[RE-wrenches] Real info for voltage

[Allan Sindelar]

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*
allan at sindelarsolar.com <mailto:allan at 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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