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I been helping a friend's yacht with AC 230V system leaking and his DC system 12V and 24V, where the 12V system is probably the one "leaking".
On yachts we call "leaking" DC current as stray current and it can eat up propellers or other underwater metal.
DC MCB/Circuit breaker does not trip when there is a leaking DC current.
This is what stray current can do :
.
The seawater or fiberglass region wet out by sea water is a decently good electrical conductor. Thus leaking DC current can travel from metal A to metal B and the metal with
lesser nobility will loose itself to the more noble metal. Like how electroplating works, electricity is the one responsible for the transfer of the coating from A to B.
Different metals has different galvanic scale. https://www.ssina.com/education/corr...nic-corrosion/
This galvanic thingy is a big deal for our cooling system where different metal are being used and the coolant is then the sort of electrolyte.
I have special AC earth leakage currentc clamp, but I do not yet own AC/DC earth leakage current clamp.
The word "earth" is equal to "ground" for AC electric works or negative if in our car...which we call it ground for cars with metal body used as negative conductor.
Those green crusties we see is not merely salty water hitting metal, such green crusty can also be the work of stray current with the help of fluid which conducts electricity...like water with dirt or road salt.
If only 2mm distance between connector pins, even tap water can conduct current...a bit.
Why would I need such DC leakage current clamp for car use ?
Well, pinched or cut or damaged wiring and wet out connectors, before it can create a true short circuit to blow the said module/device's fuse, it started as
leaking current and could be small and then grow bigger and then big enough to blow a fuse. We commonly only know there is something wrong when the fuse is blown.
I want the approach of preventive maintenance by having the capability of looking at these mild short circuit or leaking wires/connectors, where it can cause
intermittent problem you will have a hard time to find.....before it actually blow a fuse and could also blow a module, depending on where the "short" is located at.
If the short is from a fuse to a module, that is unlikely to blow a module. If the short is between a module output to its solenoid or sensor and whatever is served by the module,
our module may get damage.
The theory of finding leaking current is simple :
Be it AC or DC electrical system, it is the same.
A device consuming say 1,000 milliamps, will be carrying 1,000 mA of current from a fuse/battery/positive and back to ground/negative also the very same 1,000 mA.
If the return current is not 1,000 milliamps, that means there is another path those current took and we call that "leak".
For AC its live/phase to neutral exact same 1,000 milliamps too in and out. Any shortage of current coming back, thus have found a leaking path to earth.
In AC system, our soil is earth or return. Like our car metal body.
In the US you guys would use GFCI ( ground fault circuit interrupter ) breaker at home. By law : in bathroom, basement and water heater or any AC receptacle within 6 feet of a sink or water source.
In Europe this device is called RCCB, residual current circuit breaker. Same thing different name.
A US GFCI will trip at current leak of about 5 milliamps, in Europe or Asia our RCCD / RCBO is a 30mA rated but will trip at about 19 to 22 mA.
GFCI and RCCD uses current transfomer ( like a current clamp ) for both Live and Neutral and the imbalance between L and N is what trigger the GFCI or RCCD to trip and disconnect power.
The imbalance is the "leak".
The typical use of normal current clamp is either you clamp the neutral or live or negative or positive and you then read the current flowing on that wire.
When you clamp both L and N or Pos and Neg together, you get zero milliamps......unless there is an imbalance and the current clamp is a special one
with ultra precision to read 1 milliamps or less. Yep, it can read 0.1 milliamps, some can read 0.01 milliamps.
This video will explain better, for AC system. Do note, switching power supply has natural leak to earh a bit, usually under 3.5mA. It is from the EMI capacitor.
This is my family home in Singapore. 3 phase 230/400V , 5 wires from the Power Company. 3 of Live/phase , a neutral and a ground.
7.5 milliamps leakage, normal. See how the current clamp read all 3 live wires and neutral together .
==========
Now I got the basic explained you all. Here comes my experiment.
The set up - PART 1. Table test, to avoid any ferrous metal effect on current clamp sensor, which is a hall sensor if DC use.
