CounterAct Electronic Rust Inhibitor a Scam?

My brother just installed one of these on his car, and his description of the product sounded very fishy to me:

http://www.counteractrust.com/

The website is set up very much like any pseudoscience tech site, lots of testimonials, and "It's been patented!" claims...

I'm not an expert in this field, but I always thought that this sort of corrosion protection required the metal to be submerged in electrolyte (ie seawater)?

I noticed some of the "testing" was in 100% humidity conditions.

Has anybody heard of this product, or know if this could even theoretically work? It's claiming to use the car body as half of a capacitor. But if that's the case, then wouldn't the capacitor I use in front of my stereo power amplifier be essentially doing the same thing?

I don't see how you can be "building up a negative charge" on the car body when it's already connected to the negative terminal of the battery. Any "charge" that was of a different potential than the battery terminal would be bled off to the battery - no?

macgyver said:

I don't see how you can be "building up a negative charge" on the car body when it's already connected to the negative terminal of the battery. Any "charge" that was of a different potential than the battery terminal would be bled off to the battery - no?

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I can't speak about the accuracy or feasibility of this product, but no, you've got the capacitor/car thing wrong. The body of the car has much larger capacitance than the battery has. The battery just creates a voltage difference between the body of the car and the positive terminal of the battery. That does not mean that the body of the car cannot itself be charged. In fact, because the body of the car has a much larger capacitance than the battery, most excess charge placed on the car will NOT go to the battery, but will remain on the body of the car. That charge will create a potential for the body of the car, but the battery is still only creating a potential DIFFERENCE, at the positive terminal, with respect to whatever the potential of the body is. That's all the battery itself ever cares about: that potential difference between its terminals, not what the absolute value of the potential itself is on either side.

Whether or not there is something to the idea that a car with an electrical potential of hundreds of volts or more reduces rusting, I don't see how the device stated, or any device not actually "connected" in some way to the earth, could create such a potential. It's a "relatively" easy job to measure the potential of a car chassis re ground and I doubt the unit makes any difference in charge. There is one technique that could charge the car, coronal discharge. A high voltage together with a small sharp object can create a gradient sufficient to ionize air. How much potential the chassis will change by depends on the electronics and geometry of the discharger. Some air ionizers and most all electrostatic cleaners work by coronal discharge.

Building a charge up on a car body would increase the risk of a static discharge when filling the fuel tank.

BillC said:

Building a charge up on a car body would increase the risk of a static discharge when filling the fuel tank.

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Depends on how much voltage is created. Low enough voltage (like, say, 1V) and the risk is essentially zero. Of course, lower voltage also means less charge, so whether or not the thing can prevent rust effectively while still being at safe voltages remains a question.

marting said:

Whether or not there is something to the idea that a car with an electrical potential of hundreds of volts or more reduces rusting, I don't see how the device stated, or any device not actually "connected" in some way to the earth, could create such a potential.

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Oh sure, you can do that easily enough. All you need is for the device to create a high voltage potential somewhere on itself - in other words, the device acts like a battery itself, but it's charging a capacitor with one side of the capacitor being the body of the car, and the other side of the capacitor part of the device.

I just don't know whether or not that will DO anything to prevent rust.

Ziggurat said:

I can't speak about the accuracy or feasibility of this product, but no, you've got the capacitor/car thing wrong. The body of the car has much larger capacitance than the battery has. The battery just creates a voltage difference between the body of the car and the positive terminal of the battery. That does not mean that the body of the car cannot itself be charged. In fact, because the body of the car has a much larger capacitance than the battery, most excess charge placed on the car will NOT go to the battery, but will remain on the body of the car. That charge will create a potential for the body of the car, but the battery is still only creating a potential DIFFERENCE, at the positive terminal, with respect to whatever the potential of the body is. That's all the battery itself ever cares about: that potential difference between its terminals, not what the absolute value of the potential itself is on either side.

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I think we're describing the potential difference using two different references for "ground". I'm looking at the car as a DC system isolated from earth ground by rubber tires. I believe you're talking about the car body charge referring to earth ground.

I'm not sure, in either case, that this concept would have any real effect on corrosion. It's reminiscent of the Telco's choosing a -48VDC for their phone lines for the same reason. I might take my multimeter and measure my brothers car from the negative battery terminal to a good earth ground and see how it differs from another car.

If the body of the car is tied to the negative terminal of the battery, then the potential difference between the negative battery terminal and the car body will be zero...always. The foil on the device that is stuck to a metal portion of the car (and separated by paint and glue from the car body itself creating a dielectric) can be charged to any potential you like, but I don't see how it "charges" the body of the car (at least with respect to the isolated ground of the car body). I wasn't concerned with the potential on the car with respect to earth ground...unless that is supposed to somehow reduce corrosion?

