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Author Topic: help with "hot skin? power running through frame of camper  (Read 1629 times)

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Offline jmsokol

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Re: help with "hot skin? power running through frame of camper
« Reply #15 on: December 19, 2012, 12:45:45 PM »
I've included a standard 120volt 1156 bulb which draws about 2 amps and provides the current limiting,

Oops... That should read a 12-volt 1156 bulb. I can't figure out how to edit on this forum...

Mike

Offline Unstable_Tripod

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Re: help with "hot skin? power running through frame of camper
« Reply #16 on: December 19, 2012, 01:00:47 PM »
Quote
I can't figure out how to edit on this forum...

It's not you.  The forum only allows edits for a short time period after you post.  After that time expires the post can't be edited.  I intensely dislike this feature. 
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Offline Pup-A-Rotsee

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Re: help with "hot skin? power running through frame of camper
« Reply #17 on: December 19, 2012, 01:35:08 PM »
It's not you.  The forum only allows edits for a short time period after you post.  After that time expires the post can't be edited.  I intensely dislike this feature.

...and I can't even think about or Steve fumes!  [:O] Ouch!

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Offline Old_Geezer

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Re: help with "hot skin? power running through frame of camper
« Reply #18 on: December 19, 2012, 02:08:02 PM »
And here it is. A simple and cheap way to test your RV's ground system for current carrying ability, which is the only way to know that your ground system is intact and can save you from harm.

Wow is that a good, impressive article, and useful to boot. I had been following the thread but really have never considered it much. Guess what I'll be doing on a brand new camper that has not even seen the campground yet, probably this weekend?
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Offline jmsokol

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Re: help with "hot skin? power running through frame of camper
« Reply #19 on: December 19, 2012, 02:58:37 PM »
FYI: Here's where you can buy a simple light fixture with a 12-volt bulb:
http://www.etrailer.com/Trailer-Lights/Optronics/MC32AB.html

and here's a set of battery clips that should wok:
http://www.walmart.com/ip/Attwood-Quick-Connect-Battery-Clips/16350979

BTW: I've heard a lot of stories about brand-new RVs with high-resistance safety grounds caused by too many layers of paint on the chassis bonding point (and the worker didn't grind down to bare metal). And I've seen brand new (imported) dog-bone and pig-tail adapters that had broken internal grounds. And, of course, once your RV is on the highway with road salt and vibration for a few years, anything's possible. This simple test should find all those conditions.

Of course, now we need a test to make sure the campground and garage outlets themselves are safe.  Not to scare you all too much, but did I post my article here about RPBG (Reverse Polarity Bootleg Ground) outlets and why simple 3-light circuit testers and even $300 Ground Impedance Testers won't find them? Read about it here: http://www.rvdoctor.com/2001/07/friends-of-gary-mike.html

Mike Sokol
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Offline jmsokol

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Re: help with "hot skin? power running through frame of camper
« Reply #20 on: December 19, 2012, 10:21:02 PM »
If you have a 12-volt cigarette lighter outlet in your RV, it's certainly possible to do this same light-bulb ground test using a lighter plug for the power source rather than clipping to the positive battery terminal directly.  More on this later...

Mike Sokol
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Offline BigBaron

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Re: help with "hot skin? power running through frame of camper
« Reply #21 on: December 21, 2012, 10:44:46 AM »
Thank you Mike!
I'm going to set up a test rig and test all my friend's trailers too!
I have a grounded transformer with 220 coming in



CouldI make a pigtail or something to work with the three-prong tester, or would 220 blow it out? The wiring at Korean campgrounds would terrify you!

Most is ungrounded-hot and neutral only! I'm thinking a nice long stake-30 cm-and an 8 gauge copper wire would fix that. Correct? Water around the stake?
« Last Edit: December 21, 2012, 11:07:22 AM by BigBaron »
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Offline jmsokol

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Re: help with "hot skin? power running through frame of camper
« Reply #22 on: December 21, 2012, 11:03:52 AM »
You're most welcome.

Here's a picture of my gold-standard version of this tester. http://howtosound.com/images/RV%20Ground%20Current%20Tester%20DMM.JPG

Step 1)    Clip across the battery and read the voltage

Step 2)    Clip from the positive battery terminal to the RV frame and read the voltage

Step 3)    Clip from the positive battery terminal to the shore power ground pin and read the voltage.

Step 4)    Wiggle everything and watch for light-bulb flicker
 
Everything should read very close to the same voltage (perhaps within 1/100th of a volt), and since the voltmeter's test wires only carry voltage due to the meter's high input impedance, any series resistance introduced by the test leads is essentially nulled out. 

This would allow for very accurate ground resistance tests down to a few 1/100ths of an ohm, and is certainly much more accurate  and repeatable than using an ohmmeter alone. It's essentially the same setup I used to test R2R ladders (digital to analog converters) for nuclear missile guidance systems. You dump in some current and read the voltage drop... just that simple.
 
Anybody should be able to build this test rig for less than $25 with new parts, and much cheaper if they already have a DMM and want to pull a brake or backup light socket from their local junkyard. I think it's simple enough for the serious RV owner to build for their own troubleshooting, and exactly what every RV repair shop should use to confirm RV shore plug safety-ground continuity.

