This non-invasive current sensor (also known as a “split core current transformer”) can be clamped around the supply line of an electrical load to tell you how much current is passing through it. It does this by acting as an inductor and responding to the magnetic field around a current-carrying conductor. By reading the amount of current being produced by the coil, you can calculate how much current is passing through the conductor.
The data sheet for this device specifies a maximum of 60A so it should handle your max of 45A OK. There is a figure for accuracy and linearity with a 10Ω load resistor which according to the published graph produces an output across this resistor of 300mV at 60A. The ratio of through current to output current is 30A / 15mA. I suppose you could adjust the value of this resistor to suit your measurement range. The specs are only quoted for a 10Ω resistor but I don’t think increasing it a bit would do much. Don’t go too far though or it probably would make a difference. Probably safer to use an OP Amp to adjust the output to where you want it to be.
Cheers Bob
Hi Jeremy
Forgot to welcome you before. Welcome.
I just deleted the last post. It was mainly completely incorrect. new version.
I have been doing lots of thinking about this device and similar situation I had many years ago (it was RF but the principle is the same) which I will briefly describe later.
Consider this
You have a transformer with a single turn primary and at this stage an unknown turns secondary terminated with 10Ω.
Now a terminating resistor on the secondary will be reflected back into the primary with a value relating to the square of the turns ratio. Going from the low turns side you would multiply the low side impedance by turns ratio^2 and going from the high turns side to the low you divide the high side termination value by turns ratio^2. Thus with a 1:1 transformer the resistance seen at the primary is equal to the resistance terminating the secondary.
Determine the turns ratio. From the data sheet 30 A primary = 15mA secondary. I make this 2000:1
The secondary termination is 10Ω so the reflected impedance to the primary will be
10 / 2000^2 or 4,000,000 which is very low but will appear as a resistance in series with the primary. While this resistance is very low in this instance IT IS THERE. This is quite important as will be demonstrated below.
To my dilemma of quite a few years ago.
25W SSB transmitter. Problem no output power. Won’t go into fine detail but I could find nothing wrong. The front panel power indicator lamp was out but with no power I did not expect it to be on.
Fortunately I had access to the engineer who designed this thing. He asked if I had checked the incandescent indicator bulb. No I had not.
Result, bulb blown, replaced and lo and behold unit worked perfectly.
Egg on face. The reason. This was a coil of many turns wound as a core and was fitted around the antenna feed wire, similar to the present situation. With the open circuit bulb this was an open circuit or infinity reflected back into the one turn primary resulting in a very high resistance (open circuit) in series with the antenna wire. Result no output power.
This is one of the lessons one tends to remember.
Getting back to this discussion. UNDER NO CIRCUMSTANCES operate this device WITHOUT the 10Ω termination. I would not predict the outcome but if it has anything to do with mains circuits the result could be spectacular. OR nothing might happen at all except for nil or very low volts getting to the destination. I am not going to try it to find out but think about it and be careful.
Hope this helps and sorry about the post I just deleted.
Cheers Bob
Thanks Bob.
My use for this is a line side I/O monitor for my solar and controlled load. Thankfully I have a reference for expected values due to it being monitored via an app.
Why 45A? Because ausgrid have upped the solar output limit per phase to 10kW.
The plan is to put one of my pi3’s to good use as a power monitor/logger.
I really wasn’t expecting such a detailed response, so thanks again.
Cheers, Jerome.
Hi, I need help with this thing…Seems it should be simple, but, I am not an EE! I just want to detect when a domestic pressure pump is running. Got a test setup with the active split out… but there seems to be no documentation about earth/ring/tip…which should be used? And what load resistor? I started out with 12 ohm… just because I had one. Putting a CRO across the tip, ring and earth shows some very weird waveforms… and frequencies! Also tried making a half-wave rectifier with a IN4004 in series with said 12 ohm (also tried 100 ohm… that failed, I guess too high?) … things just got more confusing!
I am running my test on the bench with a 1kW blow heater running to simulate my pump. Still fairly low amps, but should surely be easily detectable??
Bottom line is… I just want a reliable voltage I can read on my Pico… pump running… or off.
Any help appreciated! Suggestions re alternate sensors welcome…
Your 1kW heater will be drawing about 4A Also the output from this device will only be about 20mVAC.
Do NOT use any other load resistor other than 10Ω. read my previous posts above for reasons.
The diode is in the wrong place if in series with the 10Ω resistor and anyway it needs about 700mV to turn on so even at 60A this would not operate. Probably you are seeing strange pics on the scope.
I would look at some of the Hall effect devices. Minimal circuit disruption at only a few mΩ. These will give an AC voltage output relative to AC current centred around half VCC. Look at the data sheets. They are your friend. I think Core stock some of these already mounted on break out modules in varying current capabilities.
Cheers Bob
PS: If this set up is associated with 240VAC GET AN ELECTRICIAN.