Ziggurat said:

Oh sure, you can do that easily enough. All you need is for the device to create a high voltage potential somewhere on itself - in other words, the device acts like a battery itself, but it's charging a capacitor with one side of the capacitor being the body of the car, and the other side of the capacitor part of the device.

I just don't know whether or not that will DO anything to prevent rust.

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I would estimate, for the "capacitor" dialectric shown, if the foil side was charged to 1000V, the other side (car) probably is about -1V or less, as measured from the Earth's surface, assuming the tires are perfect insulators and the car was initially at 0V. It's actually fairly easy to model as 3 capacitors, one of which acts like a delta DC source. My guess is around 500pf from the car to earth and from .01 to 1 pf for the foil to earth.

Of course tires are NOT perfect insulators, since cars would otherwise build up high levels of static charge so it wouldn't surprise me if the car had no net charge from the above device.

I must say that this is an interesting claim.

Galvanic protection works. A sacrificial anode bonded to a less reactive material, provides the electrons instead of the base material, and thus will "rust" first. The electrical polarity will be such that the sacrificial anode is more positive with respect to the base material. Traditional sacrificial anodes work only if immersed in a conductive liquid.

This product works similarly, in that the "pads" are more positive w.r.t the car body. Since no dielectric is perfect, there can be some electron migration to the base material if it started to rust. Instead of the anode being sacrificed, the electrons are provided by the power supply (which also completes the circuit)

There is some real science behind this, but I would say this product does not work.

In a sacrificial anode situation, the anode provides the electrons by becoming an ion and bonding with oxygen to "rust" first. In this power supply situation, where is the extra electron coming from? As far as I can see, the number of electrons in the system remains the same, no matter if there is a potential difference, or if there is a static charge, or if the dielectric is not perfect.

My "follow-the-money" test also thinks that it does not work, as no vehicle manufacturer offers this. Imagine "Buy a [insert] your favourite brand here [/insert] and get 10 years no rust guarantee through active protection!".

Reading more on corrosion systems I came across another galvanic process that uses DC power in conjunction with sacrificial anodes to protect pipelines. It's called Impressed Current Cathodic Protection.

http://en.wikipedia.org/wiki/Cathodic_protection

However as stormer mentioned, this system would work because there is still a sacrificial anode in play. The car system doesn't have this, unless the lead acid battery can somehow serve a similar purpose?

I'm trying to find information on the Telco's decision to use negative voltage for it's DC power plant, and I seem to recall that Lucas used positive grounds on it's UK car electrical systems for the same reason. In both cases I don't think the scheme proved successful in combating corrosion.

I remember this idea from many years ago. That was in the days of minimal rust protection on cars. Frankly, they just don't rust any more anyway. My 47 year old classic has wax injection just like modern cars and won't rust. I really can't see the need for anything else these days.

Steel ships certainly use an electronic system. There are warning symbols painted on the side, to prevent you tying up too close and dissolving your boat. (I know a guy it happened to) The symbol reminds me of the battery ground symbol.

I know there are different 'kinds' of electricity. Like being measured for body fat, different kinds flow through different tissues, it's not just total body resistance. Square waves, frequency, polarity, AC, DC, voltage,amperage...

A box the size of a commercial battery charger protects the steel hulled sailing ship "The Star of India", who's hull is directly grounded to the sea. Rather than cathodic, which creates it's own voltage, I suppose it is making a charge that would tend to electroplate the hull. I wonder how well it's matched, or if the hulls get Magnesium plated in time? Could you sink a ship by overloading it's hull?

I suppose it's possible something might work on a car's body. Maybe. With the right technology. Perhaps. Someday. Now????

PS: Do you think the proper charge would make a wax job last longer? Wax is positve charged, so repells dirt... the oxidation of the wax requires electron flow.... Oh man, I'm going to be RICH! I'll sell a woo gismo that claims to extend the wax life on your classic car! Preventing you from wearing through tha paint by excessive rubbing! Plus a companion product, a special Super-Heterodyning wax with Quantum ingredients, and Nano Crsytals! It will keep your car in tune with the frequency of my gismo! Who cares if it works? (no FDA hassles!)

casebro said:

Steel ships certainly use an electronic system. There are warning symbols painted on the side, to prevent you tying up too close and dissolving your boat. (I know a guy it happened to) The symbol reminds me of the battery ground symbol.

