Wrenches
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
Jerry
Sent via the Samsung Galaxy S™ III, an AT&T 4G LTE smartphone
<div>-------- Original message --------</div><div>From: Ray Walters
<r...@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>
</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.
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.
My guess is that it wouldn't be worth it, but I've been wrong many times.......
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 6/29/2015 3:55 PM, Benn Kilburn wrote:
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"?
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.
Benn Kilburn
SkyFire Energy Inc.
780-906-7807
On Jun 29, 2015, at 10:28 AM, jarmo.venalai...@schneider-electric.com wrote:
Hi:
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.
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.
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.
JARMO
_____________________________________________________________________________________
Jarmo Venalainen | Schneider Electric | Xantrex
Brand | CANADA | Sales Application Engineer
Phone: +604-422-2528 | Tech Support: 800-670-0707 | Mobile:
+604-505-0291
Email: jarmo.venalai...@schneider-electric.com | Site: www.Xantrex.com |
Address: 3700 Gilmore Way, Burnaby, BC V5G4M1
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From: "b...@midnitesolar.com" <b...@midnitesolar.com>
To: RE-wrenches <re-wrenches@lists.re-wrenches.org>,
Date: 06/28/2015 10:30 PM
Subject: Re: [RE-wrenches] Battery Bank to Inverter
Wiring
Sent by: "RE-wrenches"
<re-wrenches-boun...@lists.re-wrenches.org>
On 6/28/2015 9:20 AM, Allan Sindelar wrote:
>>>>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.<<<<
It is little known that with the typical inverters that use the heavy power
transformers,
have a lot of AC 120 Hz (or 100 Hz for 50 Hz systems) current mixed in with
that DC battery current.
The AC output current reflects back to the input as ripple current. This is
why you want to
have at least short as possible Sbattery cable runs AND keep the wires as close
together as possible.
Twisting the battery cables may help a bit but that is probably overkill.
The problem has to do with inductance in the battery cables. You can use as big
of cable
as you can fit in to reduce resistance, but that will not help to
lower the inductance.
The problems you can sometimes have with high inductance is that
L-C resonance at the
inverter can raise the peak voltages seen at the inverter input terminals and
can be hard on
the inverter.
Then again, the high frequency, lighter weight inverters will typically keep
most of that ripple
inside, between the DC input and AC output and battery cable inductance will
not be as much
of a problem on the battery cables.
boB Gudgel
On 6/28/2015 9:20 AM, Allan Sindelar wrote:
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.
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.
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.
I have twisted AC conductors together in the past when clients have expressed
concerns about EMF from their equipment and wiring, but only AC.
Allan
Allan Sindelar
al...@sindelarsolar.com
NABCEP Certified PV Installation Professional
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder (Retired), Positive Energy, Inc.
505 780-2738 cell
On 6/27/2015 2:40 AM, John wrote:
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.
From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf
Of jarmo.venalai...@schneider-electric.com
Sent: Saturday, 27 June 2015 5:45 a.m.
To: RE-wrenches
Subject: [RE-wrenches] Battery Bank to Inverter Wiring
Hi:
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.
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.
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,
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.
Recently this happened again and I wanted to get a better feel for it, so I did
some math.
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.
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.
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.
Given that, the voltage drop of the wire inductance is then , Vdrop = (rate of
change of current) x (inductance),
Vdrop for 1 uH = (100,000 A/s) x (0.000001 H) = 0.1V
Vdrop for 10 uH = (100,000 A/s) x (0.000001 H) = 1.0V
Vdrop for 100 uH = (100,000 A/s) x (0.000001 H) = 10.0V clearly this is a
problem.
Have any of the wrenches had systems with this issue? If so, how often.
JARMO
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