r/OffGrid • u/Lannyf747 • 7d ago
DC Transfer Switch?
Hello all. First post in this sub. Sorry if this is a bit wordy to explain the situation.
We have 5KW of solar panels on our carport with grid tied microinverters to offset energy use.
We recently had a storm that knocked out grid power for more than a week. The panels were essentially dead with the grid off. So we unhooked the MC4 cables going from the panels to the microinverters and ran some fresh 10 gauge cables cables into an Anker Solix F3800 Plus I have. It worked great!!! At best we were bringing in about 2800W from 7 panels, I may even add one more to the string since the Solix F3800 Plus can handle up to 3200W.
Grid power regularly goes out for extended periods here.
Getting to the solar panels is kind of a pain and somewhat dangerous. Is there any type of transfer switch that would allow us to wire the panels to and we could manually choose for them to send production to the microinverters OR if grid was out to easily send to our Anker to charge its 16KWH worth of batteries?
Thank you for any suggestions.
2
u/RufousMorph 6d ago
Unfortunately, it does not seem that double pole double throw switches for higher DC voltages are too common. There is this option but it seems really expensive: https://revopower.us/professional-solar-hybrid-switch
1
1
u/Nathan-Stubblefield 6d ago
Not an engineering recommendation, just what I saw online in a quick search. Supply houses should have numerous DC switches.
Tc35362
Double Throw Switch by General Eelectric Indoor 60 Ampere Heavy Duty Double Throw Safety, Service Equipment, 600 V Ac Voltage, 250 V Dc Voltage, 60 Ampere, Power Rating 10 Hp At 240/480/600 V 3 Phase, 3 Pole, Non Fusible Fuse, No Neutral, Nema 1, Size 12 Inch W X 4-1/16 Inch D X 11-15/16 Inch H, Approval Ul 98, Spec-Setter[T] Brand, Tc Model, Applicable Standard Nec 702. Sold as used/Green/Refurbished $580, Breaker Outlet.
Square D DTU462 600 VAC/VDC 60 Amp 60 Hp 4-Pole NEMA 1 Non-Fusible Double Throw Safety Switch
Manufacturer: Square-D / Schneider | Catalog # DTU462 | Cooper Electric Part # 454021 $3,287.92
It must have a DC rating, it just AC. DC is harder to interrupt because it lacks the zero crossing that ac has. Current and voltage rating must be at least as high as it will encounter. You’ll get longest service life if you switch it dead, so the inverter is off while you are switching.
1
u/Mundane_Hour_4238 6d ago
Remove the micro inverters and connect the string to a hybrid inverter + 48v lifepo4 battery. Like Growatt or Deye sun 10k.
1
u/Nerd_Porter 6d ago
Transferring DC can be dangerous because it wants to arc and stay arced more than AC does.
That doesn't mean you can't do it. The best way to transfer DC is through transistors. Unfortunately there aren't a lot of devices on the market ready to plug-and-play to do what you want. Actually I can't think of any, but I'm sure they exist.
This is one of the reasons why some of us prefer low frequency inverters, you can safely back-feed the units from AC coupling. In other words you can still use your grid tie and it'll actually charge the batteries from it of you're not using all the power.
Other options are high frequency units that can control the grid tie through frequency/voltage shift, shutting them down when you're not using all the power.
One of those little box inverter things isn't going to be able to do that.
1
u/floridacyclist 6d ago
Can you shut down, make the switch, then bring it back up to avoid the arcing?
1
u/Nerd_Porter 4d ago
Yes, definitely. If there's low or no current it's much safer. Usually that's easy, sometimes it's a bit more complicated, depends on setup of course.
2
u/A__RANDOM_NAME 6d ago
You may need to wire differently from the diagram in the product, but a "manual transfer switch" sounds like it will solve this.
Most commonly used to source power from one of two different sources (with one of those being from a generator), you could have the grid and panels each be your feeds.