Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

switching between main AC and sine wave inverter

Status
Not open for further replies.
GastonRafaelMelo

GastonRafaelMelo

Newbie level 6
Joined
Oct 6, 2021
Messages
11
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
176
Hi to all (again),
I desing a sine wave inverter and its working as suppose to do. Now I want to know how can I do to switch betwwen AC mains and the inverter output. As far as I can see is using AC relays and according to the current use. Is there other method? could you point me to some references?
Regards
GAstón
 

Sort by date Sort by votes
Switching is simple if your generated power only stays in your house.

It's vital to arrange the relay so it never connects your generated power allowing it to go out to the grid... regardless whether a blackout is on. The reason is that it might electrocute linemen working on wires close by or distant.

There are people who sell their power to the electric company, however that immediately makes everything complicated.
 

Upvote 0 Downvote
Thanks for your reply, using relay I must take care of the phase of my inverter and the grid difference? IF the grid is down I want to connect only vitals in my house, but I will like to use the grid to charge my batteries like the UPS but sadly I can't find any circuit of references.
thanks for your reply
Gastón
 

Upvote 0 Downvote
Hi,

you talk about switching "vitals" from grid to inverter when grid is down?

If so:
1) When grid is down ... what phase do you have? ;-)
2) a relay is slow in switching ... thus you can´t "synchronize" it to 50Hz/60Hz phase. (in a meaningful and reliable way)

Klaus
 

Upvote 0 Downvote
KlausST said:
1) When grid is down ... what phase do you have? ;-)
Click to expand...
OK. So you're saying it is not important to measure phase? What about in case you have reactive loads?
what about surge current in case of switching inverter back to main AC?

Thanks again for your help on this questions.
Gaston
 

Upvote 0 Downvote
Hi,

I´m saying: If grid is OFF you can´t measure phase.
GastonRafaelMelo said:
What about in case you have reactive loads?
Click to expand...
Yes - What about it? What´s your concern?

Every time you swith ON an electrical device you do this without caring about phase.
Or do you care about phase when you switch ON a light bulb or a PC or a fan?
That´s the same that your relay does: switching from 0V (grid OFF) to 230V AC (inverter)

GastonRafaelMelo said:
what about surge current in case of switching inverter back to main AC?
Click to expand...
Again: What´s your concern? You switch from 230V to 230V.

As already mentioned: you never connect your inverter to the grid. Do you?

You have to care about phase when you connect a synchronous generator to the grid...but that´s a complete different story.

Klaus
 

Upvote 0 Downvote
KlausST thanks again for your reply. So if I use a AC relay with coils connected to main AC, when the main AC is going down the contactor will switch to inverter automatically. I have to over dimension the current in the AC relays?
As far as i know the relay doesn't switch immediately (it takes a couple of ms to perform switch) and at that moment the electronics connected to the GRID is not OFF its working thats why i was asking about phase in case of reactive loads. How a UPS handle this?
The inverter is not going to be connected to the GRID, only power my house but I don't want to burn some sensitive electronics.
Thanks again KlausST
Gastón
 

Upvote 0 Downvote
Hi,

Show a sketch. It´s not clear how you want to connect everything.

Klaus
 

Upvote 0 Downvote
KlausST thanks. Something like this (attached picture below).
 

Attachments

  • inverter_mainsAC.png
    inverter_mainsAC.png
    21.4 KB · Views: 121

Upvote 0 Downvote
Hi
GastonRafaelMelo said:
I have to over dimension the current in the AC relays?
Click to expand...
Why? It´s just a standard situation for the relay. Switching a load ON/OFF.

GastonRafaelMelo said:
and at that moment the electronics connected to the GRID is not OFF its working
Click to expand...
Focus on the relay contacts:
* Grid is OFF, grid voltage is zero.
* relay contact current is zero. If you don´t think so, please tell us. We don´t know the behaviour
* then it switches over to supply the load from the inverter. This is just a standard situation. Typical load inrush current (Indeed I´d rather expect less inrush current)
If you expect something different, please tell us.

GastonRafaelMelo said:
How a UPS handle this?
Click to expand...
Again: A standard situation. Load becomes connected to the inverter.

GastonRafaelMelo said:
The inverter is not going to be connected to the GRID
Click to expand...
Please be sure to use the correct rely to keep on local safety standards. In the EU you need some safety relays with "forced" contacts.

GastonRafaelMelo said:
I don't want to burn some sensitive electronics.
Click to expand...
Again: I just see a standard situation. Nothing special.

Klaus
 
Upvote 0 Downvote
Disconnecting the mains from a load and then later connecting your inverter is simple, but,

swapping over fast so that appliances are not affected i.e. essentially do not see the changeover is much more complex

for the latter you need to synchronise the two waveforms and have the amplitudes approx the same too,

then you need a high speed break before make relay ( or SSR's ) to perform the switching

given the nature of you question the latter part may be outside your knowledge at the moment.
 

    thannara123

    thannara123

    Points: 2
    Helpful Answer Positive Rating
Upvote 0 Downvote
GastonRafaelMelo said:
like to use the grid to charge my batteries like the UPS
Click to expand...

Charging 12v batteries can be done by an ordinary car battery charger. Often it has a switch to choose Manual (full Amperes) or Automatic (tapering charge followed by trickle charge).

To assemble my home backup power system, I purchased a combination inverter-and-charger. I did things manually at separate times, rather than hooking it all up for full-time automatic operation. Anyone would say my setup was haphazard.

Our main breaker panel had a robust changeover switch to disconnect mains. Everything I did required that I remember the correct steps to disconnect and reconnect things. There were times I was careless due to fatigue.

Does your building have a changeover switch? If not then you'll need to custom place extension cords to vital appliances.
 

Upvote 0 Downvote
Many low- and medium power systems, e.g. for computers are powering the load through the inverter instead of using of using a changeover switch. This avoids even minimal voltage drops and possible risk of switch shorts. Mains is either supplying the low voltage or high voltage DC bus. Power demand of your application hasn't been mentioned yet. A pump as shown in post #9 has usually no problems to accept a short interruption.
 

Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top