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Thread: How to choose battery for high torque motors?

  1. Re: How to choose battery for high torque motors?

    Thank you very much jwatte.

    Quote Originally Posted by jwatte View Post
    A correctly manufactured, installed, used, and charged LiPo battery is not dangerous as long as you shield it from physical damage.
    Be sure to not over-charge it, and not over-discharge it, and not let anything hit it (shield it in a hard box,) buy it from a reputable source, and charge it with a balancing charger, and you'll likely be fine.
    What do you mean by not "over-charge" and not "over-discharge"? Can I control these two? I think when the battery is fully charged, the LED in the charger changes color? Not sure about discharging...

    Does vibration lead to dangers such as explosion or fire from the LIPO? I am thinking of a wheeled robot moving in rugged terrain.

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    Re: How to choose battery for high torque motors?

    Yes, soft pack LiPo cells without mechanical and electrical protection from damage (which is most hobby batteries) can be made to die a fiery death by many simple methods of abuse.

    Attempt to charge LiPo with incorrect charger or incorrect charge profile: fire.
    Puncture a LiPo pack: fire.
    Short out a LiPo pack: fire, if the wires do not quickly burn out or desolder themselves from the pack.
    Overheat a LiPo pack: fire.
    Over-charge above 4.2V per cell: fire.
    Float charge at 4.2V per cell: decreased life, possible fire.
    Over-discharge LiPo below 3.2V per cell: permanent damage to the cell, possible fire during later use and/or charging. If any cell envelope starts bloating, never use that cell/pack again.

    Simple rules: get a LiPo balance charger from a reputable source, stick the pack in a sturdy (preferably padded) plastic case, and always use a battery monitor when in the robot and listen for it beeping.
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  3. Re: How to choose battery for high torque motors?

    Thanks tician.

    Is shaking/vibrating/shocking OK if I put it in a wheeled mobile robot moving in rugged surfaces.
    Last edited by Snoopy; 05-26-2015 at 10:11 PM.

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    Re: How to choose battery for high torque motors?

    Quote Originally Posted by Snoopy View Post
    Is shaking/vibrating/shocking OK if I put it in a wheeled mobile robot moving in rugged surfaces.
    Yes. As long as the battery pack are secured and protected. It's recommended to use a hard-case LiPo to prevent accidentally puncturing.

    In addition to what Tician mention it is also recommended to store the LiPo at 50% energy. Do not store a fully charged LiPo for a long time. It's not dangerous, but it reduces lifespan.

    Overall, a LiPo isn't dangerous and will never burst into flames as long as it is used, charged, discharged, protected in a correct way.

    Oh, another thing. I've mentioned this before, always use a main fuse close to the battery connector. In case of a shortcut its better to blow a fuse or the whole robot.
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  5. Re: How to choose battery for high torque motors?

    Hello, I am looking for battery/batteries to drive two 7.2V DC motors (each motor consumes a current of 1.2A when there is no load, stall current is 18A, the averaged expected motor current is 5A) via a motor driver shield (https://www.pololu.com/product/2507). The desired running time is about 10-20 minutes. The longer the better but I also need to take the weight of the battery (ideally below 350g, the lighter the better) into consideration. Which product do you recommend? What do you think of the following products? Thanks.

    http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html

    http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html

    http://www.hobbyking.com/hobbyking/s...Boat_Pack.html

    http://www.hobbyking.com/hobbyking/s...arehouse_.html

    http://www.hobbyking.com/hobbyking/s...arehouse_.html

    http://www.hobbyking.com/hobbyking/s...arehouse_.html

    http://www.hobbyking.com/hobbyking/store/__20761__Turnigy_nano_tech_4000mah_3S_45_90C_Lipo_ Pack_US_Warehouse_.html



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    Re: How to choose battery for high torque motors?

    Quote Originally Posted by Snoopy View Post
    Hello, I am looking for battery/batteries to drive two 7.2V DC motors (each motor consumes a current of 1.2A when there is no load, stall current is 18A, the averaged expected motor current is 5A) via a motor driver shield (https://www.pololu.com/product/2507). The desired running time is about 10-20 minutes. The longer the better but I also need to take the weight of the battery (ideally below 350g, the lighter the better) into consideration. Which product do you recommend? What do you think of the following products? Thanks.

