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Author Topic: I need fast switching between 2 mains powers 220v  (Read 1700 times)
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snowman
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« on: March 16, 2018, 04:31:40 16:31 »

Hi firends,

Imagine 2 different mains power outlet. They are not connected to each other except neutral line. Lets say they are A and B. Both 220v.

I have a computer. runs with 220v. Its connected to one of these power outlets, say outlet A.
When I press a button, This computer will be disconnected from A and will be connected to B.
But it must be very fast so computer won't understand it was unplugged and plugged.

Now.. I googled and learned that offline and line interactive UPSs' switching time is about 10 to 20ms. Which I understand within this little time computers and other devices cannot detect voltage drop.

So I looked into fast mechanical relays but they are very very slow. Then I read about contactor. One pair of normally ON and one pair of normally OFF contact would be enough. But I suspect they would be slow too.

And I planned to solid state relays. As my total power is under 30A, I could find suitable SSRs. So here's my plan. I'll have 2 SSRs, their inputs connected together with NOT gate, so if one is OPEN, other would be CLOSED. Perfect. they response time measured with nanoseconds which is more than enough for me.

What would you say ?
How would you do it ? Any suggestions from my masters ?

Best.
« Last Edit: March 16, 2018, 07:31:01 19:31 by snowman » Logged
FTL
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« Reply #1 on: March 16, 2018, 11:20:02 23:20 »

I have a question about your setup:

Are the two 220 mains in phase? Are they always guaranteed to be so?

For instance, they might not be if one were the mains, and the other was from a generator or a UPS supply.

If they are in phase and from the same power source, would it be feasible to use a make before break relay? That might not be legal since these are likely fed from different breakers, or even different panels, and I'm sure the cross-connect (even very temporarily) would be against code.
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snowman
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« Reply #2 on: March 17, 2018, 02:09:09 02:09 »

there are different sub cables come with one thick cable. in other words they actually from same source. one is for my shop, other is for the shop above us, third one is for the shop next to us. all 3 shops are ours. its a very strange setup but also a very old building Smiley
So, there would be no sync problem.

But for curiosity, what happens if they are out of sync ? And if they are in sync would my setup work ?
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bigtoy
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« Reply #3 on: March 17, 2018, 10:51:59 10:51 »

Personally I wouldn't do the make-before-break. Presumably he wants to do this to create an auto fast switchover if one mains feed fails. In that case, a make-before-break would end up backfeeding the failed mains circuit & everything on it, which would likely exceed the current rating of his switch (solid state relay by the sounds of it).

Regarding being in sync, that would be ideal but shouldn't be a requirement. All mains-connected devices (like your PC power supply) need to be able to withstand the transients that can occur on the mains, so this switchover should simply appear as another transient.

The hardest part of this project is going to be monitoring the "primary" mains, to make the decision to switchover to the "backup" mains. You'll need to define a threshold voltage at which you want to switchover, and you'll want a small amount of filtering so you don't falsely trip. One way to do this while minimising the amount of mains voltage touching you need to do, is use a simple stepdown transformer. For example use a 220V to 12V transformer. Then monitor the output of the transformer - if it drops to (say) 10V then switchover. Just be careful not to have too much capacitance on the output of the transformer; otherwise it'll take you too long to detect the voltage has dropped.
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snowman
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« Reply #4 on: March 17, 2018, 12:40:26 12:40 »

That's exactly what I'll do. I'll simply switch over the mains power lines. I don't worry about detecting voltage drop, I can design it, fine tune it. The only question was would solid state relays be fast enough and would this design work. As I see your answer is yes. Also datasheets say so about SSR relaying times.

I thank you for your answer my friend.
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metal
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« Reply #5 on: March 17, 2018, 03:47:18 15:47 »

okay, here is a nice idea:

Use MCU to do the following tasks:

1. Detect both AC1 and AC2 TRIACs outputs, not the mains input, you must use interrupts to avoid delays
2. Once you break AC1 by MCU, wait for MCU to detect that AC1 has gone then connect AC2, and vice versa

You can use this circuit to detect and sync MCU and TRIACs, for the break-before-make to avoid disasters.. You might have this old building using more than one phase. You might also want to look at MOSFET SSRs, very nice performance.
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pickit2
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« Reply #6 on: March 17, 2018, 07:36:19 19:36 »

there are different sub cables come with one thick cable. in other words they actually from same source. one is for my shop, other is for the shop above us, third one is for the shop next to us. all 3 shops are ours. its a very strange setup but also a very old building Smiley
So, there would be no sync problem.

But for curiosity, what happens if they are out of sync ? And if they are in sync would my setup work ?
Uk code for such a building would be 3 phase 240V AC. you could get 480V across two phase.

