[RE-wrenches] APS rapid shutdown

Thu Oct 31 08:39:00 PDT 2024

Dave – w.r.t #3, I think this is mostly a requirement from the inverter manufacturer.

For SMA, there is a minimum DC voltage required in shutdown (when there is also no AC voltage).  This minimum can come from one string, that is, only the longest string needs to be over the minimum, the others can be shorter.

For the SBSE -US, Section 7.6 “Rapid Shutdown Equipment) (pg 28-29) of the System Manual contains this minimum (3.6 Vdc) along with other system requirements. So for the APsmart devices, this would be 6 or more devices required on one string, from the 0.6V minimum shutdown voltage APsmart states.

System manual link: https://files.sma.de/downloads/Home-Storage-Solution-BackupStart-US-SH-en-10.pdf

Please note SMA  commercial inverters may have a larger minimum standby voltage requirement, thought very short strings are not as common as in residential.

Best regards –
Mike

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From: RE-wrenches <re-wrenches-bounces at lists.re-wrenches.org> On Behalf Of Brian Mehalic via RE-wrenches
Sent: Thursday, October 31, 2024 8:03 AM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Cc: Brian Mehalic <brian at solarenergy.org>
Subject: Re: [RE-wrenches] APS rapid shutdown

Not sure about #2 or #3, but 100% yes on #1, which quite a few people (including the mfg?) “learned the hard way.”
Brian

On Oct 31, 2024, at 6:57 AM, Dave Tedeyan via RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>> wrote:

Hi All,

I am about to use the AP systems rapid shutdown units for the first time (pairing with SMA inverters). I was reading through the manual and came across a couple things that I am wondering if others have noticed issues with:

1. The manual states that you need to keep the PV conductors from each inverter (there are two in this system) separate, or else there may be crosstalk. So this would imply that you need to have two separate DC conduits from the roof to the inverters, rather than one. Has anyone noticed if this is truly a concern?

2. The manual also states that there needs to be at least 20cm (or ~8") from the RSD-S-PLC to another piece of equipment (other than the module it is mounted on). I am attaching a diagram from the manual, but it sounds like if you have three rows of modules, the RSD's need to be installed on the top of the top row, the bottom of the bottom row, and you need an 8" gap between the rows for the middle row. The diagram in the manual makes this more clear than my words can. But has anyone not installed this large gap and had issues, or did it still work just fine?

3. Lastly, I don't see a mention in the manual, but is there a string length minimum? For some reason I thought with some of the older Tigo RSD units you needed at least 5 or 6 in a string, or maybe I am thinking of SolarEdge optimizers. I just want to make sure there is no minimum, since another job coming up will have a string of 3 panels.

I appreciate your experience!
Cheers,
Dave

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