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Author Topic: Ground Continuity Current Testing  (Read 8621 times)

Mike Sokol

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Ground Continuity Current Testing
« on: January 27, 2014, 01:06:27 pm »

Here's a heads-up on a ground continuity current tester I've developed for the RV industry. It uses the 12-volt battery in the camper/trailer to send a 2-amp DC "fault" current though all the various bonding points and connectors. With a bit of reworking, it could probably be redesigned to work for the audio industry as well. The beauty of the 12-volt DC test is that it won't impose potentially shocking voltages on gear under test if the safety ground fails due to corrosion or loose connections. The bulb allows you to check for intermittent connections by flickering or dimming while you wiggle all the cables and connectors. The reason that a traditional ohmmeter sometimes fails on this test is that it only sends micro-amps of current for the test, while 2-amps is enough to created a significant voltage drop with any dodgy connections.

Take a look and tell me what you think...

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John Roberts {JR}

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Re: Ground Continuity Current Testing
« Reply #1 on: January 27, 2014, 03:09:33 pm »

The Chinese battery logo bothers me...  :P

2a @ 12V can generate 24 watts of heat, while the light bulb in series will form a divider to prevent more than maybe half that to develop across some flaky wiring load. Even half that power concentrated into a small enough area could be a fire hazard. This test, especially if the lamp only lights dimly should NOT be left connected.

I have been thinking about probing for ground integrity with a HF signal to perhaps parse out a local bootleg ground from a valid long wired safety ground path, but this os low priority back burner stuff...  I still like the idea of coming up with idiot proof back line power strips and the like, that can detect all the common threats, to protect and serve the meat puppets.

JR
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Mike Sokol

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Re: Ground Continuity Current Testing
« Reply #2 on: January 27, 2014, 03:43:25 pm »

The Chinese battery logo bothers me...  :P

2a @ 12V can generate 24 watts of heat, while the light bulb in series will form a divider to prevent more than maybe half that to develop across some flaky wiring load. Even half that power concentrated into a small enough area could be a fire hazard. This test, especially if the lamp only lights dimly should NOT be left connected. 

JR

The reason why I'm experimenting with this test is that new RVs from the factory are only high-pot tested, never ground continuity tested. And I've had dozens of emails from RV owners who were shocked from their RV and discovered their generator transfer switch or shore power connector was mis-wired at the factory or by a dealer. I think this test could really help sniff out the poor and intermittent connections. Here's the consumer version which plugs into a 12-volt lighter outlet in the RV. No Chinese brand battery visible..  :o
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John Roberts {JR}

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Re: Ground Continuity Current Testing
« Reply #3 on: January 27, 2014, 04:23:20 pm »

I still repeat my concerns... If the lamp only lights dimly, DO NOT leave it connected, or look for smoke from whatever is dropping the rest of the voltage. Of course no light means no current and no fire hazard, only the mid-impedance situation. Something somewhere could get pretty hot.  :o

JR

Note: IC lamp impedance is not linear so won't be a very well behaved divider with anything other than another lamp. 
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Frank Koenig

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Re: Ground Continuity Current Testing
« Reply #4 on: January 27, 2014, 04:51:55 pm »

An incandescent lamp can serve as a powerful piece of test equipment, at least in relation to its cost and complexity. I carry a 12 volt lamp furnished with clips in my vehicles. With a little creativity it can be used to troubleshoot most problems.

I first became aware of this as a child when we would go to an "electric" shop in downtown Palo Alto -- a sort of Norman Rockwell memory at this point. They would actually REPAIR home appliances like toasters and vacuum cleaners. The first test to which they would subject any new arrival was to plug it into a special receptacle on their test bench that was wired in series with a lamp in a porcelain lampholder on the adjacent wall. From that they could identify shorts, opens, faulty switches, and, I presume, a variety of ills from knowing the "bulb signature" of the appliance.

Sometimes you need a $20000 network analyzer, sometimes a $300 voltmeter, and often a bulb will do.

--Frank
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Jonathan Johnson

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Re: Ground Continuity Current Testing
« Reply #5 on: January 27, 2014, 05:02:33 pm »

The Chinese battery logo bothers me...  :P

And failing to remove the shipping caps from the battery is going to cause a problem, too.  :)
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John Roberts {JR}

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Re: Ground Continuity Current Testing
« Reply #6 on: January 27, 2014, 05:20:07 pm »

An incandescent lamp can serve as a powerful piece of test equipment, at least in relation to its cost and complexity. I carry a 12 volt lamp furnished with clips in my vehicles. With a little creativity it can be used to troubleshoot most problems.

I first became aware of this as a child when we would go to an "electric" shop in downtown Palo Alto -- a sort of Norman Rockwell memory at this point. They would actually REPAIR home appliances like toasters and vacuum cleaners. The first test to which they would subject any new arrival was to plug it into a special receptacle on their test bench that was wired in series with a lamp in a porcelain lampholder on the adjacent wall. From that they could identify shorts, opens, faulty switches, and, I presume, a variety of ills from knowing the "bulb signature" of the appliance.

Sometimes you need a $20000 network analyzer, sometimes a $300 voltmeter, and often a bulb will do.

--Frank
It is common industry practice to wire a 100W light bulb in series with power amp test stations. If there is a short circuit the lightbulb will light up and actually current limit at low single digit amps. If the lightbulb stays off, it is safe to apply full power.

JR

PS: I wonder what they will use when IC light bulbs are obsolete.
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Mike Sokol

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Re: Ground Continuity Current Testing
« Reply #7 on: January 27, 2014, 05:43:49 pm »

It is common industry practice to wire a 100W light bulb in series with power amp test stations. If there is a short circuit the lightbulb will light up and actually current limit at low single digit amps. If the lightbulb stays off, it is safe to apply full power.

I started doing this on cars back in the 70's by clipping a 12-volt brake light bulb across the "dead" fuse to find a short in the wiring. When the bulb was dim, the radio was drawing a little power. When the build went bright, there was a short in the wiring. By flexing everything you can make the short come-and-go, which normally would be blowing the fuse, but which was current limited to 2 amps by the bulb. I built one of these gadgets last year for my kid's car when he kept blowing fuses. It's still a great idea that's cheap to build.

Quote
  PS: I wonder what they will use when IC light bulbs are obsolete.

I've actually thought about this. You just need a 20-watt resistor of the correct value (around 100 ohms) with an LED in parallel with it (don't forget the 1,000 ohm series resistor on the LED to keep from blowing it up). I'm going to build a ruggedized version of my tester for demonstrations, but the brake light bulb is easily understood by electricians and RV technicians.

I am taking JR's comments seriously. You can certainly make some heat with this thing, so it's definitely not a "walk-away" kinda test.   
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Mike Sokol
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Mike Sokol

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Re: Ground Continuity Current Testing
« Reply #8 on: January 27, 2014, 06:06:12 pm »

And failing to remove the shipping caps from the battery is going to cause a problem, too.  :)

Good golly, this is a tough room, isn't it?  ::)
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Stephen Swaffer

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Re: Ground Continuity Current Testing
« Reply #9 on: January 27, 2014, 08:46:51 pm »

I think it would be valuable to be able to switch between a lamp and a fixed resistor with a dvm in parallel to allow you to quantify a reading.  Maybe that is over thinking its use, but I am thinking a .5 ohm resistance will only give 1 V drop and, especially in a bright setting, it may be difficult to notice the difference between a 12 V lamp at 12 V and at 11 V?  Especially without a side by side comparison.  That .5 ohms at a full 50 amps could translate into a 25 V drop.

But then I like working with numbers!
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