Red DMM Uni-T UT60BT read total power consumed/flowing to small LED bulb and including any "leak", in milliamps
Yellow Fluke DMM 179 read only power consumed by the small LED bulb, in milliamps.
Label A - Current Clamp Owon CM2100B clamping both positive and negative wire after red DMM. This baby Owon will read "leakage" current as imbalance.
Label B - Black small wire from Red DMM is positive power, to create a 6 milliamps "leak" ( 13 volt ) using resistor of 2,040 ohms ( 680ohms x 3 in series ).
Without me doing the 6 mA leak, the current clamp will read zero milliamps ( sometimes read 1 milliamp , this is cheap current clamp , but superb )
Both DMM will read 57 milliamps (+- 0.5 milliamp). That is the power conssumption of the T10 LED bulb. As you can see 2 photos up.
When I created the "leak", red DMM will read 57+6 = 63.xx milliamps and yellow DMM stay at 57.xx mA and Owon baby clamp will read the imbalance of 6 milliamp.
.
If I do not do the "leak", the Owon will read 57 milliamps OUT and 57 milliamps IN and get zero mA because the negative and positive wire flow of current
cancel each other out because they are both the same value.
============
Doing this test on a car is much more challenging when and if under 50mA is what we want to read using current clamp.
The suspension tower is ferrous metal and that impacts the reading of the Owon current clamp at setting able to read 1 milliamp resolution.
So placement of current clamp , magnetic north heading ( yes it effects ), and frequent zero-ing is a must watch and do.
For the car test, I first use the T10 LED bulb as the "leak", it is 43-44 milliamps when at battery voltage of 12.4V loaded.
The battery positve and negative is given each a small extension cable so that I can clamp both small cables.
.
Label A - Again I have to take direct battery positive to supply the "leak".
.
Label B is the ground connection of the supposed leak.
At this point in time the car is not yet in total sleep mode, it is consuming total 2.0 ish amps as seen by the big OWON.
The baby Owon clamp is reading 41 mA, that is the imbalance which is the LED bulb the yellow DMM is reading at 43.98 mA.
That's very interesting to find out where the lost metals go. On boats lead anodes are used in multiple places to act as preferencial donor for the bras propeler.
Should the rear suspension steel arms and radiator be grounded to chassis or left floating unreferenced.
Two dissimilar metals create a current without any external power source needed.
On fiberglass boats they use sacrificial zinc anode ( not lead ) as the lowest nobility metal to be "eaten" away.
But the bonding of all underwater metal must be done right and in salt water condition often it is challenging to keep copper wire strand pristine condition towards it cable lug and
towards the metal it is connected to. https://stevedmarineconsulting.com/w...tems138_05.pdf
Cali wrote : Two dissimilar metals create a current without any external power source needed.
Yes, that is how thermocouple works, mini galvanic battery. I have 12 on them on my car monitored by Banks module.
-----------
Back to the leakage current scenatio
Depending on how a load or sensor is wired to a module, it is wired like above where the load is not using engine or car chassis as negative path, we can use the leakage current method to detect if there is any "leak".
The problem is, we never know how much power does a module consumes, and it it is dynamic for sure, not super constant within say 10-20 milliamps.
We also can not catalog their power consumtion today for use next year
So the leak test can be a great help someday.
Most 5V drivers for sensors are very low power chip. I think usually no more than 500 mA or 1,000 mA.
I think if 12V drivers also for sensors, it will not be a high power variant.
Imagine if we do have high resistance earth leak , as such the sensor reading/signal get skewed. We might blame the sensor, while the cause could be that high resistance leak of low value amperage maybe 10 to 20 milliamps.
Thus when I was on the yacht, it got me thinking the WHAT-IF scenario.
Most common earth leak on a car I would think its the oldie style spark plug wire.
The high voltage cable insulation broke down bit by bit and spark power to spark plug get reduced as the spark power leaked out to cylinder head too.
Now we use COP, the equivalent spark plug wire is now the 15cm ish rubber boot of the COP.
Above rubber boot will leak overtime too.
