direction of flow of electricity

[Franklin]

I was taught this 18 years ago but, heck, I have a hard time remembering two days ago. If I put a multimeter's ground wire on the prop shaft (it's disconnected from the engine...new engine on the way) and the positive red wire on the negative battery terminal and I get a negative 1.2 volts, does that mean I have electricity flowing into the boat or out? I think that means flowing in but want to make sure.If it's flowing in, then that shouldn't be eating the zincs, correct? I believe I read that it's the out flow of electricity that eats the zincs.Just want to check before I go making changes. Thanks in advance.

 

[Ross]

Franklin, Electrons ( electricity) flows from

the cathode (-) to the anode(+). if there is no connection at all between the shaft and the battery. It is interesting but very difficult to draw any conclusions from that very limited fact. 1.2 volts does not register an alarm for me without more knowledge of your system. Zincs are referred to as sacrificial anodes because they are expected to be stripped of their electrons before anything else is harmed Read this from wikipedia:sacrificial anodeFrom Wikipedia, the free encyclopediaJump to: navigation, searchA sacrificial anode, or sacrificial rod, is a metallic anode used in an electrochemical process where it is intended to be dissolved to protect other metallic components.In laymen's terms, it's a piece of readily corrodible metal attached (by either an electrically conductive solid or liquid) to the metal you wish to protect. This piece of metal corrodes first, and generally must dissolve nearly completely before the protected metal will corrode (hence the term "sacrificial").More scientifically, a sacrificial anode can be defined as a metal that is more easily oxidized than the protected metal. Electrons are stripped from the anode and conducted to the protected metal, which, for this reason, is forced to become the cathode. As a result, the protected metal is prevented from corroding.One example is the galvanic anode used in a cathodic protection system, where the intended purpose is to prevent corrosion of the protected metal (such as a ship's hull, an oil pipeline, or a hot-water heater's tank) by being more electronegative than the desired metal. Commonly used metals for such protective purposes are zinc, aluminum and magnesium.Another example is the anode in an electroplating process, whereby the metal from the anode replaces the metal depleted from the plating solution as it is deposited on the cathode. This industry-related article is a stub. You can help Wikipedia by expanding it. [edit]External linksI hope that helps.

 

[Franklin]

So I want a positive flow then

Ross...the missing info you need is that I am loosing my zincs in 4 months. I have an electrolysis problem which is different from a normal corrosion. Electrolysis is caused by the flow of electricity out the prop shaft and in the process, taking metal with it.I've noticed that when I have the tank gauges turned off I have a positive flow and I have a negative flow when I turn them on. I normally keep the gauges off. So if I have a positive flow with them off and that means the flow is coming into the boat, then maybe I have already solved my electrolysis problem.

 

[Franklin]

now I'm really confused

(http://www.kpsec.freeuk.com/electron.htm)Which way does electricity flow?We say that electricity flows from the positive (+) terminal of a battery to the negative (-) terminal of the battery. We can imagine particles with positive electric charge flowing in this direction around the circuit, like the red dots in the diagram. This flow of electric charge is called conventional current. This direction of flow is used throughout electronics and it is the one you should remember and use to understand the operation of circuits. However this is not the whole answer because the particles that move in fact have negative charge! And they flow in the opposite direction! Please read on... -------------------------------------------------------------------------------- The electronWhen electricity was discovered scientists tried many experiments to find out which way the electricity was flowing around circuits, but in those early days they found it was impossible to find the direction of flow. They knew there were two types of electric charge, positive (+) and negative (-), and they decided to say that electricity was a flow of positive charge from + to -. They knew this was a guess, but a decision had to be made! Everything known at that time could also be explained if electricity was negative charge flowing the other way, from - to +. The electron was discovered in 1897 and it was found to have a negative charge. The guess made in the early days of electricity was wrong! Electricity in almost all conductors is really the flow of electrons (negative charge) from - to +. By the time the electron was discovered the idea of electricity flowing from + to - (conventional current) was firmly established. Luckily it is not a problem to think of electricity in this way because positive charge flowing forwards is equivalent to negative charge flowing backwards. To prevent confusion you should always use conventional current when trying to understand how circuits work, imagine positively charged particles flowing from + to -. and then(http://www.amasci.com/miscon/energ1.html) this really drives me nuts.I don't know if I should be looking for the flow of charge or the flow of electrons and I don't know which is reported by the multimeter.

 

[Paul (Affinity C320)]

electrolysis

Electrolysis may not becomng from your boat at all. It is possible for it to be coming from your neighbor in the slip next to you or from the power running through the water to the dock. I am no expert, not at all, but you need to have your marina discount these other issues.

 

[Paul (Affinity C320)]

electrolysis

Try this link.

 

[Ross]

Franklin, I think that I understand your

confusion. The Zinc is one half of a battery, the other half of which you haven't located yet. The old drycell batteries used a zinc can filled with an electrolite with a carbon rod in the middle. When you used the battery the zinc can was consumed and the battery leaked. Now when your fuel gauges are turned on the polarity of your battery ( unintended battery) is not the same as when they are turned off. The ideal situation would be to have no voltage between the prop shaft and the rest of the system. I suspect that you have a stray ground or even a stray break in the insulation on some devise in the boat. Remember that the flow of current changes direction when you stop using a battery and start charging a battery. That reverses the chemical reaction that takes place within the cells.

