Nicholas Covey wrote:
The Edison Cell battery, also known as the Nickel Iron, or NIFE battery. They are bulky, have a higher self-discharge rate than lead acid batteries, and tend to take charge slowly.
Now the plus sides. They last practically forever. The electrolyte is primarily distilled water, potash, and maybe lithium (depends on who you talk to). This rather benign mixture doesn't degrade the cells like sulfuric acid tend to do, making physical damage almost impossible as long as the cells still contain electrolyte. They can be fully discharged without damage, can be overcharged without damage, and really take more of a beating than the typical lead-acid banks we normally see in the off-grid applications.
Nicholas Covey wrote:
So in the spirit of being a little different thinking, what would it take to make your own?
The most efficient use of space is likely a coil of these two together with an insulator between them (I was thinking of the plastic rug grid that is often used for yarn art projects and available at fabric stores) then roll them together into as tight of a package as possible, place into a vertical PVC pipe with capped bottom.
Edison batteries are one of those topics that pop on alternative energy boards from time to time. Everyone seems to agree that they make a lot of sense for stationary applications, but everyone runs into the same issues with respect to availability.
Len wrote: it seems that nickel doesn't lend itself to sponging like lead. Surface area is harder and costlier to get.
If you are trying to maximize surface area, couldn't you electroplate steel wool?
Other short points. We don't run any kind of voltage regulation on the charging system. I forget why this is but i think it's to eliminate the need to equalize the battery. But there also charged slow. 100mA to 150mA is typical.
As far as something like thermal runaway i have never herd of it happening with NiFe cells. As far as i know they actually like to run on the warm side. So long as you don't get them literally boiling hot they should be fine.
I think PVC would work. My father used to make machines out of PVC which were bathing in iron perchloride. One thing thought. This is industrial PVC, not suage pvc. The difference is, the suage pvc is charged with a lot of plaster. To make it cheaper. Industrial stuff is of a far darker grey. Shiny surface. Welds well.
Len wrote:Is the potash solution high PH? would that eat the PVC? Seems to me the old ones were glass cases. PVC would be nice if it works.