Page 1 of 6 123 ... LastLast
Results 1 to 10 of 59

Thread: Can i calculate the battery side current?

              
   
   
  1. #1
    Senior Member __Tango's Avatar
    Join Date
    Aug 2010
    Location
    Mountain View, CA
    Posts
    735
    Post Thanks / Like

    Can i calculate the battery side current?

    Hey folks

    So, with my arduino and canbus setup, I can talk to my Kelly KBL brushless controller via CAN. from this, I can get the battery side voltage, motor side current, and motor side voltage (the motor side values come as triplets -- one for each of the 3 phase wires).

    Is it possible to calculate the battery side current given this info?

    I want to be able to calculate things like watt-hours and watt-hour/mile, but I feel like that info is better done from the battery side. I could always get a current sensor, but was wondering if I could do it without an external sensor.

    Thanks!
    EVs: 2007 Zapino Scooter, Honda VF500 Conversion (electriceptor.wordpress.com), Red Nissan LEAF SL (Arrived!)

  2. #2
    Moderator Nuts & Volts's Avatar
    Join Date
    Aug 2010
    Location
    Columbus, OH
    Posts
    1,702
    Post Thanks / Like
    Battery Current should be...

    bat_I = (motor_V * motor_I / bat_V )*Cntlr_eff

    I would say controller efficiency should be around 96-98% in general.
    Whats under my tank may shock you!!! R6 Build, Blog/, [/URL] OSU Current webpage

  3. #3
    Senior Member
    Join Date
    Oct 2010
    Location
    North America
    Posts
    753
    Post Thanks / Like
    Quote Originally Posted by Nuts & Volts View Post
    Battery Current should be...

    bat_I = (motor_V * motor_I / bat_V )*Cntlr_eff

    I would say controller efficiency should be around 96-98% in general.
    I don't think this equation applies to three phase AC controllers. You have a factor something to do with the square root of 3 and also maybe the power factor (applies to sine wave but I don't know about other types like BLDC). The straight forward method would be to use a current shunt or hall sensor in the battery line.

  4. #4
    Senior Member __Tango's Avatar
    Join Date
    Aug 2010
    Location
    Mountain View, CA
    Posts
    735
    Post Thanks / Like
    Quote Originally Posted by lugnut View Post
    I don't think this equation applies to three phase AC controllers. You have a factor something to do with the square root of 3 and also maybe the power factor (applies to sine wave but I don't know about other types like BLDC).
    Yeah, this is what i was thinking about. I think i remember something about how AC or BLDC controllers send about 0.7 of the voltage down the phase wires. I'm really reaching here, so i don't know.

    Anyone else know?

    Thanks.
    EVs: 2007 Zapino Scooter, Honda VF500 Conversion (electriceptor.wordpress.com), Red Nissan LEAF SL (Arrived!)

  5. #5
    Senior Member markcycle's Avatar
    Join Date
    Aug 2010
    Location
    Long Island, NY
    Posts
    234
    Post Thanks / Like
    It's very difficult to calculate the RMS of a non sinusoidal or other well known AC waveform (such as square or triangle). The AC peaks can be as high as 5 times the DC current. On the controller I'm working on the AC peak is as much as 2.5 times or more the DC current. The average power is always a little less than the DC power or equal to when including the controller losses
    Last edited by markcycle; 17 June 2011 at 1437. Reason: corrected used RMS in the wrong context
    Trying to Change the old school ways of doing things
    But I never Never try to break the laws of Physics
    http://www.enertrac.net
    http://www.evalbum.com/preview.php?vid=1543
    http://www.youtube.com/watch?v=nEldNmBgIF0
    http://www.evalbum.com/2568

  6. #6
    Empulse R #24 frodus's Avatar
    Join Date
    Aug 2010
    Location
    Portland, OR
    Posts
    2,233
    Post Thanks / Like

    My Social Networking

    Follow frodus On Twitter
    doesn't the kelly have battery current on the canbus? If not, seems a bit of a letdown.

  7. #7
    Not to be taken seriously DaveAK's Avatar
    Join Date
    Aug 2010
    Posts
    2,241
    Post Thanks / Like
    Quote Originally Posted by frodus View Post
    doesn't the kelly have battery current on the canbus? If not, seems a bit of a letdown.
    My Sevcon only gives motor side current. It does spit out battery voltage, but not current. I'm going to have to do that separately as well.

  8. #8
    Empulse R #24 frodus's Avatar
    Join Date
    Aug 2010
    Location
    Portland, OR
    Posts
    2,233
    Post Thanks / Like

    My Social Networking

    Follow frodus On Twitter
    Measure it with Noah's circuit and show on the tach.....

  9. #9
    Not to be taken seriously DaveAK's Avatar
    Join Date
    Aug 2010
    Posts
    2,241
    Post Thanks / Like
    I have a hall effect sensor I'm going to use when I get around to hooking it all up. Then I'll be able to feed it in to a microcontroller along with the CAN stuff from the Sevcon and have it all synced up and dataloggable. I could throw in a cellular module and be able to give you a real time feed.
    Last edited by DaveAK; 17 June 2011 at 1029.

  10. #10
    GUFF
    Guest
    Quote Originally Posted by DaveAK View Post
    I have a hall effect sensor I'm going to use when I get around to hooking it all up. Then I'll be able to feed it in to a microcontroller along with the CAN stuff from the Sevcon and have it all synced up and dataloggable. I'll could throw in a cellular module and be able to give you a real time feed.
    Haha! Now that would bad ass!

    Facebook Status: 120MPH.....

    I also vote measuring with the hall effect sensor. If you go that route I would be very interested to see what you come up with similar to Dave is describing above.

    This thread has me rethinking if my Curtis spyglass is showing me motor amps or battery amps. Since the spyglass and the programmer share the same connection point I would wager that if I cannot see battery amps in the software program then no, its motor amps. I did not see a battery amps value in the monitoring function listed in the manual (Frodus, correct me if I am wrong).

Page 1 of 6 123 ... LastLast

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •