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Thread: Electric 600V Design Questions

  1. #11
    Thanks again, guys. I tend to agree that the discrepancy in voltages doesn't make sense. 300V will kill you as dead as 600V will. In the end, students should be applying the same basic principles to working around any high voltage systems. I fully agree that the voltage limits should be the same.

    I do not necessarily see that dropping to 300V is a massive performance bottleneck (which I attempted to outline). I am still hoping that someone much more familiar with the electrical side will chime in with some math showing why higher voltages are beneficial in accumulator, motor, and inverter design. Those guys/gals are probably locked away doing development right now! There is unfortunately not much readily available information via Google. If it really is just cable and interconnect weight (because it isn't in the motor, inverter, or cell configuration), then I guess it would depend on drive configuration as to whether the extra is significant or not. It probably is on 4wd cars or ones with long cable runs. Doing some quick math with a 20ft cable length, it looks like you'd gain around 1.5-4lbs in cable. That's definitely not insignificant, but you could starve your driver if necessary

    I'm somewhat surprised by the lack of advancement of US E-car teams, in general. It seems like the same story in Hybrid as FSAE-E. There just are not very many US teams that have been able to put together a successful E-car. In the three years FSAE-E has existed, no US team has run dynamic events more than once. In each year, only one team has completed all events, with only one US team doing so in any of the three years. Only one team that has competed in either dynamic or static events has made it to competition all three years, and they haven't completed a single dynamic event. In fact, only three total US teams in three years have run any dynamic events at all. In Hybrid, many teams showed up with impressive specs and lofty goals, only to fail tech or even just attempt to assemble their car in the paddock. Something is very wrong here. The teams that did compete were not competitive with combustion cars. While fair or not, I've seen it blamed on the voltage limit when many teams aren't even passing tech, much less competing in all events. I don't think the 5 extra pounds of interconnect weight is explaining this disparity.
    Cole Easterling
    Brendon & Lawrence Mfg.
    2011-2012 TAMU FH/FSAE

  2. #12
    Just for fun, I made a graph that shows battery voltage distribution at the last German competition.



    And as a bonus:



    A grand total of one team would have been eligible to run in the US
    (namely the Indian team with the 134V battery. The guys from Beijing actually cited 302V, so I guess they wouldn't have been allowed either)

    Update: just found out that the 300V team runs 2 300V batteries in series, so actually 600V. I've updated all graphs accordingly

    Thijs
    Last edited by Thijs; 02-18-2016 at 11:42 AM. Reason: updated graphs
    Alumnus
    Formula Student Team Delft

    2007 - 2008: Powertrain, Suspension
    2009: Technical Lead
    2010 - present: Grumpy Old Fart/Concerned Citizen

  3. #13
    There is a team from the Czech Republic registered this year. I am not sure if they have plans for any European comps or what voltage they run.


    http://students.sae.org/cds/formulaseries/electric/teams/
    Electrical Lead / ESO
    Formula Electric Racing
    Missouri University of Science and Technology

  4. #14
    According to their website, CTU were running 260V last year (their fourth car).
    They've previously competed in Italy, Hungary and the Czech Republic.

    I hope UTA and Washington will make it to Germany this year.
    Alumnus
    Formula Student Team Delft

    2007 - 2008: Powertrain, Suspension
    2009: Technical Lead
    2010 - present: Grumpy Old Fart/Concerned Citizen

  5. #15
    Interesting. I'm hoping the bump in teams in the US helps this year across the board. The competition in the US should be well ahead of where it is with or without the voltage limit.

    One thing I noticed last year is most teams had one or two people who handled electronics in the car (ourselves included). I think that is having a big impact right now in the US as teams get a car together that works or kinda works, the electrical people graduate, the knowledge disappears and the team slips. We've been having lots of issues finding people interested in electronics since our school is geared toward power systems (substation and power plant type work). We are still trying to figure out how to get that "A team" Claude has talked about.

