[RE-wrenches] High current dc combiner vibration

[bob at midnitesolar.com]

The battery cables being close together, twisted too if possible, help 
reduce cable inductance
which can cause voltage drop across those cables at higher currents with 
120 Hz ripple.
Mainly with low frequency transformer inverter/chargers.

It's better to have them closer together than far apart, especially for 
longer battery cables.

🌜boB🌛

On 6/29/2023 9:24 AM, Starlight via RE-wrenches 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> 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
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