A box the size of a commercial battery charger protects the steel hulled sailing ship "The Star of India", who's hull is directly grounded to the sea. Rather than cathodic, which creates it's own voltage, I suppose it is making a charge that would tend to electroplate the hull. I wonder how well it's matched, or if the hulls get Magnesium plated in time? Could you sink a ship by overloading it's hull?

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The systems you describe above work because the sea is essentially the electrolyte, and the metal in the sacrificial anode will "rust" faster than the material the ship is made of. The electric box on the star of India is most likely assisting this process with additional current, much like the pipeline system described below.

Galvanizing steel (coating it in Zinc) is essentially the same idea, in that the zinc plating will oxidize before the steel will. Because a galvanized object (like a nail) is completely coated in the anode material, the electrolyte isn't required (this is an assumption, correct me if I'm wrong).

The problem I see with the "CounterAct" system is that there isn't an anode, and there isn't any current carrying electrolyte.

macgyver said:

The problem I see with the "CounterAct" system is that there isn't an anode, and there isn't any current carrying electrolyte.

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In galvanized steel, the electrolyte occurs when moisture forms on the surface. Sometimes, hydroscopic salts will initiate this even with no precipitation and humidity levels below 80%. The Zn then oxidizes in lieu of the the Fe.

The rusting process is not very sensitive to static electric fields. Current actually has to flow to make a difference.

I don't believe the device works. I don't even believe the device produces any significant electric field at the chassis surface of the car except in the immediate vicinity of the foil/dialectric patch.

Q-Rays, anyone?

Anybody spot any actual patent numbers?

Capacitive coupling

I can't make any claims about whether the thing works, but at any rate the method asserted is capacitive coupling not impressed current cathodic protection -- which does indeed require grounding and is used successfully on ship hulls and gas pipelines etc.

Capacitive coupling, by contrast, purportedly retards rust formation by using vehicle paint as a dielectric to free electrons; it places the metal at a lower potential difference. The couplers are fixed to the vehicle's painted surface and are not sacrificial; the capacitive coupler is asserted to behave like the positive half of a capacitor.

What are the supposed limitations and caveats? The claim is that if the continuity of the painted surface is interrupted -- and this can happen from a stone chip or a paint crack -- the dielectric is broken, the charge is lost and so is any rust-retarding benefit (the CounterAct people dispute this claim). If this it true, the question would be how practicable it is to maintain eternal vigilance to assure the perfect continuity of your vehicle's painted surface.

The other assertion is that the technology is not suited to vehicles because of their irregular shapes and contours -- it's impossible to hold a charge on a thin and sharp metal surface.

On the other hand, CounterAct claims both lab and field testing back up their claims. In fact, though, some of the tests merely confirm that the method produces an electrostatic charge on a metal body and an alteration in the body's surface charge. Another test supposedly demonstrated that the charge was effected across "on the entire surface of a metal automobile body to which it was applied" and that "an alteration in the surface charge" was maintained "even at a distance from the capacitive coupler."

Three other tests -- by LACOR , Intertek/ETL and Canadian Tire -- were specifically about rust mitigation and migration. CounterAct claims these tests demonstrate an 80% reduction in the rate of corrosion. However, the tests were on painted automotive-grade steel panels -- if this refers to painted flat steel panels, this doesn't really answer the claim that sharp edges and irregular shapes mitigate the effectiveness of the method.

On the other, other hand, CounterAct claims field testing of the product under real-world conditions demonstrates its effectiveness. The "field-testing," though, is largely composed of fairly subjective anecdotal testimonials from satisfied customers ('our vehicles rust less than they used to' sort of thing), which is fine as far as it goes. It should be said that many of the testimonials are from people who don't appear to have used the unit for a long periods of time and so may not really be in a position to offer judgments on the long-term effectiveness of the product.

To sum up, then: a lot of the scepticism is a little misplaced because it's scepticism about a different method, cathodic protection. However, there are good reasons to be sceptical about this method as well -- more about the real-world effectiveness in use on motor vehicles than about whether it could work in principle. On the other hand, the company asserts that independent scientific testing and real-world use under harsher conditions than most vehicle owners will experience in fact validates their claims. However, on closer inspection, the applicability of at least some of the evidence on which their claims of effectiveness are based would appear somewhat more limited than appears at first blush.

I don't mean to cop out, but as for the real question -- will the damned thing work to slow rust if I install it on my car? -- my answer would have to be beats me. Somebody try it and let me know.

