It's a small thing perhaps that so many flashlights become unreliable with use, but it's been a pet peeve of mine for quite some time.
Many flashlights depend on the tip of the bulb to make contact with the positive end of the upper flashlight cell as sketched below on the left. This works okay for a while, but eventually, the metal of the bulb's tip deforms by flattening out while the positive tip of the flashlight cell also deforms by becoming concave as sketched below on the right.
Then the flashlight doesn't stay lit as I hold it. I have to shake a little it to get light or I have to twist the light bezel back and forth a little bit.
Continue reading "Flashlight Batteries and Bulbs - John Dunn, Consultant, Ambertec, P.E., P.C." »
The question of cell balancing really comes to the surface when we are considering multi-cellular battery packs and when we are considering chemistries based on Lithium. The reason for the interest in Lithium is its high specific energy density i.e. for a given weight it stores the highest Joule level or watt-hrs/kilogram. The drawback with Lithium is its sensitivity to over-charging or over-discharging. Either condition causes permanent loss of capability for the cell. The writers experience is with the hobby industry and interest in electric powered vehicles.
SOME BACKGROUND: For the electric vehicle industry a few different chemistries have been used. Specifically lightweight lead-acid, nickel-iron, nickel cadmium and nickel-metal hydride. All these chemistries can withstand moderate over-charging and even over-discharging to the point of cell voltage reversal. Experience by Toyota (and others) has shown by keeping the SOC, State Of Charge, within a 20% to 80% range the batteries will yield long life and support peak loads such as by acceleration and fast recharges by dynamic braking. The negative point about these chemistries is weight-----compared to Lithium they are nearly 2 to 1 heavier.
Continue reading "CELL BALANCING BASICS:-- Carl Schwab" »
