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Electric motor + 12 volt battery ?

  1. May 16, 2005 #1
    I admit it, I am a complete and utter noob when it comes to electrical components. I need help. I am trying to run an electrical motor on a regular 12 volt car battery. Can this even work? If so, how much money and work needs to be done?

    This is for a little..."project". If anyone can give me a hand or point me in the right direction, I would appreciate it.

    Koop
     
  2. jcsd
  3. May 16, 2005 #2

    Integral

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    You have not provided sufficient information for anyone to help you.

    As long as you have a DC motor there should be no problems. Please provide more information. What is your power source? What motor are you driving? What is the project?
     
  4. May 16, 2005 #3
    Well, I am trying to test out a motor run on rechargeable power (basically a fully electric car), but only using the battery to "start" the motor...if that makes any sense.

    I would like to use a motor that is large enough to provide enough force to the wheels of my project cart, but can still be started by a regular 12 volt battery.

    I apologize for the lack of better information, but, my motor will depend on whether or not the battery (or some home modifications) can actually "start" it.

    Koop
     
  5. May 16, 2005 #4

    chroot

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    You don't "start" electric motors. You have to provide them a continous source of power, i.e. current.

    Your motor should be designed with a specific supply voltage in mind -- if you overpower it, you could well destroy it. A 12 V car battery can actually supply an incredible amount of current, and it could be dangerous.

    - Warren
     
  6. May 17, 2005 #5
    Right. Yeah, that makes sense.
     
  7. May 17, 2005 #6

    Cliff_J

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    koop - check out eletric golf carts as a source for common (and therefore typically cheaper with higher production and competition) source of parts like motors, gearboxes, controllers, and so on.

    At only 12V you have a large restriction in terms of delivering power to/from the battery because as current flows you end up with a lot of wasted energy as heat that is the square of the current times the resistance of the wire. Low resistance means big wire and big wire means lots of money and weight, bad for an electric car project.

    The hybrid cars like a Toyota Prius or Honda Civic operate in the hundreds of volts for their battery packs but since this is a dangerous level of voltage (lethal!!) there is a lot of protection involved in case of an accident and so on.

    But golf carts work at like 24V-36V and this is easy to achieve at roughly the same size and weight as a car battery by using something more like motorcycle batteries instead.

    There was a documentary about making a drag racing electric car and the guy featured has his own website where you can buy parts. His personality made the show amusing but not too educational, especially when it had so many mechanical problems. The website below links to his, and a google search will find many more.

    http://www.suckamps.com/ [Broken]
     
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  8. May 17, 2005 #7
    didn't he break an axle?
     
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  9. May 17, 2005 #8

    Cliff_J

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    Well, as I recall he broke off the key that tied the pulley to the shaft, and then after the pulley was welded to the shaft he shredded the belts. Impressive since that size of timing belt can drive a supercharger that might require 100HP. Not so impressive he thought he could run a 2+ ton car with that much weight from 40 batteries into the 12s with that setup.

    After I watched the show I went to his website and he had put up an update that they converted the belt/pulley over to triple chain/sprocket drive and that broke a half shaft. Again not too impressive that he's welding up Subaru parts and trying to make them work, used Corvette half-shafts or even better 3/4 ton Chevy pickup front half-shafts are much more heavy duty out of the box. Neither would be easy to adopt since he has already setup the car with the Subaru suspension, but even with a really tough half-shaft the CV joints are going to be the weak link.

    http://www.suckamps.com/index.php?page=life_of_the_postal_van [Broken]

    Not trying to be overly negative but going quick in a drag race isn't new, why deviate so far from the norm and overstress parts?

    Now, the old RX-7 they have is quite impressive, its suppossed to run 11s. Its in the top pictures:

    http://www.suckamps.com/index.php?page=build_team_vehicles [Broken]

    He does have a challenge on his hands to beat any production car though, the Enzo and Carrera GT run low 11s.
     
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  10. May 17, 2005 #9
    Motorcycle batteries? Got it.

    That site is great, and the store has some great stuff in it. Thanks for pointing that out, I have been looking for days for a motor, but all I could find were industrial sites.

