On 2007-10-29, Ned Simmons wrote:
On Mon, 29 Oct 2007 12:49:48 -0500, Ignoramus10340
wrote:


Apparently, this SED2 drive has a very small capacitor compared to
other drives. Only 20 uF compared to 1,000 uF for other drives, with
the example of a 15 HP drive. (unspecified voltage)

That might, in my mind, account for voltage sagging when run from 1
phase, and low voltage delivered to motor.

I'm sure it does explain the sag, 20uF ain't much.


So, a possibility to ponder would be to add some capacitance between
DC+ and DC-. The terminals are available for connecting, but I am not
sure of ramifications of, for example, inrush current greatly
increased.

Any thoughts on this?

Obviously the best thing would be to ask Siemens. But from my
experience building unregulated supplies for servos, I doubt 1000uF
would be a problem. Looking at the schematic for one system I built,
there's: 100V/5A xformer secondary - 25A bridge rectifier -
2100uF/300VDC cap - servo amps.

There was a never a problem with this or several similar systems I've
built.


Ned, thanks. I will approach this issue from two angles.

One is that I will use all caps that I can find at home that carry an
appropriate voltage rating. I will try to see if it makes any visible
difference.

Second is I will try to work with the unloader system and try to spin
the flywheel without the compressor doing "work".