Re: Power supply for Servos - Energy dump and such - UR...

--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers <rogersmach@y...>
wrote:

> There are actually two different dump circuits and the one that is

being discussed is the over voltage type. That monitors the voltage
and dumps anything over a set limit during operation, The DPDT dump
circuit is another type that dumps the caps at shut down so the
machine will stop abruptly rather than slowly proceed until caps are
drained. It keeps the caps drained while anyone is working inside the
enclosure, as long as the control is shut down.

> Ron
>
> Polaraligned <polaraligned@o...> wrote:
>
>
> What is the advantage of using the more complicated circuit with
> the LM393 as opposed to using the simple DPDT relay dump circuit

that

> Mariss published before this?
>
> Scott

Probably the only time I have seen Mariss create even the slightest
bit of a confusion. There are actually THREE dump circuits in the
files section of the geckodrive group..

The 'dump DC bus power when the AC is turned off / E-stop'
The automatic overvoltage clamp and dc bus off
and the minimalist overvoltage dump.

All three are labeled dump, but are dump1, dump2 and dump3

The minimalist version has a diode in the circuit between the DC
power supply and the drive. I didn't see any notes or reviews, but I
chose not to use this version as it forces any returned energy to
stay in the drives as it takes the main filter caps out for the
return energy path. In my view, a bad application, but one that
helps understanding of the topic.

Another is the DC BRUSH TYPE E-Stop circuit.

This has the AC lines in, and has a large (20 watt) resistor in a
circuit thru a relay. then across the capacitor.

When the relay is energized, (manual pushbutton) the resistor is
taken out of the circuit and the DC bus is charged. upon AC
failure, or E-stop, the relay is de-energized and the 20 watt
resistor is placed across the filter cap.

Mechanical relays have a limited life, and are very slow speed
electronically (but with electricity traveling at the speed of
lights, everything is slow in comparison) But, the mechanical relay
will see only a few changes a day. Much less than a coolant pump
relay.

In addition, there is a relay that applies power to the transformer
and these two relays work in tandem. A DPDT relay would be used
instead of two single pole double throw relays.

This circuit is one that should be used if you have no other means of
dropping the voltage of the power supply when the power if off.

The third, and more complicated, and I assume the one that we have
been discussing, is more automatic.

It powers the drivers directly, so is not in the path between power
supply and driver. This also means that the power supply caps stay
in circuit and as Jon E. was so kind to point out, virtually
eliminates the need for the return dump circuit.

This version monitors the voltage on the DC bus, and when it
increases beyond the set level, it will connect the DC bus to ground.

It operated on every half cycle and then only on part of that, so it
operated about every 0.008 seconds. Most likely, for less than 0.8
seconds, and probably never (if one follows Jon's recommendations) to
a few times a day.

Since mechanical relays being used to switch at 120 hertz is a bad
application for power, a MOSFET is used. I'm considering a MOSFET
and TRIAC to replace the relay, but that will mostly likely not be
the final use as I already have the relay.

In regards to application, I am making both the relay based E-stop
and the independent return voltage dump circuit.

Hope that sheds a little light on the subject.

Dave