I came across a load of aluminium tubes so I decided to build a seawater battery with some copper pipe I had left over. The aluminium is green anodized high military grade. I sanded one down back to bare ally and dipped it into saltwater with a copper tube and took a voltage reading, it read 0.75v, then I decided to take a reading with an un-sanded ally tube and it read 1.3v!  Is this normal? I thought I was going to have to sand them all back to bare but I think ill keep the coating now! I would love an explanation if anybody knows what's happening.

Quote from waf77 on January 21st, 2013, 08:00 PM

I came across a load of aluminium tubes so I decided to build a seawater battery with some copper pipe I had left over. The aluminium is green anodized high military grade. I sanded one down back to bare ally and dipped it into saltwater with a copper tube and took a voltage reading, it read 0.75v, then I decided to take a reading with an un-sanded ally tube and it read 1.3v!  Is this normal? I thought I was going to have to sand them all back to bare but I think ill keep the coating now! I would love an explanation if anybody knows what's happening.

That coating may be acting as a dielectric and what you have instead of a battery is a capacitor.  You may want to put some voltage across it and see if it charges up beyond 1.3 volts.