CT Clamps?

[slowbutsure]

Hi,

Can anyone simply explain to me the purpose of CT clamps in some inverters. Some people say they are essential but most inverters don't have them. What is the difference between two Hybrid inverters, one that has a ct clamp and one that does not?

Thanks.

 

[kommando]

A CT clamp is one method to measure the amount of energy being exported, another method is RS485 feed from a meter next to the grid feed also measuring export. You need one of these methods to control or eliminate export, some inverters take both, others do either one or other. If you don't tell your inverter when is being fed into the grid it has no way to control its output to match whatever grid export limits you are given.

 

[slowbutsure]

A CT clamp is one method to measure the amount of energy being exported, another method is RS485 feed from a meter next to the grid feed also measuring export. You need one of these methods to control or eliminate export, some inverters take both, others do either one or other. If you don't tell your inverter when is being fed into the grid it has no way to control its output to match whatever grid export limits you are given.

Thanks, appreciate that.

A question. If you remove grid power from the house circuit breaker box, and only supply the inverter with grid power. And in the inverter settings switch off export. Do you then still need a CT? Im still confused why some hybrid inverters do not seem to use either of the functions you mention above, but they do have internal settings to switch off exporting to the grid.

 

[kommando]

Suggest you ask the sellers where the info comes from if the inverter has no CT or meter connected.

 

[timselectric]

A question. If you remove grid power from the house circuit breaker box, and only supply the inverter with grid power. And in the inverter settings switch off export. Do you then still need a CT? Im still confused why some hybrid inverters do not seem to use either of the functions you mention above, but they do have internal settings to switch off exporting to the grid.

The hybrid AIO has internal measuring.
The purpose of external measuring is to let you export from the inverter, but not to the grid. If you want to feed loads between the two.
If you had the grid feed to a panel and then to the inverter.
You would put the external measuring device between the grid and the panel.
So that you could export to the panel, but not to the grid.

 

[slowbutsure]

The hybrid AIO has internal measuring.
The purpose of external measuring is to let you export from the inverter, but not to the grid. If you want to feed loads between the two.
If you had the grid feed to a panel and then to the inverter.
You would put the external measuring device between the grid and the panel.
So that you could export to the panel, but not to the grid.

I didn't understand that, it didn't make any sense to me.

 

[timselectric]

I didn't understand that, it didn't make any sense to me.

I'm sorry, I can't think of a simpler way to explain it right now.
If I do, I will post it.

 

[Ampster]

A question. If you remove grid power from the house circuit breaker box, and only supply the inverter with grid power. And in the inverter settings switch off export. Do you then still need a CT?

An inverter always need some measurement of output so they will always need a CT. Most are installed internally and many have the ability to use external CTs to measure current at other places in the system.

 

[ricardocello]

@slowbutsure Let’s say you have an external power/current/energy device that has external CTs on the main panel feed.
(In my case, this is a Carlo Gavazzi EM530 with 5A CTs on my incoming 200A service panel.)

Let’s assume the AIO is capable of sending power to its load (output), but also back to its input.
This is a necessary feature for backfeeding the grid, so the AIO has a bidirectional input anyway.

If all of your loads are on the output, then external CTs are not needed, because the power measurements can be made internally in the AIO.

But let’s say some big loads are not on the output side of the AIO, because there isn’t enough inverter power to run them.
They are on the input side of the AIO, but after the main panel CTs.
(In my case, this is my HVAC and water heater.)

Well, when not inverting, it is still possible to push solar or battery power back to the input side of the AIO.
For those of us who want to use PV as soon as it is generated, this is great, the battery can be smaller.

So how does the inverter know how much power it can push back through the input without going back to the grid?
That’s where the CTs and external power/current/energy meter come in.
The AIO can determine how much power to push back through its input without pushing back to the grid.

Note: I have a Victron system which does all this, but it isn’t an AIO, I had to design it.

 

[rpdom]

On my Solis hybrid (grid tied PV with battery) inverter the CT is used to measure grid import/export. This is so the inverter can work out how much power is needed from PV and battery to cover the house load, and if any is spare to charge the battery. Basically it tries to keep import to zero.

It needs an external clamp on the main feed from the grid to measure that.