[RE-wrenches] Battery Bank to Inverter Wiring
Roy Rakobitsch
windsine at gmail.com
Mon Jun 29 15:15:16 PDT 2015
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.
Roy Rakobitsch
NABCEP Certified Small Wind Installer®
NABCEP Certified Solar PV Installer®
Certified Advanced Tower Climbing, Safety & Rescue
Wind/PV Design Engineer
Windsine LLC
631-514-4166
www.windsine.org
On Jun 29, 2015 5:05 PM, "Ray Walters" <ray at solarray.com> wrote:
> 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 Engineer303 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.Venalainen at 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.venalainen at schneider-electric.com*
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> From: "boB at midnitesolar.com" <boB at midnitesolar.com> To: RE-wrenches <
> re-wrenches at 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-bounces at 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*
> *allan at sindelarsolar.com* <allan at 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 <505%20780-2738> 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-bounces at lists.re-wrenches.org*
> <re-wrenches-bounces at lists.re-wrenches.org>] *On Behalf Of *
> *Jarmo.Venalainen at schneider-electric.com*
> <Jarmo.Venalainen at 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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