[RE-wrenches] High current dc combiner vibration

[Nick A Lucchese]

Good morning all. Seems we’ve all been aware of best practices for keeping DC cables bound together and twisted when possible. Does anyone know why Simpliphi recommends the exact opposite on page 18 of their installation manual? I recall observing this awhile ago and thought it was just something that they would remedy in their next manual revision cycle but appears to still be noted. Has their own validated testing for Simpliphi specific installs concluded to be contrary to others?

Off to work, Nick


> On Jun 29, 2023, at 10:09 AM, Kirk Herander via RE-wrenches <re-wrenches at lists.re-wrenches.org> wrote:
> 
> I have not twisted them. It is a lot of Cable as you might imagine and they aren’t paired close together individual inverter to combiner or combiner to battery cabinets, not 100% of the cable lengths anyway, maybe on average 80% 
> 
> On Thu, Jun 29, 2023 at 12:25 PM Starlight <larry at starlightsolar.com <mailto:larry at starlightsolar.com>> wrote:
> You may already know but… Are your DC cables bonded together and twisted where possible to reduce magnetic fields? Higher the current and greater the loop area, the stronger the fields are. More parallel loops, the greater the combined flux = loud Hums.  
> 
> Larry Crutcher
> Starlight Solar Power Systems
> 
> 
> 
> 
> On Jun 29, 2023, at 8:19 AM, Kirk Herander via RE-wrenches <re-wrenches at lists.re-wrenches.org <mailto: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 <mailto:kirkh at vermont.solar>
> Owner|Principal, VT Solar, LLC
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> dba Vermont Solar Engineering
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> -- 
> Kirk Herander /  <>kirkh at vermont.solar <mailto: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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