 

[Franklin]

Ross

I understand that it is reversing the polarity...my guess is providing an electrical current into the grounding system. So if I understand this correctly, I have electric flow going out my shaft (when it is connected to the engine) when I turn on the tank gauges. When I have it turned off, I have a current flow coming in from the water (most marinas do have some stray current and I was just told by a guy at Blue Water that this marina is hot but a few docks down.So, I believe that if one disconnects their prop shaft from the engine and tests for a charge between the prop shaft and the engine and gets a negative volt reading, then he has an electrolysis problem. Seems I've solved most of my problem then. Yahooooo. I still have 3 ground wires that have a little continueity to the mast but that's a different problem I need to fix.Note: for zinc material to errode, electricity, either from the galvantic corrosion, or an external source, has to flow out. In flowing current will not harm that metal but if your thru hulls are bonded, then will be affected if they don't have a zinc protecting them.This is all starting to make since now. I now understand why hunter doesn't ground the green wire to the DC ground. I understand why Hunter doesn't bond all the thru hulls. I understand now why my sister boat down the dock has a fish (zinc on a wire) tied to what looks like his green wire.Thanks all.

 

[Ross]

Franklin, One method that is used

to counter galvanic corrosion is electronic. In this method the galvanic voltage is sensed and a counter voltage is applied to bring the current to a net zero. It is very complex but it does work.

 

[Landsend]

- to +

electrons flow from a negative potential to a positive potential. Thus, current flows from negative to positive. you can test this with a simple diode and a battery source. A diode is reall a one way gate.Hope this helps.

 

[Ross]

Landsend, Be careful here because

with galvanic corrosion problems You have a fundamental battery. If you are electroplating then when you apply a direct current potential between two metals in an electrolyte one will be consumed and one will gain.

 

[Landsend]

Ross... you better learn basic the basics

No matter what we're talking about, electron flow is always from a lower potential to a higher potential. Galvanic corrosion or the picture tube on your TV.

 

[Ross]

Landsend, Twenty years of electronics

employment has taught me that the flow of electrons within a battery or power supply are not the same as the flow in the load. Otherwise somewhere you will have an enormous pile of electrons around the positive terminal which would of necessity cause it to become negative. If this should happen then the flow will reverse until equilibrium is reached. Dang, I love a good debate!

 

[Franklin]

ah da ba ah da ba......

you are both right.from what I could take of the articles I posted, the flow of electricity goes from positive to negative but the flow of energy goes from negative to positive. Real confusing but it was made simple with my damn tank indicators.My tank indicators reversed the flow (of electricity, electrons, cow dodo...I don't care). It can only reverse the flow by inducing more positive current into the negative circuit in this case. So...as I said...If you want to know if you have an electrolysis problem, disconnect your negative wire from the engine (it should be on the starter or a bus bar near it) and then check for a negative volt reading (by putting the black on the prop shaft and red on the neg cable that you disconnected) and if you end up with a negative volt reading, you have an electrolysis problem. If you have a positive reading and your prop is "bonded" to other underwater metals, then they will have an electrolysis problem on your thru hulls. This is why Hunter doesn't bond it's thru-hulls because most marinas do have current flowing in the water and as along as your boat doesn't have an electrical problem, you will have current flowing into your prop shaft to the engine and into the ground system.It's amazing how people have to make things so complicated. I guess it makes them feel smart.

 

[Don12364]

Just a Thought

Hi Franklin, Digital electronic meters on their voltage ranges draw an infinitesimal amount of current. If this is what you are using then it is possible that there is no connection between battery negative and prop shaft other than a little stray leakage.May I suggest measuring the current which this stray cell can generate. Start on the 10 amps range and work towards the more sensitive ranges. If you see a current of more than a few milliamps then there really is a cell, but if not then you need to bond the pieces together. Also if, like me, you have a plastic vibration isolator in the drive chain, then this will need a flexible strap or the silver loaded rubber insert between gearbox flange and prop shaft flange. Alternatively metal/carbon brushes which run on the shaft are made for this job.It has even been known for the gearbox bearings, coated in oil, to provide insulation against a couple of volts potential difference.Apologies if you already knew all this.There's more:-On the 376 the keel (lead) is bonded to the mast strut. This connects to the mast, rigging and, by default, lifelines, pulpit, pushpit and stanchions. On the mast you probably have a VHF aerial. This will have its outer co-ax grounded to the mounting bracket which is screwed to the mast. The co-ax outer will connect to your VHF radio chassis and this, in turn, will probably be connected to battery negative. Thus --- by disconnecting the prop from the engine, you will see the electrochemical potential difference between lead and bronze. Long winded maybe but for real. I just have my prop shaft bonded to the engine and don't worry.However I did find de-zincification on my prop strut so now it too is bonded internally AND I drilled it through and fitted a small disk or saucer shape anode each side. Your boat is about the same age as mine so I suggest you try chipping at it on the edges of the mounting flange with a screwdriver to see if bits break off.BTW - My prop shaft anode lasts a whole season and I only lift out for one week a year in June when the evenings are long and the weather benign.

 

[pete]

clarify please

Frank- "red on the neg cable that you disconnected)" doesn't this cable go to the neg of the battery? If that is all it does I'm having trouble seeing why anything meaningful is going to be determined here