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CT fun

Posted By: gfretwell

CT fun - 11/10/10 09:29 AM

Warning this is a tiny CT, measuring tiny currents. Don't fool around with those big things you see in a CT can!

I was playing with one of those small CTs on a lamp holder

[Linked Image]

My original intent was to get some ideas of what to look for if I was integrating this into a project. Short answer is there is plenty of current if you drive into about 1000 ohms and it scrubs off most of the noise.
You get around a tenth of a volt with a 14w load, .5v with 60w load and 1.2v with a 100w load (into 1k ohm). That doesn't seem very linear but I didn't plot it.

The interesting thing for me was the wave form.

14w seems pretty sinusoidal

[Linked Image]

As the wattage (and output voltage of the CT) increases it starts affecting the wave form.
100w is pretty warped

[Linked Image]

When you plug in a CFL things really start getting weird

[Linked Image]
Posted By: LarryC

Re: CT fun - 11/10/10 04:30 PM

What happens if you load the CT with a 10 or 50 ohm load?
Posted By: gfretwell

Re: CT fun - 11/10/10 07:27 PM

100 ohms drops the voltage on a 60w load from .5v to about .25v so I imagine 10 ohms would just crush it.
Posted By: Trumpy

Re: CT fun - 11/12/10 08:10 AM

Greg,
What sort of 'scope are you using there?
It seems to suggest Texas Instruments, but I'm not sure about that.
It certainly looks like it has the wood over my Tek-tronic 40MHz dual trace 'scope I have here.
I have wanted a new DSO for some years, but are they all the stuff they are made out to be?
Could I justify an NZ$4000 'scope, is the question I ask myself.

Sorry for the thread-jack.
Posted By: gfretwell

Re: CT fun - 11/12/10 06:36 PM

Tektronics 465.

If I had waited around a little I probably would have got a 485 DM44 when the IBM office was going away. That is really far more scope than I have any use for. I don't really need the capabilities of the 465 either but it is a nice display. It hasn't been calibrated for 16 years so I wouldn't trust it for any serious work. Some of the pots are getting a little cranky too.
Posted By: LarryC

Re: CT fun - 11/12/10 06:47 PM

Originally Posted by gfretwell
Tektronics 465.

It hasn't been calibrated for 16 years so I wouldn't trust it for any serious work. Some of the pots are getting a little cranky too.


From the layer of dust on the cover in third picture, pots getting cranky would not be unexpected. smile

So what are you doing with the CT?
Posted By: gfretwell

Re: CT fun - 11/12/10 10:55 PM

Quote
From the layer of dust on the cover in third picture, pots getting cranky would not be unexpected. smile



I ripped a wall out in that room and cut out a piece of the concrete floor. It was a might dusty for a while.

Quote
So what are you doing with the CT?


I am looking for a way to see if things are running around the house remotely.
Posted By: LarryC

Re: CT fun - 11/13/10 02:21 AM

Originally Posted by gfretwell

Quote
So what are you doing with the CT?


I am looking for a way to see if things are running around the house remotely.


You are just doing does it draw some current or not? Not precision measurements, correct?
Posted By: gfretwell

Re: CT fun - 11/13/10 02:51 AM

Yes I just want to see if things are drawing current. (is it on or not)
Posted By: LarryC

Re: CT fun - 11/13/10 04:27 PM

How are you going to monitor them?

Visual indicators, multidrop communication scheme like RS-485, LONWorks, dry contacts, or what?

Nosey engineer wants to know. smile
Posted By: gfretwell

Re: CT fun - 11/13/10 07:46 PM

Initially I just want to light a LED but from there I can do anything. I do have a DiDo card in a PC that can look at these things.
Posted By: LarryC

Re: CT fun - 11/13/10 08:51 PM

Running twisted pair from each location back to a central point?
Posted By: gfretwell

Re: CT fun - 11/14/10 06:44 PM

Yup, probably CAT3 for things coming from the garage, simply because I have a 6 pair cable in place already. (actually 2 but one is in use). I would like to know if my well pumps are running among other things.
Posted By: LarryC

Re: CT fun - 11/14/10 10:59 PM

If the output from the CT could turn on the LED of an optocoupler, a single ended power supply could provide a go/no go DC output to a digital I/O card or even an unused parallel port.

How would you determine what is proper operation?
Posted By: gfretwell

Re: CT fun - 11/15/10 12:35 AM

If this thing really gets going I will be using my DIDO card into an old PC.
I also have some plans for a parallel port data collection deal.

I am not really sure what "normal" is until I actually run it a while. I am eventually trying to assemble some real time load data to get an idea what I would need for a battery backed up solar array

It is mostly just a "gee whiz info" project I am doing in my spare time.
Posted By: gfretwell

Re: CT fun - 11/16/10 05:31 AM

This is the CT device I came up with to get the CT in a regular box and get the low voltage on the outside.
This 3/4" adapter is potted solid with epoxy. The resistor is inside.

[Linked Image]
Posted By: LarryC

Re: CT fun - 12/10/10 08:47 PM

How is the load monitoring project coming along?
Posted By: gfretwell

Re: CT fun - 12/11/10 03:02 AM

I have been building cabinets for a few weeks. The CT deal is on the back burner.

http://gfretwell.com/ftp/tambour%20door.jpg
Posted By: mikesh

Re: CT fun - 12/15/10 09:45 PM

Scope? I have a fluke scopemeter I might like to part with. From memory it is a 97? 2 channel. Around 40mhz? 1 of Fluke's original scopemeters. I was taking an electronics course i never finished and got caught up in the whole electronics stuff so I bought it off Ebay for $700. Definitely works great but can't recall if i also replaced the rechargeable battery or not.
Not really looking to hijack the thread.

Cheers
Posted By: Trumpy

Re: CT fun - 12/18/10 02:11 PM

Greg,
Did you build that cabinet?
I like it, guys that can work with timber get my vote, every time! thumbs

BTW, Mike, the Scope-meter Fluke were selling is really only a gimmick.
I owned one for about a year and let's be honest, as "ruggedised" as they say it is, it wasn't that great.
It doesn't like being dropped at all, especially when it's so hard to hold in your hand (too top heavy).
Mine died a death when an apprentice I had working for me dropped it in a tank of water.
So much for the IP-65 (NEMA-6) rating it was supposed to have.
If I really needed a scope, I'd be using the one I own, it's done a LOT of work out in the field.


{Edit: Greg I was looking a bit closer at your pics and thought why the hell has Greg got a bottle of water in his cabinet?.
I blew it up and saw you probably shouldn't drink that, unless you're having a really BAD day!} grin
Posted By: gfretwell

Re: CT fun - 12/18/10 08:14 PM

Yup I made the cabinet. The tabour door is laid up pieces of screen mold on some kind of upholstery fabric I got at the fabric store. I really need to buff the sides of the cabinet out and shoot another coat of poly on it tho.


That is Dial body soap. (Sams Wholesale Club) The soap is OK but the pump on the bottle is great. It screws right into a motor oil bottle or the bottle for lower end grease (boat). I have found lots of uses for the old ones and they seem to last forever. Not like the pump that comes in the lower unit fill kit that falls apart the first time you use it.
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