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Thread: Car Charging

  1. #1
    Can anyone tell me how long the cars need to stay on for, during the competition?

    Also, can you start the cars using a portable charger?

    Cheers

    Sam.

  2. #2
    Can anyone tell me how long the cars need to stay on for, during the competition?

    Also, can you start the cars using a portable charger?

    Cheers

    Sam.

  3. #3
    They normally run for whatever you want to warm them up(2-5 minutes), acceleration is about 1 minute per run, normally 2 runs are done back to back, autocross would probably run for about 2 mins(1 minute waiting in line, 1 minute running the course), with 2 runs also done back to back. Same for skidpad. Endurance the car is on for about 15 minutes, off for 3 minutes, then on again for 15 minutes.


    I would strongly suggest making the car charge itself so that you can start it without a portable charger. The drivers WILL stall the car somewhere, either just screwing up or when they spin out, but your car will shut off on you at least once at competition when you don't want it to. If you can't restart it on its own, you just took yourself out of that event.

  4. #4
    What if you had a battery that could supply enough Watts to your energy consuming sources (ECU, Elec water pump and thermofan) for an hour. Then use no altenator and just swap batteries every hour, having the other one on charge.

    With all the sources running at full load i calculated about 12 Amp hours required. Would the car not be able to be started if the altenator was ripped off?

    Is this a violation of the rules? The Stator and Rotor drains about 1 to 2 HP on the F4i I have been told, and I was looking at taking it off to also for space considerations.
    Regards,

    Sam.

  5. #5
    Sam,

    Something else to cosider. The ignition coils and injectors also require battery voltage to operate. As the battery discharges, there is less potential available to these components which changes their characteristics drastically. Once the voltage drops to a certain level, the injectors won't open in a timely matter and the coils will just stop firing (this occurs long before the battery is discharged). Even if the injectors and coils operate over the range of voltages you will see for the long events, you will need to map your engine at several different supply voltages to make sure you have accounted for the changing characteristics.
    Brian Lewis
    Performance Electronics, Ltd.
    www.pe-ltd.com
    http://www.facebook.com/Perf.Elec.Ltd
    Engine Management Systems

  6. #6
    Another thing to consider is the balancing effect of the rotor. I know a mini sprint racer that wears out crank bearings when he changes the rotor. He's able to run the engine, but it reduces it's lifetime, which is fine if you're ready, willing, and able to deal with it. But, it may catch you by suprise if you're not looking for the oil pressure to suddenly drop, indicating a worn out bearing.
    You may want to keep the rotor and ditch the stator if you really want to go down this road.
    UNM FSAE 2003 to 2005

  7. #7
    Batteries last a lot longer if you don't deep cycle them like that.

    Best way to figure out how much the charging system actually hurts you is on a load-controlled dyno. Best way to waste dyno time is to spend it analyzing your charging system when you should be optimizing your engine's breathing and/or maps.
    Buckingham

  8. #8
    Senior Member
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    717
    Sam,

    Treating the electrical system this way is possibly valid for a competition. However your result will probably be much more dependant on the effectiveness of your testing program than whether you have 1 or 2 more hp at comp time. During testing you will start and stop the car a lot. Each start takes a lot of juice.

    Do some quick calcs etc to find out what the extra horsepower will give you for on-track performance. Weigh it up against the saftey margin you will be taking away.

    Our team has been through a number of battery and charging related problems. We take a very conservative approach to the area now. You only have to look at where the first non-endurance finishing car ends up. In the 6 comps I have been a part of, not finishing endurance in Australia 2003 was the worst feeling I could ever imagine. It makes it impossible for me not to have sympathy for teams that don't finish and also impossible to understate the importance of reliability.

    So there goes.

    Alternator gives reduced pain in testing and a safety margin in the comp. I think worth the weight and horsepower disadvantages.

    Cheers,

    Kev

    ex-UWA Motorsport

  9. #9
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Alternator gives reduced pain in testing and a safety margin in the comp. I think worth the weight and horsepower disadvantages.
    </div></BLOCKQUOTE>
    I agree, Kev. A couple years ago the total loss (non)charging system was our hot ticket. Turns out our battery guy wanted to make it too complicated by using two batteries, one for starting and one for operation. When it finally came down to it we did ran 2 batteries AND the alternator, due to a little miscomunication (among other things).Good info though. I with we had asked back then.

    And about starting the car, rule 3.5.1.7 states "Each car must be equipped with an on-board starter, and be able to start
    without any outside assistance at any time during the competition."
    Joel Schmidt

  10. #10
    Senior Member
    Join Date
    Mar 2005
    Location
    Australia
    Posts
    1,690
    I agree that you should be careful with your electrical system - it is possibly the most common reason for DNFs.

    If you want to ditch the alternator it might also be a good idea to do the same with the starter motor. The most reliable electrical component is the one that isn't there! A lot of racecars use pneumatic starters, which are generally lighter and more compact than electric motors with the same power output. They also don't drop the battery voltage just when the spark coils need it most.

    This would really only make sense if the car had a compressed air tank, or better yet a CO2 bottle, already on board for some other purpose (eg. gearshifting, etc.). "Recharging" a compressed air bottle is also a very quick and easy operation. However, I'm not sure about the legality of onboard "energy" sources?

    Z

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