3 ms·

You can't run an electric car on straight battery voltage, unless you want the car to go a single speed. So you have two choices: DC-AC conversion to run a 3-p

by magduf 7y ago

You can't run an electric car on straight battery voltage, unless you want the car to go a single speed. So you have two choices: DC-AC conversion to run a 3-phase AC motor, or DC-DC conversion to run a DC motor at variable voltage. Either one is going to have similar losses with modern power electronics.

hinkley 7y ago
Couldn't you though? This motor has 48 coils, and the ability to change what order and groupings they get powered. Doesn't that change the current substantially without altering voltage? I don't think you would ever run one coil alone, but that leaves at least 9 other patterns where all coils fire evenly. And what is 'battery voltage'? Battery voltage is something like 2.8 volts, and that's not consistent across all cells at all levels of charge. Any voltage higher than that is due to composition. From what I recall, recharging multiple cells in series leads to some pretty big problems when some of the cells are aging faster than others. Being hard-wired is not a given. With 48 coils on the motor and a battery pack of 120 or more cells, there are a lot of voltages and currents you could run through the system by reconfiguring instead of inverting.
- magduf 7y ago
  >This motor has 48 coils, and the ability to change what order and groupings they get powered. Ok, great, so now you have a bunch of discrete speeds you can run the motor at. How smooth a ride do you think that's going to provide? If you can't run a motor at any arbitrary speed within its range, it's useless for any kind of vehicle. >And what is 'battery voltage'? Battery voltage is something like 2.8 volts No, that's cell voltage. A battery is a group of cells. That battery in your car that produces 12V is a group of 6 cells each producing 2V, with the cells all connected in series. As I understand it, Tesla batteries are rather high-voltage. >From what I recall, recharging multiple cells in series leads to some pretty big problems when some of the cells are aging faster than others. Yet somehow it works just fine for car batteries over the last 100 years, and for most every other battery we use these days (laptops, etc.). >With 48 coils on the motor and a battery pack of 120 or more cells, there are a lot of voltages and currents you could run through the system by reconfiguring instead of inverting. Yeah, again, if you just want to run at various discrete speeds. How many people are going to want a herky-jerky car like that?
  - hinkley 7y ago
    My point is it could be done, and these guys specifically claimed they don't need a DC-DC converter, so either they're lying, or there's something you and I don't understand. I'm just speculating on ways they could solve that problem. And you're giving so much salt back that I have to ask, do you believe they are lying? If so then don't beat around the bush. Just say it. You think they are frauds. > Yet somehow it works just fine for car batteries over the last 100 years, and for most every other battery we use these days (laptops, etc.). Every time I've replaced my car battery, it's been because one cell failed after I let it deep discharge. Except once where 2 cells failed. I thought Tesla did something more sophisticated with their packs, but I'm looking at a picture here and there are for sure ~40 cells wired in series. At best there are 4 batteries per array (or they may be connected on the back side). But you don't have to use that bus architecture. It's mechanically simpler and more robust. It's the default. But it's a compromise, favoring physical robustness for reduced chemical robustness. Some day I hope to see other solutions, perhaps like what I described.
    - magduf 7y ago
      They absolutely are frauds. Every time someone comes up with some new "breakthrough" like this, whether it's a new motor, or a new internal-combustion engine, it's a scam. Also, I'm giving a lot of "salt back" because I'm an electrical engineer, so I can see how all this stuff is total garbage. You're obviously not. I've even worked on 3-phase "DC brushless" motors and their controllers, so I do know what I'm talking about. This stuff about not needing a DC-DC converter is BS. Of course you don't need a "DC-DC converter" if your motor is AC, which every motor without a mechanical commutator is. You still need some type of power control circuitry to drive the motor; you can't hook it up to a battery! >Every time I've replaced my car battery, it's been because one cell failed after I let it deep discharge. Except once where 2 cells failed. If you did a deep discharge, the other cells were degraded too, you just saw the cell that failed first. >But you don't have to use that bus architecture. It's mechanically simpler and more robust. Yes, actually you do, unless you want to have ridiculous currents at only 4.2V going to your inverter, which would be stupid because you'd need bus bars and would still have high resistive losses. This is the whole reason we have batteries with series-connected cells instead of parallel-connected cells.

