This is gonna be somewhat of a 12volt question. I have a onboard battery charger on my boat, three prong on charger and three prong plugging into it. I'm getting 36 volts on the A/C side of my meter if I touch my metal bld to any metal part of the boat when the charger is plugged in. Unplug the charger and the voltage goes away. The way I found it was my daughter touched the metal rail with her forearm and felt a light tingle. I put a 12 volt light tester on the metal and it barely and I mean just barely glows. I would think if it was a true 36 volts the bulb would be very bright. Also this is the second charger I thought at first maybe the charger was bad. Any ideas? Thanks
Phantom voltage question
- Thread starter 1haz
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ptonsparky
Tom
- Occupation
- EC - retired
IMO, if you can feel it, it is not phantom. You may not have the full 36 volts when you put another load in parallel with your meter. VD.
I agree but what I don't understand is how 120 volt charger can cause voltage to leak but when I run the boat from the batteries I get no leak how is the charger creating voltage on the metal items of the boat
mike_kilroy
Senior Member
- Location
- United States
Likely a corroded ground wire somewhere, certainly not uncommon around water, docks, and boats. To help guide you in finding it requires accurate info.
You put your bid? on metal boat part does not help narrow down where the issue is. Your meter has two leads. I ASSume you put one lead onto some metal part of your boat. WHERE would be very useful to know. I could ASSume it was the same exact metal spot your daughter felt the tingle at? Sorta important to know.
But even MORE important to know is where was the OTHER meter lead at the time you saw 36Vac? In the air? In your hand (using you as a ground)? touching the charger case? shoved into the ground hole of the outlet? over the side in the water? Without this lead's exact location, no one will be able to help guide you to find the suspected corroded ground wire.
Another good clue to help find the missing ground wire would be what ELSE did your daughter touch while feeling the tingle? She probably was in contact with another metal item on your boat that still has a good ground, or perhaps she was grounded by having part of her body in the grounded water outside the boat? Pretty important clue to help solve the missing ground quicker.
BTW, most units like your charger have filter capacitors from each phase to ground terminal; this can feed your 36v to ground easily. So the missing ground connection somewhere on your boat (or in the dock outlet) is allowing this small current to not be sent back to the dock's ground.
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The boat is sitting on concrete under a metal building. When I plug my 3 wire cord (with correct polarity) into the three wire 2nd battery charger and I hold my meter in my hand or lay it on the concrete slab and put one lead on the metal building and the other lead on any metal part of the boat I get 36 volts on the A/C side of meter. If I touch the prongs on the leads it goes away or unplugging the charger it goes away. Why would it not energize from the batteries when I turn the battery switch on and unplug the charger if I had a bad ground on the boat? Why only when it's plugged into a 120v source?
kwired
Electron manager
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- NE Nebraska
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- EC
You are extending the equipment grounding conductor to your boat. Exactly what it is bonded to within the boat IDK, but if it is a metal hull boat, very likely a lot of things.
My guess is you have voltage between the neutral, EGC (or both depending on some conditions we yet don't have information on) and the metal shed. If your battery charger is the only load at the time this is happening then it will go away when you unplug the battery charger. Try plugging in some other load and measure voltage from EGC to the metal shed. Measure ungrounded to grounded conductor voltage as well with a load on it. Could be that you have a bad neutral and if there is no separate EGC (allowed on older installs) you are raising the voltage to ground on everything bonded to that neutral whenever there is a connected load.
My guess is you have voltage between the neutral, EGC (or both depending on some conditions we yet don't have information on) and the metal shed. If your battery charger is the only load at the time this is happening then it will go away when you unplug the battery charger. Try plugging in some other load and measure voltage from EGC to the metal shed. Measure ungrounded to grounded conductor voltage as well with a load on it. Could be that you have a bad neutral and if there is no separate EGC (allowed on older installs) you are raising the voltage to ground on everything bonded to that neutral whenever there is a connected load.
The boat hull is all fiberglass just your typical metal objects like rub rail, screws, tie downs etc are metal. I have also plugged it into a separate Outlet and a separate extension cords. If I plug other metal items into the same plug with the same extension cord I do not have any voltage. I do not get any voltage from neutral to ground on the receptacle or the extension cord
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Are metal items electrically connected to one another? Like say some metal framing/reinforcement members also have metal trim pieces fastened to them. And if so do these tie to the battery charger in any way? If you do have that does that frame have continuity to the EGC for the battery charger input? No continuity to EGC and a fault on line side of battery charger equipment is a possibility if you said yes to most of those questions.
There is no continuity between cord on charger and metal on the boat. It is my understanding that a boat is suppose to have all metal objects grounded and tied together tho, similar to pool grounding
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Where do you get that from?
90.2(B)(1) says NEC doesn't apply to the boat, so it is not NEC that would have such a rule. NEC does apply to the circuit you plug the battery charger into, whether it be in your garage or at a marina.
I was just saying that boat metal is suppose to be bonded together not due to the NEC but maybe boating industry rules. Point was just no continuity between charger input and metal
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- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The charger output is connected to the + and - terminals of the battery.
The - terminal of the battery is very likely grounded to the engine and eventually to all of the bonded metal on the boat.
If there is current leakage between the primary and secondary of the transformer in the charger, or if the - of the charger is connected to the case of the charger and to the shore EGC there will be a metallic path which can put a voltage on the bonded metal surfaces and fittings on the boat.
