SW+ Voltage Sag [RE-wrenches]

William Korthof wkorthof at earthlink.net
Tue Aug 17 16:55:28 PDT 2004 

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4/0 represents a lot of copper

I'm with Ray here...

I'd venture that the internal resistance L16 batteries and terminals
waaaaaay overshadows the trivial drop from a few feet of 2/0 cable.
The SW does seem to take many milliseconds to catch up after
a jump in demand or a transfer from utility interactive to isolated;
while it catches up, the AC voltage does seem to sag noticeably.

/wk



Hi Matt;

>The manual says 2/0 to 5 ft,  4/0 to 10 ft.  I'm cheating by a foot or 
>two. The 175 A at 24 VDC draw is 0.1 second peak from the circular saw; it 
>is not anything close to continuous run amps. Battery bank is 8  L-16s. DC 
>voltage at rest is 24.6v, surge drops the voltage to 23.2. Again, that is 
>a 0.1 sec minimum. I have always noticed batteries pull down like that for 
>a second on start up surges.
>I'm going to change the cable to 4/0, but I don't think that is going to 
>fix it. I have a few of these SW + inverters installed with similar 
>complaints of lights flickering, etc when an inductive load comes on. They 
>all have 4/0 cable BTW.
>
>Ray
>
>>   Hmmmmmm.
>>
>>   You say that you're running a 2548 on 2/0 inverter cables. First-off, my
>>recollection about the SW 12 and 24 volt versions is that they actually
>>require 4/0 cables to begin with becuase of the possibility of a 400 amp
>>surge under certain startup conditions.
>>
>>   It also sounds like the batteries are on the low side, which also doesn't
>>help much, but 175 amps draw? I hope this is on your Skillsaw and not the
>>Staber. ;-)
>>
>>   How long are your inverter leads and how big is the battery bank?
>>
>>   What is the problem with the Washer?
>>
>>   Matt T
>>   ----- Original Message -----
>>   From: "Ray Walters" <ray at solarray.com>
>>   To: <RE-wrenches at topica.com>
>>   Sent: Friday, August 13, 2004 10:46 AM
>>   Subject: SW+ Voltage Sag [RE-wrenches]
>>
>>
>>
>>
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>>
>>   >Dear esteemed colleagues;
>>
>>   I am currently troubleshooting a Staber Washer control malfunction on an
>>   Xantrex SW2524+ inverter. What I found curious is that the voltage sags
>>   down to 88 VAC rms for about a tenth of a second during starting surge. I
>>   am using a worm drive circular saw after to test. Measurements are at the
>>   inverter AC terminals with a Fluke 89 set to normal MIN capture.(the fast
>>   capture would get the bottom of the wave form itself) I also measured the
>>   DC side and found the voltage to be 24.6 vdc at rest with the surge
>>pulling
>>   it down to 22.9 vdc (again regular MIN capture on the Fluke). MIN volts
>>for
>>   0.1 secs at the battery terminals was 23.2 vdc. The DC current surge
>>   measured at the shunt block with the Fluke was an amazing 175 amps for 0.1
>>   secs. AC current was harder to measure surge, but I saw a 27 amp peak at
>>   the Inverter's onboard meter.
>>   My question is this: Is it normal to see a temporary voltage sag like this
>>   when powering a heavy inductive load. I rechecked all my connections AC
>>and
>>   DC. I looked for volt drop at any tell tale points, etc. I am thinking its
>>   an inductive issue with the DC cables, and so my next visit I wanted to
>>   upsize the cables to 4/0 and twist the cables around each other.
>>Everything
>>   else on the system seems to work great, other than occasionally a UPS box
>>   for the computer beeps, again with a start surge from another appliance.
>>   Your feedback, wisdom, comments, & of course criticisms are all greatly
>>   appreciated.
>>
>>
>>   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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>
>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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