Re: [CAD_CAM_EDM_DRO] VFD's / Skates

johnhe wrote:

> > rating is based upon 3 phase input and you derate the unit by 50% if you
> are
> > on 1 phase input.
>
> I hate English Literature but I managed an A*. When you say derate by 50% do
> you mean instead of the 2hp direct to the motor I need an inverter for 4hp,
> does that mean I actually feed it 4hp?

The only part that knows the difference between single and 3-phase power
is the rectifier (and also the capacitor bank). The current on the rectifier
diodes that are actually used in single phase service is quite a bit higher
than when used in 3-phase phase. this is what needs derating. So, yes,
a 4-Hp inverter would be better able to handle the peak currents than
a 2-Hp inverter. the inverter does NOT draw 4-Hp from the lines! Where
would it get rid of that excess energy? It would have to start smoking,
and it won't.

I have a Yaskawa-made Magnetek-brand 1 Hp inverter, specified as 3-phase
input, only. I looked up the power block that houses all the internal power
components, and found the rectifier diodes were VERY generously overspecified,
and I run it at full power from single phase power with no worries. I can't
guarantee that all of them are built like that, but it seems like thay are.
They are also designed to run with no forced cooling, just natural convection,
up to a 55 C ambient, or something like that. Running it out in the open
with a small fan on it extends the ratings of the rectifier.

Jon