According to Ignoramus32225 :
I tried connecting the VFD to the compressor. The VFD is a 18.5 kW (25
HP) rated Siemens SED2 VFD. Its target market is HVAC. The compressor
is a 10 HP motor.
It was kind of unsuccessful. I made quite a few observations.
1) The motor, when VFD turns on, only spins at maybe 60 to 90 RPM. And
struggles to turn the compressor.
2) The VFD has no troubles spinning up an unloaded 1 HP motor (just
for test).
3) I measured DC bus voltage when the VFD was powering up the 10 HP
motor, it was about 220v.
What is it when *not* starting the 10 HP motor? That sounds
rather low -- I would expect the no-load voltage to be closer to about
310 VDC from a 220 VAC input.
Can you hook an isolated (for safety) oscilloscope to the bus?
I'll bet you see a *lot* of ripple.
Essentially -- here is where you hit problems trying to run a
three-phase VFD on single phase -- there is too much time when the
voltage out of the rectifiers is low. With three phase input, the
output from the rectifiers never gets anywhere near zero -- until the
input power is turned off or disconnected.
I'm rather surprised that it did not complain about input
voltage being low.
4) I used a straight piece of 10 ga wire instead of a DC choke to
connect the DC bus.
That won't help much while running the rectifier from single
phase. Is your rotary converter big enough to hang the VFD on it and to
have a chance to run the compressor?
5) If I measure voltage on the output, with my nice multimeter
(knowing that I should not trust the result too much due to square
wave), I get something like 70-90 volts instead of 220. That's what
the read on panel reads if I set it to display voltage.
That sounds fairly reasonable, given how low the bus voltage is.
Unloaded, it should be the square root of two (1.414) times the input AC
voltage.
Logically, a 25 HP VFD should spin up the 10 HP motor.
If it has enough voltage full time. Is this one rated to run
from single phase, or is it just one which happens to accept single
phase?
I looked into the manual, available at
http://igor.chudov.com/manuals/
and found reference to parameter 1300, V/F curve. It talks about
different selections, such as linear V/F, parabolic etc. It says that
linear V/F is better for constant torque and "positive displacement
pumps".
Due to family stuff, I had no time to actually try changing this, does
it sound as though this could solve it? The wikipedia Pump article
seems to imply that my piston compressor is a positive displacement
pump.
Anyway, it was a somewhat frustrating day in this respect. I will
followup to this once I try it in an hour or so.
What you need is for the unloader to stay switched in until the
VFD gets the motor up to speed.
What happens if you remove the belts? Will your VFD spin the
motor up under those conditions?
Good Luck,
DoN.
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