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CT sensor purchase fail?


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#1 iostream212

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Posted 15 July 2012 - 07:58 PM

After reading the cool posts about dryer automation i thought this week i would take a stab at it. I could not find on eBay the sensors mentioned in the original tutorial/write-up, so I settled on a different sensor. Once received I immediately started testing the sensor. Much to my dismay all this sensor does is output a little voltage if power is running through the monitored cord. We are talking fractions of milliamps in a/c. So did I fail or is there a way to use this sensor with an elk zone? If no go can someone suggest any other sensor?

Product link: http://www.ebay.com/...=item1e70195e8e

Thanks.

#2 jpmargis

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Posted 15 July 2012 - 10:07 PM

The spec sheet says a 30 A load current results in a 1 V output from the sensor. You need a sensor which will produce about 7 V at whatever current your dryer draws. So I would say you failed. That's what happens when you don't check the specs first!

I'll also bet that you are running both current carrying conductors through the sensor. Try just one.

Edited by jpmargis, 15 July 2012 - 10:13 PM.


#3 znelbok

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Posted 15 July 2012 - 11:41 PM

Not sure what you are connecting it to, but you are really looking for a current switch.

What is the average current that the dryer draws wen running?

Based on that find a CT that is close to that range. The CT is an analog device and will output a voltage/current relative to the current being measured.

Now 1V may be fine if you can detect the difference between on and off. (0V and 0.8V where 0.8V represents that dryier running). If not you need to find a different CT or a black box that will convert the 0-1V to something you can use.

And as stated, you cant put the CT around the cable, the total current flowing will be zero (one core has current flowing one way and the other core has the current flowing the other way, thus zero total). To use a CT you need to split out a core and just run that through the CT.

If you have only 15A total, you can loop it through the CT twice so that the CT will see 30A max and get better resolution. The output will also be doubled, but then you scale it (by half) to get the true value. In your case, you are only interested in on or off so scaling is not an issue.

Mick

#4 Work2Play

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Posted 16 July 2012 - 01:17 AM

Hey iostream - I think I have an extra of the current switches you're looking for (I bought a couple from another member of this board) and I live in the same neighborhood as you, just around the corner... If you want I can dig one up - I paid about $35 for them so that's all I'd be looking for.

#5 iostream212

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Posted 16 July 2012 - 10:19 AM

Oh a current switch... major fail. :wacko: Thanks for the information. Live and learn! Work2Play I am interested in buying your sensor. PM sent.

#6 MobileMe

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Posted 17 July 2012 - 02:11 PM

I had the same issue with the CT sensor. I found this little breakout board and it worked great. http://www.sparkfun.com/products/8883

#7 iostream212

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Posted 17 July 2012 - 08:02 PM

Thanks for the info mobileme. To clarify you used the same sensor and got it working with this breakout board?

Edited by iostream212, 17 July 2012 - 08:04 PM.


#8 Work2Play

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Posted 18 July 2012 - 02:16 AM

iostream - I got your PM... but I'd only have one to spare so if you're looking for several, you might be happier finding the one that works for you and getting them all the same.

#9 iostream212

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Posted 18 July 2012 - 02:23 AM

iostream - I got your PM... but I'd only have one to spare so if you're looking for several, you might be happier finding the one that works for you and getting them all the same.

Thanks for the update. Back to eBay I go. Take 2.

#10 Work2Play

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Posted 18 July 2012 - 09:56 AM

I did a quick ebay search and saw a bunch from Trane that had adjustable setpoints - and I looked at suppliers of new ones, but they wanted more like $80/each.

#11 MobileMe

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Posted 18 July 2012 - 10:55 AM

This is the CT sensor that I used with the breakout board...

http://www.seeedstud...l?cPath=144_154

There are adjustment screws to get the right levels. The board is basicly an adjustable optamp. I had gone to the trouble of getting everything I needed to make one from scratch, then I found the breakout board. I was a little mift to say the least. I think I'm going to take a different route when monitoring power from now on.

#12 Rupp

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Posted 18 July 2012 - 10:01 PM

Here are the ones I use and they work well for TV's, and my washing machine.
http://www.crmagneti...CR3100-P75.aspx

#13 Work2Play

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Posted 19 July 2012 - 12:57 AM

Here are the ones I use and they work well for TV's, and my washing machine.
http://www.crmagneti...CR3100-P75.aspx

He needs a current sensing switch that provides relay closure; the linked product is not a switch but a Current Transformer, so it'll have the same problem as the originally purchased one in that it provides an analog voltage reading only.

#14 iostream212

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Posted 21 July 2012 - 11:40 AM

Settled on sensor off eBay made by logical devices inc. model ribxgta. Arrived last night. Works great so far. It was cheap too... did an offer of $15 per and seller accepted. It is adjustable and calibrated easily. Did a test run on my toaster and viola! Notification when toast is ready. (That is if I want toast in my wiring closet). :wacko: Attached File  uploadfromtaptalk1342888808773.jpg   69.53K   21 downloads

#15 BraveSirRobbin

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Posted 21 July 2012 - 12:09 PM

That's a good find. I made an offer just to play around with one!




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