[RE-wrenches] High current dc combiner vibration

Fri Jun 30 11:33:02 PDT 2023

Hello, what do people think about the suggestion for chokes to filter this
noise out? How do I go about sizing a choke for something like that? Would
it have to be on each and every positive and negative conductor? And I
assume I’d wanna place those chokes as close as practical to the inverters
because that’s the assumed source of the 120 Hz ripple. And maybe that
approach could also harden the inverters against EMP and other outside
induced noise.

I am using 2 inch SEU connectors, metallic, to pass the cables into and out
of the combiner, I guess that’s not helping things. I was thinking of using
some heat resistant rubber tape/mastic to wrap the cables as they pass
through those connectors at least for dampening.

On Fri, Jun 30, 2023 at 12:46 PM bob--- via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

>
>
> We are talking to Kirk offline about this but the main issue here is that
> the enclosure
> for the 2000A combiner is made out of steel which is ferrous.  That means
> that when the
> 120 Hz ripple current induces into the chassis it can vibrate just like a
> transformer.
>
> Low frequency transformer inverters are have higher ripple than the newer
> HF transformer units
> but they have some AC ripple on the battery cables as well.
>
> This combiner is evidently been around for about 8 years and we haven't
> heard any complaints
> but maybe others have been silent on this.  I am not surprised at all that
> this happens.
>
> Aluminum chassis has the problem that it is a good conductor so when the
> whole enclosure forms
> around the cables, the aluminum can act as a shorted turn in a
> transformer.  It is usually just
> lossy but should vibrate much less, if at all.
>
> There are other issues in switching to aluminum that Robin mentions, here:
>
> *"One reason is cost, the other is fasteners, We would need to use press
> nuts instead of snail shells. *
> *Snail shells and sheet metal screws don’t do well in aluminum. It is too
> soft. Aluminum would not *
>
>
> *vibrate from magnetic ripple activity though." *He has some ideas to
> make aluminum work so we will try those.
>
> Now, plastic could work.   Just has to be real thick.    Darn physics !
>
> Damping can help, like Kirk tried (more can be done here too).  Keeping
> the cables
> together best as you can inside the chassis may help as well but moving
> and routing
> the cables might also reduce the buzzing some more.
>
> That's the latest buzz from here.
>
> 🌜boB🌛
>     K7IQ
>
> On 6/30/2023 8:45 AM, david quattro via RE-wrenches wrote:
>
> Ferrite cores can be used for the battery cables to pass through to reduce
> common mode current
>
> On Fri, Jun 30, 2023 at 3:59 AM Kirk Herander via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>> I have -15- sets of 4/0 cable (1 per 32 kwh stack) into the combiner.
>> They are paired and within .25 " of one another in wire cable tray for 80%
>> of their respective distance.
>>
>> The inverter to combiner sets are 2/0 for each respective inverter. They
>> are paired (not twisted) in cable tray, anywhere from 10 -20' in length.
>> Maybe I can send some photos, but can't at present due to computer issues.
>>
>> I used cable tray because the CT-rated cable is in free air, no derating
>> of current required. But merely pairing the leads may be the issue.
>>
>> I could rearrange the inverter cables and twist the sets, but doing it
>> from combiner to battery cabinets is impossible.
>>
>> And I'm wondering if this is really necessary if the customer is willing
>> to live with the issue. What are the ramifications down the road?
>> Loosening of connections I suppose would be one.
>>
>>
>>
>> On Fri, Jun 30, 2023 at 12:40 AM Jerry Shafer via RE-wrenches <
>> re-wrenches at lists.re-wrenches.org> wrote:
>>
>>> Kirk
>>> As the batteries come up to charge does the vibration subside. Are the
>>> battery cables spun together "corkscrew like" l have seen this correct DC
>>> noise. I have an 8 on 8 just like your 10 and l have no noise at all, mine
>>> come in from each side of the battery combiner, how is your install
>>> configured, how is the cable length same close or very short to very long
>>> some length is better on FLA's due to resistance under load and charge.
>>> More information may help with a solution.
>>> Fun times solar
>>> NABCEP PV Inspector
>>>
>>> On Thu, Jun 29, 2023, 8:19 AM Kirk Herander via RE-wrenches <
>>> re-wrenches at lists.re-wrenches.org> wrote:
>>>
>>>> All,
>>>>
>>>> I am in the middle of commissioning a 480kwh BP LFP battery bank,
>>>> connected to -10- OB Radian 8kw inverter/chargers.
>>>>
>>>> For the DC combiner I am using midnite 2000 amp combiner boxes,
>>>> modified to mount  class T fuses on the positive bus, for both battery
>>>> inputs and inverter outputs.
>>>>
>>>> For starters, I set the master inverter at a max charge rate of 20 AC
>>>> amps, which equates to a DC charge of about 74 A. All the other inverters
>>>> are automatically set to this charge rate as well.
