[RE-wrenches] Battery Bank to Inverter Wiring
boB at midnitesolar.com
boB at midnitesolar.com
Mon Jun 29 16:06:14 PDT 2015
On 6/29/2015 3:15 PM, Roy Rakobitsch wrote:
>
> 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.
>
Yep, that usually helps. Turns out that if you get just the right
amount of battery cable inductance AND just
the right amount of inductance, then you can have an LC resonant circuit
that makes the voltage go
sky high and let out the smoke.
But typically, raising the capacitance lowers the resonant frequency
enough below 120 Hz that it
helps the situation.
As far as batteries being part of the loop, yes they are. Just picture
their layout as
a piece of wire and you can get a feel for that contribution to the loop.
You could also place a capacitor or two right where the battery cables come
together again.
But you gotta stop somewhere. This is more educational or a way to
visualize what is going on so that you use the best wiring practices
when at all possible.
There are other related best practices sort of relating to this as well,
as far as wiring chargers and inverters electrically close to the batteries.
If you have the charge controllers wired too close to the inverter
battery terminals and also have long battery cables, then the
inverter will tend to draw more current from the charge controllers
rather than the batteries and cause problems with the CC.
By wiring the CC positive and negatives closer to the battery
terminals, then the inverter MUST draw its power from the battery
terminal... The battery acts as kind of a filter for the CC and the
CC doesn't get jerked around so much by the inverter's input
ripple current. This can help reduce wear and tear on the
CC somewhat.
But we've been used to wiring the batteries to bus bars inside of
a main connector box (E-panel, flexware, whatever), and aren't
really given the opportunity to make nice best practice connections,
except maybe to make the battery cables as short as possible
and twist them as best we can.
boB
> 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 <http://www.windsine.org>
>
> On Jun 29, 2015 5:05 PM, "Ray Walters" <ray at solarray.com
> <mailto: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 Engineer
> 303 505-8760 <tel:303%20505-8760>
>
> 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 <tel:780-906-7807>
>>
>>
>> On Jun 29, 2015, at 10:28 AM,
>> Jarmo.Venalainen at schneider-electric.com
>> <mailto: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 <tel:%2B604-422-2528> | *Tech Support:*
>>> 800-670-0707 <tel:800-670-0707> | *Mobile:* +604-505-0291
>>> <tel:%2B604-505-0291> *
>>> Email:* _jarmo.venalainen at schneider-electric.com_
>>> <mailto:jarmo.venalainen at schneider-electric.com> |
>>> *Site:*_www.Xantrex.com_ <http://www.xantrex.com/> | *Address:*
>>> 3700 Gilmore Way, Burnaby, BC V5G4M1
>>> <mime-attachment.gif> <http://www.xantrexrebate.com/>
>>> <mime-attachment.gif> <http://www.xantrex.com/>
>>> <mime-attachment.gif> <https://www.facebook.com/Xantrex>
>>> <mime-attachment.gif> <https://twitter.com/Xantrex>
>>> <mime-attachment.gif> <https://twitter.com/Xantrex>
>>>
>>>
>>>
>>>
>>> *** Please consider the environment before printing this e-mail
>>>
>>>
>>>
>>> From: "boB at midnitesolar.com <mailto:boB at midnitesolar.com>"
>>> <boB at midnitesolar.com <mailto:boB at midnitesolar.com>>
>>> To: RE-wrenches <re-wrenches at lists.re-wrenches.org
>>> <mailto: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
>>> <mailto: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_ <mailto: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 <tel: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_] *On Behalf
>>> Of *_Jarmo.Venalainen at schneider-electric.com_
>>> <mailto: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
>>>
>>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20150629/71b71784/attachment-0002.html>
More information about the RE-wrenches
mailing list