<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"></head><body ><div>Wrenches</div><div>We always try to minimize in connection cables as well as home run cables to the shorted length possible, restating batteries to aid this should always be considered as well as positive and negative runs</div><div>Jerry</div><div><br></div><div><br></div><div><div style="font-size:9px;color:#575757">Sent via the Samsung Galaxy S™ III, an AT&T 4G LTE smartphone</div></div><br><br><div>-------- Original message --------</div><div>From: Ray Walters <ray@solarray.com> </div><div>Date:06/29/2015 12:05 PM (GMT-10:00) </div><div>To: RE-wrenches <re-wrenches@lists.re-wrenches.org> </div><div>Subject: Re: [RE-wrenches] Battery Bank to Inverter Wiring </div><div><br></div>
This is fascinating because while I knew the DC cables had an AC
component, I never realized how much inductance played in the volt
drop to the inverter. Thanks for bringing this to our attention
Jarmo. <br>
Which brings up another question based on Benn's question: isn't
the battery itself part of the inductive loop? and would the lead
inside and steel cases act to increase the inductance? Should we
consider changing battery layouts not just to shorten cable lengths,
but to counter inductance in the batteries themselves? If needed,
we could actually wire the batteries to "twist" by putting every
other 2 v cell in the opposite row. <br>
My guess is that it wouldn't be worth it, but I've been wrong many
times.......<br>
<br>
<pre class="moz-signature" cols="72">R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760</pre>
<div class="moz-cite-prefix">On 6/29/2015 3:55 PM, Benn Kilburn
wrote:<br>
</div>
<blockquote cite="mid:A86E9CED-086A-49F8-A48D-E2DDE53CC893@skyfireenergy.com" type="cite">
<meta http-equiv="content-type" content="text/html;
charset=windows-1252">
<div>What about when you have the (+) and (-) terminals at
opposite ends of a larger battery bank? Sure you can run the
conductors side-by-side once they meet up on their way to the
inverter, but would you consider the distance between the end
terminals a "large loop"? </div>
<div>Ideally the battery string is laid out so the end terminals
are close together and close to the inverter, but this isn't
always the case. <br>
<br>
<div>Benn Kilburn</div>
<div>SkyFire Energy Inc. </div>
<div>780-906-7807</div>
<div><br>
</div>
</div>
<div><br>
On Jun 29, 2015, at 10:28 AM, <a moz-do-not-send="true" href="mailto:Jarmo.Venalainen@schneider-electric.com">Jarmo.Venalainen@schneider-electric.com</a>
wrote:<br>
<br>
</div>
<blockquote type="cite">
<div><font face="sans-serif" size="2">Hi:</font>
<br>
<br>
<font face="sans-serif" size="2">From the comments so far, it
appears
that within the wrenches group, good practices are the rule
and DC cables
are kept side by side, so the problem I mentioned hasn't
come up much.</font>
<br>
<br>
<font face="sans-serif" size="2">I have seen "large loop"
battery
cables a couple of times in solar installs myself out on
islands way down
south. Also on boats/RV's/motor homes.</font>
<br>
<br>
<font face="sans-serif" size="2">Please keep the cable loop in
mind when
you do bench tests of inverters, as it may screw up the
results and make
it seem like there is something wrong with the inverter.</font>
<br>
<br>
<font face="sans-serif" size="2">JARMO<br>
</font><font color="#008000" size="3">_____________________________________________________________________________________</font><font size="3">
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<td><font color="#5f5f5f" face="sans-serif" size="1">From:</font>
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<td><font face="sans-serif" size="1">"<a moz-do-not-send="true" href="mailto:boB@midnitesolar.com">boB@midnitesolar.com</a>"
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<td><font face="sans-serif" size="1">RE-wrenches <<a moz-do-not-send="true" href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a>>,
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<td><font color="#5f5f5f" face="sans-serif" size="1">Date:</font>
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<td><font face="sans-serif" size="1">06/28/2015 10:30 PM</font>
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<td><font color="#5f5f5f" face="sans-serif" size="1">Subject:</font>
