5 ms·

Why can’t you have N cables supplying power to N cells in parallel?

• Afforess 6y ago
  heat dissipation. "charging" a battery is an exothermic chemical reaction.
  • Retric 6y ago
    Air can remove a lot of heat. A 98% efficient battery charging at 400kw is only producing 8kw of waste heat. At most you need a modest radiator and some fans. By comparison a normal 200HP engine at 30% efficiency is producing 667kw of waste heat into the air with a tiny percentage of that going out the exhaust pipe.
    • alacombe 6y ago
      Air is a pretty bad thermal conductor. An average ICE is only producing 200HP at a specific RPM, for short period of time. Red-lining any sedan while being stationary will probably overheat the engine pretty quickly, as the on-board radiator fan either electric or mechanical will not provide enough airflow. They are designed to be cooled by incoming air while driving.
      • ferongr 6y ago
        Not really. The actual load on the engine when redlining it while stationary is very small. You can monitor the fuel injector duty cycle, air flow mass or the useful "Load" PID using an OBD scanner like Torque.
        • alacombe 6y ago
          Whether or not there is torque applied is irrelevant. For the sake of argument, when talking with a carburated ICE (ie. no electronic optimization), at full throttle, whether you redline with a load or not, at the same RPM, the same vacuum will be produced at the intake, and you will burn the same amount of fuel, thus produce the same amount of heat.
          • ferongr 6y ago
            Well, with a carbureted engine that has no mechanism to limit RPM, you're probably not actually producing work at maximum RPM, but rather wasting mixture due to valve float. In essence, you're not burning that mixture. If you did, the RPM would keep increasing until the entire motor disintegrated. With electronic ignition, you usually have a way to limit max RPM by stopping ignition, so you're not producing work (and heat) either way.
            • alacombe 6y ago
              There mechanism to limit RPM on carburated engine, it's called a governor.
    • ben-schaaf 6y ago
      > By comparison a normal 200HP engine at 30% efficiency is producing 667kw of waste heat into the air This isn't really a fair comparison. Cooling capacity goes up with the temperature difference to ambient. It's a lot harder to cool 8kw of heat at 20C above ambient compared to 8kw at 200C above ambient.
      • Retric 6y ago
        That is a meaningful difference but we are talking ~1/100th the heat transfer. The majority of that heat is removed via the radiator which uses a liquid coolant which should not exceed 105C even when the outside temperature is 45C so that’s only 60C of wiggle room. Though it’s a fair point batteries have lower maximum temperatures, at worst reducing charging rates when outside temperatures exceed ~(110C or 43C) is hardly deceptive or particularly relevant to most people. High end cars could even use the car’s AC in extreme situations.
• handol 6y ago
  I was thinking I would get bored waiting for it to charge for 10 minutes. But if I can spend half the time plugging in cables, and half the time unplugging them, problem solved.
• elihu 6y ago
  I suppose you could have multiple charge cables, if the car was designed that way. You'd presumably need multiple charge ports and possibly multiple chargers (by which I mean the AC-to-DC or DC-to-DC converter built into the car) and for them to tolerate being connected in parallel with each other. Just to be clear, you'd ordinarily have the cells themselves in series or a bunch of parallel groups in series to reach high voltages, and as far as the charger is concerned it's just one big battery with a single positive and a single negative terminal. On the other hand, if you're suggesting balance charging where you have an individual connection with the charger between each cell, that's not really practical to do with large batteries because the current would be very high and the voltages very low, which, as far as cabling goes, is the worst-case scenario. Charging a single cell at 100 amps and low voltage requires basically the same size cable as charging a bunch of cells in series at 100 amps and high voltage. If you need a big, thick cable for each cell, that gets unwieldy very quickly. Another unpractical option is to switch the battery into a single parallel group during charging and charge the whole group as if it was a single low-voltage high-amp-hour cell. That's unpractical for the same reason; low-voltage charging is an inefficient way to move energy around. Also, switching from series to parallel would require a lot of high-current contactors (basically, electro-mechanical relays), which are kind of expensive.
• octoberfranklin 6y ago
  You can, but that's simply one N-times-thicker cable.