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

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "washcomp" <jeff@w...> wrote:
>
>
>>I've just installed an Omron/Yaskawa G5+ variable frequency drive
>>
>>
>on
>
>
>>my Bridgeport. I intend to control it from MACH3.
>>
>>The good news is the VFD is working like a champ (manually – still
>>haven't controlled it yet from MACH3). Maybe I misunderstood about
>>the noise, or maybe the load side reactor is doing its job because
>>
>>
>it
>
>
>>sounds just like a Bridgeport 2J
>>
>>I've installed a breaking resistor. I'm trying to figure out what
>>braking mode and deceleration I should pick if I'm using a braking
>>resistor. Both manuals (Omron and Yaskawa) refer to it, but
>>
>>
>neither
>
>
>>explicitly says what function to select (DC injection braking
>>maybe?) Any help would be appreciated on this.
>>
>>

OK, first, check the RMS rating of the motor. Assume a 1 Hp, 230 V 3-phase
motor, it will be about 3.3 A. Multiply by 1.732 (Square root of 3) and that
is about the worst case DC link current it should ever deliver when
decelerating
at a reasonable rate. So, if your braking resistor can draw 3.3 * 1.732
= 5.7 A,
it should be enough. At a DC link voltage of 380 V, the resistor would be
66 Ohms. The Yaskawa manual should specify the minimum permitted braking
resistor, pick one less than 66 Ohms and more than the specified minimum.
You might double that calculation above, just to get more powerful braking.
I have my mill set up for a 0.7 S braking time (from whatever speed to
the point
it cuts over to DC braking). But, when I swap motors to my Westwind drilling
spindle, and run it up to 400 Hz (~23000 RPM) I have to set the braking time
to 5 seconds or the VFD trips on overvoltage. That tiny spindle running that
fast can deliver a lot of energy back to the VFD. As long as you don't
get an
OV fault when decelerating, everything should be fine. I actually found
out how
close to the edge I was at 5 Sec, as I had a program that was turning
the spindle on
and off about once a minute, and after the braking resistor got good and
hot I
had an OV fault. What happened is that the resistor got hot, and the
resistance
went UP, and it couldn't absorb the energy fast enough. But, I NEVER have
this with the standard Bridgeport motor.

I have it set up to use regenerative braking down to about 10 Hz, then
it switches
to DC injection braking for 1 second, at .1 times rated amps. This works
great.

I have the same setup on my 15" Sheldon lathe, but I have a 1.5 sec
braking time
there, due to the massive chuck.

Jon