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#197124 - 11/10/10 05:29 AM CT fun  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,103
Estero,Fl,usa
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]


Greg Fretwell

Tools for Electricians:

#197127 - 11/10/10 12:30 PM Re: CT fun [Re: gfretwell]  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
What happens if you load the CT with a 10 or 50 ohm load?


#197132 - 11/10/10 03:27 PM Re: CT fun [Re: LarryC]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,103
Estero,Fl,usa
100 ohms drops the voltage on a 60w load from .5v to about .25v so I imagine 10 ohms would just crush it.


Greg Fretwell

#197148 - 11/12/10 04:10 AM Re: CT fun [Re: gfretwell]  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,217
SI,New Zealand
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.

Last edited by Trumpy; 11/12/10 04:16 AM.

Let's face it, these days if you're not young, you're old - Red Green grin

#197158 - 11/12/10 02:36 PM Re: CT fun [Re: Trumpy]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,103
Estero,Fl,usa
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.


Greg Fretwell

#197159 - 11/12/10 02:47 PM Re: CT fun [Re: gfretwell]  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
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?


#197162 - 11/12/10 06:55 PM Re: CT fun [Re: LarryC]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,103
Estero,Fl,usa
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.


Greg Fretwell

#197164 - 11/12/10 10:21 PM Re: CT fun [Re: gfretwell]  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
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?


#197165 - 11/12/10 10:51 PM Re: CT fun [Re: LarryC]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,103
Estero,Fl,usa
Yes I just want to see if things are drawing current. (is it on or not)


Greg Fretwell

#197174 - 11/13/10 12:27 PM Re: CT fun [Re: gfretwell]  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
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


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