    Thanks again,

    Koop
     
  11. May 17, 2005 #10

    Cliff_J

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    Well I'm not saying to go run out and buy 3 motorcycle batteries instead of 3 car batteries to get your 36V - they're almost similar in price but their size and capacity is very different!

    For a small electric car of short range, the motorcycle/golf cart batteries would be fine. In fact, the golf cart batteries are likely the deep-cycle variety. Deep-cycle means the batteries are designed to last after being drained, a regular lead acid battery looses capacity after it has been run down. In fact, run it dead more than a few times and a regular car battery won't hold much of anything.

    So rather than just looking at the CCA (cold cranking amps, how much current at something like freezing and 7V) you should be looking at the ampere-hour rating and only at deep-cycle batteries unless you plan on using them for only a short period of time.

    Once you determine about what you need after compromising on size/weight/duration/capacity/cost then you have a few batteries to select from like some for electric wheelchairs or golf carts or trolling motors on fishing boats etc. The latter are likely the cheapest for the money at quite a few stores, the others are more specialized and will cost more per ampere-hour.

    Its all compromise koop, just try to find the best choice. :smile:
     
  12. May 17, 2005 #11
    Right, that makes sense.

    I do have two deep cycle batteries...but they weigh about 30lbs each, and are for our travel trailer.

    I think motorcycle batteries sound like the way to go.

    Now for a potentially ridiculous question:

    Can I hook up an alternator to the shaft of the motor? :confused:

    If that is a retarded question, try not to laugh too hard.

    Thanks for your help so far.
    Koop
     
  13. May 17, 2005 #12
    Is it possible? Yes. Will you gain anything? No. The power required to drive the alternator will come from the battery. Alternators are not perfect devices---they have both electrical and mechanical sources of power loss or rather some of the energy put into the alternator is converted to heat. Additionally, hooking your little electric motor to an alternator will increase the load on the motor which increases the current requirements of the motor which increases something called the "I squared R losses". The motor will convert more of the electric energy from the battery to heat energy than it would without the alternator. Essentially you will be adding more heat to the environment with the alternator than without---and heat equals power lost that you could have otherwise used to scoot around with.

    [edit] If you want to return some of the energy to the battery then you should look into regenerative breaking.
     
    Last edited: May 17, 2005
  14. May 17, 2005 #13
    That's what I was looking for, to a point...

    EDIT:

    (What if) I use small solar cells for that task (I know, energy would be used faster than converted by the panels, but it could possibly lengthen battery life per charge, right)?
     
    Last edited: May 17, 2005
  15. May 17, 2005 #14
    Yeah, you can use solar cells. You'd need enough cells to supply sufficient current to be useful. Matching solar cells is not easy or cheap either. You can't simply group 10 solar cells together and expect to charge your battery.

    Just to give you an idea of the costs involved in using solar cells: http://www.engin.umich.edu/solarcar/donate/buycell.html [Broken]

    The kind that you would need would not be cheap at all. You can't get these at radioshack.
     
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  16. May 17, 2005 #15
    I was thinking more along the lines of multiple cells that are smaller, rather than a large, single cell.
     
  17. May 17, 2005 #16
    That's not a large single cell. That cell is about 1" by 2". You can find lower quality/effeciency cells for $6-10 a piece but you still can't connect 10 and expect them to work. Cells do not all produce the same voltage for a given amount of sun light so connecting an unmatched pair means that one of the cells becomes a load on the other. Cells are usually grouped in small matched arrays and each array is connected to a grid. The arrays and the grid all have little controllers to prevent a single cell from becoming a load on the others thus releasing the black smoke the manufacturers installed at the factory. Aside: all electronic parts are made with a small puff of stinky smoke inside. If you do something like overload an electronic component then you let the factory installed puff of smoke out=>the component wont work anymore.

    You'de be better served looking into simple regen breaking rather than trying to make a solar car IMHO.
     
  18. May 17, 2005 #17
    Point taken.

    I was thinking more along the lines of that in this little drawing of said "car".
     

