Need help with 28byj power supply question

I am planning to connect 6 28byj-48 motors to Arduino mega.

I have modified them from unipolar to bipolar and using pololu A4988 drivers to control them.

Now I wanted to know what will be the amount of power and current I will need to make them all run. Will a 9V battery do?

Will a 9V battery do?

Not at all.

Get a brick power supply that can provide 12-24 V at 2-3 amperes and [u]be sure[/u] to set the current limit on the A4988 drivers correctly.

Thrift stores usually have lots of cheap laptop power bricks

Thanks @jremington Any idea what is the current requirements for these motors once they have been converted to bipolar?

I am also searching some documentation online but haven't had luck so far.

Individually they run on 9V when they are unipolar.

Ohm's law:

current = (supply voltage)/(winding resistance)

jremington: Ohm's law:

current = (supply voltage)/(winding resistance)

No, Ohm's law is not applicable here, a chopper driver is not a resistive load. These motors are about 100mA and 50 ohm windings, so from a 12V supply and chopper driver you might need 50 to 100mA from the supply, 6 of them will probably run happily from a 12V 1A supply (assuming the current settings are appropriately configured). Even a 0.5A supply might work...

No, Ohm's law is not applicable here

Nonsense. Ohm's Law is certainly applicable to determine the maximum possible coil current for a given power supply voltage. This is very important to know for safety reasons.

If the A4988 is so adjusted, or the power supply voltage is low enough that that the A4988 does not switch, then Ohm's law definitely holds and is exactly what you want to use.

I think, both of you @jremington and @MarkT are right. In the stall situation Mr. Ohm is determining the resulting current; when the motor turns, Mr. Ohm and Mr. Henry are sharing the resulting current in a way dynamically (if all EE's here allow for my simplifications).