AC Current Measurement

[Robert Roland]

On Fri, 30 Aug 2019 04:16:48 -0700 (PDT), jrwalliker@gmail.com wrote:

I have seen the innards of a meter at the UK factory where it was
being made.

Big Clive also took a UK one apart:

https://www.youtube.com/watch?v=G32NYQpvy8Q

It looks like the current sensor was resistive there as well.
--
RoRo

 

[Phil Allison]

Robert Roland wrote:

---------------------

Big Clive also took a UK one apart:

https://www.youtube.com/watch?v=G32NYQpvy8Q

It looks like the current sensor was resistive there as well.

** May well be that such meters are required to measure the DC component of any load current - something a current transformer cannot do.

I have a B&D hot air gun that draws 6.7amps at 240VAC on full setting, but drops in series at half power.

It makes any toroidal supply transformers on the same circuit growl when I use it !!



...... Phil

 

[Phil Allison]

Phil Allison wrote:

--------------------

Correction:


" I have a B&D hot air gun that draws 6.7amps at 240VAC on full setting,
but drops A DIODE in series at half power. "



..... Phil

 

[Michael Terrell]

On Friday, August 30, 2019 at 2:17:40 PM UTC-4, Whoey Louie wrote:

IDK, good points. I didn't mean to necessarily buy the kind of bulky
power meter that plugs into a meter base. Those, I agree, not clear
that most or any would display amps or even anything other than Kwh.
But some of them probably have some kind of interface to transmit
real-time data, what with all the solar folks wanting to monitor
their solar array and such.

I had pointed him to Ebay and something like this is more what I had
in mind:

271952136069

That's the item number, just put that into the Ebay search bar.
The link was a mile long. It's $13 and they've sold 3100 of them.

You don't need the entire link for Ebay. Edit from this:

https://www.ebay.com/itm/100A-AC-LCD-Panel-Digital-Power-Watt-Meter-Monitor-Voltage-KWh-Voltmeter-Ammeter-/271952136069

To this:

https://www.ebay.com/itm/271952136069

By removing the description.

 

[Harry D]

On Tuesday, August 27, 2019 at 2:59:10 PM UTC-7, Harry D wrote:

Let's say we have +/-20 Amps of AC current flowing at 250V into (Source) or out of (sinking) a node. (The node is the grid and we can either supply or sink current to that node). Measuring current is easy but how do I determine which direction it is going. Am I sourcing or sinking?
If I sense the differential voltage across a 1mR sense resistor, limiting my power loss to 0.40 watts, and trying to resolve a 100 mA current change in direction, my CMRR would be -128 DB, not easy to do. There has got to be a better way.
Cheers, Harry

Thanks for all your help. I was looking for a simpler solution to a difficult problem. If Tesla needed net-metering, then AC might not have been such a good idea. I will bite the bullet and go with a net metering chip that must battle the 135 dB CMR problem strait up.
Cheers, Harry

 

On Wednesday, 4 September 2019 20:41:22 UTC+1, Harry D wrote:

> Thanks for all your help. I was looking for a simpler solution to a difficult problem. If Tesla needed net-metering, then AC might not have been such a good idea. I will bite the bullet and go with a net metering chip that must battle the 135 dB CMR problem strait up.

Why do you need to have 135dB CMR? Why don't you would optoisolate the
output of the measuring cicuit and have the sensitive circuitry at
mains voltage?

John

 

[John Larkin]

On Wed, 4 Sep 2019 15:23:56 -0700 (PDT), jrwalliker@gmail.com wrote:

On Wednesday, 4 September 2019 20:41:22 UTC+1, Harry D wrote:

Thanks for all your help. I was looking for a simpler solution to a difficult problem. If Tesla needed net-metering, then AC might not have been such a good idea. I will bite the bullet and go with a net metering chip that must battle the 135 dB CMR problem strait up.

Why do you need to have 135dB CMR? Why don't you would optoisolate the
output of the measuring cicuit and have the sensitive circuitry at
mains voltage?

John

There are isolation amps. And transformers.

Or float the metering circuit on the shunt.

A 135 dB CMRR amp is pretty much impossible.