Fwd: Re: Voltage sag [RE-wrenches]

[Ray Walters]

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>Date: Fri, 13 Aug 2004 15:31:03 -0600
>To: Frank Fowler <cpae1 at direcway.com>
>From: Solar Ray <ray at solarray.com>
>Subject: Re: Voltage sag
>
>Hi Frank:
>
>I was going off the manual that said 2/0 up to 5 ft. My run is 5 ft. for 
>the positive and 7 ft for the negative (so I'm over just a hair). How do 
>you size cable for inverters? NEC ampacity at rated cont. power of 
>inverter including efficiency losses, or volt drop at max surge or....?  I 
>sometimes look at a collection of all the numbers to decide.
>2500 watts / 22v (lowest operating voltage) gets 113 A. Figure in the 
>efficiency at rated power = 88%, so that takes us to 130 A. (2/0 should do it)
>  Looking at it from a volt drop stand point, I was measuring a 1.25% volt 
> drop at 1/10 sec surge of 175 A. The continuous running amps were much 
> lower (about 50 for the saw).  Again, 2/0 seems like the stuff to me, but 
> I'm sure I'm missing something... I'll be out next week to go ahead and 
> upsize the cables, and I'll let the list know what that does.
>
>BTW, I just talked to Allan Sindelar and he said he noticed similar 
>symptoms from an SW+ (lights flickering when the fridge kicked on) he was 
>going to check it with a meter.
>Isn't it possible (Xantrex chime in here please) that in order to achieve 
>their fantastic surge capability of 10,000 watts for 5 secs, that the 
>Xantrex engineers relaxed the voltage regulation? Wasn't that why the old 
>SW4048  couldn't out surge a DR 3624, because it wouldn't allow the output 
>voltage to sag as much during surges? Isn't that how everyone runs big 
>well pumps off smallish generators: I've measured those pulling below 90 
>volts AC for several secs while starting a heavy load.
>
>Ray
>
>
>>Ray,
>>First of all the cables should be 4/0 from the git-go as per current draw 
>>specs. I think if you change those inverter cables, you will see somewhat 
>>less of a voltage sag.
>>Just my 2 cents worth.
>>Frank Fowler
>
>Ray Walters
>ray at solarray.com
>President, SolarRay, Inc.
>NABCEP Certified Solar PV Installer
>BS Mechanical Engineering, UT Austin 88
>Returned US Peace Corps Volunteer

Ray Walters
ray at solarray.com
President, SolarRay, Inc.
NABCEP Certified Solar PV Installer
BS Mechanical Engineering, UT Austin 88
Returned US Peace Corps Volunteer 
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