Current transformers

[Jeff Millard]

I was wondering if anyone else had decided to attempt current transformers and milliammeters to read the load of the circuits used in our displays. I have 6 small 5000:1 CTs that I have run 20amps through continuously for an hour. I read 4ma from the secondary while testing.

Doing it this way means you don't have to physically connect to the circuit. It's the same thing as a clamp-on ammeter. While the ratio I'm using is extreme, there are common CTs with ratios more suited to the 0 to 20 amp range we would need. It would be necessary to create a multiplier scale to account for the ratio, or maybe make a new graphic for the back of the meter.

I have ten dedicated 20amp circuits that I would have to monitor, and it would be very easy to add a bunch of cheap panel meters to my case. Adding the CTs wouldn't be difficult, they would be placed near the GFCI outlets on the hot leg.

There are two ways to read from these CTs. They can either be run directly to an ammeter or you can place a resistive load in series with the CT and read millivolts across the load.

An even more complicated method would be to add a A/D card and graph it with software...

Any thoughts?

Jeff

[Photovor]

I recently got a part from Allegro that's a current/hall effect sensor. Senses up to 100A.
http://www.allegromicro.com/en/Products/Categories/Sensors/currentsensor.asp

Comes in a funny TO-220 package looking thing. Could easily interface it to a PIC with an A/D. You'd have to solder or use terminals to hook it inline with your circuit.

I haven't yet had the chance to test it, but it looks pretty straight forward- but I'll let you know!

[Trepidati0n]

We use these in aerospace quite a bit...very nice devices.

[Jeff Millard]

So it's essentially a CT circuit in a chip. With all the power in series with the source and load. Not bad, but a little costly. My CT's were scrap, and I have now increased the qty to 30... I've been watching eBay for a A/D card from MC so I can go the shunt/millivolt route. It's not something I'm scrambling to do, but I'd like to have a piece of software that I could bring up on the monitor that would give me close to real time load values on as many things as I can. That way if I ever do change my mind about the news media... I can boast the ability to show what the actual consumption is during a live show. There's no reason why that couldn't lead to something that would tell me the cost of the display as it adds up too...

Just more bells and whistles for the most part...

Jeff

[Trepidati0n]

So it's essentially a CT circuit in a chip. With all the power in series with the source and load. Not bad, but a little costly. My CT's were scrap, and I have now increased the qty to 30... I've been watching eBay for a A/D card from MC so I can go the shunt/millivolt route. It's not something I'm scrambling to do, but I'd like to have a piece of software that I could bring up on the monitor that would give me close to real time load values on as many things as I can. That way if I ever do change my mind about the news media... I can boast the ability to show what the actual consumption is during a live show. There's no reason why that couldn't lead to something that would tell me the cost of the display as it adds up too...

Just more bells and whistles for the most part...

Jeff

Not really a CT in a chip but rather an open loop hall effect sensor. The picture on link below pretty well explains how it works :)

http://www.lem.com/hq/en/content/view/161/153/