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  19. May 18, 2005 #18

    Cliff_J

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    IF they can be properly setup (no releasing magic smoke as faust9 pointed out) they would assist a little yes, but the cost is typically prohibitive.

    As said, the alternator is a bad idea and would only waste energy.

    And as far as rengenerative braking is concerned, from what I've read its not a very efficient method of energy capture. Maybe if you could just always find a way to go downhill...because otherwise it will take far more power and create more losses going up the hill then could ever be recovered braking on the other side.

    Here's enough info to keep you busy for a while:
    http://www.4qd.co.uk/faq/index.html
     
  20. May 18, 2005 #19
    I read in a DOE report, just a few minutes ago, that regenerative braking is only 4% efficient.

    Good site, thanks for pointing it out.

    Koop
     
  21. May 18, 2005 #20
    Another few things you'll need to consider if you get serious about an electric car are the materials you build out of (light as possible yet strong), aerodynamics of the vehicle (wind resistance obviously), and rolling resistence of the tires (the bigger the contact patch for control/braking the more rolling friction).
    I remember back in the late 70's there was either a Popular Mechanics or Popular Science article about building a 3 wheel 2 seat car (possible source reference for you). You could power it by gas or electric.
    I found it in 1984 in my H.S. electronics class. I remember thinking why not both? A mostly electric powered car with a gas generator that kicks in to power the vehicle and recharge the batteries when necessary.
     
  22. May 18, 2005 #21
    Of course. All of those would be key in making an efficient vehicle.

    Well, you were just ahead of the times, weren't you?

    koop
     
  23. Aug 3, 2005 #22
    I am building a solar car as a high school science project. I am wanting to use the small solar panels that VW uses when shipping thier cars to the USA to maintain battery charge . I will use 100+
    They have a power rating of 12v, 3.2 watts, 170 ma. I am trying to find a motor and controller system that will meet my needs. I have been looking at the electric golf cart systems but the motor may be to big for my needs. Any advice would be appreciated.
    We do have access to a go cart frame. Really light and built for racing. We are thinking of mounting bike tires to it. We have been looking at the hub motors available on the net. I have also seen the scooter motors on E-bay that go up to as high as 900 watts at 36 volts. I do not know if they are continuous duty motors or not. They are cheap. I figure you get what you pay for. The battery system needs to be more than the small battery systems that comes with the scooters. They need to be the standard lead acid batteries to ensure the panels have somewhere to route the power they will be collecting. The panels are 9 3/4" x 12 1/4" including the frame. Outside the frame they are 8"x 9". There is a voltage regulator built into the lighter adapter for the panels. It converts the panels voltage from 24V to 12volts. So, we could get a 24 or volt system easily. There is also a blocking diode built into the adapter for each. We did a test and they put out 13.5 volts. We purchased a few of the lighter adapter gang boxes and hooked 4 of the panels together routing the power backwards thru them to a battery. It worked. But there was a little voltage drop. After going thru 2 boxes and the female adapter going to the battery it was down to 13.3 volts. These are adapters have 2 different ratings. Some are up to 5 amps some as high as 10 amp rating. I do not think this will be a factor. They cost around $5 each and we would need 30-40 of them. I know this is a lot of money but they could be reused when the project is done. We would not have to worry about blocking diodes or voltage regulators. No wiring to do. No diodes to wire in. Each panel could be checked easily for current output to ensure max power from system. Just unplug and check it.
    There are several races for these types of events. They have rules that regulate, size, type of panels, car- length, width, height. The different races all have different rules so it is kinds hard to know which rules to go by during construction. So, we are just going to do our own thing. If we decided we want to enter it in an event, we will be entered in the open class. This is kind of a almost anything goes class.
    Another issue to address is the fact the panels are equiped with 4 suction cups to mount the panel to the car window. So if we go this route we have to build the cart with plexiglass and just attach them to the inside. The rules state the panels can not be in the car. So, if I put them on the outside we will remove them from thier frames. then we could increase the number of panels we can use. I was looking a a go cart on the net that comes with a 6.5 peak HP Leeson DC motor 275 amp MOSFET controller Top speed: 7 / 15 / 25 mph (with quick key change).
    One was on e-bay and was a 4 person cart. The other was on the net but the company selling them seems to have went out of business (E-Star).
    Another issue is the fact the panels put out 12 volts. When the motor is 36 volts drawing power from 3/12v batteries or 6/6v batteries. Don't we have to be charging the system with 36 volts? Or can we just tie the 12volt panels in to the system? When we need to charge the batteries, just hook up to a battery charger, and would it have to be a 36 volt charger? I guess I am asking, do I need to step up the voltage of the panels to match the system voltage?
    Sorry for so many questions. This is all new to us and we want to get it right the first time.
     
