For my science classes, I have built multiple types of electrochemical batteries utilizing oxidation-reduction reactions, and I have demonstrated that they each produce potential difference across the different solid metals used using a voltmeter. Unfortunately, I have been unable to harness any of this to light up a simple lightbulb.
For my first demonstration, I used a copper and zinc strip in vinegar solution. There was a voltage difference across them of about 0.9V. This was lower than the 1.1V I was expecting, so I hooked up two of these in series to produce 1.8V. I attempted to light a simple light bulb (which works perfectly with a 1.5V D battery), but there was nothing. No current flowed.
For my second demonstration, I made a voltaic pile with cardboard in vinegar, zinc discs, and copper discs. Again, I had a great voltage prepared (about 3V or so), but I could get no current.
For my latest demonstration, I tried a 1.0M CuSO4 solution with a Cu strip in it connected to a 1.0M ZnSO4 solution with a Zn strip in it via a salt bridge of 0.2M KNO3. The voltage difference was about 1.1V spot-on, but again, I could get no current to flow through the light bulb.
What could I be doing wrong? Is there something fundamental I am forgetting here, or is there something perhaps wrong with the items I am using? My original copper and zinc strips were about 1mm thick, if even that, so I replaced them with thicker strips in later demonstrations, but that did not fix anything.