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Battery + dc motor question

  1. Mar 7, 2007 #1
    i want to power 2 perm 080 dc motors in an EV application, i want to know what batteries will be a good match

    motor specs--

    Typical system performance.

    Voltage: 24 V
    Angular-velocity constant: 291 rpm/V
    Torque constant: 4.64 ozf·in/A
    Terminal resistance: 0.0236 ohm
    No-load current: 7.8 A
    Peak efficiency: 83.2 %
    Power source resistance: 0.0236 ohm
    Peak power: 3.95 hp
    No-load angular velocity: 6880 rpm
    Stall current: 505 A
    Stall torque: 2320 ozf·in

    will a 12.8V 100 Ah lithium-ion battery be any good? i'm a total noob so any help is welcomed ..thanks
  2. jcsd
  3. Mar 8, 2007 #2
    Li-Ion is the only really practical cells for proper EV stuff but you need to be really careful when using them. If you over current them they will become damaged really easily. The same goes for Nickle Metal Hydrids.

    There is another cell that uses molibnium (probably spelt wrong) which give pretty good performance and are much more robust.

    Make sure that the start current the motors draw when moving from a standing start does not exceed the batteries capabilities.

    You can use resevoir capacitors to provide a high current boost but need to current limit the battery side as if you connect a Li-Ion to a discharged Ultra-Cap you end up with a very expensive fire.

    Trhe best Li-Ions on the market are made by SAFT but you need to be building a serious car to afford them (Check out the Venturi Fetish - Electric Super Car), most affordable off the shelf stuff will struggle over 200A or so.
  4. Mar 8, 2007 #3
    the ev application i'm trying to build is a souped up power wheelchair.
  5. Mar 8, 2007 #4
    ''Li-Ion is the only really practical cells for proper EV stuff but you need to be really careful when using them. If you over current them they will become damaged really easily. The same goes for Nickle Metal Hydrids.''

    I am interested in how to supply the power for typical dc permanant magnet motor too. I quote what you are saying panda because i do not understand it.
    What do you mean by over current them?

    I am doing an EV too(i hope ev means electric vehicle) that is a power wheel barrow. My ev uses a 24V 1hp dc PM motor and from what i understand, 1hp=746Watts,and so depending on the power supply such as a lead acid battery,in this case im planning to use a 24V 40Ah, which can supply about 960watts per hour,i can continuosly use this battery to run my ev for about 1 hour++( neglecting losses). If i am wrong, please correct me.
  6. Mar 19, 2007 #5
    Batteries have two important parameters. the first is the Capacity in AH, the second is the Maximum Discharge Current.
    When you look at a data sheet you will find a nominal current value called "C" and everything is refered to this.
    You will get the stated capacity in AH when discharging at between 0.1C and 1, but you can discharge at rates of up to 100C or even higher dependent on cell design with a reduction in the AH capacity.
    For example an Odyessy 1500/34 has a nominal 62AH over a wide range of discharge rates, you can even discharge it at 1500A, which at 62AH should give you 2 and a half minutes operation, but in truth you only get 5 seconds of capacity out before the cell is drained.
    If you push it beyond the 1500A limit then the dielectric will break down, and whilst you will get the energy out once really quickly you won't be able to recharge the cell again.
    Li-Ion for their weight and volume have higher capacities and higher currents but are more prone to permanent damage if you push them beyond their operating point.
    If you need high currents you need a chemistry with very low internal resistance, as when you draw the current out the internal resistance a) drops the cell voltage at the terminals and b) disipates that energy as heat inside the cell eventually leading to thermal damage of the chemistry or worse cell explosion.
  7. Jun 28, 2007 #6
    Li-ion battery pack, don't buy from GBP Battery

    I bought a 36V 17Ah battery battery pack from GBP battery http://gbp-battery.com/ for my E-bike and it was working great until one cell started to go out. I was getting over 30 miles between charges. The pack consisted of 10 3.6 volt 17 Ah cells. Unfortunately the company is refusing to replace the bad cell so I am not doing business with them any more. Do you have leads on any domestic Li-ion manufacturer?
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