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 <[email protected]>
wrote:
Subject: Re: [RE-wrenches] Quantifying power quality
To: "RE-wrenches" <[email protected]>
Date: Sunday, October 12, 2014, 1:33 PM
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
_______________________________________________
List sponsored by Redwood Alliance
List Address: [email protected]
Change listserver email address & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive:
http://www.mail-archive.com/[email protected]/maillist.html
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out or update participant bios:
www.members.re-wrenches.org
_______________________________________________
List sponsored by Redwood Alliance
List Address: [email protected]
Change listserver email address & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive:
http://www.mail-archive.com/[email protected]/maillist.html
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out or update participant bios:
www.members.re-wrenches.org
