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how can i determine how much max current can my dc motor draw?


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May I suggest in future that you tilt your forum topic more appropriately. You just called it "Battery" which tells us nothing and then you ask about motor current draw!!!!

One thing that frustrates many LMR members is people who ask for help but offer little or no information about their problem and do not even know how to ask a question properly.

Well sorry for that sir..Actually my 1st robot is completed.i didn't have too much trouble on designing or implementing the circuits or the code.

bt the prob was to properly power up my robot.and with out any experimnt i used my DSLR's Li-ion battery(8.22v 1030 MaH) and after 2 or 3 times use it was completely damaged.The battery costs around 1950 rupees in indian currency(50$ approx).i was in such a hurry to complete it.now this is the part i am afraid of.if i again damage battery.thats why i asked about motor current draw so that i could choose my battery wisely next time.

i should have given the subject more appropriete.sorry for that

thanks..any suggestion about how much current should i give for input o measure the max current.without damaging the motor?

Don't worry about that. The motor will draw only as much current as it needs. You can't feed it more current! Just make sure to not feed it with more Voltage than the motor rating.


thank you..I hve one last stupid ques to ask..

if i buy this one http://www.flipkart.com/fujicell-bc1002-battery-charger-with-4-x-2800-mah-rechargeable-battery/p/itmd5mguxghnsxch?pid=ACCD5MGTZGWDMES4&ref=71473d86-3cbd-4ffd-a927-e27c83db8533

i have 5 dc geared motor.2 servos.2 HCSR 04.

does i require more..or this will do(approx)?

Power your motor by connecting some power supply across it. Then use your multimeter to take the current readings by connecting it to the contacts of the motor.

I'm not sure though. It was suggested to me by someone and I suggest it forward to you. Never tried it before.

...that's just free running current, which is minimum current.

Max current is when the motor is stalled. The good news is that you can calculate the max current without actually having to power the motor and hold it in place, which might damage it permanently.

When the motor is stalled the current is determined solely by the resistance of one motor winding and the supply voltage. So, for a brushed dc motor, take your Ohm meter and simply measure the resistance accross the motor leads, you may want to spin the motor around very very slowly by hand until you get a minimal resistance reading. Write down the minimum resistance measured. To determine the maximum current divide the supply voltage by the winding resistance. Let's say you measure 10 Ohms and you have a 12 Volt battery, the maximum current through your motor will be 1.2 Amps

You are right! I forgot to mention that the motor has to be stalled.

I didn't know that about the winding resistance. I will keep that in mind.


Great..thanks man..i think i read somewhere-Stalled means the power to stop the motor at its top speed.

is there a huge difference between the stalled one and the method described by basile and vishu? 

thanks for the reply..all of you

You don't connect the multimeter to the contacts of the motor, but in series with the motor.
Example: http://www.allaboutcircuits.com/vol_6/chpt_2/4.html