You need to check this out.
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Parmin
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« Reply #7 on: March 17, 2018, 08:17:57 20:17 »

I would use USP, with relay or SSR on the input line, this way regardless of the switching speed, the computer would get constant supply.
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snowman
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« Reply #8 on: March 18, 2018, 12:12:53 00:12 »

Uk code for such a building would be 3 phase 240V AC. you could get 480V across two phase.

You need to check this out.

Its 380v.

Posted on: March 18, 2018, 06:10:54 06:10 - Automerged

I would use USP, with relay or SSR on the input line, this way regardless of the switching speed, the computer would get constant supply.

I agree, ideally its true. But I cant place UPS in design.
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Sideshow Bob
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« Reply #9 on: March 18, 2018, 05:38:51 05:38 »

I may sound like a nitpick here. But I would be very careful with any hobbyist solution connected to mains and left unattended. You say your power requirements is under 30A. But to say handle 15 to 20 A would require proper cabling, mounting and so on, in order to be safe. Reading from your post you do not seems to have the proper skill to do this. So your contraption may end up being a very potential fire hazard. And in worst case if the assurance company finds out that your contraption has caused a fire. They can and will reduce your payment, or even refuse to pay anything.
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enzine
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« Reply #10 on: March 18, 2018, 06:39:36 06:39 »

I fully agree with the friend Sideshow bob.
What You wants to do is neither easy nor free of dangers.
I have worked in the past on the design and validation of big ups (100kVA and more) and the static bypass block had many problems.
 I list only a few that come to mind.:

1) A protection circuit is necessary to prevent the inverse return of energy, ie in case of SSR failure the current must be prevented from flowing from the second generator to the first (possible danger: an operator who is convinced that there is no power in the first circuit can undergo electric shocks)

2) in case of doubt on the synchronism it is necessary to provide a "hole" of a few ms otherwise the load may suffer, in case of switching in opposition phase, a double instantaneous voltage (VDR can explode, any motors may have large overcurrents, etc)

3) it is necessary to insert extra-rapid fuses with breaking capacity appropriate to the electrical networks to which you connect to prevent risk of fire.

I hope my advice will help you understand that you pay close attention to these things.

Ciao
Hello
« Last Edit: March 18, 2018, 08:52:46 08:52 by enzine » Logged
snowman
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« Reply #11 on: March 18, 2018, 07:20:48 07:20 »

Thanks for your concerns my friends. I never did this kind of switching but perfectly designed and used high voltage devices before. So don't worry. I over simplified the design to explain setup easily but of course there will be some fail-safe options, sensors etc to avoid danger Smiley
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sfiga69
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« Reply #12 on: March 18, 2018, 03:58:50 15:58 »

if what you are looking for is a device that manually or automatically switches between two AC sources (i.e between main source and UPS backup source), you can look for a static transfer switch (STS).
It can be automatic ATS or manual MTS .
They are used in CEDs when 2 separate power sources are available and the equipment to be powered has only 1 power supply.
if you look for google 'static transfer switch' you will find many examples

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snowman
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« Reply #13 on: March 19, 2018, 12:40:50 00:40 »

thanks my friend, I didn't know that kind of thing exists and wondering why not anybody else needed it. I just didn't know the name of product. Now I2m relieved Smiley And the schematics looks like my dreams.
Thank you very much. May the success with you.
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metal
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« Reply #14 on: March 19, 2018, 11:44:13 11:44 »

yea... I have this installed at the work place, how did I forget it :s

It is used to switch between mains source and generator to the UPS!

But you need to check the switching time..
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solutions
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« Reply #15 on: March 20, 2018, 06:56:28 06:56 »

Thanks for your concerns my friends. I never did this kind of switching but perfectly designed and used high voltage devices before. So don't worry. I over simplified the design to explain setup easily but of course there will be some fail-safe options, sensors etc to avoid danger Smiley

Note that the danger is not to you or your equipment (both are expendable since it's YOUR butt that made the mod), but of you energizing the line back to the point where a power company person thought he was working on a circuit that he had disconnected from the grid.

A power transfer switch ensures you never can backdrive power out of the building (which I think Enzine sort of said with his point (1) )...make sure you cannot (it's code here, I don't know if it is where you are but I don't see why it wouldn't also be a requirement where you are) with whatever scheme you decide to use.
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M@X77
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« Reply #16 on: March 21, 2018, 07:03:29 19:03 »

ST producs a discrete device an AC switch, they are based on logic and triacs, depending from power you have few solution, try to look ACS series:
http://www.st.com/en/thyristors-scr-and-ac-switches/ac-switches.html

to safety it's important that you create an interlock that doesn't permits to have the 2 switch on simultaneously
the best way is the gates it's powered by the  same line that control if the line falls also the swtich turn off
the logic could be power from two lines between two diodes
« Last Edit: March 21, 2018, 07:08:59 19:08 by M@X77 » Logged
snowman
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« Reply #17 on: March 22, 2018, 01:40:18 01:40 »

Thank you.

