this set up and you connect across the top battery with your black wire at the bottom and the red wire at the top, what you think is ground is actually +12v and the top is actually +24v.  Yes you have 12v across the battery but the reference is off.  Electronics like a 0 to +12v signal swing, not +12 to +24V.

[boatnamesue]

Appreciate the schematic rick.  The simple yet stupid mistake I made was to ground the fuel gauge/sender to a battery other than the battery the fuel gauge was receiving 12v from.  Total brain fart on my part, which subsequently led me into a whirlwind of voltage drop tests, etc. 

[RickK]

Yup, different reference.  Glad you figured it out.