Sailboat Owner's Guide to Corrosion - Galvanic and Stray Current Corrosion (Collier 6 & 7)
- Thread starter Will Gilmore
- Start date
So, if the switch or the pump became connected to ground by immersion or partial immersion in an electrolytic, the 12v positive would create a completed circuit through the pump?
-Will (Dragonfly)
-Will (Dragonfly)
No!
The battery 12volt might short to the bilge, if the motor was defective. But no short on the ground side switch.
Jim...
Another way to think of it is that so many things are connected to the battery negative, that cutting the one wire path for the pump’s ground wire wouldn’t be an effective way to switch it. The pump could still get to ground through its windings and back in through the prop shaft, thru hulls, engine mounts, etc.
OK, so the electrons are coming from the negative side of the battery and flowing to the positive side. It is convention (started with Ben Franklin) to state that the current flows from the positive to the negative. This happened long before anyone knew anything about electrons. Ever since then, that is the convention and how it is spoken of - current is said to flow from positive to negative, as incorrect in the physical world as that actually is.
But, what happens is you have to switch the positive side because, that is what gives you the desire to move electrons. The electrons are moving because there is a 12V (roughly, depends upon state of charge, temperature, electrolyte yada yada) potential existing to get those electrons moving... so to speak... If you only switched the negative side, you are leaving the positive side open to attract electrons, and you will get them moving, from many sources...
Does this make sense?
dj
In a PM, with Will last night, we got it straight.
______
"The single most important discovery noted in these [Ben’s] letters is that of polarity, that is, he found that all electrical potentials were not equivalent, but could be observed holding either of two opposite charges. To these he assigned the names we still use, positive and negative. Unfortunately, from our point of view, he assigned them in the opposite sense to our understanding -- "positive" meaning a deficit of free electrons -- which is why we now call the electron a negatively charged particle."
He had a 50:50 chance of being right... oops
Electrons Always flow from...
Highest Potential to Lowest Potential
In that example, 12+ VDC is higher potential than a Ground reference of Zero.
Jim...
PS: I had to invoke the Second Law of Thermodynamics on Will.
______
This is what Ben's letter to the Academic world did...
"The single most important discovery noted in these [Ben’s] letters is that of polarity, that is, he found that all electrical potentials were not equivalent, but could be observed holding either of two opposite charges. To these he assigned the names we still use, positive and negative. Unfortunately, from our point of view, he assigned them in the opposite sense to our understanding -- "positive" meaning a deficit of free electrons -- which is why we now call the electron a negatively charged particle."
He had a 50:50 chance of being right... oops
Electrons Always flow from...
Highest Potential to Lowest Potential
In that example, 12+ VDC is higher potential than a Ground reference of Zero.
Jim...
PS: I had to invoke the Second Law of Thermodynamics on Will.
You've lost me...In a PM, with Will last night, we got it straight.
______
This is what Ben's letter to the Academic world did...
"The single most important discovery noted in these [Ben’s] letters is that of polarity, that is, he found that all electrical potentials were not equivalent, but could be observed holding either of two opposite charges. To these he assigned the names we still use, positive and negative. Unfortunately, from our point of view, he assigned them in the opposite sense to our understanding -- "positive" meaning a deficit of free electrons -- which is why we now call the electron a negatively charged particle."
He had a 50:50 chance of being right... oops
Electrons Always flow from...
Highest Potential to Lowest Potential
In that example, 12+ VDC is higher potential than a Ground reference of Zero.
Jim...
PS: I had to invoke the Second Law of Thermodynamics on Will.
Here's a simple web site talking to me at a level I better understand...
Here's a quote from that web page: "The electrons move toward a positive (+) potential in the wire."
Electrons, as I understand it, do not flow from the positive terminal of the battery to the negative terminal of the battery. But hey, I'm certainly open to fixing underlying inaccuracies to my knowledge.
dj
That is what is confusing to a few. They see a Ground as the SOURCE of electrons.
They see the Battery as the destination.
We seem to be stuck on the direction of electron flow.
Quit worrying about direction of the flow of electrons We have established that Metals are the source.
It is the Potential that causes the flow of electrical current or AMPs. [Energy flow]
_____
It is that Energy Flow that consumes a Zinc.
