Re: Question on Mariss' E-Stop circuit

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<dave_mucha@y...> wrote:

> 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.

Okay, makes sense to me. Is there an 'easy' way to calculate the
amperage needed to dump, or is it a measurement I need to make? 4
axis Xylotex board, 2.5 amp/phase max, running at 2 amp/phase and only
3 motors right now. Taig mill, 20 tpi lead screws, slow feeds and
rapids, haven't measured the speeds.

>
> 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 ?

Make a lot of noise? I watched a mill with 2" ballscrews hit the hard
stop once. The operator was adjusting a new driver and it started
occillating and blew right past all the limit switches to the end of
the ballscrew

Monte