Depending on the size of the job, a simple DC power adaptor will work fine. Larger items like and axe head or larger, you may want to use a 12V battery charger. A vinegar bath or Evaporust works good on iron too.
Not baking soda?
Here is a great article
Rust Removal Using Electrolysis
Also aquachigger has a good video on electrolysis
Cheers
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My wife collects cast iron cookware and I get the privilege of cleaning it. I built a electrolysis tank. I use a 12v battery charger and arm and hammer washing soda. Arm and hammer washing soda is a sodium carbonate as baking soda is a sodium BI-carbonate, You can put bi-carbonate into an oven and cook it at 200 degrees for an hour and convert it to a carbonate. The battery charger needs to be powerful enough to get the job done speedily. I use a SCHUMACHER SE-5212A-CA Smart Charger,50/10/2A. It runs at nearly 10 amp continuous which make for a faster cleaning cycle. Make sure the charger is a manual charger as the automatic chargers don't work for electrolysis. I clean several skillets at a time so I use a big tank. Electrolysis is the best way to clean cast iron.