Hot Skin from maintenance chargers - Page 2

walleyejim · 12-16-2021, 10:17 AM

At least you are also seeing some of the results that I have here. If it is phantom or ghost voltage, then I guess my DDM and non-contact tester are of little use? Will be interested in receiving Mike Sokol's input. Thanks again.

MikeSokol · 12-16-2021, 11:24 AM

Okay, I just talked to Brian, and I think I know what's going on. First of all, your RV chassis is isolated from earth ground since it's not connected to shore power. Normally, your shore power cord should create a connection between the chassis of your RV, thru the EGC (Equipment Grounding Conductor) all the way to the service panel's neutral/ground bus bonding point. Because your RV isn't bonded to the service panel, its chassis can float to any voltage induced by something like your battery minder/charger.

Now most every battery minder/charger I've seen doesn't have a ground pin in its power cord. UL allows this to be listed as long as the 120-volt leakage current doesn't exceed something like 0.8mA to the chassis. That's right.... EVERYTHING you plug into a wall outlet leaks at least a little current from the 120-volt line to the chassis.. Normally this current is very small, under the threshold of what you can feel, which is why you don't even know about it.

However, in most of these chargers and power supplies with a high-frequency transformer there's a pair of RF capacitors that the FCC requires the manufacturer to add. That's to prevent every PSW power supply from radiating RF energy all over the place and messing with the cell phone and television reception. So if a battery tender/charger happens to take a high-voltage spike from the power company, that can damage those RF capacitors to the point where they leak a lot more than the allowed 0.8mA of fault current. It could easily go up to 3 or 5mA, or in certain circumstances create a direct short from the 120-volt line to the chassis (or negative charging terminal), thereby electrifying your RV with a leakage current that could be deadly.

I'm going to do an experiment soon, but I think the real test would be to use a digital multimeter to measure the leakage current between the chassis of the RV and a known-good EGC ground connection in the grounded extension cord. This is a potentially dangerous test since it involves using your meter in mA mode between the RV chassis and a known EGC connection that's properly bonded. I suspect the current should be below 1mA if the charger is okay, but it's certainly possible that there's a bolted short circuit in the charger that could provide circuit breaker current (as in 20 amperes of branch current) thru your meter, which should blow the 10-amp current fuse if something went really wrong.

In any event, I'll write up something a little more detailed next week with a diagram or two and post it on my private RVelectricity blog. Hopefully the moderators here won't delete it since there's no advertising on my RVelectricity site. But it will be next week before I have time to draw up a diagram and write an article explaining this problem.

So bottom line, it's likely that there's nothing really wrong and dangerous. But there is the possibility of a potentially life-threatening leakage current due to damages RF noise capacitors in your battery tender/charger. So if you can feel a shock of any kind, its time to test.

walleyejim · 12-16-2021, 12:33 PM

Thanks to both Mike & Brian for the detailed analysis of the charger/hot skin problem. Since I have the same problem with the chargers in three different vehicles (RV, aluminum boat, Subaru Forester), I am leaning toward the possibility that the charging units became faulty. Hopefully, BatteryMinder will check out the unit and report back with their results.

I am sure it might prove useful for Mike to discuss this in his blog - that a charger could become defective and cause a potential dangerous hot skin condition. One that is not just coming from a faulty pedestal or rv wiring.

Thanks again

bigb · 12-17-2021, 06:53 AM

Jim,
Before you do anything I am going to try some more testing today, including Mike's recommendation and will post results. Mountain time here so just getting going for the day.

bigb · 12-17-2021, 10:27 AM

Today I had more time as yesterday I was kind of rushed due to some obligations. I made an error in my testing yesterday, I realized last night that although the breaker was turned off, my rig was still plugged into the 30 amp receptacle (it's hard to see in my garage because the slides are out and cannot see or access the plug without opening the big rollup door or crawling under the slides). So today I repeated all the tests with the plug removed and I was able to replicate Jim's findings. With the DMM I measured 34.5 volts from each battery terminal to the ground prong of a grounded extension cord and also from various points of metal on the rig. I was also able to get the NC tester to ring on all metal parts although I did have to have it in direct contact with the metal and it was not the same as when I use it on 120 volt circuits, it feels more like a phantom as I explained earlier, not a good strong signal like with a 120 volt circuit.
I then connected my old Simpson analog meter and here's where it got crazy. On the 50 volt scale I got 12 volts AC, on the 250 volt scale I got close to 50 volts and on the 10 volt scale I got around 2.5 volts. (meter was set to AC voltage for all tests and when set to DC no voltage was measured). I am curious with these readings and will investigate further, I always thought that an analog meter would not see a phantom voltage.
Next I plugged in another charger, but not a Battery Minder brand, to the chassis battery. When I did that my voltages jumped to nearly double and the NC tester rang even easier and stronger than before.
Finally I switched the DMM to ACmA and could get absolutely zero with either one or two chargers connected. This leads me to believe the floating voltage caused by the ungrounded chargers is in a sense a phantom or ghost as there is no measurable current. Also all of the voltages completely disappear when the coach is plugged in which establishes a ground.
I know Mike did have a story about an electrocution due to a faulty charger and will look forward to his comments next week. Meanwhile I don't think you have a problem as long as the voltage disappears when you connect your shore cord.

