Re: G201 death/repair/questions/problems (long post)

Chris,

1) That one's got me stumped because I've heard of that happening a
few times before.

About a year ago I set up a relay that turned the power supply on and
off every second on a running drive. I left it on over the weekend
where it cycled 200,000 times. No problems were experienced.

Where this will happen is if you switch the DC power to the drives.

That is a no-no and the damage occurs on turning the power off. The
inductive energy stored in the motor windings has nowhere to go so it
generates a damaging voltage whose harm only shows up the next time
you turn the drives on. The drives didn't blow when you turned the
power on; they were killed when the power was turned off the last
time.

2) You can't hurt the drives by cranking the motor while the drives
are off. The motor acts as a generator that simply begins to power
the drives. You can't crank it fast enough (>500 RPM) to hurt them
unless you are Superman.

Mariss

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Chris Brick <cbrick@t...>
wrote:

> Mariss,
>

> In my situation I turned on the machine with nothing pushing the

axes or

> any holding torque necessary and popped at least one of the two

geckos.

>
> So, the motors aren't spinning which would eliminate that unless

damage

> was done prior to the shutdown. Open circuit meaning not connected

to

> the drive, I assume. What about an intermittent connection. I

believe

> that's what may have claimed the first two G201s.
>
> I guess what I'm trying to figure out is when the motor is

connected and

> sitting and I flip the switch, what could possibly cause the FETS

on one

> phase to blow? Especially after it worked fine only minutes

before.

> That's the question that has me stumped.
>

>
> In a situation where you have a machine that will continue turning

the

> motor after power is removed, how do you stop the motor from

putting too

> much voltage through the FETS or is this even an issue? I bumped

the X

> axis on my machine and saw the light on the Gecko flicker.
>
> > A sure-fire way of eliminating overvoltage is to place an 82V, 5W
> > zener diode (1N5375, $0.80/10 at DigiKey) across the drive supply
> > inputs.
>
> I'll order some today.
>
> Thanks again for the support.
>
> Chris