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Basic electrical circuit questions

  1. Oct 3, 2011 #1
    1. Im building an electric bike from scratch and I am using 2 motors. I have a 48 volt battery, a controller and a throttle. I tried to wire the two motors together but then when I put any type of load on the motor it heated up the wire leads to the point where it melted the insulation. Is this ok, or what did I do wrong.

    2. If I do wire the circuit this way would the battery be splitting its voltage giving each motor 24 volts instead of the 48 volts?
     
  2. jcsd
  3. Oct 4, 2011 #2

    sophiecentaur

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    There is not enough information to permit a sensible answer yet.
    Can you draw a diagram (a schematic, with lines and blocks, preferably, rather than a 'picture' with curly wires and 3D looking motors). BTW, what do you mean by a "Throttle"?

    If you want an example of a proper circuit diagram then look in wiki for an idea of what I mean. Sorry if you already know this.
     
  4. Oct 4, 2011 #3
    As noted, more information would help a lot, but if the leads powering the motor are getting
    too hot, maybe the kleads are too small, or likely the motor is overloaded and/or the voltage to the motor is too high.

    Yo have to diagram or explain how you have them wired; if they are in series, they will split the 48 volts between them.
     
  5. Oct 4, 2011 #4
    schematic.png Here is a very basic schematic of what im doing with the wiring. If you guys have any advice please tell me.
     
  6. Oct 4, 2011 #5

    cjl

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    That is known as parallel wiring, and it will give each motor the full 48 volts. Are the motors rated to handle that kind of voltage? Also, what wire size are you using? 1750 watts at 48 volts is 35 amps of current, which requires some pretty thick wiring.
     
  7. Oct 4, 2011 #6

    uart

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    I think that if the speed per volt of two motors is significantly different then they could be "fighting" each other. I assume that you've already checked that the rotation direction is the same for both.
     
    Last edited: Oct 4, 2011
  8. Oct 4, 2011 #7

    sophiecentaur

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    This almost comes under the heading of 'Power Engineering". Things can get very hot at this level.
    As uart says, the motors could be 'fighting'. Even if they are both going in the right direction, if one will go faster than the other for a given voltage, then the other will take very little current as it will be spinning faster than it is supposed to and be producing a high back emf.

    This "throttle" device. Does it consist of more than a variable resistor? Has it just been connected in series with the battery and the motors? Such 'details' ned to be got right if you want a working system.

    Has the system worked with just one motor?
    We all need a much fuller explanation of what you have done and more details of this "control" box.

    !.75 kW is quite a powerful bike, when you compare it with the normal input of a human, which is probably a couple of hundred Watts, continuous. Your battery won't last long at 48A drain. How big is it? Can you keep the bike upright with it mounted? You would need something like 10mm2 cable.
     
  9. Oct 4, 2011 #8
    Yes I got everything working together but as I said it had a lot of heat when I added resistance to the shaft of the motor I am thinking about just making 2 separate systems one 48 volt pack running the 750 watt motor and one 48 volt pack running the 1000 watt motor and then using two different controllers and using the same throttle control its a little more expensive but I think. It will result in a lot more power.
     
    Last edited: Oct 4, 2011
  10. Oct 4, 2011 #9

    sophiecentaur

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    The two motors could still fight each other (or one could do all the work) if is there is no way of balancing the load. You would need quite a sophisticated control system to maintain the right proportion of power from each motor.
    This is a separate issue from the hot wires problem, though.
    Could you measure, roughly, the actual power delivered to the wheels? There are many alternative methods but raising a weight on a pulley and measuring the time taken is a common one.

    You still haven't described what sort of "controllers" they are. It may be relevant.
     
  11. Oct 4, 2011 #10
    The controller is a 48 volt 1200 watt controller from monsterscooterparts.com
     
  12. Oct 5, 2011 #11

    sophiecentaur

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    It may be a good idea to approach the makers and ask about using one controller for two different motors.
     
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