[RE-wrenches] High current dc combiner vibration

[Jerry Shafer]

Wrenches, Kirk
Once you learn what is causing the issue then deciding on what to do is
safer, If you have access to a scope that may show you a DC side
fluctuation, pulsing or plain noise in the system.
Fun times in solar

On Fri, Jun 30, 2023 at 4:00 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
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>
> --
>
> *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:
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