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Automatic AC transfer switches are pretty cool devices. A look at what they do, a practical demo, teardown, and then reverse engineering to explain how it does it.
Bonus look at how my automated home battery backup system will work.
00:00 - Automatic AC Transfer switch
02:05 - How I'm powering my home fridges from a battery
06:30 - What does an AC Transfer switch do?
09:27 - Huh? How do you do the automated battery power backup?
12:36 - Practical AC Transfer switch demo
15:57 - Teardown
18:44 - Reverse Engineering Schematic
25:46 - BONUS 2nd design teardown!
Forum: https://www.eevblog.com/forum/blog/eevblog-1500-how-an-ac-automatic-transfer-switch-works/
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By YTB

19 thoughts on “Eevblog 1500 – how an ac automatic transfer switch works”
  1. Avataaar/Circle Created with python_avatars pocoapoco2 says:

    Is there some hysteresis to the micro switches that control the main switch solenoids, or are they relying on momentum to complete the switch change?

  2. Avataaar/Circle Created with python_avatars G N says:

    This switch is a GEYA W2R and is available from Taobao for $20 US

  3. Avataaar/Circle Created with python_avatars gweilo8888 says:

    Your "better quality" one still has totally obvious typos and nonsense Chinglish on it. "Rated opertional [sic] voltage"? "Bclose" and "Aclose"?

  4. Avataaar/Circle Created with python_avatars Pieter S says:

    just check your earth connection from utiluty and genset. some genset are centre tap depending on origen.

  5. Avataaar/Circle Created with python_avatars Samuel says:

    I've been using that ats with my off grid system switching a subpanel for over a year now, all perfect, my computer doesn't even shut down when the power fails.

  6. Avataaar/Circle Created with python_avatars Frank Gennari says:

    My guess is that the switching time varies depending on where in the sine wave the switch happens. If it's near a zero crossing it will take longer because the solenoids may not pull the rod until closer to peak power. So you would get some ~10ms (half cycle) variation in the timing.

  7. Avataaar/Circle Created with python_avatars PushyPawn says:

    All made by different companies, in the same Chinese city, all working from stolen intellectual property.

  8. Avataaar/Circle Created with python_avatars mofoq says:

    neat tho….fridges tend to keep the cold pretty well (provided you don't open it)

    it got to 109°F (~43°C) last week and power failed.
    It was out for 7.5hrs
    My fridge and the food in it was fine since I did not dare open it (items in the freezer were still quite frozen when the power came back)
    That was really impressive to me

    still looking for a backup battery setup just in case 😉

  9. Avataaar/Circle Created with python_avatars Optron Cordian says:

    These micro switches are bothering me. They tend to fail without warning. And, it can fail in a way that its contact remains closed. That way a coil would remain constantly powered and will burn. Hopefuly not causing a fire!!!

  10. Avataaar/Circle Created with python_avatars NeverTalkToCops1 says:

    Daiyve, Daiyve, Daiyve, this lash up may be frowned upon by Aussie government. Your refrigerators must never disconnect from the grid, even for 20 milliseconds. It's all on page 278 of the International Internet of Things Treaty, IIoTT.

  11. Avataaar/Circle Created with python_avatars bumelant says:

    Still waiting for MacGyver project update…

  12. Avataaar/Circle Created with python_avatars azpcox says:

    Was very impressed with the portrait DaveCAD. Indeed rare and it looks like you have plenty of portrait cycles left based on the thickness of the DaveCAD Pad. DCP

  13. Avataaar/Circle Created with python_avatars sven dongle says:

    Wouldnt the solenoids have opposite polarity?

  14. Avataaar/Circle Created with python_avatars Wong David says:

    A good ATS should be 'make before break' to provide uninterrupted power source.

  15. Avataaar/Circle Created with python_avatars slypig24 says:

    I found that very interesting, to see how it works. Hope to see the whole system working soon. Will you have an under voltage output alarm, from your battery inverter?

  16. Avataaar/Circle Created with python_avatars ToomsDotDk says:

    How much power does the relay use by it self to hold the solenoid ?

  17. Avataaar/Circle Created with python_avatars slypig24 says:

    For your 3 fridges, I have seen someone make a 3 relay box, to prevent all 3 loads starting at the same time. It's a very low chance of this happening, but with thermostats opening & closing, it can happen.

  18. Avataaar/Circle Created with python_avatars nigozeroichi2501 says:

    Big Clive took a similar unit to bits a while back, but it used a motor, much smother but the transfer time is longer

  19. Avataaar/Circle Created with python_avatars Bob Bakley says:

    I remember BigClive tearing down a version of one of these.

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