Somebody asked about patents. The US patent number is 4767512, and the Canadian one is 1329918

Thanks Ron B,

I'd actually completely forgotten that I'd posted this question. You're points are good ones, and I agree that what I had assumed was the process behind the marketing was in error. However, I remain very skeptical of the capacitive coupling concept as well. When I first heard of this unit, I actually thought that is what they might be trying to do. However, I can't think of a more imperfect, and variable capacitor than a painted car body. Also, if the paint needs to be perfect, then you really wouldn't have much of a rust problem to begin with, IMHO.

It strikes me a bit as similar to the whole "Slick 50" scam. The idea that you could put Teflon in your engine, and it would bind to the parts and lubricate better than oil (and in fact even in the absence of oil) sounded great...until you realized that the Teflon particles would quickly be extracted by a decent oil filter, most likely clogging it, and causing it to bypass...thereby removing filtration from your oil system and potentially causing damage.

There was a lot of testimonials for that product too such as "all the oil accidentally drained out of my car, but the engine was saved because I used Slick 50" However, these people probably had zero experience with oil draining out of a car in the past, and really had no reference to draw from.

RonB, thanks for the patent reference. Things are so much easier when I can look at a circuit diagram and relate it to a description.

I think I see a problem with their design. The basic idea appears to be to cause a small current to flow in the metal object intended to be protected. this current will be AC, simply because a capacitor will not pass DC and a pulse train, even if it is unipolar, consists of AC components superimposed on a DC component. Apply such a voltage to a capacitor and the AC components will pass through it while the DC component is blocked. IOW, the current in the metal object will flow in opposite directions on alternate half-cycles.

The circuit itself is very similar in principle to a capacitive discharge ignition system, in which you use an inverter to produce something on the order of 400VDC from the car's 12VDC power, charge a capacitor to around 400VDC and discharge it through the primary of a step-up transformer, producing a high voltage pulse at the secondary of the transformer. (In a CD ignition system, the transformer is the car's ignition coil and the secondary winding connects to the distributor rotor and thence to the spark plugs.)

The big difference in this circuit is the addition of a half-wave rectifier in series with the secondary winding. This, plus the capacitance of the coupling thingy, convert the circuit into, essentially, a DC power supply. Because the rectifier will block the flow of reverse current back through the transformer secondary, what will happen is that the capacitor formed by the coupling thingy and the metal object will charge up to the peak voltage of the transformer's output pulse. Once the voltage between the high-side plate of the coupler and the metal object has built up to this value, the only current that will pass through the coupler and flow in the metal object will be the current due to ripple voltage across the coupler, which will be due only to the reverse leakage current of the rectifier, the leakage current of the coupler and a component due to the stray capacitance of the rectifier.

Simply put, what the diagrams show is a high voltage DC power supply whose main filter capacitor is the capacitance of the coupler and which has no load. What I would expect to happen is that when the circuit is turned on, a diminishing series of current pulses will flow in the metal object and through the coupler, ultimately reaching a steady state in which the magnitude of the current pulses is reduced to near-zero. In fact, if the rectifier and the dielectric of the coupler were perfect, the ripple current would ultimately reach zero.

Since the flow of current in the metal object is essential to the device's claimed operation, this seems like a mighty inefficient means of achieving it.

I'll see if I can work up a sim over the next couple of days, but just based on my experience with flyback power supplies, I don't think that this circuit will behave electronically the way the inventors expect. That's entirely separate from whether or not the idea is grounded (pun not intended but I like it anyway) in sound electrochemistry.

I doubt it works as well as "sacrificial anode" methodologies, with which I am familiar, but as for where the electrons come from, they come from the vehicle battery. So I think it's an excellent conception, I just question how good the execution of that conception is. And that site is absolutely full of hype.

marting said:

I would estimate, for the "capacitor" dialectric shown, if the foil side was charged to 1000V, the other side (car) probably is about -1V or less, as measured from the Earth's surface, assuming the tires are perfect insulators and the car was initially at 0V. It's actually fairly easy to model as 3 capacitors, one of which acts like a delta DC source. My guess is around 500pf from the car to earth and from .01 to 1 pf for the foil to earth.

Of course tires are NOT perfect insulators, since cars would otherwise build up high levels of static charge so it wouldn't surprise me if the car had no net charge from the above device.

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Actualy cars do at times develop high charges, there are chains you can hang below the car to discharge the car in that situation as it can be dangerous with regards to filling the gas tank.

Why not just attach a sacrificial anode to the car as an easier way?

Asolepius said:

I remember this idea from many years ago. That was in the days of minimal rust protection on cars. Frankly, they just don't rust any more anyway. My 47 year old classic has wax injection just like modern cars and won't rust. I really can't see the need for anything else these days.

