Read a round a bit,
Used the "majority rule" method of design, went and picked through the junk and....
5 gallon plastic bucket
about 15' of old barbed wire wound inside the bucket. Should give good line of sight, the wire is evenly spread top to bottom and all around. (Non rusty would be better but this is working so far.)
Some plastic mesh screen I had to reduce the odds of the battery box touching the barbed wire.
An old battery charger set at 10 amps 12 volts.
about 1/2 cup of Arm and Hammer Super wash soap
Used hot soft water to fill the bucket, speeds up dissolving the soda and reactions?
red wire on the barbed wire, black to the part.
Now it's bubbling away.
Breathless updates later.
Notes; New "Automatic" battery chargers won't work unless you also have a "good" battery in parallel with the solution.
A few "internet experts" cautioned against stainless, galvanized, zinc copper etc. cathode, shrug, carbon is noted as an ideal cathode. Much or most of my old metal is either painted or galvanized, neither is a good thing for the sacrificial plate.
The ding against stainless is that it contains chromium no reason make a witches brew out of your waste "water".
Thought this was a good do/don't list.
"check the label of the "Laundry Soda" and make sure it's actually (mostly) sodium carbonate. If it's not the first material listed, I'd say try again. (don't use Borax)
don't use galvanized materials. The process should still work- I'm not sure- but the zinc leaches out into the water. No reason to contaminate it, especially if you're going to be disposing of it by dumping it on the lawn, in a storm sewer or down the drain.
add more sacrificial plate. The positive or waste plate should be roughly the same surface area as you're trying to strip. A small sheet of 22 or 24 ga sheetmetal is cheap, and easy to cut into sections with some snips. Or be creative- I used a bunch of pieces left over from dismantling a large copier, and you might find somebody throwing away an old microwave or something, that you can cut some panels off of. Any clean steel will do, and it gets nasty-rusty, so make it cheap as possible and stuff you won't mind throwing away.
It's a slow process, and slower still if you have a very small positive plate. Expect the process to take at least all day, overnight. Large pieces with heavy rust could take several days. It won't hurt a thing to leave it in even longer. Some people have said that a low amperage and longer time does a more thorough cleaning.
The data: Red/positive to the waste plate(s), black/negative to the piece to be stripped. About 1/3rd to 1/2 cup of washing soda or baking soda per five gallons of water. Don't use galvanized, don't use stainless steel. Have a hose and several stiff brushes to give it a good scrubbing when you're done. I use a small wire toothbrush on some stubborn spots. Have a good protectant on hand, as it'll instantly get surface rust as soon as it dries."
Doc.
The labeling of cathode and anode is a bit confusing but I guess since this is a power "consuming" device; the plus side is the anode, the negative side, the part being de-rusted, is the cathode.
From Wikipedia;
The polarity of voltage on an anode with respect to an associated cathode varies depending on the device type and on its operating mode. In the following examples, the anode is positive in a device that consumes power, and the anode is negative in a device that provides power:
In a discharging battery or galvanic cell (diagram at right), the anode is the negative terminal because it is where the current flows into "the device" (i.e. the battery cell). This inward current is carried externally by electrons moving outwards, negative charge moving one way constituting positive current flowing the other way.
In a recharging battery, or an electrolytic cell, the anode is the positive terminal, which receives current from an external generator. The current through a recharging battery is opposite to the direction of current during discharge; in other words, the electrode which was the cathode during battery discharge becomes the anode while the battery is recharging.