    I would be interested in seeing what types of continuous powers and currents teams are seeing with their cars at the lower and higher voltages. Our team had a very limited car last year: realistic 50kW peak, 20kW cont and 100A cont. for reference which makes me wonder how much of a weight penalty there is with the lower voltage limit.
    Electrical Lead / ESO
    Formula Electric Racing
    Missouri University of Science and Technology

  6. #16
    Thijs,

    That's some great information! I, too, think it would be interesting to see what kind of power teams are quoting for their stated voltage, as well as their actual competition weight.

    I guess one of the main points I haven't articulated well is that I think there are much greater contributors to car weight than the voltage spec'd for a system, at a given power. Still assuming you'd gain <5lbs total at 300V vs. 600V, bare chassis design weight alone varies much more. Tire choice, too. What I see from the graphs is that the average voltage of the top 10 cars is around 450V. I haven't kept up with competition placings, but how much more dominant are the top few cars over the rest of the top 10?
    Cole Easterling
    Brendon & Lawrence Mfg.
    2011-2012 TAMU FH/FSAE

  7. #17
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    Thijs,

    Thanks for posting the graph, it is very interesting. For clarity I have put a rough line for the Pareto set which shows the boundary of the data.



    Given the number of teams around 450 and 600V a t-test on the data might be interesting.

    Kev
    Last edited by Kevin Hayward; 02-17-2016 at 05:29 PM.

  8. #18
    more graphs!

    Quote Originally Posted by coleasterling View Post
    I haven't kept up with competition placings, but how much more dominant are the top few cars over the rest of the top 10?
    pretty dominant:


    Although it's worth mentioning that (based on their autocross times) three teams would have probably been able to finish around top 5 or 10 but broke or DQ'd in endurance, so it may not be quite as bad as the above graph suggests.

    Quote Originally Posted by coleasterling View Post
    I, too, think it would be interesting to see what kind of power teams are quoting for their stated voltage, as well as their actual competition weight.


    This uses stated power and official competition weights.
    Zürich is the only team that's above a boundary that appears to limit all other data points.
    Do keep in mind that the highest specific power values are achieved through enormous amounts of power, that you're not actually allowed to use at the competition
    (1/3 of all teams have 100+kW which is well over the power limit, and 5 teams have over 130kW)

    disclaimer: I'll happily leave it up to everyone to decide for themselves if they want to conclude anything from these graphs, but yay, data!
    Last edited by Thijs; 02-18-2016 at 11:39 AM.
    Alumnus
    Formula Student Team Delft

    2007 - 2008: Powertrain, Suspension
    2009: Technical Lead
    2010 - present: Grumpy Old Fart/Concerned Citizen

  9. #19
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    I performed a two-tailed t-test on the data looking at final placing. The two populations were teams above 500V and teams between 300 and 500V. The average placings were as follows:

    > 500V : 16.2
    300-500V : 21.2

    Given the difference in mean it is worth considering a t-test. Making the assumption of unequal variance the p-value was 0.17. On that basis from the data supplied we cannot make the claim that having a voltage of above 500V is a significant indicator of finishing place when compared to 300-500V.

    Obviously more data could be used to refine this value, and may show that there is a significant difference.

    It is probably better to do this against dynamic points rather than position, but you work with what you have.

    Actually considering just outright performance it might be worth just looking at the autocross event as the final points will be very influenced by reliability of the endurance event.

    Kev
    Last edited by Kevin Hayward; 02-17-2016 at 06:05 PM.

  10. #20
    Quote Originally Posted by Kevin Hayward View Post
    Actually considering just outright performance it might be worth just looking at the autocross event as the final points will be very influenced by reliability of the endurance event.
    The data is there. We can always make more graphs


    Although obviously this too is still very noisy data from very small data sets (6 teams from the top 10 only drove two laps) and we have no idea of the influence of driver skill, but I guess it's the closest thing we have to putting a number on outright speed for each car.
    Last edited by Thijs; 02-18-2016 at 11:42 AM. Reason: updated graph
    Alumnus
    Formula Student Team Delft

    2007 - 2008: Powertrain, Suspension
    2009: Technical Lead
    2010 - present: Grumpy Old Fart/Concerned Citizen

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