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Also there are more and more galvanized bodies and that covers the whole body in a sacrificial anode.

ponderingturtle said:

Actualy cars do at times develop high charges, there are chains you can hang below the car to discharge the car in that situation as it can be dangerous with regards to filling the gas tank.

Why not just attach a sacrificial anode to the car as an easier way?

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Most static discharge fueling fires occur when the driver gets back in, then out, of the car after starting the fueling. When the driver slides across the seat and doesn't ground themselves to the carframe first, they can get a hefty spark upon stepping on the ground or, if well insulated shoes, upon touching the gas pump handle. Before the start of fueling there are numerous places safe discharge can occur first. A chain doesn't prevent fires here since it doesn't stop the voltage buildup on the driver.

Airplane fueling is always preceded by attaching a ground strap. There is no doubt absolutely huge charges build up on the plane in the air. While tire compositions have some degree of conductivity, the area of contact is much smaller in a plane than car and the higher voltages and body capacitance would take longer to discharge.

marting said:

Airplane fueling is always preceded by attaching a ground strap. There is no doubt absolutely huge charges build up on the plane in the air. While tire compositions have some degree of conductivity, the area of contact is much smaller in a plane than car and the higher voltages and body capacitance would take longer to discharge.

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Yes there is. It's called P-Static. In helicopters it can reach over 300kV. It's why you see the flight deck personnel on some navy ships holding long grounding rods so they can touch the rails before allowing hovering rotor-craft to discharge any passengers or cargo. I'm not sure what the upper limit is on fixed wing craft, but I'd imagine that it's pretty comparable to rotor.

marting said:

Most static discharge fueling fires occur when the driver gets back in, then out, of the car after starting the fueling. When the driver slides across the seat and doesn't ground themselves to the carframe first, they can get a hefty spark upon stepping on the ground or, if well insulated shoes, upon touching the gas pump handle. Before the start of fueling there are numerous places safe discharge can occur first. A chain doesn't prevent fires here since it doesn't stop the voltage buildup on the driver.

Airplane fueling is always preceded by attaching a ground strap. There is no doubt absolutely huge charges build up on the plane in the air. While tire compositions have some degree of conductivity, the area of contact is much smaller in a plane than car and the higher voltages and body capacitance would take longer to discharge.

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Sure, but if you are getting shocked every time you get out of the car, you need one of these chains. It might not be the main cause of such fires, but the condition does happen if you get the wrong tires.

ponderingturtle said:

Sure, but if you are getting shocked every time you get out of the car, you need one of these chains. It might not be the main cause of such fires, but the condition does happen if you get the wrong tires.

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Not true, actually. The charge is on your body, not the car. It was generated by sliding across the plastic and textiles of the interior. Your shoes act as insulators to ground, so you could generate a decent charge on your body, get out of the car, and then touch the car body (already at a lower potential than you) and still get a shock. In fact the grounding strap on the car body would ensure that the car body potential would always be at or near ground so you would guarantee a shock. The only way to eliminate the shock is to bleed the static charge from your body to the metal body of the car through a high resistance, like a grounding strap used commonly in the Telecom industry.

macgyver said:

Not true, actually. The charge is on your body, not the car. It was generated by sliding across the plastic and textiles of the interior. Your shoes act as insulators to ground, so you could generate a decent charge on your body, get out of the car, and then touch the car body (already at a lower potential than you) and still get a shock. In fact the grounding strap on the car body would ensure that the car body potential would always be at or near ground so you would guarantee a shock. The only way to eliminate the shock is to bleed the static charge from your body to the metal body of the car through a high resistance, like a grounding strap used commonly in the Telecom industry.

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No your car can get charged if you have the right tires.

See
Cartalk discussion of the issue

Patent about how the use of silica is related to this

snopes on this issue pointing out that 20 out of 81 cases involved initial pumping and 29 out of 81 involving returning to the car. 15 involved neither and 17 did hot have enough information reported to categorize

ponderingturtle said:

No your car can get charged if you have the right tires.

See
Cartalk discussion of the issue

Patent about how the use of silica is related to this

snopes on this issue pointing out that 20 out of 81 cases involved initial pumping and 29 out of 81 involving returning to the car. 15 involved neither and 17 did hot have enough information reported to categorize

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Hmm interesting, although the advice is always to discharge the static by touching the car body. The question would be, is the charge travelling from the car to you, or from you to the car?

