1
\$\begingroup\$

I am building a robot using two 12v windshield wiper motors. I wish to buy a good quality LiPo battery on the following weeks, but until I do, I am thinking of using an old Li-ion 11.1v 4100mAh laptop battery.

I think I can't safely connect the motors straight to the battery, because they can draw up to 30A and that kind of current draw would most likely make that battery burst into flames.

Is there a way I could limit the current draw from the battery? I'd love to be able to feed constant 5A to the motors, for example (I know torque on the motors would be greatly reduced).

\$\endgroup\$
  • \$\begingroup\$ speed can be controlled by controlling the duty cycle of motor drive circuitry. if your problem is specific, share your design so that others can help much better. \$\endgroup\$ – Umar Jan 19 '17 at 6:00
  • \$\begingroup\$ DC/DC converter with current limit? \$\endgroup\$ – winny Jan 19 '17 at 8:58
1
\$\begingroup\$

Assuming you're looking to control the speed/torque of your motor, you're going to need a motor driver. Look into an H-bridge - you can easily build one with discrete components or buy ICs that do it for you.

Next, you're going to need a way to control the duty cycle of your motor driver. One easy and popular option is to use an MCU to send a programmable PWM to the driver, it's up to you.

Finally, you'll decide how fast you want to run your motor. If using PWM control, you're actually cycling between fully on (as if it's directly connected to the battery), and fully off for the motor. Your effective current draw (and therefore speed, torque, etc.) is the average current taking into account the duty cycle of the PWM.

\$\endgroup\$
  • \$\begingroup\$ Yes, I was already looking for an H-bridge, I am going to use an ARM SBC (Linux) to control the motors. I think I didn't quite understant H-bridges until now, I should probably just check what is the max duty cycle I can use safely with this temporary batteries. Thanks! \$\endgroup\$ – Thums Jan 19 '17 at 6:39
-1
\$\begingroup\$

There are circuits to limit the current, but I think you can easily use a fuse, for safety. Of course it is not meant to keep your motor speed constant. If you want something fancier you can do it with a microcontroller, which is an overkill most of the times.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.