My advice would be to use a DC charge controller, and forget the
frequency control/ AC coupled goofiness all together. This has been
covered ad nauseam in the past on the list. Its just not a good idea
off grid. I occasionally will design large systems with some AC coupled
array, but only enough to match the daytime AC loads. Newer AC coupled
systems with better communication between the inverters work better, but
if frequency shifting is your main control, its just never going to work
very well.
Besides the issues you're having, you can add poor battery management
and premature cell failures to the list, along with the unforgivable
"Dark Start" when the batteries are discharged below the LBCO setting.
Ray Walters
Remote Solar
303 505-8760
On 11/23/20 8:57 AM, Mac Lewis wrote:
Hi Chris,
I have no direct experience trying to troubleshoot devices that can't
handle frequency shift, that seems hard to do. However, I might
utilize a relay approach to solve it. You could use the relay
functions in the Sunny Island to start dropping strings and/or
inverters to keep the frequency shift from occurring in the first
place. There is probably a more elegant way to do this, but it may
work. I believe there is a way to keep frequency shift from happening
in one of the many setpoints on the Sunny Island. I think this is a
serious disadvantage of frequency shift to control PV output because
so many devices are designed to work at a precise frequency.
Good luck
On Wed, Nov 18, 2020 at 8:09 AM Chris Anderson
<[email protected] <mailto:[email protected]>> wrote:
Wrenches community,
Hope folks are well out there. I am wondering if anyone has
experience addressing a frequency oscillation with a split phase
off grid Sunny Island system. I am working on an off grid home
project with 2 units that has just not worked right since
installation. The small number of 240 volt loads and most notably
the geothermal heat pump goes into a loud vibration as the
frequency shifts and does so for 20 seconds, then settles down
into normal operation. 45 seconds later, it does it again and just
repeats itself until the water in the storage tank is up to
temperature. The current draw doubles when it is vibrating and it
seems to drain the batteries faster than expected when left on.
Wondering if anyone out there has any thoughts or is experienced
off grid tech in New England interested in some troubleshooting
work to help resolve things.
Please email me directly if possible at the following address -
[email protected] <mailto:[email protected]>
Thanks and stay safe out there.
--
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