Expert: Mike Fulcher - 2/7/2009

Question
Mike,
I have succeeded in getting a Zamboni type cell to output 1.5V. Thank you for your previous assistance. I ended up stacking Alum foil, paper covered on one side with manganese dioxide and then conductive vinyl on the bottom. I have a nice cell that holds it's voltage.

My question has to do with a voltage problem when I stack the completed cells one on top of another. Plus to minus.
Let use say that I have 3 cells. Each cell tests out at 1.5 V. When I stack any 2 cells, I get 3.0 V. The problem happens when I attempt to stack a third cell or subsequent cells. The voltage goes to 3.4 or sometimes even lower. In fact, if I leave the 3 cells connected to the voltmeter long enough, it drops all the way down to 1.7 or even lower.

I then tried taking the same 3 cells and connecting each one in a separate clamp and then wiring up all 3 cells plus to minus. When I do that, I get 4.5 volts.

When you stack 1000 cells (as I have done), it behaves just like one big 1.5V battery, even though they are stacked plus minus plus minus etc. I was wondering if you had any idea what might be causing this?

I have been using a digital volt meter to test the voltages. Could I be in need of an electrostatic voltmeter to accurately measure the total voltage?

I was thinking that perhaps with the microscopic amperage of each cell that might make a difference. It just seems so strange that wiring them up separately gives the proper voltage, but stacking them makes one 1.5v battery.
Thanks for looking into this,
Paul

Answer
Paul

Sorry i took so long to get back to you, but work has been pretty overwhelming lately.  What you are describing sounds a lot like a phenomena referred to as current leakage.  This occurs in bipolar stacked cells (like the one you're building) when you have a ionic conductive path between cells that isn't impeded by the separator you have between the positive and negative plates.  Bipolar cells can function with positve and negative on opposite sides of a metal plate because while there is an electrical path through the metal, there is no ionic path to cause the cell reaction.  However, when you have a secondary path (typically electrolyte leakage around the edge of a plate or separator) the ionic reaction can occur and the stack will slowly discharge.  By disconnecting the cells and using wire to connect them, you've effectively isolated them from leakage and your voltage stays where it should.  It's difficult for me to accuartely diagnose what may be happening here without some graphical aids, but I'm not sure if there's any way to send drawings via this site.  If you'd like I can provide an e-mail by which we can exchange pictures of what we're talking about and maybe that will help us get to where you need to be.