Science experiments at home - what have you learned recently?

Discussion in 'Chemistry' started by wegs, Jun 12, 2023.

  1. wegs Matter and Pixie Dust Valued Senior Member

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    So, over the weekend, I’d placed several ice cubes in a bowl of cold water, and the combination almost instantly reduced the heat of hard-boiled eggs fresh out of boiling hot water (15 minutes), to room temperature. It’s a game changer! I’m amazed at how rapidly the temperature decreases.

    What scientific discoveries have you made/tested on your own?
     
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  3. billvon Valued Senior Member

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    A lot of discoveries about power electronics. A new way to do lithium ion balancing for example
     
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  5. wegs Matter and Pixie Dust Valued Senior Member

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    That sound fascinating. How do you safely test this at home? How do cells become “unbalanced?”
     
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  7. billvon Valued Senior Member

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    Lead acid batteries are very tolerant of overcharging. If you put a bunch in series and charge them, the "high" cell (the cell with the highest voltage) will just stop at about 2.5 volts and outgas (i.e convert water into hydrogen.) So if you charge them for long enough all cells hit 2.5VPC and you are then fully charged.

    Lithium ions are not. So if you put a bunch in series and try to charge them without a balancer, one will hit 4.2 volts before the others. (4.2 volts is their maximum.) If you keep charging, that cell will go over 4.2 volts and eventually either fail or catch fire. If you stop charging right at that point, then the other cells will not get a full charge.

    This is somewhat important with laptops since they have three cells in series to get around 10.8 volts. It is VERY important with electric vehicles since they are often 96 cells in series to get 360 volts.

    So how do you balance them, to make sure that no cell ever gets above 4.2 volts while not undercharging the rest of the cells? That's the question. There are a lot of ways to do it. I found a way to do it with two "fast" switches (like MOSFETs) and a number of slow switches (like relays or bipolars) equal to the number of cells. For large batteries this will be much cheaper than other ways that have a lot of circuitry per cell.
     
  8. Seattle Valued Senior Member

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    I cooked a steak this weekend, in the oven, using a grilled pan. After the steak was done, I took the pan and filled it up with water. It instantly cooled off, from 400 F or so to room temperature.

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  9. wegs Matter and Pixie Dust Valued Senior Member

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    Lol - I should have elaborated. As compared to say taking the eggs out of boiling water and placing them directly in the refrigerator, this method of ice cubes in a bowl of water reduces the heat much faster. Like in two minutes. It takes 30 -40 minutes in the refrigerator and they’re still slightly warm to the touch.

    What can I say, it was amazing.

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    Last edited: Jun 13, 2023
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  10. exchemist Valued Senior Member

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    Water has a very high specific heat capacity, i.e. it can absorb a lot of heat without increasing much in temperature. I have always cooled hard boiled eggs by replacing the boiling water with just cold tap water, changing it once after 5 mins. Your use of ice avoids the need for even that. As you say, 15 mins is enough. Cooling in the fridge relies on contact with cold air and will be far less efficient. Chilling wine is similarly much faster using cold or iced water than putting the bottle in the fridge.

    Another tip with hard boiled eggs is not to cook them for too long if you want to avoid that grey ring round the edge of the yolk, which is due to sulphur compounds. About 10 mins if they are cooked from room temperature, or a couple of minutes longer if you keep eggs in the fridge.
     

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