-Original Message-
From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On
Behalf Of Ray Walters
Sent: Sunday, October 12, 2014 16:21
To: RE-wrenches
Subject: Re: [RE-wrenches] Quantifying power quality
Hi Dan;
I, like Larry, must be amazingly lucky then, because we've solved power
quality issues for many years with 50mf caps. Usually, its been front
loading washers not running on Trace SW inverters, but also Grundfos CP
pumps, too. Never had a problem, and some of these have been running that
way for over 15 years.
I never had a power quality issue with an Exeltech, so I've never used this
trick with your inverters.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 10/12/2014 12:58 PM, Exeltech wrote:
Wrenches,
Be careful about connecting *any* capacitors across an inverter's AC
output. It's not a smart thing to do.
While a capacitor may help in some cases when a load has a substantially
poor power factor due to significant inductance, there are two serious
concerns here:
1. The power factor seen by the inverter will be equally bad in the
opposite polarity when the inductive load turns off, and IF the capacitor is
still connected across the lines. Larry implied the capacitor he connected
was disconnected when the load turned off.
2. Larry shot-gunned a solution. He guessed, and got lucky. We don't
know how much actual capacitance was needed in this specific situation.
Capacitors connected across an inverter's AC output can destabilize its
voltage control loops, leading to erratic AC voltage, resulting in possible
damage to the inverter, the load(s) .. or both.
Power factor is one of the most misunderstood aspects of electricity.
Dan
(Professional inverter design engineer .. among other things...)
On Sun, 10/12/14, Starlight Solar Power Systems la...@starlightsolar.com
wrote:
Hi William,
If you recall a couple years ago we had some discussion here about a
problem with a specific make appliance being powered by a Magnum inverter.
The problem, it was discovered, was the appliance input PF was creating
current demands that the transformer based inverter could not keep up with.
When I powered the load with a low cost, high frequency inverter, it worked
fine. Apparently the HF inverter can keep up with the current changes faster
than the Magnum.
To fix the problem, a 50mf run type capacitor was installed in the
appliance so that it was applied across the AC input when powered on.
Everything worked fine then because the cap was taming the wild current
created by the low PF.
Try looking at the current and voltage waveform together (AC shunt, dual
trace scope) at the UPS input. If the current is displaying large spikes
and/or is out of phase, you may have found the problem is with a non linear
load from the UPS. It may be the SI, like the Magnum, can not keep up and so
the UPS input circuits are throwing a fit.
Or, something else you can try, connect a high frequency inverter and try
to power the UPS. This can be a portable 12 volt battery and inverter. If
the problem disappears, well, you take it from there.
Larry
Hi William,
Power quality, in your case, refers to how close to 60 Hz (frequency
component), 120/240 VAC RMS (amplitude component) your voltage waveform is.
Every waveform is the superposition of different frequencies, amplitudes
etc. Power quality requirements for a devices input or output are usually
defined in total harmonic distortion (THD %) and in voltage ranges. THD is
an attempt to quantify harmonics on a waveform. It is the ratio of the sum
of all harmonics to the fundamental frequency (60Hz in your case).
A Sunny Island has THD and amplitude tolerances similar to that of the grid
(3%, 105-132VAC). I have found that most generators aren't as close and the
distortion in a waveform is easily discernible.
My approach to your problem might be to ask for the power quality
requirements for the UPS not to beep. Document that the Sunny
Islands/Generator system is delivering these requirements during beep events
using a power quality analyzer. Put problem back on UPS guy if you can
prove that your system is delivering adequate power quality. This is how
our utility deals with alleged power quality problems.
If the SI system has enough reserve, run it totally off-grid with the grid
as backup. Then they will never see any transitions.
A Sunny Island that switches to and from grid power probably does not
transfer smoothly enough to protect sensitive equipment, but if it is online
all the time, using solar to charge the batteries, I would not bother with a
UPS.
On Sun, Oct 12, 2014 at 11:27 AM, toddc...@finestplanet.com wrote:
perhaps i am not understanding the set-up, but why feed a ups with a ups?
doesnt the sunny island already provide ups capabilities for the loads
connected to it?
todd
On Sun, Oct
