[Vwdiesel] More on radiator as a battery (weekend science thread)

paulr reichp at earthlink.net
Wed Nov 3 21:26:10 EST 2004

There is a ship, I believe the Queen Elizabeth II, that is permanently
anchored off the California coast.  There is a series of rods placed around
her in the seawater, all wired together. Think she's been there quite a while

A DC current is fed continuously between the rods and her hull to prevent
hull breaches.   Don't know what how many amperes are required to neutralize
corrosion.  The surface area of her hull would suggest a fair amount.

The actual voltage that appears between the rod-to-hull "battery" is set
by the electro-chemical potential between the rod material and the ship's
steel hull. They might be using copper, don't quote me.

Principle is identical to why a proper, *working* lead acid cell *always*
has about 2 volts open circuit voltage, and *always* charges at 2.2 - 2.4
volts (DC), depending on temperature. It's derived from the periodic table
of the elements (chemistry).

Alternating current is absolutely the Wrong Thing to do.

Sorry, I can't remember the article where I read about it. Perhap's
googling for the QE-II museum would turn up some details.

As far as our Al-Fe corrosion, the surface areas of the various parts and the
sacrifical metal type would determine the "reverse" current required to prevent
corrosion.  DC current value is critical. Too little and corrosion occurs
(more slowly). Too much, and the flow of metal reverses.

Couldn't even hazard a guess.  The current requirement needs to be determined
over a significant period of time, considering the presence of Fe/Al, and what
ever sacrifical anode you might use. Perhaps magenesium, as in a water heater?
A perfect amateur science experiement.


2000 Golf TDI


Mark Shepherd wrote:
> Ah! several people have pointed to the 'Evans' site for
> their coolant alternative. I'm not particularly impressed
> with the sense of  uniqueness that is portrayed by their
> site... All it seems to me is an Ethylene/Propylene Glycol
> mixture which for the NPG+ is improved by 32% on NPG for
> thermo-conductivity (from what initial value?)... As pure
> glycols are about 2/3 that of water and not much better than
> half the SHC of water. Does this account for the offer to
> sell a higher performance pump?
> Anyone any thoughts of the reverse voltage idea to protect
> the radiator?
> Miser
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Paul Reich                Electrical Engineer

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