current sensor,  transducer - Page 1
Forum section: electronics / beginners

author: J4e8a16n
author_rank: Regular Contributor
timestamp: June 27, 2015, 12:47:09 pm
content: Hi everybody,I am looking around for a tutorial showing how to use current sensor(see attachments). Even though I found one on Digikey, there is no 'how to use it' :-/http://www.prc68.com/I/JouleThief.shtml#CCI found this ... wich does not really seem to be the samehttp://www.interferencetechnology.com/the-hf-current-probe-theory-and-application/When I put my Joule Thief on scope I want to know the current flowing from emitter to ground. It seems to me that the multimeter ( between emitter and ground) interfere with the circuit.I tried to built one temporarily. Is it the way to use it?How about this?http://www.ebay.co.uk/itm/Hantek-CC-65-AC-DC-Current-Clamp-Meter-Multimeter-with-BNC-Connector/271544767995?_trksid=p2047675.c100013.m1986&_trkparms=aid%3D555012%26algo%3DPW.MBE%26ao%3D1%26asc%3D30773%26meid%3Dd654e7e24e424a4986370bd71e53eb17%26pid%3D100013%26rk%3D6%26rkt%3D15%26sd%3D230837571744JPDaviau

author: PSR B1257
author_rank: Frequent Contributor
timestamp: June 27, 2015, 02:18:42 pm
content: QuoteYou have to either conect a certain resistance (which is usually specified) to the secondary side an measure the voltage drop accros it or directly to an ampere meter. Do not operate it with the secondary side floating or connected to a high impedance (i.e. DMM in volt-range)QuoteThe current is most probably too low anyway for such a transformer. It's rated current is 70A.What current do you expect?QuoteNot uncommon. They have (depending of the partucular model) a quite high voltage drop (up to 300mV for instance). A circuit operating at 1V will not tolerate this.Quote35$ seems to be suspiciously low, for the spec's they claim.Have you ever heard about Dave's µCurrent?

author: SeanB
author_rank: Super Contributor
timestamp: June 27, 2015, 02:33:48 pm
content: You can use that, with it terminated into 50R, either the scope terminator or an external resistor. Not going to be easy to read though, you will see around 10VAC at 70A primary current, so at 1A the voltage on the scope will be around 160mV.If you use an external 100R resistor ( with the 1M scope input impedance), you will get roughly double those figures. You can also use more turns in the primary, using 2 turns doubles the voltage on the output across the resistor, but increases the inductance.The circuit you propose with a 30 turn secondary will also work, and if you use a small toroid with good permeability and low loss it works quite well, and has been used often. If you can wind 50 turns or 25 turns then the turns ratio and a 50R termination makes the math easier on calculating current, as it is a simple conversion.Just be careful as the terminating resistor does dissipate current, and as well the CT does introduce some phase angle in the primary side as it abstracts energy.

author: J4e8a16n
author_rank: Regular Contributor
timestamp: June 27, 2015, 10:19:51 pm
content: Quote from: PSR B1257 on June 27, 2015, 02:18:42 pmYes. I have the first batch model of uCurrent. It won't it interfere with the circuit?And I will try the clamp model described by SeanB)_

author: J4e8a16n
author_rank: Regular Contributor
timestamp: June 27, 2015, 10:25:16 pm
content: Quote from: SeanB on June 27, 2015, 02:33:48 pmIs the interference of that kind of measure more important than the use of uCurrent?Thanks for your attention.JPD

author: PSR B1257
author_rank: Frequent Contributor
timestamp: June 28, 2015, 06:53:51 am
content: QuoteEverything you put additionally in a circuit will (more or less) interfere with it. IIRC the shunt resistance in the highest range is 10mOhm. Therefore the interference is rather small (which is exactly wherefore this unit was designed).

author: SeanB
author_rank: Super Contributor
timestamp: June 28, 2015, 07:52:19 am
content: Only problem is the lead inductance, which will make a joule thief stop working, or it will change the frequency of operation or how it oscillates. You will need to have a minimal lead length for it to work.

author: J4e8a16n
author_rank: Regular Contributor
timestamp: June 28, 2015, 01:15:48 pm
content: Hi,Here are some results.There are 25 turns on the wire from the emitter to ground.There are 5 turns and a 51 Ohms resistor to the oscilloscope : 12.4 p-p primary 2.48 secondary : 5 timesIf I plug uCurrent between the 30 turns and ground I read 95mA.If I plug it between the two ends of the five turns (no resistance) I read 2.4 mA.Wel what are the odds...)Thanks for reading.JP