AC voltage measured between negative battery terminal and ground

[senormechanico]

Sounds like the inverter is not a split phase output, so no "center tap" ground reference. That would make the symptoms you have.
Jedi is (imho) hinting at the same thing.

[Nor]

Originally Posted by s/v Jedi

Exactly. Ghost reading

If you take something like a screwdriver and test against the metal of that, do you also get the reading? Do you have that metal bonded to something else?

No reading between a screwdriver and the chair. As far as I can see the chair is not connected to other boat ground.

Originally Posted by s/v Jedi

So you said you felt tingling when touching battery negative? Set meter to resistance and measure between metal and battery terminals as well as inverter housing. If the reading is infinite or MegaOhms, repeat the measurements described below for DC as well.

Infinite reading between battery terminals and the chair metal.

Originally Posted by s/v Jedi

Configure meter to measure AC current, put one probe on battery negative and the other on the metal. Same for positive.

The meter only has one setting for current (not sure if AC or DC). I measure 0.56 when the scale is set to 2M.

[Nor]

Originally Posted by senormechanico

Sounds like the inverter is not a split phase output, so no "center tap" ground reference. That would make the symptoms you have.
Jedi is (imho) hinting at the same thing.

The inverter is the Victron Multi RS 6000. I'm not sure if the electrician has connected the output ground correctly. However the instructions says that it will connect earth to negative when in inverter mode and no AC connected.

[s/v Jedi]

Originally Posted by Nor

The meter only has one setting for current (not sure if AC or DC). I measure 0.56 when the scale is set to 2M.

Oh… I recommend you find someone to help you with this install. You must be able to tell for sure if the chair is electrically connected to something and you must have a decent meter, as well as an understanding of basic laws of electricity and how circuits work.

[Nor]

Originally Posted by s/v Jedi

Oh… I recommend you find someone to help you with this install. You must be able to tell for sure if the chair is electrically connected to something and you must have a decent meter, as well as an understanding of basic laws of electricity and how circuits work.

Thanks, yes I'm hoping to have the electrician come back today to check this out. But I'd like to learn also more for myself about this.

I read on the Victron website about IT and TT network, and for me it appears I have a IT network now, at least when only using the inverter.

https://www.victronenergy.com/media/...al-safety.html

I had another look at the helm chair. I'm 99% sure it's not electrically connected to anything, (but a small chance there could be a ground wire on the underside of the feet under the fiberglass, if that's common to have, it's difficult to get access to see that there).

[Nor]

I got an electrician to come here. He's the main guy around here and quite knowledgable of marine systems. He grounded the inverter chassis, and said (as several of you had mentioned) that the measured voltage from 48V battery to ground was a phantom reading.

There are however a few things I don't understand or follow.
The AC output from the inverter that goes to the breakers don't have the earth wire connected. He said we shouldn't, as the inverter is already grounded.
The AC input (from generator/shore - not currently connected) also doesn't have the ground wire connected. Is this normal?

The outlets has the ground cable connected, it goes into the breaker box. But the breaker box is not grounded, and as mentioned the connection from there to the inverter doesn't have the ground cable connected. So I don't see how the outlets can be grounded?

[moseriw]

Well maybe I'am missing something but the inverter usually serves the AC net on board and therefore it is usually grounded via the breakers and the GFCI.

So, if your DC minus has AC too there is something terrible wrong with your wiring aboard. Yes, it is a logical guess that the AC earth is grounded to a plate at the hull and the DC minus is connected to this plate too. or you have broken cables somewhere in the wiring that connects DC minus to AC Earth.

Btw... some installation howto's say that DC minus should always be connected to the grounding plate too. OR maybe the sacrifying anode?

Good luck..

[GypsyOwner]

Probably you were seeing ‘ghost’ AC voltage jumping across the tiny stray capacitance that is always present between wires. Probably if you short the floating DC- to the boat -ve there is no power behind it; the current will be nano-Amps and the AC voltage difference will drop to zero. BUT…

Electrical and electronic equipment such as chargers or inverters have to pass radio-frequency emissions testing. This is to make sure that when you turn the device on, unwanted high frequency RF emissions do not upset your neighbour’s TV and stop your wi-fi from working. It can be a hard test to pass.

The usual trick is to shove your circuit in a metal box and earth it, then add some blocking components on the way in and out to stop the high frequencies escaping down the wires. You cannot easily do this on an IT system if there is no earth.