I found devices for motors, computers, electronics etc. Basically this transfer device is "a kind of SSR" with lots of safety equipment. I need to be sure about safety and take precautions against malfunctions, and its done.

okay here is a question. I found a product called "automatic transfer switch" and claims it does the job.


https://www.aliexpress.com/item/4P-63A-MCB-Q6-63-4P-type-Dual-Power-Automatic-transfer-switch/2028405861.html?spm=2114.search0104.3.23.4bb532f8yKPlor&ws_ab_test=searchweb0_0,searchweb201602_3_10152_10151_10065_10068_10344_10342_10343_10340_10341_10696_10084_10083_10618_10307_5711215_10313_10059_10534_100031_10103_10624_10623_443_10622_10621_10620,searchweb201603_25,ppcSwitch_2&algo_expid=be3b7b7e-26a7-48f8-a627-b24e3df92c6d-3&algo_pvid=be3b7b7e-26a7-48f8-a627-b24e3df92c6d&transAbTest=ae803_5&priceBeautifyAB=0


also there are other equipment much more expensive.

Can a mechanic device (the link above) does the job ? Will it be fast enough ? or should I just use try-and-see method. It won't be fast as SSR of course but its a ready to use product and I won't need to design a circuit, boxes etc. I'm old school and mechanic switches when playing with mains power always comforts me. You know there are just contacts, no electronics.

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M@X77
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« Reply #18 on: March 22, 2018, 05:49:18 05:49 »

I'm not shure that this dispositive is quite fast that is needed, surely in the world exist mechanical switch that close contacs less than 10ms are used into power plant and use preloaded springs, but surely are not the solution for you, I can suggest to used electronic switch
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zielpunkt
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« Reply #19 on: April 14, 2018, 12:39:16 12:39 »

I believe that often the simplest solutions are the best and, in your case, relays are still the best option. In a quick search, I found this model from Phoenix Contact, but there are many others with very fast response times below 20ms (DigiKey is great for parametric searches). Their prices are not low, but they seem quite adequate for what you intend to do:

https://www.phoenixcontact.com/pxc-oc-itemdetail-pdf-web/eshop?lineItemType=LineItem&UID=2834054
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Cyberrat
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« Reply #20 on: May 07, 2018, 04:09:58 04:09 »

I would forget such silliness.

Just get a UPS, power the computer from that.
If you then need to power the UPS constantly simply use a contactor/relay capable of handling twice the current (so it is longer lasting) and have a simple detection circuit on both 220v inputs and switch over when one fails.

Ensure you use adequate fusing on both inputs and that there is no possibility of power from one being transferred to the other. I.E. use a 2PCO relay with the UPS circuit on the common.
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Manuel
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« Reply #21 on: May 07, 2018, 05:05:26 05:05 »

SSR with a proper driving circuit is a good solution!

CHECK:
SHARP for 3KVolt insulation
S108T02 Series
S208T02 Series
Max 10ms

SHARP for 4KVolt insulation
S216S02
Max 10ms

Add both Snubber circuit to output for Surge absorption and reversal diode on SSR opto-in !

 Grin
Take note about the following effect:
http://www.omron-ap.com/service_support/FAQ/FAQ02237/index.asp

take care,
Manuel.
« Last Edit: May 07, 2018, 05:20:19 05:20 by Manuel » Logged

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snowman
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« Reply #22 on: May 07, 2018, 02:23:13 14:23 »

I would forget such silliness.

Just get a UPS, power the computer from that.
If you then need to power the UPS constantly simply use a contactor/relay capable of handling twice the current (so it is longer lasting) and have a simple detection circuit on both 220v inputs and switch over when one fails.

Ensure you use adequate fusing on both inputs and that there is no possibility of power from one being transferred to the other. I.E. use a 2PCO relay with the UPS circuit on the common.


"Computer" term is to simplify the project. Actually its computer based but consumes too much power. Of course if I could use UPs that would be wonderful. But I cannot. For some reasons that I cannot overcome.

Posted on: May 07, 2018, 02:20:51 14:20 - Automerged

thanks Manuel, I'll keep it in my mind.

best.
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techneo
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« Reply #23 on: September 01, 2018, 02:34:19 02:34 »

I think there could be two topologies:-

  1. Use a heavy UPS as already indicated in the forum because the detection time between AC1 going OFF and switching ON AC2 would be in milliseconds and corresponding power consumption will also be limited.

  2. Utilization of solid state relays like the one provided by Crydom (about 40A) here

  https://eu.mouser.com/ProductDetail/Crydom/DP4RSC60E40?qs=sGAEpiMZZMu%252bisyu8Ze4rx%2f9huAtjBi2r42HHBtldoc%3d

   The change over topology may vary, but AC1 has to completely go OFF and then AC2 has to be switched ON. Had a same instance with me, in which i had to see a lot of damage... Wink


-Techneo
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