Re: [CAD_CAM_EDM_DRO] Re: Bullet-Proof G201 / G210

Mariss,

This is interesting probably only from my point of view because of my
machinations over the last week with my Harrison. I hope I have now repaired
the driver but I would have bought your unit at the beginning of the week if
it could have been fitted to the machine without building another power
supply. A lot of the commercial equipment runs at much higher voltages than
your 80 volt limit. My machine is 85 volt nominal and is in fact 95 ish.
There is also the question of available transformers to build a power supply
from. 55 volt secondarys are common here because we have a site transformer,
used in the building trade, to run their 110 volt equipment, this works out
around 77 volts DC at the drivers, but I would think it is easier to find 60
volt secondarys in the rest of the world.

If I have read the below correctly, and without wanting to up your returned
due-to operator/wired up wrong rates, you have rated the max voltage @ a 20%
safety factor and Gecko's could be run @ 85 volts?

It seems to me there are two types of CNC machine converters. The
retro-fitters, who don't look at the original controls but just rip out and
start again with a PC based system, and the repairs who would like the old
operating system because the modern software doesn't do what the old stuff
on the machine will. I'm in the latter group because there are many features
on my lathe I don't want to lose, like the canned screw-cutting cycle which
will cut both sides of a thread using a tool of a smaller included angle
than the thread angle. The result is a perfectly formed thread and not one
with flat/pointed crests. As far as I know, none of the software running
lathes for retro-fitting does this.

Regards,

Terry

> The problem there is the MOSFETs. We use IRF530s which are 100V
> rated, the next size up is 200V. The physics of MOSFETs is if the
> voltage doubles then the "on" resistance quadruples, meaning the chip
> size must quadruple in order to get the same "on" resistance.
>
> That requires a much larger TO-247 package, blowing the whole thing
> out of the water. Furthermore, many motor mfgs. now rate their motors
> with a maximum operating voltage, usually around 65V.
>
> Mariss