DC Speed Motor with Batteries

Discussion in 'General Electronics Chat' started by Nara Shikamaru, May 10, 2008.

  1. Nara Shikamaru

    Thread Starter Active Member

    Nov 24, 2007
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    Hey Everybody!!....i have an Inquiry!!......

    Can you run a motor of maximun 12000 RPM with batteries??.....

    I mean....can you drive a DC motor of those speeds with batteries??...or perhaps can you do an adaptation so you can plug it to the AC line of the Alternator in the car so you can use the motor on outsides???....
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Yes, you can run the motor on batteries. How long you can run it depends on the capacity of the battery/s and the current draw of the motor.

    Automotive alternators have a DC output because the rectifiers are built into them.
     
  3. mik3

    Senior Member

    Feb 4, 2008
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    If the battery is capable of providing the amount of current you can drive it. I guess it is a 12V DC motor so i think a car's battery is sufficient to drive it. How many amps it sinks at 12000 rpm ? But take care not to stall it and blow the battery or even the motor itself.
     
  4. Nara Shikamaru

    Thread Starter Active Member

    Nov 24, 2007
    92
    3
    Alternators have a Built in Rectifier??.....Whoa!!....thanks for that!!...so technically it would be easy to connect it to the alternator then??.....

    the motor wont Drawn more that 15Amps.....so with what kind of batteries would you need then??.....maybe i would need the motor on outsides perhaps 4 to 6 minutes.....at intervals of maybe 30 minutes......like 10 times a day......i mean......ill use it for 5 minutes...then ill turn it off.....half hour later....5 more minutes......an so on like 10 times....
     
  5. mik3

    Senior Member

    Feb 4, 2008
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    If you connect the motor directly on the car's battery you connect it also to the alternator. Its better because if the alternator wont be able to supply enough current (when you start the motor or if it stalls) the motor will take the more current from the battery and wont stress the alternator
     
  6. Nara Shikamaru

    Thread Starter Active Member

    Nov 24, 2007
    92
    3
    ok heres the thing.....i work at a Hospital in the medical equipment section...we need to go to a Rural (country) deep in the "jungle" zone to obtain Blood samples of the people...

    what i want to do is to modify the circuit of a Blood Centrifuge so we can take it to the jungle and perhaps run it with batteries to take the blood samples....

    so do you think its possible???...to run a Blood Centrifuge with batteries???......im thinking yes....cause the new Hand Drills run with batteries!!
     
  7. mik3

    Senior Member

    Feb 4, 2008
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    Whats the operating voltage of the Blood Centrifuge?
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    Unless you are qualified or know someone who is you do NOT want to modify medical equipment. It would be better to use an invertor, which converts DC (from a battery) into AC. There are plenty high quality commercial units to choose from, and they aren't that bulky. How do you plan on recharging this battery anyhow? Solar cells?

    An additional benifit is you can bring other off the shelf equipment if the need arises, you are opening your options up with a standard outlet, though you don't want to overload it.

    Motor speed generally doesn't dictate how much power they use, this is more a function of load, or resistance to the motors movement. The more load the more power used. A motor starting from being still tends to pull more current, because it takes power to come up to speed. Once it is turning it settles down constant draw.
     
    Last edited: May 11, 2008
  9. Nara Shikamaru

    Thread Starter Active Member

    Nov 24, 2007
    92
    3
    What if a Convert a drill battery to use with the centrifuge. will supply enough amps and last long enough to process. The centrifuge should give an amp or watt rating on it. The drill battery will also. From this you can estimate power requirement and how long it should run. Baterries have to be recharged.....

    so i came up with that idea......buy a Cordless Drill with its batteries.....and create the digital circuit to control the RPMs and the time.....how about it??
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    What is the power requirement of the centrifuge?
    It probably says something like 230V, 50Hz, and a number of Watts, or perhaps Amperes.
    It may also say 1 phase or 3 phase.

    You will have to provide the centrifuge with what it requires. Otherwise, it is very likely
    that you will damage or destroy it. Centrifuges are expensive to replace.

    Single-phase power inverters are widely available and relatively inexpensive.

    Three-phase power inverters are not widely available and are relatively expensive.
     
  11. Nara Shikamaru

    Thread Starter Active Member

    Nov 24, 2007
    92
    3
    Im thinking to buy a Good Battery Powered Drill.....open it and modified it to conver it into a Blood Centrifuge!!....and design the digital circuit to control its RPMs and the time.....

    so do you think its a good idea??......will the batteries withstand the Power needed??....

    or maybe could a plug to the Car`s Battery??.....im thinking...with the Car turned on...the alternator will work...the motor wont stall....so i would connect it to the batterie and then i would have the power needed......

    sombody told me that i should use a Large Capacitor in paralel with the car`s battery and my DC motor.....what for??
     
  12. beenthere

    Retired Moderator

    Apr 20, 2004
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    282
    Using a portable drill is an interesting idea. Can you get the separation you need at only 600 RPM? That is the usual limit for them. If so, be sure to find one that is very close to the automobile battery voltage - a 14.4 volt drill might just work, but a 9.2 volt drill would burn up. I don't think you would need a capacitor in the line to the drill, or have to worry about having the engine on the whole time.The car battery can supply several amps of current for at least an hour before needing a recharge.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    A cordless drill on high speed will run about 2,000 RPM, some really fast (and expensive) drills may go up to 2,400 RPM. You need a motor that spins 5 times that fast.

    Cordless drill motors (and practically all hand-tool type motors) have brushes. While they might seem pretty "smooth" to us, a centrifuge would need to have an exceptionally smooth torque curve in order to avoid vibrating (and thereby agitating/stirring up) the samples being processed.

    3-phase variable speed drive motors ARE exceptionally smooth, and have a very broad range of speed while maintaining torque. Unfortunately, they are also usually rather expensive.

    Besides the problem of finding and adapting a motor that is affordable, there is also the problem of constructing the centrifuge rotor. There will be a tremendous amount of stress on it when it is turning at maximum speed; the centrifugal forces will be trying to tear it apart. It would also have to be perfectly balanced, as even a slight out-of-balance condition at these kinds of speeds would vibrate the machine apart.

    In order to machine a centrifuge rotor, you would likely require a very large metal turning lathe to machine the basic shape out of a billet of something like aircraft grade aluminum, and then a method to index and drill the holes at a precise angle, diameter and depth to receive the test tubes. You would also need a method to statically and dynamically balance the rotor as an individual piece, and again when the centrifuge was completed.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I did a bit more poking around, and came across this:
    [​IMG]

    It's BLDC (Brushless DC) motor with a driver board and controller, which operates at up to 6500 RPM no-load on 12v for $105 (US dollars) plus shipping. This kind of motor may be just what you need.

    The seller is on E-bay, and indicates he has other models available that run on 12v and 24v at speeds up to 15,000 RPM.

    Link to this auction:
    http://cgi.ebay.com/ElecMech-BLDC-M...ryZ78197QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

    But before you purchased something like this, you would need to figure out how much torque it would take to spin your centrifuge rotor at 12,000 RPM. Some of that would be overcoming the bearing and wind resistance (drag) inside the motor itself. The remainder would be aerodynamic drag resulting from how well or how poorly the rotor was designed and finished.

    If there were a university near you, this could be a good project for a budding mechanical engineer to design and machine.
     
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