-------
For our M276/M278/M157 direct injection, the highest voltage flowing on our small wire is only for the GDI injector at approx 140-150 volts.
Not bad, 390 watts of short burst.
If by insulation failure, the COP and wires to injectors are what we need to watch as the engine aged.
Basically the injector wires are at unhappy underhood 80-90C ambient temperature all day long when engine is driven already 30+ minutes for guys like me in the 30-32C ambient temperature
of the tropics and not to mention insane 85% or more humidity all year round.
I think most common leak occuring will be those wet out connector, mild water ingress and then green crusty and leak get worse and woser as crusty build up.
If damaged wire or pinched wire is a possibility but for what I am seeing, unless you messed up your car wiring harness locking/securing position, W212 E400 of mine seems to have
a very good wiring securing and routing and protection jacket.... but Uncle Murphy still may pay you a visit.
--------
This is my not-so-close friend's yacht oldie generator already failing at its winding insulation. This send mild electrocution to passenger when at the right time, like wet splashy ride at sea.
Hence I was helping him, as this is a matter of life and death and not financial.
For now , I don't usually troubleshoot yachts when I am not close to the owner as friends, I dont sell my services anymore to Tom , Dick or Harry. I only do it if it owner is a friend and it will usually be FOC.
0.5 megaohm insulation value at 500V test voltage for a 230V single phase marine generator at its live or neutral winding to its chassis ( earth ) is BAD !!!
This is what been lthe low voltage/current electrocuting passengers.
Well above 10 mega ohms is what it need to be. In humid engine room in the tropics, one can't expect superb value like in drier countries or home use generator.
----------
I do still enjoy troubleshooting on yachts and now I can bring over the questions I have on those yachts to our car
The WHAT-IF.
I know EV cars have very good earth leak monitoring system in place, of course they should.
Those batteries can be 200-800V DC, damn !!!!!! I respect anything close to 1,000 volts and DC has more killing power than AC, no joke.
I fear 20,000 volts system.
------------
So, I hope one day, this DC leak testing method might come handy.
Last edited by S-Prihadi; May 12, 2025 at 03:55 AM.
I been helping a friend's yacht with AC 230V system leaking and his DC system 12V and 24V, where the 12V system is probably the one "leaking".
On yachts we call "leaking" DC current as stray current and it can eat up propellers or other underwater metal.
DC MCB/Circuit breaker does not trip when there is a leaking DC current.
This is what stray current can do :
.
The seawater or fiberglass region wet out by sea water is a decently good electrical conductor. Thus leaking DC current can travel from metal A to metal B and the metal with
lesser nobility will loose itself to the more noble metal. Like how electroplating works, electricity is the one responsible for the transfer of the coating from A to B.
Different metals has different galvanic scale. https://www.ssina.com/education/corr...nic-corrosion/
This galvanic thingy is a big deal for our cooling system where different metal are being used and the coolant is then the sort of electrolyte.
I have special AC earth leakage currentc clamp, but I do not yet own AC/DC earth leakage current clamp.
The word "earth" is equal to "ground" for AC electric works or negative if in our car...which we call it ground for cars with metal body used as negative conductor.
Those green crusties we see is not merely salty water hitting metal, such green crusty can also be the work of stray current with the help of fluid which conducts electricity...like water with dirt or road salt.
If only 2mm distance between connector pins, even tap water can conduct current...a bit.
Why would I need such DC leakage current clamp for car use ?
Well, pinched or cut or damaged wiring and wet out connectors, before it can create a true short circuit to blow the said module/device's fuse, it started as
leaking current and could be small and then grow bigger and then big enough to blow a fuse. We commonly only know there is something wrong when the fuse is blown.
I want the approach of preventive maintenance by having the capability of looking at these mild short circuit or leaking wires/connectors, where it can cause
intermittent problem you will have a hard time to find.....before it actually blow a fuse and could also blow a module, depending on where the "short" is located at.
If the short is from a fuse to a module, that is unlikely to blow a module. If the short is between a module output to its solenoid or sensor and whatever is served by the module,
our module may get damage.