by magduf 7y ago

hinkley 7y ago

Couldn't you though? This motor has 48 coils, and the ability to change what order and groupings they get powered. Doesn't that change the current substantially without altering voltage? I don't think you would ever run one coil alone, but that leaves at least 9 other patterns where all coils fire evenly. And what is 'battery voltage'? Battery voltage is something like 2.8 volts, and that's not consistent across all cells at all levels of charge. Any voltage higher than that is due to composition. From what I recall, recharging multiple cells in series leads to some pretty big problems when some of the cells are aging faster than others. Being hard-wired is not a given. With 48 coils on the motor and a battery pack of 120 or more cells, there are a lot of voltages and currents you could run through the system by reconfiguring instead of inverting.

magduf 7y ago
>This motor has 48 coils, and the ability to change what order and groupings they get powered. Ok, great, so now you have a bunch of discrete speeds you can run the motor at. How smooth a ride do you think that's going to provide? If you can't run a motor at any arbitrary speed within its range, it's useless for any kind of vehicle. >And what is 'battery voltage'? Battery voltage is something like 2.8 volts No, that's cell voltage. A battery is a group of cells. That battery in your car that produces 12V is a group of 6 cells each producing 2V, with the cells all connected in series. As I understand it, Tesla batteries are rather high-voltage. >From what I recall, recharging multiple cells in series leads to some pretty big problems when some of the cells are aging faster than others. Yet somehow it works just fine for car batteries over the last 100 years, and for most every other battery we use these days (laptops, etc.). >With 48 coils on the motor and a battery pack of 120 or more cells, there are a lot of voltages and currents you could run through the system by reconfiguring instead of inverting. Yeah, again, if you just want to run at various discrete speeds. How many people are going to want a herky-jerky car like that?
- hinkley 7y ago
  My point is it could be done, and these guys specifically claimed they don't need a DC-DC converter, so either they're lying, or there's something you and I don't understand. I'm just speculating on ways they could solve that problem. And you're giving so much salt back that I have to ask, do you believe they are lying? If so then don't beat around the bush. Just say it. You think they are frauds. > Yet somehow it works just fine for car batteries over the last 100 years, and for most every other battery we use these days (laptops, etc.). Every time I've replaced my car battery, it's been because one cell failed after I let it deep discharge. Except once where 2 cells failed. I thought Tesla did something more sophisticated with their packs, but I'm looking at a picture here and there are for sure ~40 cells wired in series. At best there are 4 batteries per array (or they may be connected on the back side). But you don't have to use that bus architecture. It's mechanically simpler and more robust. It's the default. But it's a compromise, favoring physical robustness for reduced chemical robustness. Some day I hope to see other solutions, perhaps like what I described.
  - magduf 7y ago
    They absolutely are frauds. Every time someone comes up with some new "breakthrough" like this, whether it's a new motor, or a new internal-combustion engine, it's a scam. Also, I'm giving a lot of "salt back" because I'm an electrical engineer, so I can see how all this stuff is total garbage. You're obviously not. I've even worked on 3-phase "DC brushless" motors and their controllers, so I do know what I'm talking about. This stuff about not needing a DC-DC converter is BS. Of course you don't need a "DC-DC converter" if your motor is AC, which every motor without a mechanical commutator is. You still need some type of power control circuitry to drive the motor; you can't hook it up to a battery! >Every time I've replaced my car battery, it's been because one cell failed after I let it deep discharge. Except once where 2 cells failed. If you did a deep discharge, the other cells were degraded too, you just saw the cell that failed first. >But you don't have to use that bus architecture. It's mechanically simpler and more robust. Yes, actually you do, unless you want to have ridiculous currents at only 4.2V going to your inverter, which would be stupid because you'd need bus bars and would still have high resistive losses. This is the whole reason we have batteries with series-connected cells instead of parallel-connected cells.