</td>
<td><font face="sans-serif" size="1">Re: [RE-wrenches]
Battery Bank to Inverter
Wiring</font>
</td>
</tr>
<tr valign="top">
<td><font color="#5f5f5f" face="sans-serif" size="1">Sent
by:</font>
</td>
<td><font face="sans-serif" size="1">"RE-wrenches" <<a moz-do-not-send="true" href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>></font></td>
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<hr noshade="noshade">
<br>
<br>
<br>
<font size="3"><br>
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:</font>
<br>
<font size="3">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>
</font>
<p><font size="3"><b>Allan Sindelar</b></font><font color="blue" size="2"><u><br>
</u></font><a moz-do-not-send="true" href="mailto:allan@sindelarsolar.com"><font color="blue" size="2"><u>allan@sindelarsolar.com</u></font></a><font size="2"><br>
NABCEP Certified PV Installation Professional<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
Founder (Retired), Positive Energy, Inc.<b><br>
505 780-2738 cell</b><br>
</font>
</p>
<p><font size="3"> </font>
</p>
<p><font size="3">On 6/27/2015 2:40 AM, John wrote:</font>
<br>
<font face="Cambria" size="2">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.</font>
<br>
<font face="Cambria" size="2"> </font>
<br>
<font face="Tahoma" size="2"><b>From:</b> RE-wrenches [</font><a moz-do-not-send="true" href="mailto:re-wrenches-bounces@lists.re-wrenches.org"><font color="blue" face="Tahoma" size="2"><u>mailto:re-wrenches-bounces@lists.re-wrenches.org</u></font></a><font face="Tahoma" size="2">]
<b>On Behalf Of </b></font><a moz-do-not-send="true" href="mailto:Jarmo.Venalainen@schneider-electric.com"><font color="blue" face="Tahoma" size="2"><u>Jarmo.Venalainen@schneider-electric.com</u></font></a><font face="Tahoma" size="2"><b><br>
Sent:</b> Saturday, 27 June 2015 5:45 a.m.<b><br>
To:</b> RE-wrenches<b><br>
Subject:</b> [RE-wrenches] Battery Bank to Inverter
Wiring</font>
<br>
<font face="Times New Roman" size="3"> </font>
<br>
<font face="Arial" size="2">Hi:</font><font face="Times New
Roman" size="3">
<br>
</font><font face="Arial" size="2"><br>
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.</font><font face="Times New Roman" size="3"> <br>
</font><font face="Arial" size="2"><br>
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.</font><font face="Times New Roman" size="3">
<br>
</font><font face="Arial" size="2"><br>
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,</font><font face="Times New
Roman" size="3"> <br>
</font><font face="Arial" size="2"><br>
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.</font><font face="Times New Roman" size="3">
<br>
</font><font face="Arial" size="2"><br>
Recently this happened again and I wanted to get a better
feel for it,
so I did some math. </font><font face="Times New Roman" size="3"> <br>
</font><font face="Arial" size="2"><br>
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. </font><font face="Times
New Roman" size="3">
<br>
</font><font face="Arial" size="2"><br>
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.</font><font face="Times New Roman" size="3"> <br>
</font><font face="Arial" size="2"><br>
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.</font><font face="Times New Roman" size="3"> <br>
</font><font face="Arial" size="2"><br>
Given that, the voltage drop of the wire inductance is
then , Vdrop = (rate
of change of current) x (inductance), </font><font face="Times New Roman" size="3"><br>
</font><font face="Arial" size="2"><br>
Vdrop for 1 uH = (100,000 A/s) x (0.000001 H) = 0.1V</font><font face="Times New Roman" size="3">
</font><font face="Arial" size="2"><br>
Vdrop for 10 uH = (100,000 A/s) x (0.000001 H) = 1.0V</font><font face="Times New Roman" size="3">
</font><font face="Arial" size="2"><br>
Vdrop for 100 uH = (100,000 A/s) x (0.000001 H) = 10.0V
clearly
this is a problem.</font><font face="Times New Roman" size="3"> <br>
</font><font face="Arial" size="2"><br>
Have any of the wrenches had systems with this issue? If
so, how
often.</font><font face="Times New Roman" size="3"> <br>
<br>
</font><font face="Arial" size="2"><br>
JARMO</font><font face="Times New Roman" size="3"> </font>
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