Hi Jason, 

The downside of an all-in one, that may be acceptable for
grid, is in a failure an all-in-one becomes unusable unless there is a
spare. Even with one it is often a bigger job to deal with. This was my
feedback to Schneider when they were looking into this 5 years back. I know
they made the right decision for offgrid.  

Dave Angelini Offgrid
Solar
"we go where powerlines don't"
http://members.sti.net/offgridsolar/
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On Thu, 21 Jan 2021
16:05:44 -0500, Jason Szumlanski  wrote:      It's already built - 6 years
old - I didn't do it. The new property owner just purchased a very
expensive battery bank and wants to protect it, understandably, because she
had problems with her generator not starting as expected when not at the
property. It was suggested by the original installer to install a load
shedding contactor as the manual suggests (albeit in an opaque manner). I
just can't seem to wrap my head around why this is a good idea. The
integrated battery protection mode should handle this function. A contactor
(or series of relays and a contactor) carries too much risk of failure that
could result in another problem for the owner altogether. I understand
protecting the battery, but the cure can't be worse than the disease. I'm
looking for a balanced approach, which I believe is to just implement the
BPM unless I'm missing some deficiency in that strategy.   The system
worked great in an AC coupled configuration until the generator started
becoming unreliable. In Florida I like AC coupling in a scenario like this
where the most challenging load is in the summer, essentially concurrent
with peak sunlight (air conditioning). However, I have been looking at
trying out a Sol-Ark as soon as the opportunity arises with a combination
of DC and AC coupling. With no separate charge controller involved, it
becomes much less complicated and you get the best of both worlds in
theory.   Jason                          
  On Thu, Jan 21, 2021 at 3:36 PM
Tump  wrote:  IF this system has yet to be built I would STRONGLY suggest
that AC coupling is NOT considered. IF it is them i would consider HV CC DC
coupling. T
   On Jan 21, 2021, at 3:15 PM, Jason Szumlanski  wrote: 
     
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  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  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  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
[8]   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  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  
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