All you need is a 'dumb' 12V battery charger (as in, one old enough that doesn't shut off when it thinks your battery is shorted), a plastic container, water, a piece of sacrificial junk steel, and either TSP or washing soda.
It's quite simple; mix about 1/4 cup of washing soda/TSP per gallon of water, and put that and your wheel into a plastic tub. Put in the scrap steel (make sure a clean spot of it is protruding from solution so there is a place to connect the battery charger) and make sure the scrap piece isn't touching the wheel. Connect the positive terminal of the charger to the sacrificial piece, the negative terminal to the thing you are trying to clean, and plug in the charger. Bubbles should start forming on the piece to be cleaned, and the charger should indicate a current draw. If not, the solution is not strong enough to conduct, or there is a bad connection. Come back in a few hours and wire wheel off the remaining paint and black residue that has formed.
The solution can be reused almost indefinitely- I have been using the same 10 gallons for 2 years now to clean dozens of things.