Easy Homemade Electrical Devices for TD systems

Anything electric, AC or DC

Easy Homemade Electrical Devices for TD systems

Postby Dee Bee » Fri Nov 25, 2005 8:13 pm

I made two other devices for the safe operation of my electrical system. I used one to monitor the battery through the DC circuits in the Zephyr. I used the other to correct an occasional problem with AC shore power connections.

The first device is pictured below at the top of the photo. I attached a 12 volt DC plug to the end of a set of spare leads for a multimeter. I was careful to match the polarity of the plug to the polarity of the DC outlets in the Zephyr. If this was reversed, then the meter would read negative voltage. I plugged this into any 12 volt outlet in the Zephyr to read the state-of-charge in the battery.


In some campgrounds, the line and the load side of the AC circuit are mistakenly reversed in the shore power outlets. This condition isn't safe, even though a simple device, like a light, will work if plugged into such an outlet. Other electronic devices, like my AC-DC power converter and battery charger, will not work and can be damaged if plugged into an outlet that is wired incorrectly.

To guard against this, I bought a simple plug-in polarity tester. With the tester, I could verify correct polarity in the AC shore power outlets at campgrounds. The pattern and color of the LED display on the plug-in tester indicated correct polarity and a safe outlet or reverse polarity. I made the device shown in the bottom of the above photo to use when the tester showed the polarity was reversed. It consisted of female and male three-prong, grounded plugs connected via six inches of suitable wire. I purposefully switched the line/load polarity in this plug. I made sure that the continuity of the grounded leg (green wire) remained. When I found reversed polarity in the shore power outlet at a campsite, I plugged in my adapter at the shore power location. The adaptor switched the AC current back to the correct polarity. It was a temporary fix and I used it with care. I made it very short and marked it with unmistakable colors. I did this so I wouldn't use it by mistake when not needed and cause a dangerous problem.

Dee Bee
Last edited by Dee Bee on Sat Nov 26, 2005 6:45 am, edited 1 time in total.
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Postby Steve_Cox » Fri Nov 25, 2005 8:31 pm

Dee Bee
That polarity switcher is a great idea! My AC panel has an automatic reverse polarity detector in it and the main breaker won't reset if the polarity is reversed.... Thanks for the great idea to make a cord with the line and neutral switched... mine will also be marked so there is no mistake as to what it is and what it is for....

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Postby Chris C » Fri Nov 25, 2005 11:48 pm

Hey, that IS a great idea. I'd always wondered what RV'rs did when faced with that problem. Good solution. :applause:
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Postby TomS » Sat Nov 26, 2005 11:55 am

I've got a question.

Will a GFCI work (test and reset) if the polarity is reversed?
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Postby GeorgeTelford » Sat Nov 26, 2005 1:08 pm

Hi Tom

As far as I can tell a GFCI is the same as an RCD in UK, if thats the case it will work even is polarity is reversed.

They work due to differences in current between Live and Neutral lines, If there is a difference (ie if some of the power is taking a detour) then the difference between the two operates a coil which throws the breaker.
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