[RE-wrenches] MidNite SOB problem and possible solution

[bob at midnitesolar.com]

Eric, this is very interesting that the foil (Faraday shield) used in 
this way would help that situation !

A Faraday shield using aluminum foil will only shield electric fields 
and not magnetic fields of course

so something interesting is going on here.   SO, the foil was not 
grounded in any way ?

The mechanism should hopefully become obvious  after some thought and 
experimentation.

We will definitely be looking into your fix.

Than you !

boB



On 12/16/2020 3:36 PM, Eric Smiley wrote:
> Season's Greetings Wrenches
>
> We have been attempting to use MidNite SOB's with Sol-Ark inverters 
> this year. In Canada we only need one SOB per string since our Code 
> requires Rapid Shutdown for PV source or output circuits more than 1 
> meter from the array.
>
> However, not all the SOB's were closing the circuit when we had two 
> strings on one MPPT - both when we combined two strings on the Sol-Ark 
> PV input terminals or when we used MC4 Y connectors outside the 
> Sol-Ark to combine two strings. MidNite had no solution for this back 
> during the summer and tech support there only suggested that we had 
> configured the system incorrectly or that we shouldn't combine strings 
> that way. This array also had a very long underground run between the 
> array and inverter. So, at that time, not knowing if it was distance, 
> interference from something else or gremlins, we just took out all the 
> MidNite equipment and installed a DC SunVolt Rapid Shutdown box.
>
> Diagnosing the problem was a challenge since only one of the parallel 
> strings on each MPPT was not producing power at any given moment. 
> Also, everything worked fine while I made voltage and current 
> measurements but when I pushed the coil and wires into the JB I lost 
> half my solar power.
> Anyway, today I solved the problem on a new system I was commissioning 
> by wrapping the SOB Transmitter coil, with the positive conductors 
> passing through it, in aluminum foil.
>
> I hypothesized that with the coil on the positive conductors, the 
> negative conductors, which were very close to the coil, all of which 
> was inside a metal junction box, were picking up a signal from the 
> coil and this was interfering with the signal on the positive.
>
> It's a bit cludgy, but shielding the coil seems to be the solution.
>
> I'd love to hear if anyone else has had this problem and/or solution.
> Eric Smiley, MASc
>
> Project Manager, North Island
>
>
> E: eric at vecoop.ca <mailto:eric at vecoop.ca>
>
> T:  1-888-386-0116 ext 702 (toll free)
>
> C:  250-703-6004
>
> W: viridianenergy.ca <http://www.viridianenergy.ca>
>
>
> <http://www.viridianenergy.ca/>
>
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