In one case the argument is that the charge is built up on the car body, and the discharge would therefore travel through you to ground. But then other evidence states that people were wearing rubber soled shoes, which would indicate that they would be a very poor circuit path to ground.

Your links seem to provide evidence that there are two conditions possible:

The charge is built up on the drivers body through interaction with the cars interior, and the charge is built up on the car body through interaction of atmosphere and car tires on the roadway.

Perhaps both of these conditions can occur, but I would still place the more common of the two on the driver carrying the charge.

In part, I would blame the dry interior conditions due to common A/C use compared to the more humid outdoor conditions which would aid conductivity between the car and the ground. Of course, this scenario could be reversed, especially in very cold weather, where the interior of the car would be considerably more humid than outdoors?

If grounding straps are provided to bleed charge off the car to ground, and they are functioning correctly, then I still maintain that you could get a static discharge from your body to the car.

macgyver said:

Hmm interesting, although the advice is always to discharge the static by touching the car body. The question would be, is the charge travelling from the car to you, or from you to the car?

In one case the argument is that the charge is built up on the car body, and the discharge would therefore travel through you to ground. But then other evidence states that people were wearing rubber soled shoes, which would indicate that they would be a very poor circuit path to ground.

Your links seem to provide evidence that there are two conditions possible:

The charge is built up on the drivers body through interaction with the cars interior, and the charge is built up on the car body through interaction of atmosphere and car tires on the roadway.

Perhaps both of these conditions can occur, but I would still place the more common of the two on the driver carrying the charge.

In part, I would blame the dry interior conditions due to common A/C use compared to the more humid outdoor conditions which would aid conductivity between the car and the ground. Of course, this scenario could be reversed, especially in very cold weather, where the interior of the car would be considerably more humid than outdoors?

If grounding straps are provided to bleed charge off the car to ground, and they are functioning correctly, then I still maintain that you could get a static discharge from your body to the car.

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More than likely, it's a charge building up on the car. No matter what, you're going to be the lower-impedance path to ground.

kmortis said:

More than likely, it's a charge building up on the car. No matter what, you're going to be the lower-impedance path to ground.

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Why would you assume that, necessarily?

That would certainly dispell any claims that gas pump fires were caused by individuals returning to their cars during refueling and that they were found to be wearing rubber soled shoes. Those statements were clearly putting the higher potential on the driver, not the car.

You may be correct, I just haven't seen any evidence to prove it.

macgyver said:

Why would you assume that, necessarily?

That would certainly dispell any claims that gas pump fires were caused by individuals returning to their cars during refueling and that they were found to be wearing rubber soled shoes. Those statements were clearly putting the higher potential on the driver, not the car.

You may be correct, I just haven't seen any evidence to prove it.

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If you're talking about the far more common practice of getting in and driving, I'd suspect that the car would build up quite a nice charge as it travels through the air. You will too, if your clothing is too far away from the charge of the material your car's interior is.

To be honest, I don't have any deductive reasons why I think it's primarily the car. Part of my job is to help circuits withstand ESD and P-Static, and generally in aerospace, it's the vehicle that's charged to the greater potential. This does not preclude the driver from gaining a charge, mind you, just that the vehicle would be higher.

Of course, my assumption of you carrying the charge in either case still stands unmodified. Since, in most cases, you'll have a lower impedance path to ground than the car, you'll be the main channel. Now, of course, the car could be carrying more current, but it doesn't feel pain, now does it?

kmortis said:

Of course, my assumption of you carrying the charge in either case still stands unmodified. Since, in most cases, you'll have a lower impedance path to ground than the car, you'll be the main channel. Now, of course, the car could be carrying more current, but it doesn't feel pain, now does it?

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In my line of work (telecom) however, the opposite tends to be true. My equipment is grounded, but I can easily carry a charge of several thousand volts. Enough voltage, obviously, to jump between my finger, and an object (such as a door handle) which is not necessarily at ground potential, but suitably lower than me. I wear a megohm resitor grounding strap to bleed that charge safely, so I don't damage sensitive components. Obviously my "lower impedance to ground" isn't low enough to dissipate the charge on it's own!

Back to the car scenario, then. While I agree that the car could carry a charge, it's the relative potential between myself and car that will determine the direction of the current, when a spark jumps between us.

In a refueling situation, I would also maintain that the metal fuel nozzle (and jacketed high pressure hose connected to the bonded pump) would quickly bleed any charge on the exterior of the car, before any fuel even leaves the nozzle. So now we have a bonded car -- I return to the interior of my car, build up a charge and, due to the insulation of my shoes, it remains even when my feet touch the ground , grab the pump nozzle...there's a spark...who's to blame? We've already proven that the insulation of my shoe soles is good enough to allow several thousand volt charges to accumulate on my body, because we've all experienced shocking ourselves on grounded metal surfaces.

