Newbie question concerning voltage motor

Hi guys,

I have the following situation: H-bridge with a 12V - DC motor.
I used 2 9V - batteries and made a voltage divider to have 12 Vout for the motor.
But this doesn’t work. I measured Vout and it was 12 V.

When I didn’t use the voltage divider, and attached 18 V to the motor, it worked.

Can somebody explain this?

I have another analog motor that I will attach to the right side of the H-bridge, but then my question is
the amount of current I need to provide to the motor voltage input pin (there is only one of these pins on
the H-bridge).

Thank you,
the newbie, yet full in progress in my own project, but with more downs that ups, but will get there…
eventually…I hope
:wink:
fig 1 = motor I used
fig 2 = scheme with voltage divider
fig 3 = scheme without voltage divider (this works)

Off hand, I would say that motor requires more current than those batteries can supply.

You cannot use a voltage divider to provide a power demand.
Current delivery of voltage dividers should always be considered as 0 ( to permit the R1/R2 ratio provide the calculated voltage)
Since power is the product of voltage x current then power = 0

You need batteries capable of a decent current output - small 9V batteries are
hopeless for powering motors. Consider LiPo or SLA or NiMH rechargables -
motors require amps, not milliamps.

You also need to do some calculation for capacity - how much current is your
application using on average? How long do you want it to run for between
charges or battery-changes?

Brushed DC motors like that one have a minimum current needed to overcome
friction, and are only efficient at the higher end of their power range as a result,
which means choosing the right size of motor is important for maximising
battery life.