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how to measure the direction of a.c. power flow
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soldar:
With strictly resistive loads it should not be difficult to do a rough indication by taking a semicycle and seeing in what direction the current flows during that time.

The problem starts when you have reactive loads. Now you can have energy flowing back and forth so you need to do a total measurement and see in what direction is the net flow. Not straightforward or simple.

I wonder if the old electromechanical KWH energy meters would turn backwards. If I remember correctly they probably did but had a ratchet to prevent it.

In that case an old meter could be used to detect the direction of energy flow.

I have a crate full of them. Maybe One day I can do some tests.
richard.cs:
The mechanical meters without ratchets turn backwards, the ones with usually rotate backwards up to one turn of the disc and then stop. Some types have flags that drop to indicate that this has happened.
soldar:
Come to think about it, if volume is no problem, a quick and easy way of detecting power flowing out would be to have some switch in place of the ratchet so that when the disk is trying to turn back it is activating a switch. That would be very simple to do using an old meter.
rgody:
An easy way is to use a known load ( for example "test load" of 220V 220ohms) in conjunction with an ammeter measuring total current to the house .
The test load should be connected for a few seconds only to "see" the ammeter.
If you connect test load and the current in ammeter arise, your house is in "load" mode. If you connect the test load and current decrease, your house is a source.
If you know whether your house is a load or a source, then you can calculate the power just measuring current with no test load connected.
I this idea you just need a contactor, a known resistance, a TC and a simple circuit that just need the current signal to calculate power as a source or load.
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