On 2008-09-02, Gunner Asch wrote:
On Tue, 02 Sep 2008 14:46:57 -0500, Ignoramus2176
wrote:

So, I have a 1 HP Bridgeport on a VFD. The time has come to install a
braking resistor. I had it for a while, but wanted to install the DRO
first. With the DRO, and wiring better organized, installing brake
resistor is more pleasant.

The question is about stopping time.

Right now (without the external brake resistor), I have the mill set
to stop in 1 second. That works at most speeds, except at highest RPM
it trips on overvoltage and then coasts to stop.

Just what can I realistically expect with a brake resistor? Would you
say that I could expect to stop it in 1/2 second at all speeds?

Yes. I tap with my Gorton Mastermill, which has a HEAVY motor (5hp)
and a big spindle.

I can do an "invisible reverse" at speeds up to 5000 rpm. Changes
direction so fast you never see it.

I do have a 5hp VFD and a big breaking resistor. A tubular ceramic
btw.

A braking resistor is essential if you are doing braking, or fast
reverses.

I specialize in OmniTurn CNC lathes, which use a 5hp motor and can do
an invisible reverse at 4000 rpm, and they too have a big braking
resistor.

I have a 3/4hp motor on my Big Delta drill press, with an older
Hitachi VFD..no braking resistor..and it trips if I try to tap with it
at just about any speed.

Some VFDs come with a small internal resister, some with none, some
with no provisions for an external resistor

This is very encouraging. I think that what I will do after installing
the resistor, is try to take the stopping time as low as possible, at
highest RPM. Then I will back out just a bit. Almost instant stop, is a
very convenient thing.

i