Re: [CAD_CAM_EDM_DRO] safety

I'm never going to get safety "nuts"..... I know a few who go overboard.

Most of what I know about what NOT to do I learned by doing it. Well, that and the common sense that drifted in when I did the stuff I shouldn't have.

In regards your example, there were more considerations made than just safety.....It just might be that in the case of a computer supply, issues like warranty, and replaceability outweighed any safety
issue. When a supply went bad, it could be verified untampered because it is in a case and tagged accordingly AND it could be removed by a customer easily and sent back. Safety ? Well, maybe a little,
in the fact that people who shouldn't ever open a PC case would no doubt do it at some point, and of course they would be the type to be not smart enough to remove any power first. Obviously, Live
wall current would not be a good choice in such a retail device.

In the viewpoint of making a cabinet with a seperate power supply box inside of it, .....Redundant.

Even OEM's put live 220-240 sources right in the same cabinet as the Drivers. Often they just have a "forced" disconnect in the cabinet door handle. And, don't foget a dozen or so safety warning tags
for those who just don't get it !!!

Too, even if the Power supply was in its own haven, the DC level going to the drivers is often high enough for you to get a pretty good suprise! So, would those be in a different box in a box as well
? What about all the connectors going in and out ? How do we make sure some little 2 year old doesn't stick a bobby pin in the terminals ? In that regard, I am amazed that Layers have not been able to
succesfully "remove" our common "twin blade" AC receptacle found in every home in the US. Well, not yet at least. maybe right after the "Lead Paint" issue is over.

I figure if they are not smart enough to remove the power first.... there shouldn't be any possibility of a lawsuit either. But, that isn't the way it is these days.

Safety, Lies totally with Common sense when you are making your own CNC Electronics and machines. Outside of that, you just need to carry enough insurance to cover the damages on any thing that could
go wrong when you try to market something.

Chris L

andrewyslee wrote:

> Hi
>
> Most of the discussions on the list had been on how to do this/that
> or how to do it better. But how about HOW TO DO IT SAFER. I don't see
> much discussions on this?
>
> Perhaps it is boring, but I think it is very important. For example,
> many seem to be making their own power supply, but I think most will
> just put a naked transformer, bridege rectifier, etc in the same box
> as the other electronics. When I dismantle computer, independent disc
> drive units, etc., I see that they put the power supply in a separate
> box inside the main box itself (box-in-a-box). Is this good practice
> for driver box or is it considered redundant?
>
> What do most people on the list do from the safety aspect?
>
> Thanks in advance
>
> Lee
>
> --- In CAD_CAM_EDM_DRO@y..., "paul_alz" <paul.w@a...> wrote:
> > Having commercially manufactured a drive similar to this since
> 1986,
> > see RS and Farnell catalogues, re: PVP2435, it still sells
> amazingly
> > well. So, as the designer I offer some additional tips.....
> >
> > When using phase chopping mode use the lowest Vf, highest current
> > diodes you can afford. A lot of power is dumped and these diodes
> can
> > make toast for you ;-) Use maximum copper fill in this PCB area.
> >
> > Strongly suggest you limit the max rail to 40Vdc. Fast
> deceleration
> > rates with big inertia loads give rise to large back emf's. I've
> > clocked them at +50V (outside L298 specs) which can produce some
> nice
> > pyrotechnics and bits of driver embedded in the opposite wall.
> >
> > Take care with your PCB layout and decoupling, the L297 can give
> you
> > some unsusual results.
> >
> > Good luck,
> >
> > Paul @ http://www.alzanti.com
>
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