The theory of finding leaking current is simple :
Be it AC or DC electrical system, it is the same.
A device consuming say 1,000 milliamps, will be carrying 1,000 mA of current from a fuse/battery/positive and back to ground/negative also the very same 1,000 mA.
If the return current is not 1,000 milliamps, that means there is another path those current took and we call that "leak".
For AC its live/phase to neutral exact same 1,000 milliamps too in and out. Any shortage of current coming back, thus have found a leaking path to earth.
In AC system, our soil is earth or return. Like our car metal body.
In the US you guys would use GFCI ( ground fault circuit interrupter ) breaker at home. By law : in bathroom, basement and water heater or any AC receptacle within 6 feet of a sink or water source.
In Europe this device is called RCCB, residual current circuit breaker. Same thing different name.
A US GFCI will trip at current leak of about 5 milliamps, in Europe or Asia our RCCD / RCBO is a 30mA rated but will trip at about 19 to 22 mA.
GFCI and RCCD uses current transfomer ( like a current clamp ) for both Live and Neutral and the imbalance between L and N is what trigger the GFCI or RCCD to trip and disconnect power.
The imbalance is the "leak".
The typical use of normal current clamp is either you clamp the neutral or live or negative or positive and you then read the current flowing on that wire.
When you clamp both L and N or Pos and Neg together, you get zero milliamps......unless there is an imbalance and the current clamp is a special one
with ultra precision to read 1 milliamps or less. Yep, it can read 0.1 milliamps, some can read 0.01 milliamps.
This video will explain better, for AC system. Do note, switching power supply has natural leak to earh a bit, usually under 3.5mA. It is from the EMI capacitor. https://youtu.be/VH1S8Up5Zd8
This is my family home in Singapore. 3 phase 230/400V , 5 wires from the Power Company. 3 of Live/phase , a neutral and a ground.
7.5 milliamps leakage, normal. See how the current clamp read all 3 live wires and neutral together .
==========
Now I got the basic explained you all. Here comes my experiment.
The set up - PART 1. Table test, to avoid any ferrous metal effect on current clamp sensor, which is a hall sensor if DC use.
Red DMM Uni-T UT60BT read total power consumed/flowing to small LED bulb and including any "leak", in milliamps
Yellow Fluke DMM 179 read only power consumed by the small LED bulb, in milliamps.
Label A - Current Clamp Owon CM2100B clamping both positive and negative wire after red DMM. This baby Owon will read "leakage" current as imbalance.
Label B - Black small wire from Red DMM is positive power, to create a 6 milliamps "leak" ( 13 volt ) using resistor of 2,040 ohms ( 680ohms x 3 in series ).
Without me doing the 6 mA leak, the current clamp will read zero milliamps ( sometimes read 1 milliamp , this is cheap current clamp , but superb )
Both DMM will read 57 milliamps (+- 0.5 milliamp). That is the power conssumption of the T10 LED bulb. As you can see 2 photos up.
When I created the "leak", red DMM will read 57+6 = 63.xx milliamps and yellow DMM stay at 57.xx mA and Owon baby clamp will read the imbalance of 6 milliamp.
.
If I do not do the "leak", the Owon will read 57 milliamps OUT and 57 milliamps IN and get zero mA because the negative and positive wire flow of current
cancel each other out because they are both the same value.
============
Doing this test on a car is much more challenging when and if under 50mA is what we want to read using current clamp.
The suspension tower is ferrous metal and that impacts the reading of the Owon current clamp at setting able to read 1 milliamp resolution.
So placement of current clamp , magnetic north heading ( yes it effects ), and frequent zero-ing is a must watch and do.
For the car test, I first use the T10 LED bulb as the "leak", it is 43-44 milliamps when at battery voltage of 12.4V loaded.
The battery positve and negative is given each a small extension cable so that I can clamp both small cables.
.
Label A - Again I have to take direct battery positive to supply the "leak".
.
Label B is the ground connection of the supposed leak.
