Hi Mac, Yes, I considered using a pilot relay - it makes sense to run it on 120V because relays are readily available. I had the exact same concern - more to fail.
In this scenario, the inverter/battery room is remote from the house so there is only one load I can switch easily with a contactor, and that's the whole house load. Otherwise, I would definitely consider switching non-critical loads in a low battery situation. It just seems prudent enough to use the integrated Battery Preservation Mode (BPM), even in this AC coupled system. I considered a small DC array to charge the batteries in a heavily depleted situation, but it's a 60kWh battery so I would need a pretty substantial "backup" array I think. It does not seem like a reasonable solution. I would expect BPM to do it's job and keep the batteries from reaching a state that they are not recovered quite easily. Jason On Thu, Jan 21, 2021 at 2:37 PM Mac Lewis <maclew...@gmail.com> wrote: > Hi Jason, > > The only reason to load shed, without using the internal preservation mode > is if you have certain loads you'd like to keep on longer than other loads > that you shed. The various preservation modes can be complex, especially > if you are AC coupled, so you really have to think through your strategy. > > You can always use a pilot relay, with a coil rating that suits your > needs, and then feed the 100A contactor with that. Unfortunately, its just > one more piece to fail... > > On Thu, Jan 21, 2021 at 12:13 PM Jason Szumlanski < > ja...@floridasolardesigngroup.com> wrote: > >> I just learned from the manufacturer that the mercury displacement >> relay's coil is rated for 43.2 to 52.80V. Obviously, the battery voltage >> can exceed 52.8 pretty significantly. Does the Sunny Island regulate the >> output voltage on this relay to 48V or is the actual battery voltage passed >> through on this terminal? >> >> The more I read about this load shedding strategy, the more it seems >> overly complicated. It's also another thing to fail. If the N.O. contactor >> coil fails, the loads to the house are going to lose power. That's not good >> for a remote installation. I guess you have to weigh battery protection >> with how critical the loads are. >> >> I'm wondering why the internal Battery Preservation Mode isn't sufficient >> enough. What's the purpose of load shedding if the BPM does effectively the >> same thing. I can see perhaps shedding some parts of the load and that is a >> nice feature, but to protect the batteries, why isn't BPM enough? >> >> Jason >> >> >> >> >> On Tue, Jan 19, 2021 at 8:48 PM Mac Lewis <maclew...@gmail.com> wrote: >> >>> Hi Jason, >>> >>> I have done this with mercury displacement relays: >>> >>> https://www.mdius.com/mercury-relays/two-pole-relays-contactors/two-pole-100-amp >>> <https://mailtrack.io/trace/link/ff30c111d75d78887f17a5ed3e3b04bfe2cd428a?url=https%3A%2F%2Fwww.mdius.com%2Fmercury-relays%2Ftwo-pole-relays-contactors%2Ftwo-pole-100-amp&userId=1613865&signature=0abdef13355136e0> >>> >>> They do have a 100A 2P 48V coil relay. They seem to work perfectly. >>> >>> Good luck >>> >>> On Tue, Jan 19, 2021 at 2:51 PM Jason Szumlanski < >>> ja...@floridasolardesigngroup.com> wrote: >>> >>>> Does anyone know where I can get a load shedding contactor described in >>>> SMA documentation for use with a multi-function relay in a Sunny Island? >>>> >>>> Thanks, >>>> >>>> Jason Szumlanski >>>> _______________________________________________ >>>> List sponsored by Redwood Alliance >>>> >>>> List Address: RE-wrenches@lists.re-wrenches.org >>>> >>>> Change listserver email address & settings: >>>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >>>> <https://mailtrack.io/trace/link/dc696cbe05b3c1c168fc9a22231ca0ead130049f?url=http%3A%2F%2Flists.re-wrenches.org%2Foptions.cgi%2Fre-wrenches-re-wrenches.org&userId=1613865&signature=faa967f05b00e2a4> >>>> >>>> There are two list archives for searching. 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