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3v Motors on a 9v Battery

Demonstrates that conventional wisdom may not be correct

It's kind of taken for granted often that a 9v battery (thanks mixmar ;-) won't provide the current to drive a 3v hobby motor, especially when you run a microcontroller off of it too. Ignoblegnome and I were trying to drive that point home today in this post.  However, CrazyCreator was insistant that the motor ran off of his battery.  I got curious and rigged (essentially) the circuit you see in the image above.  What it amounts to is holding one input low and one input as well as the enable on each motor channel high on a dual h-bridge to engage each channel at "full speed."

According to everything that every website and robot book in the world tells us, this shouldn't work.  The cells in a 9v battery are just too small to provide enough current to drive a motor, let alone two of them, right?

Well, the experimental science says "Wrong!"  Apparently, there's enough juice to spin up two standard yellow Dagu gearmotors for at least a minute or two.

This is not to say that it's a good idea, or that you'd be able to run more than a single servo of your UNO with a 9v battery as the sole power source (and I still don't think you could get even one motor to work on a 9v if it was used on a microcontroller too.)  However, in this situation, the conventional wisdom is apparently wrong.  Either that or Magnum Thunderbolt off-brand batteries pack a really cool surprise.

Since every video service I try to use can't seem to play nice with LMR today (at least on iPads,) here's a link to the video.

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If the motors had any load on them then they would not start at all.

If the 9V battery was a cheap brand then it might not have driven the motors at all. A rechargeable NiMh 9V (actually 8.4V) will drive the motors.

To say a 9V battery won't run the motors is an oversimplified claim. It depends on the ability of the battery and the current draw of the motors.

The ability of the battery depends on the chemistry of the battery as well as the size. The amount of current drawn by the motors depends on the construction of the motor as well as the load.

The reason it is never recommended to use the 9V batteries to drive the motors is because, even if you do get it to work, it will not work for long. If you are using non-rechargeable batteries then it is an expensive excercise in futility.

Hello Maxhirez

I still think it's granted a 9V motor wont provide current to run the 3V motors... ;)