How to block AC current

[fca]

hi
i mean with DC if you put diode on the positive line you prevent current to come back ...
is there any device that that do this with ac current ?

thanks

[justjed]

Since AC is "alternating", i.e the voltage swings from positive to negative in a cycle, I'm not sure what you're asking.

You can block 1/2 of the cycle using a diode. Take a look at rectification.

A coil will offer impedance to an AC signal, depending on frequency. But I don't think this is what you're asking about.

[fca]

i want to use a grid tie inverter but i want to be sure that no power flows out of that circuit to the others...
thanks

[Docedison]

What is a "Grid Tie Inverter?

Doc

[fca]

is a device that you connect a powersource solarpanels or wind turbine and invert the dc power to ac synchronizing the sine wave with your existing grid suppyer ..
a good example http://www.mastervolt.com/solar/products/soladin-600/soladin-600-es-versie/

thanks

[Docedison]

Ok now I understand you are trying to control a wind or solar power installation. I fail to see where you need to block anything with that device. I would connect it EXACTLY as the Mfr suggests and leave it alone, if your connections aren't correct you could do a lot of damage. Be Very careful with anything that connects and or supplies power back... That Circuit breaker that is inline is a pretty big one. Lots of AMPS available. I do know why a diode is used with a PV system but that simply prevents the solar cells from discharging the battery, usually it is a schottky diode rated at about 4 X the available charge current from the PV panels.

Doc

[xolroc]

In the spirit of answering the question that's asked, though, I think what you probably want is an optoisolator or an AC relay.

[jackrae]

Commonly called a reverse current relay.  Current direction is determined by the "difference" in voltage between the source and the sink. This senses the direction of current flow and trips out if the current tries to flow from sink to source.   After that, the source voltage is monitored and when sufficiently high to ensure current flows in the correct direction (source to sink) it closes the circuit.

[teding]

@fca Soladin wil not work if no grid is connected.
because soladin needs to sync with te grid before its starts its inverter.

[fca]

Hi I know that It needs poweR from grid, what i want is that power that is generated don't  flow back outside of that circuit but power from the grid can flow in..

Is this possible with ac ?

[teding]

No, you can't prefent power flow from the inverter to the grid.
But why do you want to do that ?

If you want to contect a arduino to a soladin, I wrote this lib
https://github.com/teding/SolaDin

[Docedison]

You can sense the current without much 'flowback' by using a transformer... That will limit it to the ratio of the transformer. What I failed to understand is, the usual phase sensing circuitry draws no real power from the line, the line is used to synchronize your inverter to line frequency and phase. This is a process that draws milliamps from the line.

Doc

[tjbaudio]

No, you can't prefent power flow from the inverter to the grid.
But why do you want to do that ?

It is a life safety thing. In normal operation a grid tied  inverter like his unit uses the grid as a huge storage battery.  During a power outage (lets say a car hits the pole out side his house and knocks the wires down) the unit MUST stop sending power to the grid.  When the power company worker kills the feed to the line so he can fix the wire it must be dead.  If the inverter continues to back feed the line will still have voltage on it.

Looking at the literature his unit already has that feature built in. There is no need for the OP to build it in.  In fact I would bet any thing like this he adds to the install would void any warranty or life safety guarantee already in place.  If he wants to add a battery backup it should go down stream of this unit.

[Docedison]

That is a much better explanation than mine was I couldn't see any device that could feedback any power in that manner, If you lost the line phase information you must disconnect to damage your own equipment. It didn't occur to me that it could be otherwise for example If the power company did a load drop or a switchover on the grid happened due to operator load balancing or any other interruption of the line happened you should drop your equipment off the line until you could with a small delay determine correct frequency and phase. Since it about 16.6mS/cycle I would think it would probably need at least 100 mS to be assured that frequency and phase information were correctly measured and tested. If not an additional wait for line stability.

Doc

[MarkT]

Surely all the grid-tie stuff is legally required to be correctly certified and connected by a certified professional in most countries ??