Jim...
They see the Battery as the destination.
We seem to be stuck on the direction of electron flow.
Quit worrying about direction of the flow of electrons We have established that Metals are the source.
It is the Potential that causes the flow of electrical current or AMPs. [Energy flow]
_____
It is that Energy Flow that consumes a Zinc.
Jim...
Ah, I see where you are coming from. I believe I captured this in my post #25, I just should have clearly broken the link between the battery posts and where all the electrons may come from... Nice, I now know how to explain this better...
dj
I was trying to avoid Energy, but mentioned it in the other post topic.
We charge a battery to store Energy. [Amp-hrs so to speak]
We want the bilge pump motor [the load] to consume that Battery Energy using Voltage as the Potential, and current, Amps, to do Work.
This is a great example of avoiding possible...
Stray Current Corrosion.
And not..
Stray Electron Corrosion.
The Battery "pushes" and the Motor pulls, is the current flow direction. It is counter intuitive to think of Electron Flow.
Thus Ben Franklin got it backwards.
Jim...
We charge a battery to store Energy. [Amp-hrs so to speak]
We want the bilge pump motor [the load] to consume that Battery Energy using Voltage as the Potential, and current, Amps, to do Work.
This is a great example of avoiding possible...
Stray Current Corrosion.
And not..
Stray Electron Corrosion.
The Battery "pushes" and the Motor pulls, is the current flow direction. It is counter intuitive to think of Electron Flow.
Thus Ben Franklin got it backwards.
Jim...
Perhaps the term "sucks" rather than pushes may be better.. It is only counter intuitive when you are living under the convention our boy Ben created...
dj
Tangentially related to where to put the switch is the convention of which cable to disconnect from a battery first. Always disconnect the negative cable first. That way if your wrench touches another grounded surface, like the engine, you’re only connecting surfaces of the same potential, so there’s no circuit for the electrons to follow.
That's in the now more common negative ground systems I used to have an old vehicle that had positive ground system. That one you did the other way...
dj
Ok ok.. Sucks electrons, but not from the bilge water or ocean, but actually from the...
Negative side of the Battery. [The source of Energy]
If your boat is wired per ABYC, then the Battery negative terminal is the source.
so...
Do what the book says to avoid possible...
Stray Current Corrosion
Jim...
I went back and re-read what Collier was saying and thanks. It makes more sense now.
He's saying, as you guys are also, that if water invaded the pump windings or, even worse, just the ground side leads, it's basically like bringing ground to the motor, no matter where the switch position is.
-Will (Dragonfly)
He's saying, as you guys are also, that if water invaded the pump windings or, even worse, just the ground side leads, it's basically like bringing ground to the motor, no matter where the switch position is.
-Will (Dragonfly)
Chapter 7 seems to be where we really get started on issues of the maritime concerns with corrosion.
I particularly found interesting what Collier is saying about AC current. From previous threads, I gathered that most people believe AC current doesn't cause corrosion, but what Collier writes about the experiment conducted in the 80s that showed an increase in the rate of corrosion in the presence of a stray AC current makes sense to me.
The anode metal loses electrons because those electrons have a looser bond to the atom than the electrons bound to the cathode atoms. Therefore, the electrical force that strips them from the anode won't have equal work replacing them when the AC current reverses. The result should be more elections are stripped off than replaced per cycle.
-Will (Dragonfly)
I particularly found interesting what Collier is saying about AC current. From previous threads, I gathered that most people believe AC current doesn't cause corrosion, but what Collier writes about the experiment conducted in the 80s that showed an increase in the rate of corrosion in the presence of a stray AC current makes sense to me.
The anode metal loses electrons because those electrons have a looser bond to the atom than the electrons bound to the cathode atoms. Therefore, the electrical force that strips them from the anode won't have equal work replacing them when the AC current reverses. The result should be more elections are stripped off than replaced per cycle.
-Will (Dragonfly)
While true, AC current normally has little impact as stray current corrosion. Certainly you want to control it, but really control of your AC side has implications more towards safety issues than corrosion issues.
dj
Hey! That's my tank!
for reference, the tank spent time sitting in a small amount of water right in that corner. the water was in a fiberglass basin with nothing else, no grounds or anything.