>>>>
>>>> Turning the chargers on one by one, I started to get quite an audible
>>>> vibration from the combiner box at a combined charge of about 400 to 500 A.
>>>>
>>>> So I took the cover off of the combiner, which was vibrating
>>>> noticabllly by feel. Most of the noise was from the cover not fitting
>>>> tight. But the The box itself is also vibrating by feel.
>>>>
>>>> I took the combined charge up to 640A dc. This level of vibration
>>>> definitely increases with an increased charge rate. And I am surprised
>>>> because after all, we’re not talking AC here we’re talking DC. It almost
>>>> reminds me of a large AC transformer in its behavior. The vibration did not
>>>> seem to be originating at the inverters, then resonating to the combiner.
>>>>
>>>> I can dampen the vibration by adding a few things, but I’m surprised
>>>> that this is happening. All connections in the combiner are tightened
>>>> properly. Ideas?
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>>
>>>> *Kirk Herander / **kirkh at vermont.solar <kirkh at vermont.solar>*
>>>>
>>>> *Owner|Principal, VT Solar, LLC*
>>>>
>>>> *Celebrating our 32st Anniversary 1991-2023!!*
>>>>
>>>> dba Vermont Solar Engineering
>>>>
>>>> 802.863.1202
>>>> _______________________________________________
>>>> List sponsored by Redwood Alliance
>>>>
>>>> Pay optional member dues here: http://re-wrenches.org
>>>>
>>>> List Address: RE-wrenches at lists.re-wrenches.org
>>>>
>>>> Change listserver email address & settings:
>>>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>>>>
>>>> There are two list archives for searching. When one doesn't work, try
>>>> the other:
>>>> https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/
>>>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>>>>
>>>> List rules & etiquette:
>>>> http://www.re-wrenches.org/etiquette.htm
>>>>
>>>> Check out or update participant bios:
>>>> http://www.members.re-wrenches.org
>>>>
>>>> _______________________________________________
>>> List sponsored by Redwood Alliance
>>>
>>> Pay optional member dues here: http://re-wrenches.org
>>>
>>> List Address: RE-wrenches at lists.re-wrenches.org
>>>
>>> Change listserver email address & settings:
>>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>>>
>>> There are two list archives for searching. When one doesn't work, try
>>> the other:
>>> https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/
>>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>>>
>>> List rules & etiquette:
>>> http://www.re-wrenches.org/etiquette.htm
>>>
>>> Check out or update participant bios:
>>> http://www.members.re-wrenches.org
>>>
>>>
>>
>> --
>>
>> *Kirk Herander / **kirkh at vermont.solar <kirkh at vermont.solar>*
>>
>> *Owner|Principal, VT Solar, LLC*
>>
>> *Celebrating our 32st Anniversary 1991-2023!!*
>>
>> dba Vermont Solar Engineering
>>
>> 802.863.1202
>> _______________________________________________
>> List sponsored by Redwood Alliance
>>
>> Pay optional member dues here: http://re-wrenches.org
>>
>> List Address: RE-wrenches at lists.re-wrenches.org
>>
>> Change listserver email address & settings:
>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>>
>> There are two list archives for searching. When one doesn't work, try the
>> other:
>> https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/
>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>>
>> List rules & etiquette:
>> http://www.re-wrenches.org/etiquette.htm
>>
>> Check out or update participant bios:
>> http://www.members.re-wrenches.org
>>
>>
> _______________________________________________
> List sponsored by Redwood Alliance
>
> Pay optional member dues here: http://re-wrenches.org
>
> List Address: RE-wrenches at lists.re-wrenches.org
>
> Change listserver email address & settings:http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
> There are two list archives for searching. When one doesn't work, try the other:https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>
> List rules & etiquette:http://www.re-wrenches.org/etiquette.htm
>
> Check out or update participant bios:http://www.members.re-wrenches.org
>
>
> _______________________________________________
> List sponsored by Redwood Alliance
>
> Pay optional member dues here: http://re-wrenches.org
>
> List Address: RE-wrenches at lists.re-wrenches.org
>
> Change listserver email address & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
> There are two list archives for searching. When one doesn't work, try the
> other:
> https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/
> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>
> List rules & etiquette:
> http://www.re-wrenches.org/etiquette.htm
>
> Check out or update participant bios:
> http://www.members.re-wrenches.org
>
> --

*Kirk Herander / **kirkh at vermont.solar <kirkh at vermont.solar>*

*Owner|Principal, VT Solar, LLC*

*Celebrating our 32st Anniversary 1991-2023!!*

dba Vermont Solar Engineering

802.863.1202
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20230630/faccaee5/attachment.htm>