On Sat, 15 Sep 2007 01:01:44 -0500, Jon Elson wrote:
Ignoramus32529 wrote:
PS, I also have a braking resistor that I want to install, which is
very large. I think that I will install it far from the VFD in some
inconspicuous location on the mill. It has its own heatsink already.

The resistor is pictured here

http://cgi.ebay.com/ws/eBayISAPI.dll...m=230168242134

i
Oh oh, that is a 100 Ohm braking resistor! On a 240 V VFD, the
DC link is 340 VDC, so the current would only be 3.4 A This may
not be enough to drain energy out of a larger motor. It would
probably be fine for a 1 Hp mill, but not good enough for a 3
Hp, for instance. I am using a 40 Ohm resistor on mine, with 1
Hp motor and drive. Even that is not enough when stopping my
high speed spindle, which has a lot more momentum at 24,000 RPM,
and the VFD will get an over-voltage trip when the resistor gets
hot.

Resistance should be mateched to the drive. My drive specifies 80-200
ohm resistor, IIRC. I found some junk brackets and may try to re-mount
the drvie today.

i