You might be better off investigating a lower voltage pressure switch or detector. Then you might need a plumber.
Yes. DO NOT USE without the 10Ω load. See above for reasons.
Cheers Bob
Be aware the ground clip on the scope is probably connected to mains earth unless it is battery operated and the case is floating.
Hi trevor
Well I finally found out what a “SS101990059” is. It would be a great help in the future if you could provide a link or a Core product number as at first glance this description means absolutely nothing.
After looking at this data sheet please disregard the “Yes” above re tip and ring connection. This one has connection to tip and sleeve apparently. I was only going by audio convention. Chinese logic perhaps. Anyway you have only 3 connections, find out for yourself, you should be able to measure the coin resistance across 2 of them.
Back to this product. The Core page has a couple of useful links. One to the data sheet which doesn’t say much. Another refers to connecting to an Arduino which is much more informative and should supply all the info you require including the offset applied to get the AC signal all on the positive side of zero volts and how to do it. There are also calculations for 3.3V systems if needed.
Remember DO NOT just clamp this device around a complete mains cable. It MUST be around 1 wire, either active or neutral, but not both.If around both they will cancel and you will see nothing.
What you do with this level shifted sine wave signal when it gets to your controller is up to you
Cheers Bob
PS. In reply to your original question. Yes this one would be better as it is a lot more sensitive. Max 10A compared to Max 60A.
Sorry about that, Bob… I thought quoting the Core product code would make it easy to find! Yeah I could have just put a link in… noted.
And yes, this device actually gives the pins used on the jack… nice.
I already have my test setup with the thing clamped around the active conductor only… not an issue When it is installed in situ I will obviously do the same there.
Lastly (?) I looked up my pump specs… it doesn’t actually give a power rating (yup…) only the ref to max current, which is probably just a blanket statement. I will call the supplier (Grundfos) tomorrow, as I suspect the operating current draw is way less than 10 amps… so it may be even better to go for the 5 Amp version here Assuming that it will be more sensitive,
End of the day, as I said, I only need a basic “ON/OFF” indication for my planned purpose.
Really appreciate your taking time to help me out.
I must apologise Trevor.
that number you quoted I see now IS the Core product number. It is just an unusually long one and it was not a link so I did not associate it with Core.
That is what you have to allow for. The start up (or inrush) current will be more that the running current.
I don’t know how an Arduino (or other similar) is going to process the shifted AC signal as an On/Off situation but I imagine you have something in mind.
I don’t know how an Arduino or RPi handles a negative (WRT Ground) signal as I haven’t seen anything officially published about it. Jeff105671 in a previous post said it should be avoided and the application notes for this device connected to Arduino have gone to the trouble of shifting so ALL of the sine wave is positive WRT Ground so there must be something in it and avoiding that happening is not a bad idea. Saves potential trouble. So my advice is follow the application note and level shift to half Vcc as in the sample schematic.
Cheers Bob
Noted… and I just found on my invoice the pump is rated as 0.9kW… which I figure is around 3.75 Amps. So 5 should cover it… if I ignore inrush. I guess the 10 AMp version is safer.
I’ll have to study the Arduino notes re shiting voltage up, see if I can manage that without breaking anything
Hi Trevor
There are some links on Core page for this product you should probably read. Especially the middle one where it explains level shifting and the reasons why.
Please note that the documentation included with the product page include references to a different type of sensor. The SS101990059 is a ‘voltage ouput’ type, so the section on the burden resistor (the 10Ω resistor you have mentioned) can be ignored.
Yep… I’m aware of that. It was one of the reasons I liked this product… inbuilt load resistor, and just outputs a voltage between 0 and 1. Can’t get any easier than that to interface to my Pico GPIO pin, huh? I have ordered one.
I am a bit suspicious my SEN-1105 is not behaving itself, albeit my current draw is pretty close to its lower limit. On my DSO, I see very short spikes at 50Hz… this across a 12 ohm load. When I have a little more time, I’ll post a pic of the trace.
Please check the output connections (Tip, Ring, Sleeve) as my assumption of tip and ring might not be correct. The 10A one has the connection at tip and sleeve and I base my guess on audio convention in the absence of this info in the Data sheet.
It is easy to check, you should be able to measure the coil resistance of about 250Ω across the correct connections.
You are probably seeing a small capacitive differentiated version of the proper signal. It should be a reasonable (as reasonable as the mains voltage) sine wave. The amplitude might be only a few mV.
Cheers Bob
Jeff is correct, the 10A-1V device wold be a voltage output device with a built in burden resistor.
It would seem the only current output in this range is the SCT-013-000 100A device.
There is a voltage one with the “V” suffix after the “000”.
Cheers Bob
There is one strange figure.
The Core specifications for the 5A device says
" Build-in sampling resistance(RL): 372Ω"
This seems a bit high, more like the coil resistance alone which makes me suspect that this one might be a current output, It is marked differently to the others in the same series also.
Can someone please confirm.
