# slowing a motor down

#### Justin Johns

Joined Feb 28, 2017
8
Hello,
I have a motor that works off a 1.5 volt battery and i would like yo slow it down to about half its speed with the fully charged battery. I think i have to put a resistor in parrallel with it or should i be using some other part and what value would it need to be. Thanks

#### AlbertHall

Joined Jun 4, 2014
11,718
A resistor in parallel will only discharge the battery faster.
To do it with a resistor put the resistor in series. This will reduce the speed but will also reduce the motor power.

#### Justin Johns

Joined Feb 28, 2017
8
Hello,
ok if i understand it i put a resistor on the positive side of the motor. The only drawback with this as far as im aware is that when the motor as been running for a bit it will slow domn and stop, and there will still be juice left in the battery. Is there a method i can use up all the battery power. I know i could do it with a variable resistor but is there another way.

#### Dodgydave

Joined Jun 22, 2012
10,139
Using a constant current source, but it's not much use on a 1.5v battery, your better using different power source.

#### strantor

Joined Oct 3, 2010
5,753
use a diode

#### AlbertHall

Joined Jun 4, 2014
11,718
Hello,
ok if i understand it i put a resistor on the positive side of the motor. The only drawback with this as far as im aware is that when the motor as been running for a bit it will slow domn and stop, and there will still be juice left in the battery. Is there a method i can use up all the battery power. I know i could do it with a variable resistor but is there another way.
Put a switch across the resistor to connect the motor directly to the battery as the battery runs down.

#### djsfantasi

Joined Apr 11, 2010
8,086
What is the motor used for and what is the rated voltage that is expected? @ 0.75 volts, it may not run and if it does, it's power will be reduced. Have you already tried the resistor idea?

I'd recommend a PWM method. You can search online for a simple circuit like this*, but basically, the circuit would "chop" the 1.5V so that it is on (almost) only half the time. I saw "almost" because a simple circuit uses a 555 IC, which can't be on exactly half the time. But you can get close. I've used a 555 circuit that was on 52% of the time.

Of course, this will draw some extra current and may not be practical for you.

* the link to a circuit is presented as an example, not a solution to your case. For example, the switch (on the right) is not necessary unless you plan on reversing the motor.