Branch Circuit Monitoring

[rowlandsw]

Hello,
I am looking for cheap current sensors for a Branch Circuit Monitoring project I am wanting to put together for my home. I am completely new to these kind of projects, so I don't have a good grasp on suppliers, etc...

All I need is a voltage to come out of a sensor that is proportional to the amount of current flowing through the current.

I have found several of these, but the all seem, to me at least, to be rather expensive. I am looking for something in the $1-$5 range, since I need 30, and about $200 is all I can devote to a hobby project right now. Most of the ones I have found have been between $20 and $50 EACH!
Any advice is much appreciated!
Thank you

 

[kchriste]

Have you tried DigiKey? They have a **broken link removed** for apx $5.02 in 25 lot qty.
Some other suppliers you might want to check:
Mouser Electronics - Electronic Component Distributor
US - Electronic Components Distributor | Newark.com

 

[rowlandsw]

Thank you. I did check DigiKey, but didn't find that item in any of my searches, they have so many products, and these things seem to go by so many names, I guess I didn't enter the appropriate search terms. I even got on an online chat with them, and the only thing they offered me was about $40.
I will search there for some higher amperage transformers as well, since I want to monitor all of my circuits, and my well, water heater are 30A, my heatpump is 40A and the backup heat for the heatpump is 60A.

 

[rowlandsw]

Ok, I think I will use some of those CT's from DigiKey, so here is my next question.
There seems to be an unlimited amount of products that I could use to interface with these devices.
Does anyone have any recommendations on what products would work the best. I will be polling every so many milliseconds, and want to read what the voltages are from the multiple CT's.
Again, this is my first stab at this kind of project, so please excuse my ignorance, I am doing this mainly to learn, and maybe do something useful at the same time.
I think I am starting to suffer from "information overload" when I am searching for these items.
I am a software/database developer, so I think I can handle the programming aspect of it, but I have no experience with interfacing with anything other than the standard PC interfaces (keyboards, drives, printers, that sort of stuff). Once I get to a point where I can read these values, using a PC, I can start having fun with it.
Any advice is much appreciated.
Thanks,

 

[kchriste]

Have a read of this document. While it uses a microcontroller, the section entitled PRINCIPLES OF MEASUREMENT will give you an idea of what is needed.
You can also use an IC designed for Kwh measurement and not use a CT at all:
https://www.electro-tech-online.com/custompdfs/2009/01/51565a.pdf

 

[rowlandsw]

For that circuit, it looks like I would need to build one of these for each circuit (that I want to monitor), correct?

 

[kchriste]

Correct. You would need a MCP3905/6 for every branch. The CT is better because it totally isolates the circuit from the line where as the MCP3905/6 circuit is connected inline. I mentioned it because it was another option to a CT.
For safety, and since this is a hobby project, a CT is the better option.