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On 6/28/2015 9:20 AM, Allan Sindelar wrote:<br>
>>>>I'm not an EE, but I can't see what difference
twisting would make in<br>
the absence of a building/collapsing field as is normal with AC.<<<<<br>
<br>
It is little known that with the typical inverters that use the
heavy power transformers,<br>
have a lot of AC 120 Hz (or 100 Hz for 50 Hz systems) current
mixed in with that DC battery current.<br>
<br>
The AC output current reflects back to the input as ripple
current. This is why you want to<br>
have at least short as possible Sbattery cable runs AND keep the
wires as close together as possible.<br>
<br>
Twisting the battery cables may help a bit but that is probably
overkill.<br>
<br>
The problem has to do with inductance in the battery cables. You
can use as big of cable<br>
as you can fit in to reduce resistance, but that will not help to
lower the inductance.<br>
The problems you can sometimes have with high inductance is that
L-C resonance at the<br>
inverter can raise the peak voltages seen at the inverter input
terminals and can be hard on<br>
the inverter.<br>
<br>
Then again, the high frequency, lighter weight inverters will
typically keep most of that ripple<br>
inside, between the DC input and AC output and battery cable
inductance will not be as much<br>
of a problem on the battery cables.<br>
<br>
boB Gudgel<br>
<br>
<br>
<br>
<br>
On 6/28/2015 9:20 AM, Allan Sindelar wrote:<br>
</div>
<blockquote cite="mid:55901EB0.4070507@sindelarsolar.com"
type="cite">
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As a matter of course I have always run the positive and negative
conductors of high-current cable pairs together, but have never
deliberately twisted them, and have never known of any related
problems. <br>
The most obvious example of this would be 4/0 battery/inverter
cables in a 24V system, with a 250A GJ-class breaker or (prior to
that) a 300A or 400A Class T fuse. It's pretty tough to thread a
twisted pair of 4/0 USE/RHH/RHW cables through a 2" elbow or LB
from inverter enclosure to battery enclosure.<br>
I'm not an EE, but I can't see what difference twisting would make
in the absence of a building/collapsing field as is normal with
AC. <br>
I have twisted AC conductors together in the past when clients
have expressed concerns about EMF from their equipment and wiring,
but only AC.<br>
Allan<br>
<br>
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<p class="MsoNormal"><b>Allan Sindelar</b><br>
<span style="font-size:10.0pt"><a moz-do-not-send="true"
href="mailto:allan@sindelarsolar.com">allan@sindelarsolar.com</a></span><br>
<span style="font-size:10.0pt">NABCEP Certified PV
Installation Professional<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
Founder (Retired), <span
style="mso-bidi-font-weight:bold">Positive Energy, Inc.</span><br>
<b>505 780-2738 cell</b><br
style="mso-special-character:line-break">
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<div class="moz-cite-prefix">On 6/27/2015 2:40 AM, John wrote:<br>
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Cambria","serif";color:black">That
is why for years we have been twisting those leads around
each other. I was told it was to cancel out the opposing
fields on the wires, but for whatever the correct
technical reason is, we have always twisted those heavy
wires. John V.<o:p></o:p></span></p>
<p class="MsoNormal"><span
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<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif""
lang="EN-US">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif""
lang="EN-US"> RE-wrenches [<a moz-do-not-send="true"
class="moz-txt-link-freetext"
href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>]
<b>On Behalf Of </b><a moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:Jarmo.Venalainen@schneider-electric.com">Jarmo.Venalainen@schneider-electric.com</a><br>
<b>Sent:</b> Saturday, 27 June 2015 5:45 a.m.<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> [RE-wrenches] Battery Bank to Inverter
Wiring<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Hi:</span>
<br>
<br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">From
time to time over the years I've come across systems where
the routing of DC cables between the batteries and the
inverter has been the cause of issues.</span> <br>
<br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">I'm
not referring to wire thickness or quality of
terminations. For the purposes of this discussion, just
assume that wire thickness and terminations are perfect.</span>
<br>
<br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">What
I am referring to is the routing of the positive and
negative battery cables. In particular, the loop area
within the + and - cables as shown in the image below,</span>
<br>
<br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">The
problem I've seen in systems with a large loop in the
setup is that the inverter does not provide good surge
power and can even go into low voltage shutdown during
large surges.</span> <br>
<br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Recently
this happened again and I wanted to get a better feel for
it, so I did some math. </span> <br>
<br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">For
a cable length of about 12', the loop is an inductor which
has a value of inductance of about 1 uH for side by side
cables and as much as 6 uH for cables about 1 foot apart.
</span> <br>
<br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">This
inductance is greatly multiplied by any ferrous metal in
the loop and can easily be in the range of 10's to 100's
of uH. Examples being cables which run in steel conduits
or along the steel frame of a motor home.</span> <br>
<br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Inductance
causes a voltage drop proportional to the rate at which
the current is changing. To get an idea of how large that
rate can be for typical inverters, I did surge tests with
a 5kW inverter and found that the rate of change of
current can be as high as 100A per milli-second or 100,000
Amps/second.</span> <br>
<br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Given
that, the voltage drop of the wire inductance is then ,
Vdrop = (rate of change of current) x (inductance), </span><br>
<br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Vdrop
for 1 uH = (100,000 A/s) x (0.000001 H) = 0.1V</span> <br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Vdrop
for 10 uH = (100,000 A/s) x (0.000001 H) = 1.0V</span> <br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Vdrop
for 100 uH = (100,000 A/s) x (0.000001 H) = 10.0V
clearly this is a problem.</span> <br>
<br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Have
any of the wrenches had systems with this issue? If so,
how often.</span> <br>
<br>
<br>
<span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">JARMO</span>
<br>
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