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for 8 of this motor i need batteries. i want to use li poly battery. the battery should run at least 15 minutes. please tell me which battery should i use? also give the linkweight should be as light as possible
Hi.Quote from: mechaboy on December 12, 2012, 03:58:12 PMfor 8 of this motor i need batteries. i want to use li poly battery. the battery should run at least 15 minutes. please tell me which battery should i use? also give the linkweight should be as light as possibleImpossible!You cannot find a battery without knowing the average load current and you cannot find that without knowing all the details of the entire 'bot and it's working environment. So mount them and test the thing to find the average current while it does what it's supposed to do.You didn't mention anything about gearing and you cannot drive the wheels directly from these motors, if that's what you were going for.
We would have to guess what you're trying to do (how much load it is.)Free running, these motors draw 3 A; stalled, they draw > 40x as much.Let's say that you will be running them at the half-way point, which works out to about 65 A.Similarly, you need a battery that doesn't over-volt the motor, so fully charged, it shouldn't be over 20 V (unless you use an inverter, but you probably aren't.)Fully charged, a LiPo is 4.2V per cell, so a 5S LiPo fully charged would be 21V. However, when drawing actual current, the LiPos sag in voltage, so I think they'll actually be safe. Fully discharged (assuming you do safety cut-off,) a 5S would be 16V.So, 5S LiPo, capable of giving 8x65A, for 15 minutes. That's a total of 16500 mAh per motor. You also need high-discharge-rate batteries, because you're going to be loading at > 2 times the mAh capacity of the battery.Thus, I would recommend something like three of these in parallel, per motor (so, 24 total):http://www.hobbypartz.com/98p-25c-5500-5s1p.htmlOr maybe two of these in parallel per motor (so, 16 total):http://www.hobbyking.com/hobbyking/store/__18209__Turnigy_nano_tech_8000mAh_5S_25_50C_Lipo_Pack.htmlIf you don't know what your load is actually going to be, you could start by buying one per motor, and see how far that takes you, and then multiply out by however much runtime you need.Some more comments:- You need one battery circuit per motor, because the maximum stall draw of the motor would otherwise destroy the batteries (akin to shorting them out.) The "C" rating of the battery times the capacity of all the batteries in parallel for a single motor need to be at least as much as the maximum (stall) current of the motor.- You need some kind of battery management. When a LiPo goes below 3.2V, you will ruin the battery, and if you load it so it gets too hot, it may even burst into flames and possibly explode! Heat sensors, voltage sensors, and fail-safe cut-offs are important. Either a large number of very low-Rdson MOSFETs, or a relay with very high-amperage rated contacts, can do the job.- You also need to think about motor control. What controllers are you using that won't fry out at > 130A current draw?
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