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@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@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@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@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@vermont.solar <kirkh@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@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@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@vermont.solar <kirkh@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@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@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@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@vermont.solar <kirkh@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@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
