Control 12V DC motors with a 4S LiPo with a RoboClaw + fuse dimension for 5.5A stall current

Robotics and electronics discussion Electronics
1

Hello,

I’m trying to design a drive system for a robot that is composed of :

I want to connect my motors and my RoboClaw like this :

14+ V LiPo ---- RoboClaw ------ Pololu 12V motor
                            └-- Pololu 12V motor
  1. Is there a problem with powering my 12V motors with a higher voltage ? Can it break or have unexpected behaviors when powered at that voltage ?
  2. Other question : my motors have a stall current of 5.5 A. if I plug a fuse between my LiPo and my RoboClaw, should I find a fuse that cuts at 2x5.5=11 A ? Or should I find a fuse that cuts at a smaller current ?

Pardon me if my questions are too obvious, I am a relative beginner in electronics

2

Hello.

In general, these kinds of motors can be used at voltages higher than they are rated for, which will result in higher speeds and more torque at the cost of operating life. At some point, raising the voltage too much could cause the motors to fail almost immediately. Running those motors between 14.8 and 16.8V will probably lower their lifetime compared to 12V, but I would not expect any immediate problems as long as you keep the current draw to around 20% to 30% of the rated stall current.

The RoboClaw has a built-in current limiting feature that you can configure through the Basicmicro Motion Studio software, so it will probably be easier to use that to protect your motors. Adding a fuse between the battery and the RoboClaw to help protect the whole system is still a good precaution though, but what specific fuse value you use depends on your particular application and desired safety margins. If the RoboClaw and motors are the only things in your system, then a starting guideline would be to use a fuse no higher than your RoboClaw’s peak current rating.

There are other protective measures you might also want to consider. Here is a link to a Basicmicro article about motor controller hardware precautions.

- Patrick

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3

Thanks Patrick. I see what you mean

So I may take a fuse that is closer to the stall current of the Pololu motors. Should I try to find a fuse that is rated for ~20-30% of 11A (two 5.5 A motors) ? Or that stall current is reached by the motors when we start to power them ?

Thanks

4

Motors like these will usually draw their stall current briefly when they start up from a stop or switch directions at high speeds. So, if you are powering your system around the motor’s nominal voltage (12V) and your system included a fuse rated for about 20-30% of your motor’s combined stall current, then you might find that you regularly blow the fuse (depending on its response time) unless you are taking some other measures to prevent the current from exceeding the fuse rating (e.g. limiting accelerations or using the RoboClaw’s built-in current limiting feature like I suggested in my last post).

- Patrick

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