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

To: CAD_CAM_EDM_DRO@yahoogroups.com
From: "washcomp" <jeff@...>
Date sent: Wed, 10 Mar 2004 23:43:18 -0000
Subject: [CAD_CAM_EDM_DRO] Re: Sizing of braking
resistors for a VFD
Send reply to: CAD_CAM_EDM_DRO@yahoogroups.com


I don't understand 'braking resistors' on a 3 phase induction motor.
Can someone please clarify???

Bob
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On one of their VFD drive families (not the one I'm using),
Automation Direct recommends:

1HP 200 ohms 80 watts
2HP 100 ohms 300 watts

If I have a 100 ohm 250 watt resistor, do you think that's close
enough for my motor?

1.5 HP 5.7amps, 208 volt 3 phase

Jeff

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson
<elson@p...> wrote:

> > > 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



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