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Static Transfer Switch (STS) Recommendation?

earthvu

New Member
Joined
Feb 2, 2025
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9
Location
Creede CO
I have two (redundant) banks of panels/controllers/batteries/inverters that I switch between to feed my home's service entrance (when one set of batteries gets low, I switch to the other). An Automatic Transfer Switch (ATS) works fine, except the switching delay disrupts power to the house, which is tough on appliances and sensitive electronics (not to mention flashing all the device clocks).

Anyone know of an affordable 120v Static Transfer Switch (something that switches in 4-5 ms)? They use these in data centers, hospitals, etc., but I can't find one appropriate for a residential application. I'd consider a UPS if I could find one that was fast enough and could switch back-and-forth between the two banks, but I haven't found that either. Seems like an obvious product, so I'm sure someone here has cracked it :-)
 
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Switching to another supply with an arbitrary phase change, can cause issues with your electronics and/or large currents to flow.

Why do you want to keep the two system separate? Why not run them in parallel?
 
Switching to another supply with an arbitrary phase change, can cause issues with your electronics and/or large currents to flow.

Why do you want to keep the two system separate? Why not run them in parallel?

@wpns My understanding is that I can't operate the two inverters in parallel because of the phase mis-match issue, and there isn't a "safe" way to sync the outputs.
 
@wpns My understanding is that I can't operate the two inverters in parallel because of the phase mis-match issue, and there isn't a "safe" way to sync the outputs.
Well, you didn’t tell us what kind of inverters you had, so it was marginally possible that you would be able to run them in parallel.
 
Or remove one inverter and combine the battery banks? Seems like you're doing something more complex than needed, but we don't have many details.
For all the reasons that have been hashed out in a dozen places in this forum, I'd rather not mix battery types. Plus, the objective here is to build redundancy. I've been completely off-grid for 30+ years and have learned (the hard way) that everything eventually fails. At the worst possible moment. The house is in the mountains at 9500', an hour from the nearest stoplight, only accessible via snowmobile in winter, so downtime for me is measured in weeks, not hours.
 
Based on the use case and the method of operation, it sounds like BOTH systems are undersized as "one set of batteries" shouldn't be getting low.

Not mixing brands of identical chemistry and cell count is exclusively BS. Not sure what parts of this forum you're talking about. If I knew about them, I'd give them a piece of my mind. The only reason to not mix brands are 1) if you're a battery manufacturer, and you want to sell more of your batteries by saying they shouldn't be mixed with others, and you should replace them all or 2) You're OCD, and your medication isn't strong enough.

IMHO, Join the two systems at the battery bank, i.e. combine the bank and allow both systems to draw. Switch between them on a schedule at a time of your choosing where disruptions can be minimized. You lose ZERO redundancy and likely improve reliability and longevity as you are using the batteries less aggressively overall.

I'm pretty sure it's a sin to have available battery capacity unused.... especially when the battery in use is being depleted.
 

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