There goes battery charger number 3!

[stranded]

Can I join back in now!

OK, so I am on the boat. The wiring at the back of the ammeter looks very like that in pvb's diagram.There seems to be a power supply for the light, which also runs onto the voltmeter. The lights work. I am unable to measure any voltage at the sensor terminals on the ammeter, having progressively turned my multimeter down to its lowest setting. so hopefully that settles that I have bugger end it. Minor issue.

I have also found a connection which I think must mean that the boat has the undesirable 'common ground'. It has 6 large blue cables attached to a post bolted onto a wooden bulkhead between the service and engine banks. They are held on by a big nut that was very loose, almost falling off, which I have tightened up. Two are definitely the negatives from the service and engine batteries. The third is presumably from the bow thruster battery. It is not clear where the other three go.

It sounds like there is a chance at least that one or other or both of tightening the nut on the ?common ground point, and taking the broken shunt out of the system, might have resolved the issue, but is there a way of testing that without risking connecting the Ctek charger into the system?

 

[pvb]

Perhaps then you would care to explain how this one will work. It only has two terminals. there is no provision to connect 12 volts or any other power supply

Gosh, Vic, that's an old one! It will most likely be a moving iron or moving magnet mechanism inside, with the whole current passing through the meter. Because of this, meters of this type tend to only read fairly small currents, such as the 15A max of the one you've illustrated.

Many old motor cruisers have something like this on the instrument panel, sometimes reading up to 50A, but it means all the current is flowing through long cables up to the instruments and back, which isn't considered very efficient these days.

 

[PaulRainbow]

I can't see anything undesirable about having all of the negatives connected together in the way you describe. The three cables that you can't identify are likely to be connected to the engine/s and negative busbars for your various systems.

I'd say that the loose nut could well have caused our problems, more likely that than the ammeter shunt. I can't see a way of verifying that other than connecting the charger though.

What i would do before trying it though is to check every connection to batteries, isolator switches, breakers etc. Put a spanner on every bolt on connection you can find.

 

[PaulRainbow]

Gosh, Vic, that's an old one! It will most likely be a moving iron or moving magnet mechanism inside, with the whole current passing through the meter. Because of this, meters of this type tend to only read fairly small currents, such as the 15A max of the one you've illustrated.

Many old motor cruisers have something like this on the instrument panel, sometimes reading up to 50A, but it means all the current is flowing through long cables up to the instruments and back, which isn't considered very efficient these days.

I've got one of those. Was probably state of the art in the 80's

 

[pvb]

Can I join back in now!

OK, so I am on the boat. The wiring at the back of the ammeter looks very like that in pvb's diagram.There seems to be a power supply for the light, which also runs onto the voltmeter. The lights work. I am unable to measure any voltage at the sensor terminals on the ammeter, having progressively turned my multimeter down to its lowest setting. so hopefully that settles that I have bugger end it. Minor issue.

I have also found a connection which I think must mean that the boat has the undesirable 'common ground'. It has 6 large blue cables attached to a post bolted onto a wooden bulkhead between the service and engine banks. They are held on by a big nut that was very loose, almost falling off, which I have tightened up. Two are definitely the negatives from the service and engine batteries. The third is presumably from the bow thruster battery. It is not clear where the other three go.

It sounds like there is a chance at least that one or other or both of tightening the nut on the ?common ground point, and taking the broken shunt out of the system, might have resolved the issue, but is there a way of testing that without risking connecting the Ctek charger into the system?

Welcome back!

You shouldn't be able to measure any current on the sensing wires if the ammeter is disconnected from the shunt.

Don't see why you think it's undesirable to have a common ground. Most boats have a common ground system, often using the engine block as a convenient place to attach battery negatives. If yours wasn't securely connected, it could have caused problems.

 

[pvb]

I've got one of those. Was probably state of the art in the 80's

I think it was state of the art in the 50s!

 

[PaulRainbow]

I think it was state of the art in the 50s!

Ouch !!

 

[RichardS]

Well I wasn't looking for an argument but suggesting that you can burn out an ammeter with the shunt removed when removing the shunt disconnects the ammeter from the supply completely is just daft. Calling it misleading was perhaps my effort at being polite.

I always thought that the ammeter was wired in parallel to the shunt. Therefore removal of the shunt (alone) from the circuit would force the entire current through the ammeter. Richard was seeking to help and, even if he is wrong (and I have no reason to believe he is), it doesn't warrant that retort.