Perhaps an electric field meter is the only way to end the debate.

macgyver said:

In my line of work (telecom) however, the opposite tends to be true. My equipment is grounded, but I can easily carry a charge of several thousand volts. Enough voltage, obviously, to jump between my finger, and an object (such as a door handle) which is not necessarily at ground potential, but suitably lower than me. I wear a megohm resitor grounding strap to bleed that charge safely, so I don't damage sensitive components. Obviously my "lower impedance to ground" isn't low enough to dissipate the charge on it's own!

Back to the car scenario, then. While I agree that the car could carry a charge, it's the relative potential between myself and car that will determine the direction of the current, when a spark jumps between us.

In a refueling situation, I would also maintain that the metal fuel nozzle (and jacketed high pressure hose connected to the bonded pump) would quickly bleed any charge on the exterior of the car, before any fuel even leaves the nozzle. So now we have a bonded car -- I return to the interior of my car, build up a charge and, due to the insulation of my shoes, it remains even when my feet touch the ground , grab the pump nozzle...there's a spark...who's to blame? We've already proven that the insulation of my shoe soles is good enough to allow several thousand volt charges to accumulate on my body, because we've all experienced shocking ourselves on grounded metal surfaces.

Perhaps an electric field meter is the only way to end the debate.

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I wouldn't have a clue where to find one of those....

kmortis said:

More than likely, it's a charge building up on the car. No matter what, you're going to be the lower-impedance path to ground.

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For one thing, the Cartalk folks are giving advice that only makes sense in the context of a differential charge being built up as the person exists the car - from sliding on the seat. Otherwise the person would be charged to the identical level that the car body itself was at and the advice quoted below would have no effect at all.

Ray: There are two options, Gina. One is to touch the car with the tip of the key before you close the door. That would discharge the static through the key, leaving your finger unzapped. The problem is that you have to remember to do it, and be careful not to touch anything accidentally on the way out of the car.

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When a person is charged by sliding out of the car, the car would be charged opposite the person and the voltage would change based on the overall gnd-car capacitance and gnd-driver capacitance which is probably on the order of 10 to 1. So if the driver was at +3000V, the car would be at -300V relative to gnd. Which would bleed off the fastest would depend on the resistance of the drivers shoes and the car tires.

If the car was really charged up to 3000V or so by driving, the smart thing to do would be to jump out of the car door so that the much higher coloumb charge of the car doesn't find it's way right through the driver when his feet touches gnd. It apparently isn't much of a problem though so I suspect Ray is simply confusing two.

marting said:

If the car was really charged up to 3000V or so by driving, the smart thing to do would be to jump out of the car door so that the much higher coloumb charge of the car doesn't find it's way right through the driver when his feet touches gnd. It apparently isn't much of a problem though so I suspect Ray is simply confusing two.

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However, wouldn't the car voltage and the driver voltage be equal in this scenario, therefore, no charge delta between the two?

It seems there can be a significant differential in charge between the car body (exterior surface), and the car interior, so if a driver exits the car, and doesn't touch the body (easy to do, you can even close the door using the window glass) the driver will still get a shock when he touches metal on the car. I maintain the driver is higher potential than the car in this case, and the charge was generated by friction between the interior and his clothing.

Now, if the car interior is oppositely charged as a result of this, then the driver may receive a shock from the interior, when he enters the car again?

macgyver said:

However, wouldn't the car voltage and the driver voltage be equal in this scenario, therefore, no charge delta between the two?

It seems there can be a significant differential in charge between the car body (exterior surface), and the car interior, so if a driver exits the car, and doesn't touch the body (easy to do, you can even close the door using the window glass) the driver will still get a shock when he touches metal on the car. I maintain the driver is higher potential than the car in this case, and the charge was generated by friction between the interior and his clothing.

Now, if the car interior is oppositely charged as a result of this, then the driver may receive a shock from the interior, when he enters the car again?

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That was exactly my point. If the car was charged, so would be the driver. Ignoring, for a moment, the charge the driver might incur from sliding out, the driver would still be charged to the same potential as the car but by jumping, the coloumbs that represents that would go through the driver would be reduced 10 fold or so by jumping free of the car. Thus, the problem isn't that the car is charged and the advice was wrong. The problem is the differential charge from sliding out of the car while not touching the car chassis.

marting said:

That was exactly my point. If the car was charged, so would be the driver. Ignoring, for a moment, the charge the driver might incur from sliding out, the driver would still be charged to the same potential as the car but by jumping, the coloumbs that represents that would go through the driver would be reduced 10 fold or so by jumping free of the car. Thus, the problem isn't that the car is charged and the advice was wrong. The problem is the differential charge from sliding out of the car while not touching the car chassis.

