# Small question about DC motor voltage

#### yaron02

Joined Jan 29, 2022
10
Hi,
I bought a 24V 500W (output power) DC brushed motor.
A friend offered me to borrow a 20v 30ah battery he doesn't need.

So my power source is 20V instead of 24V.

Do you guys think it is possible to use such battery to run the motor ?
I know I will lose some RPM but will the output power reduction be severe or minor ?

Please let me know what you think.
Thanks!

Joined Jul 18, 2013
28,060
As you say, the top RPM will most likely be affected and the maximum rated torque, otherwise, for simple, non-demanding tasks you should have no problem.
You may however find that battery limited if you want to use it in any high current demanding jobs.

#### crutschow

Joined Mar 14, 2008
33,365
I bought a 24V 500W (output power) DC brushed motor.
A friend offered me to borrow a 20v 30ah battery he doesn't need.
Depends upon how big a load you put on the motor.
At full load it will take over 20A.
Will the battery tolerate that much current?

#### MisterBill2

Joined Jan 23, 2018
16,622
Certainly the motor can run quite well on 20 volts instead of 24 volts. The output power will be less because the input power is less. Variable speed and power are major benefits of brush type DC motors.

#### yaron02

Joined Jan 29, 2022
10
Certainly the motor can run quite well on 20 volts instead of 24 volts. The output power will be less because the input power is less. Variable speed and power are major benefits of brush type DC motors.
Thank you sir.
If at 24V the motor ouput power is 500W, Is it reasonable to expect that at 20V the motor output power will be around 500*20/24 ?
In other words, is the relation between the input voltage and the output power Linear ?

#### yaron02

Joined Jan 29, 2022
10
Depends upon how big a load you put on the motor.
At full load it will take over 20A.
Will the battery tolerate that much current?

The battery Is actually 6 batteries parrallel conected.
Each battery has 20Vand 5ah capacity with rated current of 5 Amps
So I think it will be fine

Joined Jul 18, 2013
28,060
So I think it will be fine

#### yaron02

Joined Jan 29, 2022
10
Well, to be honest this is somthing I need to figure out.
The motor is supposed to drive a small electrical cart with self weight of around 40kg and external weight of one grown human (around 75kg).

My plan is to use gear ratio such that the cart speed will be very low but with high torque.

Joined Jul 18, 2013
28,060
Going to be pushing it!
The best set up for maximum torque is probably a Worm-gear set up may be best, they can achieve very high gear ratios, giving you a fairly high torque output,
Use Largest dia driven gear you can.

#### MisterBill2

Joined Jan 23, 2018
16,622
You will need some gearing to provide a reasonable drive speed. Not a worm gear reduction because they have higher friction.The speed reduction is fairly linear , but so is the torque reduction, fairly linear. (=not perfectly linear, but close)

Joined Jul 18, 2013
28,060
. Not a worm gear reduction because they have higher friction.The speed reduction is fairly linear ,
DO NOT agree, they are among one of the more friction less high ratio applications.

#### crutschow

Joined Mar 14, 2008
33,365
One interesting characteristic of a worm gear is that it can't be readily back-driven, so in a vehicle application, it will provide automatic braking (not necessarily desirable) when the motor is slowed down or stopped.

#### Lightium

Joined Jun 6, 2012
118
Most likely it will run, but at reduced power and rotation.

#### Lightium

Joined Jun 6, 2012
118
It's best to have some margin when considering power.