This is a good representation of poor battery design. Reducing the # of strings by increasing the capacity of the battery should always be considered. Yes this is a cheap way to go but in the long run this type of install can be very expensive. Without someone as experienced as Jarmo, the installer may never have figured this out. LESS STRINGS & more Ahours = less interconnects & potential for inductance and gives one far better performance charging & discharging. One bad cell and one is chasing their tail for quite a while w/ this install. On Jun 29, 2015, at 6:28 PM, jarmo.venalai...@schneider-electric.com wrote:
> Hi: > > I'm not sure how much trouble this has caused, so that's why I asked the > question. With large battery banks, it is possible to end up with a cabling > layout which has a potentially very large loop area as was the case at one of > the sites where I saw problems. Here's a picture of the battery bank they > had created. > > <Mail Attachment.gif> > > The + and - cables were not run side by side and the rack is made out of > steel. The inverters did not like it until we ran the cables along the > battery bank and then side by side. Once that was done, things worked as > expected. > > 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 > <Mail Attachment.gif> > <Mail Attachment.gif> <Mail Attachment.gif> <Mail Attachment.gif> > <Mail Attachment.gif> > > > > *** Please consider the environment before printing this e-mail > > > > From: Ray Walters <r...@solarray.com> > To: RE-wrenches <re-wrenches@lists.re-wrenches.org>, > Date: 06/29/2015 03:05 PM > Subject: Re: [RE-wrenches] Battery Bank to Inverter Wiring > Sent by: "RE-wrenches" <re-wrenches-boun...@lists.re-wrenches.org> > > > > > 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 > <mime-attachment.gif> > <mime-attachment.gif> <mime-attachment.gif> <mime-attachment.gif> > <mime-attachment.gif> > > > > > *** Please consider the environment before printing this e-mail > > > 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 > > > > > ______________________________________________________________________ > This email has been scanned by the Symantec Email Security.cloud service. > _____________________________________________________________________________________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > > > > ______________________________________________________________________ > This email has been scanned by the Symantec Email Security.cloud service. > _____________________________________________________________________________________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > > t...@swnl.net www.SWNL.net > Solarwinds Northernlights > Serving Mid Coast Maine & Northern California > 207-832-7574 Cl. 610-517-8401 > > Blair "TUMP" May > ******** MAINE'S CHARTER ******** > NABCEP "Certified PV Installer" > > ******** MAINE'S CHARTER ******** > Trace Xantrex "Certified" Dealer / Installer" >
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