So some manufacturers resort to the dubious practice of deliberately adding very small capacitors between the DC + and - and the AC. Both to live and neutral. You can legally do this if they are high voltage capacitors and of small enough value to be ‘safe’ (and not nuisance-trip any RCDs). Different countries have different views on what ‘safe’ is but a mA or less usually does the trick.
This does 2 things:
1) If you are lucky, the nasty unwanted RF voltages settle down and you start to pass the RF emissions tests. You can now stamp your product with that vital CE or FCC mark and ship it
(If you are unlucky nasty unwanted RF currents go up and the emissions are worse)
2) The DC section now tries to float at 1/2 the AC voltage so 120V in Europe, 60V in the US. Touch it and it tingles as 1/2 a mA flows into your sweaty hand

How do I know this? I design this stuff. I have also seen sparks plugging in DC power supplies I bought for home use so I pulled them apart to investigate. And it’s interesting to pull apart competitor’s and supplier’s designs to see what NOT to do

[GypsyOwner]

Originally Posted by GypsyOwner

Probably you were seeing ‘ghost’ AC voltage jumping across the tiny stray capacitance that is always present between wires. Probably if you short the floating DC- to the boat -ve there is no power behind it; the current will be nano-Amps and the AC voltage difference will drop to zero. BUT…

Electrical and electronic equipment such as chargers or inverters have to pass radio-frequency emissions testing. This is to make sure that when you turn the device on, unwanted high frequency RF emissions do not upset your neighbour’s TV and stop your wi-fi from working. It can be a hard test to pass.

The usual trick is to shove your circuit in a metal box and earth it, then add some blocking components on the way in and out to stop the high frequencies escaping down the wires. You cannot easily do this on an IT system if there is no earth.

So some manufacturers resort to the dubious practice of deliberately adding very small capacitors between the DC + and - and the AC. Both to live and neutral. You can legally do this if they are high voltage capacitors and of small enough value to be ‘safe’ (and not nuisance-trip any RCDs). Different countries have different views on what ‘safe’ is but a mA or less usually does the trick.
This does 2 things:
1) If you are lucky, the nasty unwanted RF voltages settle down and you start to pass the RF emissions tests. You can now stamp your product with that vital CE or FCC mark and ship it
(If you are unlucky nasty unwanted RF currents go up and the emissions are worse)
2) The DC section now tries to float at 1/2 the AC voltage so 120V in Europe, 60V in the US. Touch it and it tingles as 1/2 a mA flows into your sweaty hand

How do I know this? I design this stuff. I have also seen sparks plugging in DC power supplies I bought for home use so I pulled them apart to investigate. And it’s interesting to pull apart competitor’s and supplier’s designs to see what NOT to do

I am going to reply to my own quote here to hopefully shine some light on these murky subjects

The people who design electronic and electrical equipment have one set of skills and are bound by a set of industry rules to keep things legally safe. They work in companies that have customers that want a cheap product and shareholders that want a big profit. They are supervised by bosses who try to balance all these things, but are generally judged and paid by how quickly they can get stuff out of the door.
Electronic/Electrical Design Engineers operate in a clean, theoretical world where you are trying to make a million identical units that are safe good and cheap. (For us to make, not necessarily for you to buy).

The Installers have another set of skills. They need to deal with a new set of practical wiring problems every day and they have to operate in a real world of broken, damp, previously-miswired stuff. And deal with overbearing boat owners who want the thing done instantly with no dust or mess. They have similar pressures from bosses. They are also working blind, not given 1% of the information about the product they are installing that the Engineers who design it have. I have huge admiration for the installers. They are the real creatives!

The two sides SELDOM MEET! Well, they sometimes do by accident round a dockside bar and then they go ‘ah so that’s why we get stuff returned all burnt out’ or ‘so that’s why the thing blew up when I wired it like that’.

So what is the take-away from all this? You should obey your local wiring laws and the instructions on the box. Normally they will agree pretty well.
But you should know that the boxes you are buying are a best effort to meet lots of conflicting obligations. There is a bit of wiggle-room in the regulations that may mean the boxes you buy do things that occasionally confuse the installers. Sorry if this is not the clear-cut black and white message you want to hear, but there may be all sorts of unexpected connections (big value 1Meg Rs and small value 1nF Cs) are built in by the designers of the equipment that link the AC and DC sides in funny ways inside the boxes you are buying. They are there for various reasons like damping RF emissions so your VHF still works when your inverter is on
For example: I sent back the WD external disk drive main power supply that sparked when I plugged it into my PC’s USB socket. It had 120V AC between the USB plug and my earthed PC metal case (European 240V mains). 1 mA AC flowed between the two when I carefully measured it with my meter. They sent me another one. It had the same behaviour. IT WAS DESIGNED LIKE THAT and perfectly legal. I’ve seen marine chargers do the same thing

