Re: [CAD_CAM_EDM_DRO] Re: Question about how to set up VFD for braking resistor

washcomp wrote:

>Jon:
>
>Using your calculation method, I end up with 43 ohms (1.5 hp motor).
>The minimum resistance is 16 ohms. I have a 100 ohm resistor. Will
>it work even though it's roughly twice the value we calculated?
>Yaskawa (in the manual) calls for a 70 ohm resistor on this drive for
>a 3HP motor and 100 ohms for their 2 HP and 1.5 HP VFD (reason I
>picked this one)
>
>

Hmm, looking over my calculations, the resistor values I came up with DID,
in fact, work out too low. I think I neglected to consider how these drives
work, and the fact that the DC link voltage is TWICE the line peak voltage.
So, my numbers for resistance should have been about twice what I gave
before.
That puts them a lot closer to the number you give above.

Putting a 70 Ohm resistor on the drive will not hurt anything, as it
uses the braking
resistor to keep the DC link voltage below 390 V or so. In other words,
it uses just
enough pulse width to keep the voltage from going any higher, so you
really don't have
to match the resistor to the motor size. As long as the resistor is not
too LOW a value.
If Yaskawa says 100 Ohms R is fine for 1.5 - 2 Hp, then what you have
should be OK.

Jon