    Last edited: Aug 3, 2005
  24. Aug 3, 2005 #23

    Danger

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    Hi;
    I don't have time to get into this before I go to work, but I want to post a quick reply in case I lose track of the thread. (It happens a lot!) To save weight, rather than using an alternator for recharging in your brake system, just design the circuitry so that the motor becomes a generator driven by the wheels.
    Faust... I've sniffed way more than my share of that stinky smoke! :rofl: Sometimes I wish that the manufacturers would just leave it out.
     
  25. Aug 4, 2005 #24

    Cliff_J

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    Jesse - you've got a tons of questions there! If your questions remain unanswered, try assigning numbers to ease the seperation, and its usually easier if you add more returns to make things easier to read. :smile:

    You may very well want to run a motor at much higher than specified voltages for your car. For the same power, the higher voltage offers less I^2*R losses in the wiring so you may be able to gain efficiency. Especially true if you use a PWM motor drive to limit the current in the motor so you don't end up delievering (and extracting) more power than the motor is designed to handle, although cooling could prevent that and would likely be advisable to minimize the thermal resistance rise in the windings.

    Lead acid batts have less energy density than NiMH or Li but do have massive cost benefits. How you array the batts and cells for higher voltages you can likely find some system that will allow the system to be arranged as two parallel stacks or some other logical grouping depending on how many are determined to be used. If you're using 50lb car batteries I couldn't imagine you'd use too many of them...

    Regardless, it can be setup as isolated systems (one panel charges one battery) and those isolated systems (say 3 of them) can then be wired in series to produce the 36V you need. Charging could be tricky because of isolation - it may very easily not be as simple as hooking up 3 chargers with one on each battery beacause sometimes the negative lead is tied to the neutral (ground) of the AC outlet. So then you'd need isolation switches to allow the batteries to be isolated from each other and break the series wiring to prevent a charger from shorting out. You can find 36V chargers but the rarity means big money.

    You may also want to oversize the panels and use a charging regulator to accomodate the sunlight angles and respective intensity. It would be better than having a charging condition under ideal conditions and nothing other times.

    Seeing as how the standard PMDC motor runs at peak efficiency at roughly 1/2 peak unloaded RPM, I'd be looking at motor graphs and pick that item as soon as the rough chassis is built and a bicycle chain drive or whatever is chosen. A gear reduction drive like on wheel chair motors may help get the RPMs inline for large bicycle tires and so on, or even some of the battlebot motors that surfaced have high efficiency and power density.

    Sounds like a fun project with tons of variables to work out and multiple ways to accomplish the goal. Good luck.
     
  26. Aug 4, 2005 #25
    Thanks for the response. You answered a few of my questions but brought up just as many more. I was afraid I would have to step up panel voltage to allow the system to charge off the panels and supply the motor, or I can just stick with a 12 volt system. I know I can gain so much by stepping up the voltage but I am afraid I will loose more than I can gain in system problems. I can easily get 24 volts by removing the adapter but like I said I will have to put in a blocking diode for each of the panels and buy a voltage regulator that can handle the power. I am not familiar enough with the motors you mentioned. I have been doing some checking around. There are so many companies and so many different types and sizes of motors It will just be a shoot in the dark when it comes to picking a motor. I will say my end choice will more than likely be a cheaper motor and control system to make any mistakes in my purchase not as drastic if I buy the wrong motor size.
     
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