Q for Mariss (was Re: Here's my proposed power supply setup.)

Dave,

PLEASE DON'T DO THAT!! A light bulb is a resistor. Your idea works OK
as long as current flows from the supply to the drives. All this
turns around when a motor stalls or you decelerate rapidly from a
high speed. Current then flows from the drive to the power supply! If
you have an 80VDC supply and the current is going "the wrong way"
then the bulb will add its 12V on top of the supply voltage giving
you 92V! If it burns out, then the voltage can become 200 to 300
volts. Wave bye-bye to the drive then.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "turbulatordude" <davemucha@j...> wrote:
> Hi Ralph,
>
> suffering a recent blowout of a controller, I wish I had taken the
> time to put in an automobile brake light.
>
> one puts the 470uF cap on the Gecko power input, and the fuse as
you
> mention, but then also adds an autombile light as another
protection
> device.
>
> if something went wrong, the light would light as the current was
too
> high. this would bring the voltage down at the same time.
>
> if everything was right then the light would just let the
electricty
> flow normally.
>
> Dave
>
>
>
> --- In CAD_CAM_EDM_DRO@y..., "rawen2" <rawen2@y...> wrote:
> > Hi Mariss,
> >
> > I'm currently building my 4 axis power supply and would prefer to
> do
> > it right the first time.
> > I'm assuming fuses or circuit breakers are placed between the
power
> > supply main filter capacitor and each individual motor driver as
> > Lloyd mentioned in his setup.
> > A while back there was a discussion about disconnecting motors
> while
> > powered up and the back EMF generated by the collapsing magnetic
> > field in the motor would damage the driver. So what happens when
a
> > fuse blows on the driver's supply side?
> > Do you have any general guidelines for placement and sizing of
> fuses
> > or CB's in our stepper power supplies? What if the main
capacitor
> > breaks down and shorts? Should the primary or secondary sides of
> the
> > transformer have fuse or CB protection that would kick in before
my
> > garage's 20A CB does?
> >
> > X,Y,Z steppers are 3.5 V 5A 650oz/in. No 4th axis yet.
> > Transformer is 700VA Plitron toroid 50VAC @14A output. Should be
> > around 70VDC after bridge.
> > Bridge rectifier is 25A 600PIV.
> > Surplus capacitor is rated 56,000uF 80VDC. Kinda big I guess
after
> > seeing your calc but the higher voltage ones are harder to find
and
> > the price was right.
> > Drivers are APC CMD260's (Sorry, got 'em cheap)
> >
> > Thanks,
> > Ralph Wenzl