0
\$\begingroup\$

I am looking at some datasheets for 5-12V DC motors. The datasheets specify the stall current is ~1.9A at 12V DC. They do not specify anything with regards to maximum safe operating current.

In my application there is built-in overcurrent protection in the circuit but it made me curious; Is there a rule of thumb for safe maximum current for small DC motors?

\$\endgroup\$
  • \$\begingroup\$ I don't think you can generalize - some motors will sit happily in stall all day - they might get fairly warm but they won't go pop. Other motors might fry if left in stall for over a minute or so. \$\endgroup\$ – Andy aka Feb 17 '14 at 17:45
  • \$\begingroup\$ That is what I thought. I wish they would clarify in the datasheets whether the lack of information about maximum current is or isn't because the motor is fine when stalled. \$\endgroup\$ – SomeEE Feb 17 '14 at 17:59
  • \$\begingroup\$ You can add a heatsink if you can't avoid stall; RC shops may have an appropriate diameter heatsink to wrap around the casing. \$\endgroup\$ – Emyr Feb 17 '14 at 18:12
  • \$\begingroup\$ Heatsink won't save the motor if the brushes burn out. It really does depend on the motor (carbon brushes are usually tougher than the metal ones) \$\endgroup\$ – Brian Drummond Feb 17 '14 at 18:32
  • \$\begingroup\$ @MathEE If the absence of specific information to the contrary, you should assume that the stall current says nothing about the maximum continuous current. Stall current allows you to infer DC resistance, and thus, speed regulation and maximum torque. It also gives you some idea of the maximum current your drive might need to handle. It's also possible to have more current than the stall current: try driving the motor against the direction of mechanical forces. \$\endgroup\$ – Phil Frost Feb 17 '14 at 19:23
2
\$\begingroup\$

It's not so much a maximum current issue but a power dissipation issue. If the motor has a stall current rating, certainly it can take that current for at least a little while. That means the windings, brushes, and whatever are designed to handle that current.

The real issue is how hot it needs to get to be able to dissipate all that power. 1.9 A x 12 V is 23 W that all goes to heating the motor when it's stalled. Can your motor safely dissipate that much without overheating? There is no way to know up front without consulting the datasheet or asking the manufacturer.

Some motors are designed to handle their stall current indefinitely, some aren't. There is no way to tell how long a specific motor can withstand the full stall current just from the specs you have provided.

| improve this answer | |
\$\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.