[RE-wrenches] High current dc combiner vibration
bob at midnitesolar.com
bob at midnitesolar.com
Fri Jun 30 09:45:45 PDT 2023
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*
>
> *Owner|Principal, VT Solar, LLC*
>
> */Celebrating our 32^st 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*
>
> *Owner|Principal, VT Solar, LLC*
>
> */Celebrating our 32^st 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
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20230630/cddd1d36/attachment.htm>
More information about the RE-wrenches
mailing list