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<div class="moz-cite-prefix">On 6/29/2015 3:15 PM, Roy Rakobitsch
wrote:<br>
</div>
<blockquote
cite="mid:CAL2u1ufriseSm5noVBwZMjma8KuWtrjRg-FHiPeRBKFYu1Tz+A@mail.gmail.com"
type="cite">
<p dir="ltr">In my experience, adding large electrolytic filter
caps at the inverter seems to help quite a bit with ac ripple
issues and increases inverter efficiency a bit as well. </p>
</blockquote>
<br>
Yep, that usually helps. Turns out that if you get just the right
amount of battery cable inductance AND just<br>
the right amount of inductance, then you can have an LC resonant
circuit that makes the voltage go<br>
sky high and let out the smoke.<br>
<br>
But typically, raising the capacitance lowers the resonant frequency
enough below 120 Hz that it<br>
helps the situation.<br>
<br>
As far as batteries being part of the loop, yes they are. Just
picture their layout as<br>
a piece of wire and you can get a feel for that contribution to the
loop.<br>
You could also place a capacitor or two right where the battery
cables come<br>
together again.<br>
<br>
But you gotta stop somewhere. This is more educational or a way to<br>
visualize what is going on so that you use the best wiring practices<br>
when at all possible. <br>
<br>
There are other related best practices sort of relating to this as
well, <br>
as far as wiring chargers and inverters electrically close to the
batteries.<br>
<br>
If you have the charge controllers wired too close to the inverter<br>
battery terminals and also have long battery cables, then the<br>
inverter will tend to draw more current from the charge controllers<br>
rather than the batteries and cause problems with the CC.<br>
By wiring the CC positive and negatives closer to the battery<br>
terminals, then the inverter MUST draw its power from the battery<br>
terminal... The battery acts as kind of a filter for the CC and
the<br>
CC doesn't get jerked around so much by the inverter's input<br>
ripple current. This can help reduce wear and tear on the<br>
CC somewhat.<br>
<br>
But we've been used to wiring the batteries to bus bars inside of<br>
a main connector box (E-panel, flexware, whatever), and aren't<br>
really given the opportunity to make nice best practice connections,<br>
except maybe to make the battery cables as short as possible<br>
and twist them as best we can.<br>
<br>
boB<br>
<br>
<br>
<br>
<br>
<br>
<blockquote
cite="mid:CAL2u1ufriseSm5noVBwZMjma8KuWtrjRg-FHiPeRBKFYu1Tz+A@mail.gmail.com"
type="cite">
<p dir="ltr">Roy Rakobitsch<br>
NABCEP Certified Small Wind Installer®<br>
NABCEP Certified Solar PV Installer®<br>
Certified Advanced Tower Climbing, Safety & Rescue<br>
Wind/PV Design Engineer<br>
Windsine LLC<br>
631-514-4166<br>
<a moz-do-not-send="true" href="http://www.windsine.org">www.windsine.org</a></p>
<div class="gmail_quote">On Jun 29, 2015 5:05 PM, "Ray Walters"
<<a moz-do-not-send="true" href="mailto:ray@solarray.com">ray@solarray.com</a>>
wrote:<br type="attribution">
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"> 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 cols="72">R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
<a moz-do-not-send="true" href="tel:303%20505-8760" value="+13035058760" target="_blank">303 505-8760</a></pre>
<div>On 6/29/2015 3:55 PM, Benn Kilburn wrote:<br>
</div>
<blockquote type="cite">
<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><a moz-do-not-send="true" href="tel:780-906-7807"
value="+17809067807" target="_blank">780-906-7807</a></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"
target="_blank">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"> <br>
</font><font face="Arial" size="1"><b><br>
Jarmo Venalainen</b> | </font><font
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<td><font color="#5f5f5f" face="sans-serif"
size="1">From:</font> </td>
<td><font face="sans-serif" size="1">"<a
moz-do-not-send="true"
href="mailto:boB@midnitesolar.com"
target="_blank">boB@midnitesolar.com</a>"
<<a moz-do-not-send="true"
href="mailto:boB@midnitesolar.com"
target="_blank">boB@midnitesolar.com</a>></font>
</td>
</tr>
<tr valign="top">
<td><font color="#5f5f5f" face="sans-serif"
size="1">To:</font> </td>
<td><font face="sans-serif" size="1">RE-wrenches
<<a moz-do-not-send="true"
href="mailto:re-wrenches@lists.re-wrenches.org"
target="_blank">re-wrenches@lists.re-wrenches.org</a>>,
</font> </td>
</tr>
<tr valign="top">
<td><font color="#5f5f5f" face="sans-serif"
size="1">Date:</font> </td>
<td><font face="sans-serif" size="1">06/28/2015
10:30 PM</font> </td>
</tr>
<tr valign="top">
<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"
target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>></font></td>
</tr>
</tbody>
</table>
<br>
<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"
target="_blank"><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>
<a moz-do-not-send="true"
href="tel:505%20780-2738" value="+15057802738"
target="_blank">505 780-2738</a> 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"
target="_blank"><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"
target="_blank"><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> </p>
<br>
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