Oh dear no pvb! Sorry I should have made it clear that I was sniping at Richard not you and I agree that you are only trying to help. The problem here as always is that if you dare to disagree with anyone (Richard in this case) they take umbrage and start to get personal. All I said originally was that his posts were perhaps misleading. IMHO they were in suggesting that the OP had removed the shunt and left the gauge in circuit which he clearly hadn't and rabbiting on about two shunts when the OP only had one. Also when trying to make an explanation simple for the OP I was perhaps oversimplifying. When I read the original post I removed reference to current in the sensing wires as I predicted someone would point out the difference between voltage and amperage. When I said the voltage across the shunt would not change I should have said "The voltage though the shunt to main supplies would not change to any appreciable extent" I was not talking about the gauge sensor wires. It's very difficult to be so precise that misunderstandings are eliminated entirely. So sorry..... not you!

Mike .... why can't you just accept that you are 100% out of order here. You are the only person who is "mistaken", has become "personal" and the only one to do any "sniping". For someone of your age to act in such a childish manner is quite dispiriting.

Perhaps Poecheng is also mistaken?

Richard

 

[stranded]

Mike .... why can't you just accept that you are 100% out of order here. You are the only person who is "mistaken", has become "personal" and the only one to do any "sniping". For someone of your age to act in such a childish manner is quite dispiriting.

Perhaps Poecheng is also mistaken?

Richard

I think on my shunt, Mike is right if I have understood the disagreement correctly. The sensor cables which parallel the meter are connected directly to the big metal block at either end of the shunt, so by removing the negative cables from shunt you necessarily also disconnect the sensor cables. Is that what you meant?

Anyway, I have connected the charger now and am running the fridge on high to give it some work to do. If that runs ok for an hour I'll start the engine and see if that tries to draw on the domestic bank again.

Yes pvb's, I think I was confusing myself over the undesirable common ground - from a quick read of my marine electrics bible (which might as well be written in Chinese) the controversy is over common ground for AC and do - is that right?

 

[RichardS]

I think on my shunt, Mike is right if I have understood the disagreement correctly. The sensor cables which parallel the meter are connected directly to the big metal block at either end of the shunt, so by removing the negative cables from shunt you necessarily also disconnect the sensor cables. Is that what you meant?

I've no idea. All I have ever said is that if you try and operate the electrics with the shunt disconnected (or badly damaged, of course) then you run the risk of frying your ammeter. You've now confirmed that this is what has happened.

I've also no idea why Mike thinks "suggesting that you can burn out an ammeter with the shunt removed when removing the shunt disconnects the ammeter from the supply completely is just daft" but he appears to be sticking to his guns.

Richard

 

[pvb]

Yes pvb's, I think I was confusing myself over the undesirable common ground - from a quick read of my marine electrics bible (which might as well be written in Chinese) the controversy is over common ground for AC and do - is that right?

Ah, yes, you could be getting confused by that. Connecting AC ground to DC ground is a safety measure, and is prescribed by many authorities. However, many posters seem to think it's wrong. Their boats; their lives; their choice.

 

[stranded]

Ah, yes, you could be getting confused by that. Connecting AC ground to DC ground is a safety measure, and is prescribed by many authorities. However, many posters seem to think it's wrong. Their boats; their lives; their choice.

Anyway, an enormous thank you to everyone who has taken the time to offer a view - so far, so good. And I now know more about shunts than any none electrics man should!

 

[stranded]

A further update. The Mass Combi charger is on its way back from Mastervolt. Apparently there is nothing wrong with it - "I must have turned it off wrong (on the unit rather than the Masterview screen)'! Which rather ignores what I should have thought was the fairly pertinent fact that I didn't switch it off at all, or at least not until after it 'switched itself off' in clouds of smoke. Is it really possible that such an event would leave no trace inside the unit?

 

[Ruffles]

Thanks Rob. We're getting way beyond my electrical knowledge here, but just had a quick look at Wikipedia. ...

The reason I ask is that unearthed 'mobile' devices powered by switch mode power supplies can have problems. I have a laptop with an unearthed PSU that will tingle against bare legs. It's because though the output is only 20v or so that 20v is allowed to float relative to earth and capacitive coupling through the supply can allow a high impedance voltage to appear on the outside of the laptop. It's not dangerous to people because the current is tiny. But it can take out electronics.

Now a boat is effectively a mobile device! Is the 0v of the charger bound to the AC earth in anyway? Internally or externally via one of those posh galvanic isolators. Assuming you still have a working charger what do you measure with a high impedance DVM between AC earth and battery 0v?