If you see two installers arguing about the best way to wire (ground?) something, they may both be right (and what is right may vary from job to job and boat to boat). And unfortunately you’ll never know who is right because the designers are forbidden from showing anybody the circuit diagrams. And the installers may be prioritising the problem of the day (stopping RCD trips on the Marina / stopping that annoying buzz on the VHF might require that ground connection be snipped or wired back in place)

Generally the installers have a good nose about this kind of thing and can tell the difference between a bit or harmless leakage and a bloody dangerous AC fault. So trust what they say, but let them touch that ‘harmless’ floating DC ground first before you do! They’ve got insurance for that type of thing. And very thick rubber boots!





One last thing. I never resorted to putting shonky capacitors to the mains to fix my RF problems. Honest! Put holes or pads for them ‘just in case’ but never had to fit them. Got questioned about why my designs have an extra $0.5 of extra metal shields and ferrites, but I always sailed through those RF emissions tests. You get what you pay for

[Nor]

Originally Posted by GypsyOwner

Probably you were seeing ‘ghost’ AC voltage jumping across the tiny stray capacitance that is always present between wires. Probably if you short the floating DC- to the boat -ve there is no power behind it; the current will be nano-Amps and the AC voltage difference will drop to zero. BUT…

Electrical and electronic equipment such as chargers or inverters have to pass radio-frequency emissions testing. This is to make sure that when you turn the device on, unwanted high frequency RF emissions do not upset your neighbour’s TV and stop your wi-fi from working. It can be a hard test to pass.

The usual trick is to shove your circuit in a metal box and earth it, then add some blocking components on the way in and out to stop the high frequencies escaping down the wires. You cannot easily do this on an IT system if there is no earth.

So some manufacturers resort to the dubious practice of deliberately adding very small capacitors between the DC + and - and the AC. Both to live and neutral. You can legally do this if they are high voltage capacitors and of small enough value to be ‘safe’ (and not nuisance-trip any RCDs). Different countries have different views on what ‘safe’ is but a mA or less usually does the trick.
This does 2 things:
1) If you are lucky, the nasty unwanted RF voltages settle down and you start to pass the RF emissions tests. You can now stamp your product with that vital CE or FCC mark and ship it
(If you are unlucky nasty unwanted RF currents go up and the emissions are worse)
2) The DC section now tries to float at 1/2 the AC voltage so 120V in Europe, 60V in the US. Touch it and it tingles as 1/2 a mA flows into your sweaty hand

How do I know this? I design this stuff. I have also seen sparks plugging in DC power supplies I bought for home use so I pulled them apart to investigate. And it’s interesting to pull apart competitor’s and supplier’s designs to see what NOT to do

That's very interesting!
I got some measurements also when only the Victron inverter was connected to the batteries. Is Victron one of those companies you talk about that add a capacitors to solve emissions?

[GypsyOwner]

Originally Posted by Nor

That's very interesting!
I got some measurements also when only the Victron inverter was connected to the batteries. Is Victron one of those companies you talk about that add a capacitors to solve emissions?

I saw it with CTEK chargers for cars/boats and Western Digital external hard drive power supplies for PCs. Didn’t test Victron. It was some time ago so these designs may have changed. Not accusing these companies of shipping faulty goods BTW. They’ll be carefully acting within the law to deliver a balance of good performance to you

If you are a skilled professional and have some basic test equipment you can probe for off-state DC stray voltage, resistance,, capacitance, isolation breakdown voltage to assess likely state of the unit (highly insulated, deliberately leaky by design for RF reasons, dangerously faulty) and then go on to measure AC leakage voltage and even the AC leakage current itself if you are careful. You can then compare to local laws if you know them.
Was going to describe the procedure in detail but had second thoughts - don’t want someone getting over-confident and killing themselves or blowing up their equipment

[GypsyOwner]

BTW lots of other good answers previously - you have to consider the thing as part of a much wider system - one that your installer will be well-equipped to investigate (and will know more than me on these matters)

Just filling in some gaps in what goes on inside these power supply boxes that the manufacturers will not necessarily tell you (they might say something like ‘2kV isolation’ in accordance with some wiring code that specs max AC leakage if you look it up, but won’t tell you about the small 2kV X and Y capacitors they may fitted between AC and DC to damp the RF - too much detail).
These things, if fitted, are detectable externally by probing and they are pretty easy to spot if you break the box open. There will be an obvious dividing line from AC to DC side only crossed by magnetics, optos and just maybe RF capacitors