[RE-wrenches] High current dc combiner vibration

Sat Jul 1 15:09:26 PDT 2023

Hi you have the correct people on the job but get at the basics the forces
causing the vibration is magnetic. You have to break the magnetic path.  If
it was electrical a simple cut in the enclosure.  But it is magnetic which
is much harder to stop. If the hum stops with the cover off replace the
cover with polycarbonate plastic

On Sat, Jul 1, 2023, 3:17 PM Kirk Herander via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Hi,
> yes I read Robins email, but the class T fuses are in series only with the
> large DC cable breakers (Heineman, Airpax, etc.) in the Outback GSLC. I
> might be missing something, perhaps again.
>
>
> On Sat, Jul 1, 2023 at 3:09 PM Robin <Robin at midnitesolar.com> wrote:
>
>> Ryan thinks it may be the classT fuses. We have a vibration issue when
>> classT fuses are connected to CBI breakers.
>>
>> Sent from my iPhone
>>
>> On Jul 1, 2023, at 11:32 AM, bob at midnitesolar.com wrote:
>>
>> 
>> Hi Kirk.  Did you receive the email that Robin sent to you ?
>>
>> You can measure things like, with your scope but you would want to look
>> at the current
>> from the inverter to battery.
>>
>> You could also use your clamp meter and look at DC  and AC.
>> Set it to AC to view the ripple current.
>>
>> I will copy/paste what Robin and Ryan sent to you and our support team
>> below in case it didn't come through.
>>
>> 🌜boB🌛
>>
>>
>>
>>
>> On 6/30/2023 7:55 AM, ryan at midnitesolar.com wrote:
>>
>> Kirk,
>>
>> Any chance this is the Class T Fuses resonating from the PWM on the DC
>> current? Feel free to give me a call would love to discuss this further
>>
>>
>>
>> 207-416-2006
>>
>>
>>
>> *From:* robin <robin at midnitesolar.com> <robin at midnitesolar.com>
>> *Sent:* Friday, June 30, 2023 10:47 AM
>> *To:* kirkh at vermont.solar
>> *Cc:* bob at midnitesolar.com; ryan <ryan at midnitesolar.com>
>> <ryan at midnitesolar.com>; James Parish <jparish at midnitesolar.com>
>> <jparish at midnitesolar.com>; todd at midnitesolar.com; Michelle Neville
>> <mneville at midnitesolar.com> <mneville at midnitesolar.com>
>> *Subject:* Vibrations
>>
>>
>>
>> Kirk, Although this is the first I have heard of this, boB says he isn’t
>> surprised. I am copying the tech support group here in hopes we can all
>> learn something.
>>
>>
>>
>> We have been shipping these boxes for about 8 years now and not a peep.
>>
>> boB says the ripple current is 120Hz AC and with that many amps it is not
>> surprising. I will check with our metal suppliers and ask what the cost
>> ramifications are to add stiffening ribs to the cover and possibly other
>> surfaces.
>>
>> I did this years ago on the Trace DR chassis to give it strength, but the
>> idea is the same.
>>
>> I hate to suggest this, but can you epoxy some ¾” x ¾” angle iron or
>> angle aluminum to the inside surface of the cover? Not sure about other
>> surfaces as I tend to fill them up with knockouts and busbars. I suppose
>> you could just span some unused knockouts though. Maybe even add a couple
>> more mounting screws towards the center of the box.
>>
>> We would be very interested in hearing the results.
>>
>> boB says our Rosie may exhibit less noise also as it will have less
>> ripple. We are testing many Rosie inverters paralleled so soon will be able
>> to have this same configuration tested although we don’t have loads large
>> enough to do ten Rosie’s justice.
>>
>> I don’t want to change the enclosure to aluminum for a couple of reasons,
>> but we may have little choice. Aluminum would not vibrate!
>>
>> 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.
>>
>> OK, I will ask about changing to aluminum. That would probably be less
>> expensive than adding stiffening ribs.
>>
>>
>>
>> Let us know how it goes.
>>
>> Then ask Ryan for a couple of free SPD’s for your trouble.
>>
>>
>>
>> Thanks,
>>
>> Robin Gudgel
>>
>> MidNite Solar
>>
>>
>>
>>
>>
>>
>>
>>
>> On 7/1/2023 9:19 AM, Kirk Herander via RE-wrenches wrote:
>>
>> I'm going to first obtain access to an oscilloscope to characterize and
>> screenshot this phenomena, both before and after any mitigation I do.
>>
>> 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
>>>>>> _______________________________________________
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>>>>>> _______________________________________________
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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
>>>>
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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
>>
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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
>
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