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Okay, I probably misunderstood. So essentially if the driver touched the surface of the car body while still in the car (through the window), there would be no potential difference between him and the car until he left the car, and became an independantly charged body. Due largely to surface area the car would have the higher potential?

So we need to determine if sliding out of the car would produce a larger potential on the driver than already exists on the car. I supposed too, that the polarity of the charge needs to be determined as well?

macgyver said:

Okay, I probably misunderstood. So essentially if the driver touched the surface of the car body while still in the car (through the window), there would be no potential difference between him and the car until he left the car, and became an independantly charged body. Due largely to surface area the car would have the higher potential?

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Right. Think of the car as a Faraday cage. Upon leaving the car, his potential would change inversely to his effective capacitance to the surroundings. This capacitance would increase as the person landed on the ground hence the person's voltage would decrease slightly. The key equation is vC=constant, so long as there is no discharge. Same with the car but C is much larger for the car and it remains unchanged so the v on the car is also reduced a slight amount when the driver exits so the net coloumb charge of the two is conserved. Energy is conserved too. The decrease in E=(Cv^2)/2 is offset by acceleration forces on the driver.

macgyver said:

So we need to determine if sliding out of the car would produce a larger potential on the driver than already exists on the car. I supposed too, that the polarity of the charge needs to be determined as well?

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This is the real issue and is why most fires are due to the person getting back into then out of the car while fueling. The person now has a net potential and the car an opposite but far smaller potential. However, if the car is grounded through the fueling line/nozzle, only the driver will be charged (relative to gnd). When the driver approaches the fuel port/handle - zap.

kmortis said:

More than likely, it's a charge building up on the car. No matter what, you're going to be the lower-impedance path to ground.

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It depends on the composition of the tires. more carbon black better connection and you don't get the charge build up. More silicon worse conductivity and more charge built up.

At least that seems to be how it works from a quick internet search. Any tire engineers on the forum?

kmortis said:

If you're talking about the far more common practice of getting in and driving, I'd suspect that the car would build up quite a nice charge as it travels through the air. You will too, if your clothing is too far away from the charge of the material your car's interior is.

To be honest, I don't have any deductive reasons why I think it's primarily the car. Part of my job is to help circuits withstand ESD and P-Static, and generally in aerospace, it's the vehicle that's charged to the greater potential. This does not preclude the driver from gaining a charge, mind you, just that the vehicle would be higher.

Of course, my assumption of you carrying the charge in either case still stands unmodified. Since, in most cases, you'll have a lower impedance path to ground than the car, you'll be the main channel. Now, of course, the car could be carrying more current, but it doesn't feel pain, now does it?

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This does not seem to be the case, as most cars seem to be somewhat grounded, hence the need to add a grounding strap to the car if you keep getting shocked by it. They are common but not universal so that would seem to indicate that charge build up on a car is not as universal as it is in your environment.

macgyver said:

In my line of work (telecom) however, the opposite tends to be true. My equipment is grounded, but I can easily carry a charge of several thousand volts. Enough voltage, obviously, to jump between my finger, and an object (such as a door handle) which is not necessarily at ground potential, but suitably lower than me. I wear a megohm resitor grounding strap to bleed that charge safely, so I don't damage sensitive components. Obviously my "lower impedance to ground" isn't low enough to dissipate the charge on it's own!

Back to the car scenario, then. While I agree that the car could carry a charge, it's the relative potential between myself and car that will determine the direction of the current, when a spark jumps between us.

In a refueling situation, I would also maintain that the metal fuel nozzle (and jacketed high pressure hose connected to the bonded pump) would quickly bleed any charge on the exterior of the car, before any fuel even leaves the nozzle. So now we have a bonded car -- I return to the interior of my car, build up a charge and, due to the insulation of my shoes, it remains even when my feet touch the ground , grab the pump nozzle...there's a spark...who's to blame? We've already proven that the insulation of my shoe soles is good enough to allow several thousand volt charges to accumulate on my body, because we've all experienced shocking ourselves on grounded metal surfaces.

Perhaps an electric field meter is the only way to end the debate.

Click to expand...

No when you touch a railing that is more or less grounded in the winter and get a shock, that also shows that people can generate quite a charge and hold it for a while.