6 ms·

That is one sweet vehicle. I'm working at a college where students are restoring a Detroit Electric from 1918. The car is in excellent shape, electrically, mech

That is one sweet vehicle. I'm working at a college where students are restoring a Detroit Electric from 1918. The car is in excellent shape, electrically, mechanically and visually. The lead acid batteries were removed by the previous owner. The students are now fitting in Li-Ion batteries. There will be no power electronics, just a mechanical switch that can put coils of the 4 pole DC series wound motor either in parallel (high torque) or in series (high speed). The motor has 4.5HP and the car has a top speed of 35km/h.

homero 9y ago
No electronics is hard. By the time my temptations are done, the inside would be full of lcds.
justin66 9y ago
Why would putting the batteries in parallel offer more torque?
- deleted 9y ago
  [deleted]
- tonyarkles 9y ago
  http://www.me.umn.edu/courses/me2011/arduino/technotes/dcmotors/motor-tutorial/ http://www.me.umn.edu/courses/me2011/arduino/technotes/dcmot... My guess is that this is putting the coils in parallel, not the batteries. According to that link, the applied voltage determines the speed and the applied current determines the torque. I don't know the exact configuration of the windings in these motors, but having the coils in series should be putting a higher voltage on the motor (higher resistance), and having the coils in parallel should have more current (lower resistance). Pretty neat way to get a "2 speed" transmission. Of course, it's not going to be as good as the current generation of BLDC motors (variable speed is tricky with bang-bang control...), but for the time it's a pretty clever solution.
  - donquichotte 9y ago
    Great explanation, as far as I recall that is exactly how it works.
  - justin66 9y ago
    Thanks!
  - andars 9y ago
    This seems potentially backwards to me. If we apply a voltage source across the terminals, parallel coils between the terminals would result in higher voltage across each coil than would series coils. With series coils, the total voltage applied would be divided between the coils. Could someone clarify?
    - tonyarkles 9y ago
      I'm looking at it as a total system. You've got, say, a 12V battery with some internal series resistance. And, say, the two coils are 6 ohm each. Let's say the internal resistance of the battery is 1 ohm, arbitrarily. If the two coils are in series, you'll have a total coil resistance of 12 ohms (13 ohms incl internal resistance), and will get 0.923A (12V/13ohm) through the motor, with a terminal voltage of 11.07V (12V x 12ohm/13ohm). If the two coils are in parallel, you'll have a resistance of 3 ohms, and a current of 3A through the motor (12V/4ohm), and a terminal voltage of 9V (12V x 3ohm/4ohm). Lots more current, but lower terminal voltage. Edit: formatting
  - cr0sh 9y ago
    > Pretty neat way to get a "2 speed" transmission. It's almost identical to how the two speed "transmission" works on 12 volt Power Wheels toy ride-on vehicles. In those, there are two motors connected to the rear wheels; one for each wheel. Using a couple of switches on the "shifter", the motors can be connected to the battery in series (high speed) or parallel (low speed). Also interesting is that by using two separate motors in that manner, you gain a form of "electromechanical" differential (not that it matters much, as the plastic wheels have insane amount of slippage on most surfaces).
dsfyu404ed 9y ago
> I'm working at a college where students are restoring a Detroit Electric from 1918. The car is in excellent shape, electrically, mechanically and visually Having worked with ME students in the past I can say with confidence you won't be using those adjectives to describe the project when they're done with that. Rookie mistakes aside, what you do for grades has little overlap with what you do to get a good result. Every college engineering project has this problem. The things you'd do to deliver the best result possible with the resources you have are not the same things you'd do if you're optimizing for grades. You do dumb things run a simulation to prove you can and check the box when in reality you should just over-build it and spend the time on part of the project that's gonna require a few revisions to get right.
- rosser 9y ago
  Wait, what? You do things differently when the goal of the exercise is learning instead of production? Of course you do. Why on earth would you think that's a bad thing?

homero 9y ago

No electronics is hard. By the time my temptations are done, the inside would be full of lcds.

justin66 9y ago

Why would putting the batteries in parallel offer more torque?

deleted 9y ago
[deleted]
tonyarkles 9y ago
http://www.me.umn.edu/courses/me2011/arduino/technotes/dcmotors/motor-tutorial/ http://www.me.umn.edu/courses/me2011/arduino/technotes/dcmot... My guess is that this is putting the coils in parallel, not the batteries. According to that link, the applied voltage determines the speed and the applied current determines the torque. I don't know the exact configuration of the windings in these motors, but having the coils in series should be putting a higher voltage on the motor (higher resistance), and having the coils in parallel should have more current (lower resistance). Pretty neat way to get a "2 speed" transmission. Of course, it's not going to be as good as the current generation of BLDC motors (variable speed is tricky with bang-bang control...), but for the time it's a pretty clever solution.
- donquichotte 9y ago
  Great explanation, as far as I recall that is exactly how it works.
- justin66 9y ago
  Thanks!
- andars 9y ago
  This seems potentially backwards to me. If we apply a voltage source across the terminals, parallel coils between the terminals would result in higher voltage across each coil than would series coils. With series coils, the total voltage applied would be divided between the coils. Could someone clarify?
  - tonyarkles 9y ago
    I'm looking at it as a total system. You've got, say, a 12V battery with some internal series resistance. And, say, the two coils are 6 ohm each. Let's say the internal resistance of the battery is 1 ohm, arbitrarily. If the two coils are in series, you'll have a total coil resistance of 12 ohms (13 ohms incl internal resistance), and will get 0.923A (12V/13ohm) through the motor, with a terminal voltage of 11.07V (12V x 12ohm/13ohm). If the two coils are in parallel, you'll have a resistance of 3 ohms, and a current of 3A through the motor (12V/4ohm), and a terminal voltage of 9V (12V x 3ohm/4ohm). Lots more current, but lower terminal voltage. Edit: formatting
- cr0sh 9y ago
  > Pretty neat way to get a "2 speed" transmission. It's almost identical to how the two speed "transmission" works on 12 volt Power Wheels toy ride-on vehicles. In those, there are two motors connected to the rear wheels; one for each wheel. Using a couple of switches on the "shifter", the motors can be connected to the battery in series (high speed) or parallel (low speed). Also interesting is that by using two separate motors in that manner, you gain a form of "electromechanical" differential (not that it matters much, as the plastic wheels have insane amount of slippage on most surfaces).

dsfyu404ed 9y ago

> I'm working at a college where students are restoring a Detroit Electric from 1918. The car is in excellent shape, electrically, mechanically and visually Having worked with ME students in the past I can say with confidence you won't be using those adjectives to describe the project when they're done with that. Rookie mistakes aside, what you do for grades has little overlap with what you do to get a good result. Every college engineering project has this problem. The things you'd do to deliver the best result possible with the resources you have are not the same things you'd do if you're optimizing for grades. You do dumb things run a simulation to prove you can and check the box when in reality you should just over-build it and spend the time on part of the project that's gonna require a few revisions to get right.

rosser 9y ago
Wait, what? You do things differently when the goal of the exercise is learning instead of production? Of course you do. Why on earth would you think that's a bad thing?