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Thread: How long will a certain amount of batteries run a motor?

  1. #1 How long will a certain amount of batteries run a motor? 
    Forum Sophomore kingjacob's Avatar
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    For the sake of this post lets say the rating of one Li-Ion Cell is 3.7V 5000 mAh (18.5Wh, 10A rate), How would you go about calculating how long each cell could run a 400V motor?

    I know watt =volt *amp, so this cell would have 18.5Watts but not sure how to factor time in to solve for it?

    Note:Im getting the ratings and stuff from batteryplace and this random motor store.


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  3. #2  
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    Well, Jake, a 3.7 volt battery won't run a 400 volt motor at all.


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    Forum Sophomore kingjacob's Avatar
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    Quote Originally Posted by Harold14370
    Well, Jake, a 3.7 volt battery won't run a 400 volt motor at all.
    Sorry about that, I forgot to mention multiple cells are going to be used so there can be 100+ 3.7V cells in series.

    It'll probably help yall if you know what I'm trying to do, so I'm trying to figure out how many, what type and the proper way to connect Li-Ion cells to create a battery pack for an electric SUV.
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    Okay, but the voltage rating of the motor won't tell how much power it uses.

    That link you listed was for a 1 horsepowr 3-phase ac motor. You will need a d-c motor, but let's say you had a 1-hp d-c motor. A horsepower is equal to 746 watts. This means an 18.5 watt-hour battery will power your motor for 18.5/746=.0247 hr, or about a minute and a half, and a hundred of them would give you around 2.5 hours
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    746 watts is 1.85 amps @ 400 volts. The batteries will be 4.1 - 4.2 volts for a short time after they were just charged. So for a bit you'll get the 400+ volts and not 370. Those cells you mention are rated at 5000mah (5ah) at a 10 amp rate. You will only be drawing around 1.85 amps with a 1 hp motor. So the capacity will increase a bit. I'm going to go with 3 hours or so with a 740 watt 400 volt motor. Free running will also be much different then under a load. My 1 hp high volume pool pump sucks down about 1700 watts @ 240 VAC and it's a high efficiency motor. that's about 2 years old. Your millage will vary...widely.
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  7. #6  
    Forum Sophomore kingjacob's Avatar
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    Wow! I'm retarded. I forgot a=c/s.

    Quote Originally Posted by Harold14370
    That link you listed was for a 1 horsepowr 3-phase ac motor. You will need a d-c motor, but let's say you had a 1-hp d-c motor. A horsepower is equal to 746 watts. This means an 18.5 watt-hour battery will power your motor for 18.5/746=.0247 hr, or about a minute and a half, and a hundred of them would give you around 2.5 hours
    Why do you say I'll need a d-c motor? Wouldn't an AC motor be a more efficient choice?
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    Quote Originally Posted by kingjacob
    Why do you say I'll need a d-c motor? Wouldn't an AC motor be a more efficient choice?
    I guess you could use an a-c motor but you would have to have an inverter to change the battery voltage to a-c.
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