jeanpaulsc said:
I need to power a 40V 5A DC motor for short (~30 sec) infrequent intervals. I have 48V DC available. I wouldn’t mind a bit higher RPM but don’t want to damage the motor. Is it safe to use 48V?
Wow . Lots of good discussion above.
Being completely practical...
Leaf blower is a centrifugal fan.
Look at Fan Laws at
https://www.nyb.com/pdf/Catalog/Letters/EL-02.pdf to get some feel for blowers .You propose 20% overvoltage . I don't think that would hurt the motor for the short bursts you describe.
It would make the motor attempt to increase its speed by 20%
Since fan power is proportional to cube of speed, 20% overspeed would cause the power demand to rise by a factor of 1.78 .
That'll deposit heat in the motor conductors almost 1.5X the rate at normal operation.The motor should handle that for a few seconds.
I'd worry more about the plastic blower mounted to the motor shaft.
Centrifugal force goes up as square of speed.
1.2 squared is 1.44 .
Not knowing how much margin they built into that blower ,
and having actually witnessed fan blades coming apart from centrifugal force (it's violent)
I cannot tell you it's safe, .
You'll have to run a controlled test .
1. Block the air outlet completely, apply 40 volts and measure how fast it turns.
2. Place it somewhere that if it flies apart the pieces won't hit anything or anybody.
3. Rig up a remote power switch at least twenty feet away from it.
4. Block the air outlet completely. Standing twenty feet away and behind a car door, apply 48 volts. If it stays together measure how fast it turns.
5. Block the air outlet with an opening the same area as the turbine you plan to start, apply 48 volts and measure how fast it turns.
If result of step 5 is less than 90% of step 4 then i'd say you've demonstrated by test that it's safe.
old jim