    Hmm. The first two links are for a 2S (7.4V battery) and will likely work fine with your 7.2V motors. The others are 3S (11.1V battery) and when fully charged (about 12.6V) they will likely damage or shorten the life of your motors unless you have a voltage regulator that you didn't mention. All of the battery packs are the same brand so there isn't much to compare aside from voltage, capacity, discharge rating. If you are only expecting to pull 10A (5A average x2) from the motors the discharge rating on any of these packs seems irrelevant. Now to power these motors for 20 minutes @ 10A equates to 3.33Ah (or 3,300mah) which means they will all satisfy your capacity requirement.
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  7. Re: How to choose battery for high torque motors?

    Quote Originally Posted by r3n33 View Post
    Hmm. The first two links are for a 2S (7.4V battery) and will likely work fine with your 7.2V motors. The others are 3S (11.1V battery) and when fully charged (about 12.6V) they will likely damage or shorten the life of your motors unless you have a voltage regulator that you didn't mention. All of the battery packs are the same brand so there isn't much to compare aside from voltage, capacity, discharge rating. If you are only expecting to pull 10A (5A average x2) from the motors the discharge rating on any of these packs seems irrelevant. Now to power these motors for 20 minutes @ 10A equates to 3.33Ah (or 3,300mah) which means they will all satisfy your capacity requirement.

    Thanks r3n33 for your expert opinion. So, I just choose a battery that can offer over 3.33Ah with the size and weight I prefer? How do I connect such battery to the Pololu Dual VNH5019 Motor Shield for Arduino?

    In this case, is it worth to get the 3S ones for higher than advertised torque?

    I chose Turnigy due to availability. How is this brand compared with others? Any other brand worth looking? I read postings that the Turnigy batteries got swollen easily.

    In the hobby king website, they are listed as LIPO but in other site, they are listed as LiFePO4. I am confused.

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    Re: How to choose battery for high torque motors?

    Quote Originally Posted by Snoopy View Post
    Thanks r3n33 for your expert opinion. So, I just choose a battery that can offer over 3.33Ah with the size and weight I prefer? How do I connect such battery to the Pololu Dual VNH5019 Motor Shield for Arduino?
    The wiring information for connecting your battery power to the motor shield is on the product page provided by Pololu. I would propose you could connect a 2S battery directly to the motor power +/- inputs.

    Quote Originally Posted by Snoopy View Post
    In this case, is it worth to get the 3S ones for higher than advertised torque?
    No. You should choose a motor that produces the correct amount of torque and provide it with the recommended voltage.

    Quote Originally Posted by Snoopy View Post
    I chose Turnigy due to availability. How is this brand compared with others? Any other brand worth looking? I read postings that the Turnigy batteries got swollen easily.

    In the hobby king website, they are listed as LIPO but in other site, they are listed as LiFePO4. I am confused.
    I've never used this brand so I cannot compare. All of the batteries you provided links to are listed as LiPo.
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    Re: How to choose battery for high torque motors?

    Turnigy is one brand that produces multiple battery chemistries (LiPo, LiFePO4, NiMH, etc.). I have not yet had a bad experience with their batteries, but there will almost always be some 'not great'/dud cells that sneak past quality control. Since those motors are unlikely to get anywhere near the peak current levels of the large brushless motors used in planes, it decreases the likelihood of damaging the cells from over-current/over-heating. Just never let the LiPo drop below 3.2V per cell or charge above 4.2V per cell.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
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  10. #20

    Re: How to choose battery for high torque motors?

    How do I connect such battery to the Pololu Dual VNH5019 Motor Shield for Arduino?
    You find a connector that matches the one on the battery, and ends up in pig tails (stripped wires) on the other end.
    Or, like I do when buying from HobbyPartz or HobbyKing: cut the default connector, and solder a female Deans T connector to the wires.
    This requires care, for a few reasons:
    1) The wires and the Deans are very thick, so they take a lot of heat to actually melt the solder.
    2) You don't want to over-do it so you melt the nylon connector housing, or even worse, transmit too much heat to the battery.
    3) If you cut and strip both wires at the same time, they can easily touch each other, and short the battery. If you're unlucky, this contact welds, at which point you likely have a battery fire on your hands.
    4) Don't forget to thread the heat shrink onto the wire before soldering. Then securely wrap the first connector you solder before you strip the second wire, to reduce risk of shorts.

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