Please send pictures if you build one of these things.

Mike Sokol
mike@noshockzone.org

Offline jmsokol

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Re: help with "hot skin? power running through frame of camper
« Reply #23 on: December 21, 2012, 07:11:38 PM »
Thank you Mike!

I'm going to set up a test rig and test all my friend's trailers too!
I have a grounded transformer with 220 coming in

CouldI make a pigtail or something to work with the three-prong tester, or would 220 blow it out? The wiring at Korean campgrounds would terrify you!

Most is ungrounded-hot and neutral only! I'm thinking a nice long stake-30 cm-and an 8 gauge copper wire would fix that. Correct? Water around the stake?

Hmmm.... So you have a power source with neutral and hot only, no safety ground? And you have an RV with a 120-volt electrical system, hence the 220 volt to 120 volt step-down transformer?

If that's indeed the case, then this is going to take some thinking "outside the box".

A few months ago I drew up plans for the "ground plate" that could be used on portable generator powered RVs. Now, the National Electrical Code does not require a portable generator be grounded, even though many of them have ground clamps. And I never felt totally safe with a floated ground system. So I came up with the idea of an 18 inch by 18 inch square plate with a bunch of sharpened bolts sticking out like golf-shoe cleats. The plan was to use expanded metal for the plate and a bunch of bronze 1/4" by 2" bolts with sharpened tips. Then you simply step this down into the ground either by foot or under the RV tire, then dump a gallon of water through the expanded metal. I think it would offer a reasonably good ground.

However, you still should probably install a GFCI breaker on the shore power cord of your RV. I'll have to think about it a bit more, so don't wire up any of this just yet.

Mike Sokol
mike@noshockzone.org 

Offline BigBaron

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Re: help with "hot skin? power running through frame of camper
« Reply #24 on: December 21, 2012, 09:10:15 PM »
Wow. I feel like I should send you some money for all the work! LOL
I have two analog multi-meters. Are they accurate enough to conduct the tests? If not, I would need to get the "pen-type" tester you showed earlier, and a simple DMM, right?
If the three-prong tester can't handle 220V, have you written a piece about how to test without a three-prong tester? I plan on going through our house and school once I know how to do the test.
I presume from your drawings the the larger blade on a 110V plug is the neutral. My concern is that since the Korean 220V plug is symmetrical, it would be easy to reverse the hot and neutral going into the transformer, resulting in a reversed condition on the 110V output.
Here is an inside pic of my transformer, all soldered and tightened. My incoming ground is directly to the chassis of the transformer-yes, I sanded off the paint! ;)
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Offline jmsokol

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Re: help with "hot skin? power running through frame of camper
« Reply #25 on: December 21, 2012, 09:56:09 PM »
Here is an inside pic of my transformer, all soldered and tightened. My incoming ground is directly to the chassis of the transformer-yes, I sanded off the paint! ;)

More on the DMM and NCVT later, but I'm curious if your 220 to 120 volt transformer has isolated primary and secondary windings. There are basically two types of transformers that can be used... autotransformers and isolated transformers.

If you're using an autotransformer, there's no isolation between the primary and secondary windings. See the diagram below.



In that case, accidental reversal of the plug will flip the hot and neutral wires. Now, that in itself is not a problem... but it does complicate how to generate a local ground.

However, an true transformer with isolated windings will look like this:



Using a transformer with isolated windings between the 230 volt primary and 120 volt secondary windings would allow you to add a simple ground stake or plate, and properly "earth ground" your RV with a high degree of confidence.

Let me  know what sort of transformer you're using and I'll let you know what might work.

Mike Sokol
mike@noshockzone.org


Offline BigBaron

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Re: help with "hot skin? power running through frame of camper
« Reply #26 on: December 21, 2012, 10:53:38 PM »
I can tell by looking to see if there are any common wires from the input to the output, right?
From my first impression, it's a good ol' simple transformer.
My EE 101 class is a distant memory, but I remember EMF and the right-hand rule (left-hand in Korean schools. They can't do anything correctly here) so I understand how transformers work.
I'll scour through the pics I have since the transformer is buried inside the trailer...
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Offline BigBaron

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Re: help with "hot skin? power running through frame of camper
« Reply #27 on: December 21, 2012, 11:18:28 PM »
I had a duplicate transformer in our kitchen for our microwave, and by looking at the yellow wire bridging the input and output, I'd say it's an autotransformer.

There are only two wires into the coils, and four on the other side. It looks like the four are for adjusting the output by changing the location of the short to neutral in the windings.

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Offline BigBaron

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Re: help with "hot skin? power running through frame of camper
« Reply #28 on: December 22, 2012, 03:17:00 AM »
Which non-contract tester should I use? I found the one I think you have, but there are many different models by the same manufacturer.
Also DMMs are fairly inexpensive. Any caveats or brands that are better?
Thanks,
Baron
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Offline catmanblue

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Re: help with "hot skin? power running through frame of camper
« Reply #29 on: December 22, 2012, 04:28:35 AM »
BigBaron----I prefer Fluke when it comes to test equipment. That's what I use at home and at work, may be a little more expensive but they stand behind their test equipment and it is pretty durable.
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