This assumes that the metal on the boat is in fact bonded, for whatever reason.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
That was the road I was to go on next - something within the charger being the cause.
Still not sure how he gets 36 VAC, peak voltage of a 24 volt secondary would be near his readings, but chances are pretty good his meter displays RMS voltage. I guess we need to know some more about the charger before making too many assumptions of what may be going on in there, unless someone knows something that is pretty typical for this application.
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
The 36 VAC could be ripple from the DC output.
What happens when one side of the DC is disconnected & isolated ?
Then the other side ?
What happens when both sides of the DC are disconnected & isolated ?
I am thinking one side of the DC may share a common connection with the AC input.
mike_kilroy
Senior Member
- Location
- United States
As stated next, it is typical for at least the ground/case of your charger to be tied to that ground pin in the 120v ac plug, and I believe it is equally common/typical for the metal parts in a boat to be tied to the same ground point. I assume the - of the charger output is also tied to this ground since as stated it typically goes to engine body. So all probably should be tied to ground - YET YOU HAVE AT LEAST ONE POINT FLOATING - that railing.
Not tying metal to ground leads to galvanic action on water - especially salt water. So not grounding the metal pieces exposed to the sea helps them deteriorate faster. My aunt and uncle ran 6 charter boats on Lake Erie for 30 years. I had to help on many occassions fix their marine radios and electrical issues. They had ground wires everywhere (from the boat mfgr). Again, I suspect you have a corroded ground wire that has disconnected at least that railing.
Kwire said: Are metal items electrically connected to one another? Like say some metal framing/reinforcement members also have metal trim pieces fastened to them. And if so do these tie to the battery charger in any way? If you do have that does that frame have continuity to the EGC for the battery charger input? No continuity to E
YOU NEED TO CHECK AROUND and see if ANY other metal stuff is electrically tied. Check from engine to battery -, engine to other big metal items, engine to that railing. Find if you have SOME tied together. I assume you will find this, and thus you can begin making a picture of which are tied and which are not - so you can find the missing corroded ground wire between them. That is my stance until you find otherwise.
The 36Vac is very typical leakage from the typical .01 or .1 mfd cap from hot lead on 120v plug to ground - without the ground, you see that. Typical design in stuff like your charger. Somehow YOUR metal on YOUR boat is not grounded to the charger ground - as it should be IMO. You stated this is the case. That is the bottom line also: YOUR metal stuff on your boat should have ground wire to the charger case/ground. If you do not believe this, call your boat mfgr and ask them. They can give you lots of good advice to fix your issue - they do not want their boat out there with stray voltages running around.
mike_kilroy
Senior Member
- Location
- United States
Good easy test to prove it is normal and proper and that you are just missing a ground wire from charger to those metal things.
Just remove BOTH output 12v to battery wires and measure again: I would bet 2 cases of beer your 36Vac is STILL there. Nothing to do with the DC side of your charger - just a missing required ground wire.
For kicks, tell us the model and brand of your charger. I have quite some experience in marine chargers, have a few around here I can test too. We use some good marine brands in our old GMC motorhomes; our forum has like 5,000 members, and chargers are often a discussion. Might be I have schematic on yours and can show the cap on input causing this or duplicate it here.
- Location
- Simi Valley, CA
So it's a fiberglass boat, but you're showing voltage on the rails? How is that possible, unless there is a screw cutting into something.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Probably is going into metal. Important structural things like rails are not just screwed into fiberglass, they would break out way too easy. They often build a metal stick frame first, then the hull gets laid up over it, then the rails are bolted to that frame afterward. It's that frame that should be grounded.
I'm thinking that this a portable charger, not one designed to be mounted in the boat (or it WAS a portable charger that someone mounted permanently because it was cheaper, not fully understanding why). The difference would be that a portable charger would not have a bonded connection of the DC negative / frame and the AC ground conductor, as it should (per Coast Guard regulations by the way). That's because if there is a short in the AC hot to the DC negative or boat frame and there is no bonding connection, the entire boat metallic frame goes to 120V potential, waiting for some poor soul to touch it. The breaker would not trip because with no ground return path yet, there's no current flow until that person makes connection.
On some types of boats, like commercial fishing vessels with aluminum hulls, where bare metal is in contact with the water, they isolate on purpose to avoid galvanic corrosion when the boat is plugged into the charger while in the water. But when a boat charging system is designed like that, there are all kinds of warning stickers about this because of exactly what you are experiencing and that danger of shock.
The charger is a Genius Noco Genn3. It's a on board charger not a portable. I'm getting the voltage on metal rail, motor bracket, trim tabs, almost all metal. This is the second charger as I thought the first one was leaking the voltage but still didn't make since that it was conducting thru the fiberglass which is what the charger is mounted to. I unplugged the onboard (new) charger that when plugged in causes the voltage and connected a portable charger to each battery one at a time and no voltage on metal parts.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
If you bond the metal case of the charger to any piece of the network of bonded metal parts of the boat, hopefully the phantom voltage you see will go away.
If it does not, then the most likely thing is that there is no EGC in the AC line feeding the charger or that EGC is for some reason at an elevated voltage with respect to the water around the boat.
If it does not, then the most likely thing is that there is no EGC in the AC line feeding the charger or that EGC is for some reason at an elevated voltage with respect to the water around the boat.
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