[RE-wrenches] High current dc combiner vibration

[Kirk Herander]

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
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