Can you “trick” rapid shutdown devices to allow solar production for mini split during power outage?

[ginmtb]

I have a call into Tigo and will update when I hear back but thought I’d throw this out to the group also.

Okay here is my scenario - I have an EG4 hybrid mini split (24K). I have dedicated off-grid panels for it (NEM2 limit reached) and the mini split is connected to the grid. Because the panels are roof mounted I had to install rapid shutdown devices. I chose the Tigo TS4-A-O optimizers.

When the power goes out (no battery), my understanding is the Tigo CCA will detect no power and shut every panel down. This is good for emergency personnel, but with PG&E we seem to have plenty of power outages when there is no local emergency. And of course those outages are often at the peak of summer heat when the grid is taxed so the mini split will be shut down too. Hello hot house!

My question is, if I were to disable/isolate the grid power connection to the mini split (I have a disconnect installed) and then provide power to the CCA via a portable power station (10-25VDC input), would the CCA then tell the solar panels all is well and go ahead and produce energy? Then in theory that energy will power the hybrid mini split via the direct DC connection, giving us the much needed cooling.

Tigo CCA connection - I could run a pigtail off the CCA (green unit) with a wago connector and plug in a DC wall block (12V, 1A) powered by a portable power station. Having the wago would allow me to easily switch between the stepped down power from the power supply (white unit) and the temp power:



Does this make sense? Am I going to burn the place down? Do I know just enough to be dangerous? Thanks for your assistance!

 

[Ampster]

Yes, that will work for the panels connected to your hybrid mini split unless it needs to see the grid. That is a question for EG4. The problem is if your inverter is grid tied it needs to recognize the grid. It won't operate without seeing a grid. . The purpose of TIgos is to shut down the the panels on the roof. They will still produce voltage even though the GT inverter is not calling for current. It is a safety requirement to protect firemen who may go on your roof after turning off the grid.

 

[BentleyJ]

If the dedicated roof mounted PV's are feeding DC directly to the mini-split what you are describing should work in theory if the AC spoof voltage supplied to the Tigo CCA is acceptable to it. The PV's will produce voltage and the mini-split will operate provided solar conditions will produce enough current.

The issue I see is not one of safety but of reliable operation. When the grid is also available to the mini-split any extra power can come from there. Without the grid a battery would be highly recommended as a buffer otherwise I suspect you would have unstable, variable power output from the panels. Possibly damaging the mini-split.

 

[Hedges]

Not clear to me there is an "inverter" in this system, other than inverter drive mini-split.
It has PV inputs and panels have Tigo RSD, with keep-alive coming from transmitter powered by wall-wart.
Sure, alternate DC supply would wake it up. Could be a battery, how about a PV panel and voltage regulator?

Do you have a safety switch, or just AC breaker feeding this?
I'd suggest installing an RSD initiator, just a switch to open the DC power to keep-alive transmitter regardless of source.

I'm using visible-blade safety switch for my GT PV disconnect. When I install new system with RSD, removing AC from GT PV inverter, that will trigger shutdown. If I add battery backup, I will use either 3rd pole of 3PST switch, or install a handle position microswitch for RSD.

 

[ginmtb]

Sorry, I have a fully separate grid tied system with microinverters. These 6 panels are dedicated to the mini split, no inverter, just direct wired to the mini split. As I mentioned above, since I just got in under NEM2, I can't add more to my system (I am allowed to add up to 1kw, I added two panels). I know there are arguments for and against running dedicated panels for the mini split, but this was my option to gain more solar production.

The mini split has its own breaker, but there is also a disconnect as required at the exterior unit. That disconnect when pulled kills power to the exterior unit and the Tigo CCA (which will trigger RSD). I don't have any batteries in my systems. I was thinking with a 12V/1A requirement, I could easily plug a wall wart into my small Ecoflow battery and run it for a long time. Hopefully this doesn't have to happen very often, I just know that we've had a couple every summer and while we can survive, it would be nice to be able to utilize the solar to power the mini split. That could be a definite vote for running separate panels for the mini split.

Here is what I have - this is without the DC wires connected at the DC disconnect switch and exterior unit.

 

[Ampster]

Here is what I have - this is without the DC wires connected at the DC disconnect switch and exterior unit.

