DIY Electronic Vehicle Rust Prevention

[Computer Nerd Kev]

While looking into rust-proof paints, I stumbled upon the world of electronic rust prevention gadgets:

Much like with the paints, the question is whether it works, or whether it's just snake oil. It's supposed to use conductive pads to create a static charge on the steel vehicle body by using the paint as a dilectric layer forming a capacitor. The charge prevents oxidation of the metal.

In this discussion it's mentioned that by relying on the paint to form the dilectric, it won't work in areas where the paint is weak, which is where rust would start anyway:

Then again much of my trouble is from cavities in old vehicle bodies rusting out from inside*. The paint on the outside is OK until the rust eats right through, so would the electric charge prevent that rust starting on the inner side?

This also says "There are to date no official reports which show that cars with electronic rust proofing have less corrosion than they would without the device":

On that basis I certainly wouldn't buy one at the prices these systems are advertised at, but it seems they should be temptingly easy to make, and maybe try out in some experiments.

I can't find any DIY designs online, but the specifications on this page suggests that the electronics just make a 50V peak-to-peak AC voltage at 12.5KHz which is applied to the adheasive contact pads (copper tape?):

Input Voltage > 12V/24VDC Operating Voltage > 9V-32VDC Output Transformers > Two (2) Output Power (to each Pad) > 50Vpk-pk @ 12.5kHz Ground > Negative Current Draw > 25ma +/-

If that's all there is to it, then it shouldn't be hard to build my own equivalent.

Anyone know of existing DIY projects or authoritative proof that it doesn't (or does!) work?

• Waxy cavity coatings like this were actually what I was investigating when I stumbled onto these gizmos:

[Noddy]

<snip>

Don't waste your time. It's already been done. They don't work.

The best prevention against rust is to ensure that the metal is adequately coated with something that forms a durable and effective moisture barrier, and while electric processes exist to remove rust, there are none that prevent rust from occurring.

[Bud Frede]

A friend of mine tested this in the lab when I was in college. The devices don't work. They've been around for decades and they've never worked.

He wrote a paper on it for the class he was in, but I don't think it was ever published since it just debunked some junk science and didn't actually represent any new and valuable research in terms of chemistry.

[Clare Snyder]

My sister had one installed on her new Neon - which was later purchased by my youngest daughter. The entire front lip seam of the hood rusted away along with several brake lines and there was significant rust on the bottom door seams. This on a car that was kept pretty clean at all times. My "strong impression" was that the device was useless.

A good friend had the device installed on his new Pontiac car and GMC pickup. Both vehicles went back to the dealer/installer for the annual checkups and had THOUSANDS of dollars of rust repair performed under the provided rust warranty. Truck fenders replaced, truck hood replaced, box sides replaced - cab coprners and body mounts repaired - even rear step bumper replced IIRC. The hood and trunk were repaired on the car as well as front fender and lower rear quarter replcaement. The only value he got out of those devices was the rust repairs done because the devices did nothing. He sure got his money's worth out of both of them but it almost appeared the vehicles rusted MORE than average - - - certainly not less. I asked my neighbor - a chemical engineer - his opinion of the device and process and he stated unequivically there was no valid scientific hypothesis behind the product. He said on steel ships immersed in salt water the theory "held water" as well as on iron bridges subjected to road salt brine - but the implementation on a vehicle was at the very least "extremely problematic" - and this from a prof with numerous very advanced patents to his name - mostly in nanotechnology and advanced chromaography and instrumentation / sampling.

My Ford Ranger without the device - having been oil sprayed regularly for the first 10 years of it's life and sporadically for the last 18 has a LOT LESS rust than either the Neon, Pontiac or GMC and is still on the road after twice as many yars as any ot the three. (yes, I replaced the box but it was in better shape before replacement at 25 years of age than the GMC was after all the repairs at age 12). My 1988 Chrysler with 244000km on it at 18 years of age, oil sprayed twice in it's life, with no device installed had one hole repaired in the passenger's side floor and no visible rust when I sold (not scrapped) it in 2006.

These experiences are from south western Ontario, where in an average year (this year is ANYTHING BUT!!!) we have a lot of snow and use a LOT of salt on the roads. Just about 30 miles from Hubcaps

[Clare Snyder]

For cheep test parts go to your local panel beater and ask for damaged take-off panels. But trust me, the crap does NOT WORK on cars. The principal works on boats - but I think the implementation is different

[Bob F]

It works fine if you park in a pool of salt water. I can't imagine how it would work in air. What is the current path?

[Clare Snyder]

They only draw less than 1 Ma of current. Some claim as little as

1/3 of a ma (most of that from the tiny LED that indicates it is on, I would imagine) There does not need to be any current draw to provide a difference of potential between 2 components, and it is that potential difference (basically voltage) that is supposed to prevent corrosion

[Xeno]

That was my understanding, very little current draw.

Good point.

I was under the impression some of them mentioned a *frequency* of some sort but, as I have said previously, I have seen nothing in the way of detailed documentation on how they operate.

[Computer Nerd Kev]

As a capacitor, I expect the car body is very 'leaky', so keeping it charged would require a constant current to offset losses. This may be why the pulsed signals are preferred by at least the better documented designs. The first concern by the Canadian regulators seems to have been whether there was a capacitance effect at all or simply a dead short, hence a lot of test documention is about showing that the charge can be measured all over the surface of the vehicle's paint.

I already posted links to papers which describe how at least one device uses short pulses to charge then discharge the capacitance. There's more detail in the patent for an earlier device from that manufacturer:

It uses inductors in order to most efficiently generate current-limited electrical pulses. For my static experiment I'll be lazy and just limit the current with resistors in my DIY equivalent circuit, since for that I can use mains power.