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These cells have been covered quite a bit already but I wanted to share some experience I have had with them. I have made many different versions from copper end caps to copper pipe buried in Alum with mag,, my latest seems to be the way to go so here it is.
I started with 1 inch PVC end caps for the base. This gives a great non conducting base to attach the magnesium too without need for a separator. I used 1 inch type M copper pipe and cut it to 3 1/2cm. The magnesium is pure, not electrodes which I cut to 4 1/2 cm.
On most of my previous attempts I uses electrodes which have a steel core. When I have taken them apart I did see corrosion so I do not recommend them, use pure magnesium and copper only.
Before beginning any construction I drilled a tap hole in the top for mounting a eye connector and attached that. Next I hot glued the core to the base and it is ready for filling.
Here is a shot of the parts before any treatment of the copper.
On previous builds I had completely submerged the core and cut grooves into it to tightly wrap the electrode around it. Over time that method did fail and caused loose connections, that is why I used screws this time and most importantly I intentionally let the top protrude so that the screw will not be in the electrolyte. You do not want a third metal in the electrolyte such as a screw or wire, this was one problem with earlier builds I have made.
Now for treating the copper. I learned a great deal this time about how to get the best semi conductor layer. I used to over do it with the heat. I would do three heats and dips into the Borax each time bringing the copper to cherry red. This is not the best way! You will notice in the picture below the vast color difference between an early build, the small one, and the new cell.
For the first burn I did bring it to cherry red. I did this to burn off all oils or debris that were on the pipe. Let it cool for a bout two min and dip it in the borax.
For the second and third burns pay attention to the metal while you are heating it. It will get to a point where you see all kinds of swirling colors in it, this is almost where you want it. Continue for a very short time after this until it looks uniformly grey not red or glowing, just grey. This is where you want it to be, stop heating it and set it aside. Now let it cool long enough to form a good layer on it but still a bit hot when you dip it. You may have to play around with the timing but it is important not to dip it too soon, the cooling process is just as important as the heating.
Here is a picture of the finished cell along side of an earlier build. The cell is putting out 1.5 volts and two of them in series drives an LED with no problem. I have not done much testing on them but I can tell this is the best model I have made so far. I already know what to expect from them since I have made so many other versions.
These were really easy to construct and I think I have overcome some design flaws of my earlier attempts.
------BobZilla
I started with 1 inch PVC end caps for the base. This gives a great non conducting base to attach the magnesium too without need for a separator. I used 1 inch type M copper pipe and cut it to 3 1/2cm. The magnesium is pure, not electrodes which I cut to 4 1/2 cm.
On most of my previous attempts I uses electrodes which have a steel core. When I have taken them apart I did see corrosion so I do not recommend them, use pure magnesium and copper only.
Before beginning any construction I drilled a tap hole in the top for mounting a eye connector and attached that. Next I hot glued the core to the base and it is ready for filling.
Here is a shot of the parts before any treatment of the copper.
On previous builds I had completely submerged the core and cut grooves into it to tightly wrap the electrode around it. Over time that method did fail and caused loose connections, that is why I used screws this time and most importantly I intentionally let the top protrude so that the screw will not be in the electrolyte. You do not want a third metal in the electrolyte such as a screw or wire, this was one problem with earlier builds I have made.
Now for treating the copper. I learned a great deal this time about how to get the best semi conductor layer. I used to over do it with the heat. I would do three heats and dips into the Borax each time bringing the copper to cherry red. This is not the best way! You will notice in the picture below the vast color difference between an early build, the small one, and the new cell.
For the first burn I did bring it to cherry red. I did this to burn off all oils or debris that were on the pipe. Let it cool for a bout two min and dip it in the borax.
For the second and third burns pay attention to the metal while you are heating it. It will get to a point where you see all kinds of swirling colors in it, this is almost where you want it. Continue for a very short time after this until it looks uniformly grey not red or glowing, just grey. This is where you want it to be, stop heating it and set it aside. Now let it cool long enough to form a good layer on it but still a bit hot when you dip it. You may have to play around with the timing but it is important not to dip it too soon, the cooling process is just as important as the heating.
Here is a picture of the finished cell along side of an earlier build. The cell is putting out 1.5 volts and two of them in series drives an LED with no problem. I have not done much testing on them but I can tell this is the best model I have made so far. I already know what to expect from them since I have made so many other versions.
These were really easy to construct and I think I have overcome some design flaws of my earlier attempts.
------BobZilla
i do follow your suggestion on making semiconductor copper (0,4mm copper sheet).. treated 4x dip on borax water 
.. TIA
....... it is also happen on my first attempt on treated copper with different size (1mm) 
) and it seem the Mg still deteriorate 
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