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Topic: 9v battery for 2 mini servos : Enough? (Read 1 time) previous topic - next topic

vslo

Hi there,
Ok, I need some help about powering 2 mini servos. Is a 9v battery connected to the 2.1mm arduino power jack enough to supply the necessary current to the servos? I took off their potentiometer and they are working as ordinary DC motors, connected through a H-bridge to the arduino.
I made some tests and the servos worked fine. But I am afraid they can draw excessive current at some point.
Can I have any kind of problems?

terryking228

Hi, what is the type and ratings of the Battery??

This is like saying, "Is 50 PSI enough pressure to put out that fire?"..

(I had to try to keep up with Crossroad's Analogies  ;)   )
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

vslo

Its an ordinary 9v alkaline battery.

CrossRoads

Me? Analogies? Doesn't sound like me  :smiley-zipper:

Grumpy-Mike replied another thread that 9V batteries have about 500mAH of capacity.
Is your plan to use the 5V regulator to knock that 9V down to 5V to drive them?
That will definitely waste a lot of their capacity as heat in the regulator.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

vslo

Yes, I am planning to plug it trough the 2.1mm jack.
Its a fast presentation, will not take more than 5min demonstrating the robot.
About the heat, should I be worried?

Grumpy_Mike

Quote
About the heat, should I be worried?

No

vslo

I do know that I will need a separated power supply to run the servos properly. But, for a fast presentation, do you guys think that a 9v ordinary alkaline battery will make? If so, how long? I am using those mini 9g servos!

retrolefty


I do know that I will need a separated power supply to run the servos properly. But, for a fast presentation, do you guys think that a 9v ordinary alkaline battery will make? If so, how long? I am using those mini 9g servos!


Well you can make a better conclusion based on a measurement. Run one of the motors at 5vdc at full speed and under whatever mechanical load they will be subjected to and measure the current draw. If both servos are to be running at the same time then double that measured value. When you have that number then we can talk some more.

  If you want my gut opinion your wasting your time planning on using a 9vdc battery to power two servos. Get a 4 alkaline AA battery cell holder and plan on powering your servos separately with that, saving the 9 volt to just power the arduino board.

Lefty



vslo

The thing is: I got a broken feet and my presentation is tomorrow !! I was going to search for a 4AA holder, but I broke my feet last friday, so I can't drive ! I just made a test here, and they seem to be working fine. I don't know for how long the battery will supply enough power. THey have 2.7kg stall but the robot weight is less than 1kg.

vslo

One more thing. If they stall, and request more current than the arduino regulator can handle, will I have a problem?

retrolefty


One more thing. If they stall, and request more current than the arduino regulator can handle, will I have a problem?


Yes that will be a problem as the regulator will shut off on overcurrent, which will then cause the arduino to reset and start up gain when the current draw is removed and then it will happen again and again until the mechanical stall condition is removed.

Lefty

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