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4Comments418 County Road 4709Joined June 1st, 2013

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  • Salvaging Rechargeables for Projects

    Actually, placing a bad cell in parallel with a good one is dumping energy from the good cell into the bad one with no current limiting other than the internal resistance of the cell. This can damage the good cell because the discharge rate is potentially very high, and it can result in excessive heat generation in both the discharging and dead cell. It can result in a fire hazard if either cell goes into thermal runaway. It is far safer, and better, to use current and thermal limited charging of lithium ion batteries. Most battery packs, especially for laptops, include thermistors attached to the cells to provide temperature information to a charge controller in the pack, or at least bring that out to pins on the connector to allow an external charger to control the charge current. ...see more »Actually, placing a bad cell in parallel with a good one is dumping energy from the good cell into the bad one with no current limiting other than the internal resistance of the cell. This can damage the good cell because the discharge rate is potentially very high, and it can result in excessive heat generation in both the discharging and dead cell. It can result in a fire hazard if either cell goes into thermal runaway. It is far safer, and better, to use current and thermal limited charging of lithium ion batteries. Most battery packs, especially for laptops, include thermistors attached to the cells to provide temperature information to a charge controller in the pack, or at least bring that out to pins on the connector to allow an external charger to control the charge current. As the temperature increases, the charge current should be decreased.

    I dont understand how putting the good cell in parallel with the bad one, and charging them as a pair does anything. As you pointed out, the bad cell will draw most of the current. The current limiting is performed by the charger. The good cell voltage will not rise until the bad cell voltage rises, meaning that it is beginning to charge. So, placing the bad cell on the charger is essentially all that is happening here. The good cell is basically along for the ride and gets whatever current is not used by the bad cell.

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  • dhafenstein commented on jimustanguitar's instructable De-Rust Your Old Table Saw1 year ago
    De-Rust Your Old Table Saw

    Actually, the story I heard was that WD-40 stands for "Water Displacement formula #40", and that is backed up by their own web site: http://wd40.com/cool-stuff/history. My father worked on the Atlas missile in the Air Force (545th SMS) and I can attest that they did indeed "sneek" WD-40 out for their own use. It was developed as a machining lubricant for aerospace and used by McDonnell-Douglas, Convair, and others for machining and protecting materials like aluminum and stainless from water. As far as I know, it contains no water, and is a water repellent/displacer. It was designed to not leave much of a residue and to be easy to clean up.

    I've done this exact same thing with a delta contractor saw that was also left out in the weather. I used "Naval Jelly", which is the same thing, and also finished up with Johnson's paste wax. I would like to comment that this is a very good way to clean up cast iron tools because as you pointed out, it is non-abrasive and will not deform the surface if reasonable care is exercised. I've also cleaned a band saw table that way after removing it from the saw. Keep naval jelly away from anything that you want to remain painted :) . Disassembly and cleaning, polishing, waxing, and reassembly is the way to go. Very good job describing the process. A++

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