I need to build a battery pack that will last a min 2hrs to power a motor through a speed controller. The motor will be run at the slowest speed possible.Motor Specifications:? Torque: 12.0kg/cm? Rated Voltage: 12.0V? Operating: 4.5 - 18V max? Current - No load: 70mA? Current - Full load: 1380mA? Gear Ratio:
Cannot answer, as you have not given the load on the motor (current varies from 70 to 1380). Speed makes little difference. And is there anything to show how much current the controller uses? They don't use nothing, you know. No free lunch. Read the amp-hours on the batteries to determine how long they would last under a given draw.
You need to do two things to work this out as you have not provided enough detail. Step one: Determine average motor current over the two hour period. Step two: Calculate the required AH (amp hour) rating required for the batteries. Step one: connect an ammeter to the supply side of the speed controller. Run the motor at the speed you require. Measure the current. (lets assume 300mA) Step two: Battery Capacity. Lets say you need 3 hours run time. 300mA * 3 hours 900mAhours required. Check the AH rating of your batteries. (lets assume they are 450mAH rated) Building the battery pack: You neeed 8 batteries in series to get the required 12V. But if you did this you would only have a 450mAH rated battery pack. You need to double that, so put another 8 batteries in series. That will give you 900mAH which is what you require. (total 16 batteries) If you have 900mAH batteries you would only need 8. If you have 450mAH battaries you would need 16 (two parallel lots of 8) If you have 100mAH batteries you would need 72 batteries (9 parallel lots of 8)etc If you have 1800mAH batteries you will still need 8 to get the required voltage, but the motor will run aproximately twice as long as with the 900mAH solutions. Hope this helps!
