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

Mariss,

> 3) Nothing wrong.

Interesting.

> (1) and (2) combined constitute 50%, (3) is about 25%. (4) thru (10)
> make up about 20%, leaving the remaining 5% for everything else.
>
> Overvoltage edges out everything else and can be very sneaky. Our
> drives are rated at 80VDC, all power section parts have a specified
> 100V breakdown and the drives actually come apart at 108V to 113V. I
> know because five out of every 1,000 drives are tested to destruction
> for quality control reasons.
>
> On the otherhand, a little NEMA 23 2A motor (Vexta PK268-02) will
> happily generate 100V open circuit at 3,000 full steps per second,
> 330V at 10,000 full steps per second.

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.

> It is entirely possible to overvoltage (blow up) a drive with a 24VDC
> power supply if there isn't a large (10,000uF) capacitor on the
> output of the supply. The capacitor absorbs the voltage.

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