bigb · 12-17-2021, 10:30 AM

Here's some more pics showing the NC tester working on all metal parts, the zero reading on the mA and the 12 volts on the Simpson using the 50 volt AC scale

walleyejim · 12-17-2021, 05:40 PM

Brian - Thanks for the additional testing. I have been busy all day today, but plan on doing some additional testing on Saturday. Very interesting results from your additional tests. I will plug into shore power which will then connect the rv with the ground and turn off my converter. I assume that I will have similar results that you came up with. If so, I guess that would be a safe solution for me to continue the use of the maintenance charger but just to have the shore power cord connected at the same time.

But then that still does not leave me completely in the clear with using the chargers on my boat and subary. They are not connected to a ground unless I do so manually.

bigb · 12-17-2021, 06:55 PM

Quote:

Originally Posted by walleyejim

Brian - Thanks for the additional testing. I have been busy all day today, but plan on doing some additional testing on Saturday. Very interesting results from your additional tests. I will plug into shore power which will then connect the rv with the ground and turn off my converter. I assume that I will have similar results that you came up with. If so, I guess that would be a safe solution for me to continue the use of the maintenance charger but just to have the shore power cord connected at the same time.

But then that still does not leave me completely in the clear with using the chargers on my boat and subary. They are not connected to a ground unless I do so manually.

Jim,
From the results of my miliamp test it shows virtually no measurable current so I don't really think you have anything to worry about safety wise. Also when you plug into shore power you do not need to have the circuit breaker on, the ground will still be connected. I never turned on the circuit breaker for my testing.

orangeminnie · 12-22-2021, 06:47 PM

Quote:

Originally Posted by bigb

Today I had more time as yesterday I was kind of rushed due to some obligations. I made an error in my testing yesterday, I realized last night that although the breaker was turned off, my rig was still plugged into the 30 amp receptacle (it's hard to see in my garage because the slides are out and cannot see or access the plug without opening the big rollup door or crawling under the slides). So today I repeated all the tests with the plug removed and I was able to replicate Jim's findings. With the DMM I measured 34.5 volts from each battery terminal to the ground prong of a grounded extension cord and also from various points of metal on the rig. I was also able to get the NC tester to ring on all metal parts although I did have to have it in direct contact with the metal and it was not the same as when I use it on 120 volt circuits, it feels more like a phantom as I explained earlier, not a good strong signal like with a 120 volt circuit.
I then connected my old Simpson analog meter and here's where it got crazy. On the 50 volt scale I got 12 volts AC, on the 250 volt scale I got close to 50 volts and on the 10 volt scale I got around 2.5 volts. (meter was set to AC voltage for all tests and when set to DC no voltage was measured). I am curious with these readings and will investigate further, I always thought that an analog meter would not see a phantom voltage.
Next I plugged in another charger, but not a Battery Minder brand, to the chassis battery. When I did that my voltages jumped to nearly double and the NC tester rang even easier and stronger than before.
Finally I switched the DMM to ACmA and could get absolutely zero with either one or two chargers connected. This leads me to believe the floating voltage caused by the ungrounded chargers is in a sense a phantom or ghost as there is no measurable current. Also all of the voltages completely disappear when the coach is plugged in which establishes a ground.
I know Mike did have a story about an electrocution due to a faulty charger and will look forward to his comments next week. Meanwhile I don't think you have a problem as long as the voltage disappears when you connect your shore cord.

You were getting very different readings with the Simpson analog meter on different full-scale ranges, because the internal resistance is different for different ranges. Indeed, your Simpson readings confirm that the phamtom voltage can only supply a fraction of 1ma, and should be safe. On the 10 volt scale, the Simpson analog meter has a lower internal resistance than it does when the higher ranges are used, loading down the phantom voltage and causing it to read lower. Good quality analog meters might have 200k (200,000) ohms of internal resistance on the 10V scale. Digital voltmeters tend to have an internal resistance of 10M (10,000,000) ohms or more.

rgill · 12-23-2021, 05:00 AM

Check for a bad element in your water heater?

Shedboy · 12-23-2021, 08:16 AM

Wild ideas - assuming the stray voltage is not Direct Current

1. You mentioned utility pole replacement - Are the power line wires/pole transformer magnetically inducing a voltage in the RV/boat/automobile metal skin? How about underground conduit to a street light/substation? Would explain "no current flow". Does the voltage go away when RV has no power cables or earth ground?

2. Not sure how to do it wo a freq meter/spectrum analyzer - what is the frequency of the stray voltage? Would answer possible leakage through battery minder capacitors.
3. Mentioned that when RV pigtail is attached, stray voltage goes away. Are the 2 battery minders connected to different branch circuits? Possible ground loop between branches?
4. With "legacy" dumb battery chargers, does the issue persist?
5. Hi freq interaction between the two battery minders?