Re: Question on Mariss' E-Stop circuit

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Monte" <montejw@e...> wrote:

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

wrote:

> > For a dump circuit you need 7 ohms. The caps must be dumped

quickly

> so >the servos will stop abrubtly rather than slowly wind down to a
> stop >like slowly proceed into the vice before it stops.
>
> Another thought, according to Mariss' instructions I would use a 2.8
> ohm resistor on my 28vdc power supply. That would dump faster than
> the 7, right? Or would a 7 ohm be fast enough? I did a quick look

at

> RS tonight, nothing there in 20 watt power resistors.
>
> Monte

The ohmage of the resistor is the result of a calculation, it is not
a fixed value.

That calculation is rather involved and quite frankly, the simple
version Mariss offered is not very complete.

He proposes to dump 10 amps, and assumes 68 volts, ergo 68 volts
divided by 10 amps = 6.8 ohms. One would change both the current
and the voltage for your power supply. there is no reason a 3 amp
power supply at 24 volts needs to dump 10 amps. Just as someone with
a 30 amp 100 volt power supply would have to work with a whole
different set of values.

Types of machines are also not included. rack and pinion and belt
drive have the potential to have large pulleys, so a flywheel effect
is very possible. An ACME screw will impart a considerable
resistance as opposed to a leadscrew.

The whole dump circuit is a guideline, a starting point, not a end-
all and be-all of e-stop circuits.

Someone asked about a less abrupt power supply drain, then I think
they said they will add a lighted indicator. Considder a simple
110VAC light panel indicator. it is incandescent, has an internal
resistance and will be lit from many DC power supplies. Different
value bulbs are also available. But, that bulb will drain that power
supply in short order when the power is turned off.

Another concept not discussed is that 250 pound gantry on your rack
and pinion plasma cutter shooting along a 400 ipm rapid, hitting that
endswitch, and initiating that e-stop. if you unpower a stepper or
servo, it freewheels. So, just what does that gantry do after the
loss of power ?

The e-stop dump does not apply to all machines.

Dave