BLDC Motor, voltage pumping due to braking or reversing

Thread Starter

riscy00

Joined Jun 23, 2010
6
I have 50W 4 pole BLDC Motor as used for servo acuator (or CNC) with screw.

I have 3 phase generator and 6 rectifier diode with provide 48V under steady rpm.

I wish to calculate sizing of the capacitor in case of motor slow down (reversing torque) or estabishing braking. Is there guideline to do that. The cap sizing is critual due to space constraints.

I know that current pumping into generator is impossible due to rectifier diode which work only for forward current, so capacitor bank play important role to limits voltage from approaching breakdown area.
 

MaxHeadRoom

Joined Jul 18, 2013
19,466
If CNC you should obviously have a suitable BLDC drive, what make of motor. drive and type of present DC supply?
If you have a 3 phase rectified supply you should already have a large capacitor for the drive?
Max.
 

Papabravo

Joined Feb 24, 2006
12,702
I don't think you can make a successful servo drive with the listed components. A BLDC motor will not move just because you connect it in some fashion to a power source. Doing this without knowing what you are doing could have disastrous consequences including serious injury or death.
 

MaxHeadRoom

Joined Jul 18, 2013
19,466
I have 50W 4 pole BLDC Motor as used for servo acuator (or CNC) with screw.

.
Also that is a very small motor for typical CNC purposes, the ripple on a 48v full wave rectified supply is <5%, so a smoothing capacitor size would be relatively trivial.
The drive should take care of the concerns you have in the OP.
Max.
 
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