Bill,
A true RMS meter shouldn't be necessary with a gennie in most cases, as
the gennie is a rotating source, so the waveform is naturally true sine,
or close. The true-RMS meter is more important with mod-square
inverters, as cheap DMMs estimate RMS voltage as a proportion to peak
voltage, and a mod-square inverter won't create the 164V waveform peak
voltage necessary to read 117V by direct conversion.
There's an exception here, though, that may be in play. What's your
elevation? Drawing off of one AC output leg on that Onan will give you
at most 2000 watts, and that's reduced by (rule of thumb here) 3.5% per
1000 feet above sea level. So if you're pulling 1.7 KW on that leg,
whether or not the other house is also drawing, you may be overloading
the Onan enough to pull down the voltage waveform peak voltage.
First, yes, try measuring with a true-RMS meter, as a
process-of-elimination troubleshooting initial step. Then try reducing
the VFX3648's input current and observing how the voltage changes.
Third, add a PSX240 or equivalent to allow both gennie legs to feed the
inverter.
I haven't run voltage drop calcs in making these recommendations, but I
don't think that the #10 wire is the source of the troubles.
Allan
*Allan Sindelar*
al...@sindelarsolar.com <mailto:al...@sindelarsolar.com>
NABCEP Certified PV Installation Professional
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder (Retired), Positive Energy, Inc.
*505 780-2738 cell*
**
On 9/25/2016 11:03 PM, frenergy wrote:
Wrenches,
I have a customer that is reading voltage with a non-RMS
meter in the following scenario: 4000 watt Onan RV generator (older)
at ~5500 foot elevation...its output is connected to the "AC in leg 1"
of an OB VFX3648 using (customer installed, I came on this job
after-the-fact) 10 gauge running about 75'. Genny fires up, feeds AC
IN in VFX, sends about 1.7 KW to the batts, while also running
moderate loads in house /another/ 75' away, again through 10 gauge.
She is complaining about the voltage reading ~95 volts at
times in the house. Voltage at genny is still around 120 (I am told)
I suggest up sizing wire to 6 gauge, which they do but voltage is
still in the 105 V range in the house, same scenario. As the batts
come up to charge and input tapers, voltage also comes up some.
Shouldn't the voltages be read with an RMS type meter to be accurate?
She thinks the inverter is not working right though I've tried to
explain to her that in standby the inverter is not inverting, its just
passing genny power through, unchanged other than the load its pulling
to charge the batts.
Other insights to voltage drop in this case other than an
RMS meter? Does it matter if the last loads are seeing just 105 volts?
Thanks,
Bill
--
Feather River Solar Electric
Bill Battagin, Owner
4291 Nelson St.
Taylorsville, CA 95983
530.284.7849
CA Lic 874049
www.frenergy.net
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