<font size=2 face="sans-serif">Hi:</font>
<br>
<br><font size=2 face="sans-serif">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 size=2 face="sans-serif">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 size=2 face="sans-serif">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 size=2 face="sans-serif">JARMO<br>
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<td><font size=1 color=#5f5f5f face="sans-serif">From:</font>
<td><font size=1 face="sans-serif">"boB@midnitesolar.com" <boB@midnitesolar.com></font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">To:</font>
<td><font size=1 face="sans-serif">RE-wrenches <re-wrenches@lists.re-wrenches.org>,
</font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Date:</font>
<td><font size=1 face="sans-serif">06/28/2015 10:30 PM</font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Subject:</font>
<td><font size=1 face="sans-serif">Re: [RE-wrenches] Battery Bank to Inverter
Wiring</font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Sent by:</font>
<td><font size=1 face="sans-serif">"RE-wrenches" <re-wrenches-bounces@lists.re-wrenches.org></font></table>
<br>
<hr 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 size=2 color=blue><u><br>
</u></font><a href=mailto:allan@sindelarsolar.com><font size=2 color=blue><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><font size=3> </font>
<p><font size=3>On 6/27/2015 2:40 AM, John wrote:</font>
<br><font size=2 face="Cambria">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 size=2 face="Cambria"> </font>
<br><font size=2 face="Tahoma"><b>From:</b> RE-wrenches [</font><a href="mailto:re-wrenches-bounces@lists.re-wrenches.org"><font size=2 color=blue face="Tahoma"><u>mailto:re-wrenches-bounces@lists.re-wrenches.org</u></font></a><font size=2 face="Tahoma">]
<b>On Behalf Of </b></font><a href="mailto:Jarmo.Venalainen@schneider-electric.com"><font size=2 color=blue face="Tahoma"><u>Jarmo.Venalainen@schneider-electric.com</u></font></a><font size=2 face="Tahoma"><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 size=3 face="Times New Roman"> </font>
<br><font size=2 face="Arial">Hi:</font><font size=3 face="Times New Roman">
<br>
</font><font size=2 face="Arial"><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 size=3 face="Times New Roman"> <br>
</font><font size=2 face="Arial"><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 size=3 face="Times New Roman"> <br>
</font><font size=2 face="Arial"><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 size=3 face="Times New Roman"> <br>
</font><font size=2 face="Arial"><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 size=3 face="Times New Roman">
<br>
</font><font size=2 face="Arial"><br>
Recently this happened again and I wanted to get a better feel for it,
so I did some math. </font><font size=3 face="Times New Roman"> <br>
</font><font size=2 face="Arial"><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 size=3 face="Times New Roman">
<br>
</font><font size=2 face="Arial"><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 size=3 face="Times New Roman"> <br>
</font><font size=2 face="Arial"><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 size=3 face="Times New Roman"> <br>
</font><font size=2 face="Arial"><br>
Given that, the voltage drop of the wire inductance is then , Vdrop = (rate
of change of current) x (inductance), </font><font size=3 face="Times New Roman"><br>
</font><font size=2 face="Arial"><br>
Vdrop for 1 uH = (100,000 A/s) x (0.000001 H) = 0.1V</font><font size=3 face="Times New Roman">
</font><font size=2 face="Arial"><br>
Vdrop for 10 uH = (100,000 A/s) x (0.000001 H) = 1.0V</font><font size=3 face="Times New Roman">
</font><font size=2 face="Arial"><br>
Vdrop for 100 uH = (100,000 A/s) x (0.000001 H) = 10.0V clearly
this is a problem.</font><font size=3 face="Times New Roman"> <br>
</font><font size=2 face="Arial"><br>
Have any of the wrenches had systems with this issue? If so, how
often.</font><font size=3 face="Times New Roman"> <br>
<br>
</font><font size=2 face="Arial"><br>
JARMO</font><font size=3 face="Times New Roman"> </font>
<p>
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