The simplest approach would be to disable the RSD with a switch if you can figure that out. It could be as simple as disconnecting the power supply to the RSD system. There has to be a relay in there somewhere which is either normally open or normally closed.
EDIT: @svetz came up with a solution with knowledge of how the TIgos work

 

[Bkord]

Sorry, I have a fully separate grid tied system with microinverters. These 6 panels are dedicated to the mini split, no inverter, just direct wired to the mini split. As I mentioned above, since I just got in under NEM2, I can't add more to my system (I am allowed to add up to 1kw, I added two panels). I know there are arguments for and against running dedicated panels for the mini split, but this was my option to gain more solar production.

The mini split has its own breaker, but there is also a disconnect as required at the exterior unit. That disconnect when pulled kills power to the exterior unit and the Tigo CCA (which will trigger RSD). I don't have any batteries in my systems. I was thinking with a 12V/1A requirement, I could easily plug a wall wart into my small Ecoflow battery and run it for a long time. Hopefully this doesn't have to happen very often, I just know that we've had a couple every summer and while we can survive, it would be nice to be able to utilize the solar to power the mini split. That could be a definite vote for running separate panels for the mini split.

Here is what I have - this is without the DC wires connected at the DC disconnect switch and exterior unit.

View attachment 210014

could you just leave it plugged into your Ecoflow or a UPS all the time?

 

[Hedges]

You don't disable RSD, you enable PV output by modulating a keep-alive signal onto the PV wires.
Tigo has a transmitter box which does that, powered by 12V from a wall-wart.

I have similar interests for my system, but that will have battery inverter.

For OP, could use Ecoflow as he says. Or 12V battery. Or PV panel with voltage regulator on the output.
I'd suggest killing two birds with one stone, setting up low voltage PV panels and SCC to maintain AGM battery, use that to feed keep-alive and telecom gear.

Put an RSD kill switch near the meter, out of respect for firemen.

But I'm not clear whether OP has a Tigo keep-alive transmitter. He does mention Tigo CCA, which I thought was communications for optimizer/panel level monitoring.

The mini split has its own breaker, but there is also a disconnect as required at the exterior unit. That disconnect when pulled kills power to the exterior unit and the Tigo CCA (which will trigger RSD).

That seems to indicate CCA is the keep-alive transmitter.

Another way someone could have done this was for separate GT PV system to be a string inverter having keep-alive built in, and inductively couple to PV string for mini-split.

But if CCA does it, just need power to that.

 

[timselectric]

Sorry, I have a fully separate grid tied system with microinverters. These 6 panels are dedicated to the mini split, no inverter, just direct wired to the mini split. As I mentioned above, since I just got in under NEM2, I can't add more to my system (I am allowed to add up to 1kw, I added two panels). I know there are arguments for and against running dedicated panels for the mini split, but this was my option to gain more solar production.

The mini split has its own breaker, but there is also a disconnect as required at the exterior unit. That disconnect when pulled kills power to the exterior unit and the Tigo CCA (which will trigger RSD). I don't have any batteries in my systems. I was thinking with a 12V/1A requirement, I could easily plug a wall wart into my small Ecoflow battery and run it for a long time. Hopefully this doesn't have to happen very often, I just know that we've had a couple every summer and while we can survive, it would be nice to be able to utilize the solar to power the mini split. That could be a definite vote for running separate panels for the mini split.

Here is what I have - this is without the DC wires connected at the DC disconnect switch and exterior unit.

View attachment 210014

Short answer is yes, that would work.

 

[ginmtb]

I’m messing up my Tigo products sorry!

The CCA is powered by 12VDC but also has a power/communcation wire that is connected to the Tigo TAP (photo below). Then the Tigo TAP communicates wirelessly with the optimizers that handle the RSD. When power is lost to the CCA, it is lost at the TAP as well. The optimizers then sense no signal from the TAP and go into RSD (or something like that).

 

[ginmtb]

could you just leave it plugged into your Ecoflow or a UPS all the time?

I just want it for emergency situations but the small 12V battery idea above is compelling…

 

[ginmtb]

This is an interesting option - found this photo courtesy of @onokai on this forum. The Ecoflow has a 120V output, could do this too, would be very easy. Again, just for emergency backup, I would just coil it up and put it in the box and connect to power supply when needed.

 

[HarryN]

Definitely following along with what you come up with.

 

[onokai]

I never turned on my Tigos with power .Went thru all that work with the wiring and never activated them. They optimize without it anyway. I want solar power when the power is out . I have 3 mini splits now myself for heating and cooling.If its a fire I can manually shut it off. I have a grid tied syetem .

 

[Ampster]

.If its a fire I can manually shut it off

I don't have TIgos but I did install a rapid shut down switch for my SolArk backup. The inspector never asked to see it work, he was more concerned about labeling.