At this point in time the car is not yet in total sleep mode, it is consuming total 2.0 ish amps as seen by the big OWON.
The baby Owon clamp is reading 41 mA, that is the imbalance which is the LED bulb the yellow DMM is reading at 43.98 mA.
Leak stopped, below
I created the leak again, below :
Will continue..................
When a vessel suffers propeller cavitation the material’s surface is subjected to a continuous bombardment of impacts from a fluctuating pressure field.
Cavitation is a different thing.
Even water pump impeller can get cavitation when too much resistance in the suction.
Its metal pitting result is unlike stray current.
Well designed propeller on a proper yacht and bottom is clean, props do not cavitate.
==========
Back to the test again...........
2nd method using double ampmeter , 2 DMMs , one at negative wire and one at positive wire........ but limited to 10 amps maximum.
This time I use 6 milliamps load
Current clamp still can read 6 mA imbalance but not as good as when on wooden table.
Car is already sleeping at about 27 milliamps, almost deep sleep ( 5 milliamps is the deep sleep ) and big OWON can't read too low a current thus showing 0.01 amp.
.
Hioki below is only for current load of the resistor
.
.
Last edited by S-Prihadi; May 12, 2025 at 11:22 AM.
Cavitation is a different thing.
Even water pump impeller can get cavitation when too much resistance in the suction.
Its metal pitting result is unlike stray current.
Well designed propeller on a proper yacht and bottom is clean, props do not cavitate.
==========
Back to the test again...........
2nd method using double ampmeter , 2 DMMs , one at negative wire and one at positive wire........ but limited to 10 amps maximum.
This time I use 6 milliamps load
Current clamp still can read 6 mA imbalance but not as good as when on wooden table.
Car is already sleeping at about 27 milliamps, almost deep sleep ( 5 milliamps is the deep sleep ) and big OWON can't read too low a current thus showing 0.01 amp.
.
Hioki below is only for current load of the resistor
.
.
Cavitation does't start " when too much resistance in the suction". This is one of most complex phenomenon and only very few can keep it manageable.
In the EU one of the most powerful MB engine was 420CDI with million sollution for a simple cavitation happening on cylinders cooling part.
Experiment with a swimming pool pump , with a suitable "adjustable" manifold system on suction side we can create cavitation on the impeller, not for plumbing after the impeller.
Engine cooling system various channels is another different beast.
Some marine diesel engine, its water cooled liner can get cavitation damage, the bubbles imploding.
I think that is the cavitation you speak of.
I am here discussing leakage current and as to why you bring up cavitation.... I don't understand ?
One tip : For yachts related system and electrical video or books, go for Nigel Calder and not Mr Lopez.
Why don't you contribute something postive to this thread for automotive type leakage current you have encountered and measured its magnitude,
that will be helpful for us non techy.
BTW,
Yesterday, I saw a weird signature ( at the bottom of your post, that is Signature isn't it ? ) on you post, which you have deleted today. Its about someone seemingly doing something to your business, someone you call "Peter the Nigerian" stealing something ?? And the about calling the Police yada yada.
Something along that line . It reads really weird , like you are frustrated. It is not my business to screen capture such signature.
However, my advice to you is, please do not bring in your personal problems to this forum.....if you have any.
We are here as friends sharing knowledge and asking for knowlegde.
Could be my racism the reason for why your picture with the propeller looks exactly like it was eaten by the bubbles?
That's my opinion I don't claim anything more, that's not sharing?
Cavitation pitting or erosion is different to stray current, does look similar when beginning to happen.
This is one example of cavitation damage. Propeller edge and center hub is where usually it cavitate.
Where pressure change the most and very sudden, that's usually where the bubbles implode and caused super heat to eat metal.....called cavitation.
Some propellers uses mild cupping at the edge to reduce cavitation.
Your wrote : Could be my racism the reason for why your picture with the propeller looks exactly like it was eaten by the bubbles? what is there to be racist about ?
.
Anyway, do share your car leakage current findings with us, the type which does not blow fuse but effecting module operation.
So we can stay on topic.
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
, but superb )
