SMA rapid shutdown a POS

[DaveDE2]

The manual clearly states that each inverter requires its own RS box.

Hmm...I don't know why that would be because presumably the rapid shutdown box doesn't know anything about what it's connected to on the output side and presumably both inverters share a common ground if they're located side-by-side. Perhaps the RS box can somehow sense if the inverter is powered up or not in which case if one was powered up and the other powered down it has a problem with that. Best to install per the manual though. Thanks.

@max2k
I'll see if I can dig up some photos of my control wiring.

[max2k]

Hmm...I don't know why that would be because presumably the rapid shutdown box doesn't know anything about what it's connected to on the output side and presumably both inverters share a common ground if they're located side-by-side. Perhaps the RS box can somehow sense if the inverter is powered up or not in which case if one was powered up and the other powered down it has a problem with that. Best to install per the manual though. Thanks.

@max2k
I'll see if I can dig up some photos of my control wiring.

They share the same AC ground but DC side is 'ungrounded' at least in my case and all other transformerless inverters and my guess is such inverters switch PV DC output between neutral-L1 and neutral-L2 at 15-25 kHz frequency. In this situation unless RS channels are very well isolated I can see them having problem doing independent MPPT tracking.

[DaveDE2]

I wired the RS boxes together per the manual. From the RS control switch, a cable goes to the upper connector slot of RS box 1 (lower box in the photo). Then from RS box 1 lower connector slot a cable runs to RS box 2 upper slot. Then another connector is plugged into RS box 2 lower slot with pins 3 and 4 jumpered together.

Here's a photo, but it's hard to see the details: IMG_3075 (1).JPG

[max2k]

I wired the RS boxes together per the manual. From the RS control switch, a cable goes to the upper connector slot of RS box 1 (lower box in the photo). Then from RS box 1 lower connector slot a cable runs to RS box 2 upper slot. Then another connector is plugged into RS box 2 lower slot with pins 3 and 4 jumpered together.

Here's a photo, but it's hard to see the details: IMG_3075 (1).JPG

I did the opposite- connected cable from RSController to the lower row of the first box then connected its upper row with the lower row of the second box and put jumper in the upper slot. I thought it better fits overall pattern as it matches single box installation and also p 11 on page 29 makes more sense:
"Connect the Rapid Shutdown Boxes together. To do so, connect the incoming conductors to a plug and plug this into the lower pin row of the connecting terminal block RSC, and always
connect the outgoing conductors to a plug and plug this into the upper pin row of the terminal block RSC." Here it sounds like lower row more like an input and upper one is more like an output.

Based on connector's pinout it sounds like all boxes have 4 out of 5 contacts in parallel (I didn't verify this) and only #4 green LED may be different in upper and lower rows. I'm sure you verified your setup passes check outlined on page 35 and curiously enough mine passes that too .

[ButchDeal]

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[DaveDE2]

max2k, I see your line of reasoning. The written explanation for connecting two boxes together in the manual contradicts the drawings. So your and my systems are wired opposite and both are working. 'Incoming" and 'Outgoing' are incredibly confusing because they don't indicate which box they are talking about. I'm thinking your configuration is probably what SMA intends though. I'll try flipping mine around if I ever have more problems before ditching RS. - thanks and regards

[max2k]

max2k, I see your line of reasoning. The written explanation for connecting two boxes together in the manual contradicts the drawings. So your and my systems are wired opposite and both are working. 'Incoming" and 'Outgoing' are incredibly confusing because they don't indicate which box they are talking about. I'm thinking your configuration is probably what SMA intends though. I'll try flipping mine around if I ever have more problems before ditching RS. - thanks and regards

well at least we both know now that both wiring variants work and don't cause any harm.

I'm fairly sure contacts 1, 2 & 3 are connected together between the rows. I suspect contact 5 might be connected too and it is connected internally to 'open collector' or 'open drain' type of output allowing that contact to be grounded by any box in the 'chain' as both LEDs are connected to +12V inside RS Controller. I don't know how they went about #4 though as it sounds like it is some kind of input in one row (requiring jumper to the ground) and output on another to drive green LED. Since RS Controller has green LED connected to pin 4 of RS box in the lower row I thought it must be some kind of 'output' to drive the LED to the ground and then the upper row pin 4 must be some kind of input to get the same signal from the 'next' RS box that it is done with shutting down its strings. This way RS box can check value on pin 4 of the upper row and if it is close to 0V check its own strings and ground pin 4 of its lower row to eventually lit RS Controller green LED. This is the theory I had in mind trying to make sense of their instructions. I wish I checked this theory at least by verifying continuity between pins and the ground/+12V but I didn't. My RS boxes are under the panels so it would take me couple hrs to get to them and then put everything back so I'm simply lazy to do this out of curiosity .

SMA could go wild and make #4 pin bi-directional and if the interface chip allows it detect in which row the pin is grounded and then make it 'input' dynamically. This way both variants would work and all their instructions make sense .

[Billybob9]

The space under a solar panel on an array is there to allow air to circulate freely thus cooling the panel. If that space is taken up by a SMA rapid shut down box then over heating will begin. The Relays in the SMA box would be more subject to failure in this case, since they are a moving part . So if a relay were in an off position and stuck or vice versa this would cause all sorts of problems. I just Installed an SMA system but put the Rapid shutdown box on the rack 1' away from the panels. It will have a cover over it that allows ventilation.