Re: [CAD_CAM_EDM_DRO] Sizing of braking resistors for a VFD

washcomp wrote:

>I am looking for the proper size dynamic braking resistor for an
>Omron G5+ VFD.
>
>My motor is a 1.5 HP 3 phase 208 volt on my Bridgeport.
>On their house brand of VFD, Automation direct recommends about 150
>ohms, 300 watts. Do different drives take different values or is it
>strictly based on the motor size?
>
>

Motor size is the most important, since the drive won'd DRAW more
current from the motor than it will SOURCE to it.

150 Ohm at 360 V DC will drain about 2.4 A. Is that enough? I would expect
the line current on a 1.5 Hp, 208 V motor to be about 5 A. That could be
about 1400 W. So, you'd want to be able to dissipate that much energy
in the braking resistor. I = P/E =3.89 A, R=E/I = 92 Ohms. I'd go for
about
a 100 Ohm resistor to be sure. I'm pretty confident the VFD can handle
4 A in the braking resistor, for the millisecond periods where it is needed.

I'm using something like 50 Ohms on my 1 HP drive on my Bridgeport.

Jon