I have a Emonpi with and arduino. I ordered the 100 amp current sensors and like everyone else in the US/Canada that has 200Amp services, they are too small. I have been searching high and low throughout the forum and was unable to comeup with an answer. Does anyone know which current sensors are compatible with the arduino wireless transmitter shield that are rated for up to 200 Amps?
Thanks in advance!
Colin
Hi Colin,
I’m in the US too. There’s a list of suitable subs here.
Unless you have a very large house, or more than a few large electrical loads (that run at the same time), you might find (even though you have 200 Amp service) that a 100 Amp CT will do the job.
There are multiple choices from four manufacturers (with links) on the page linked to above.
I’m in no way accusing you, but are you able to put your finger on why you missed the page that Bill linked to? The reason I ask is, there are discussions (that you might have stumbled across) concerning how all the information here is presented and indexed. We failed you, if you can tell us why it would be quite helpful.
No, the link worked fine. But I am unsure which one to use. As the current sensors that I have (the 100 amp ones that are available in the store) worked great. And I noticed that the output for those sensors was 0-50mA. I am unable to find 200Amp sensors that are 0-50mA. We recently moved to a new house and the electrical service is underground so I need to connect the current sensors to the feed wires in the electrical panel. On the old house, I was able to go up to the roof and connect the current sensors to the incoming feed as the utility wiring was smaller than in the house.
So where I am confused is if the current sensors are a “drop in” replacement for the YHDC sensors that are supplied by the shop (100A). And do they just need to be calibrated because they are now 200A instead if 100A. And if they need a change in burden resistors or not.
Also, being from Canada, I would like to avoid using a US supplier due to Duty, Exchange rate, etc and purchase within Canada. So if I knew exactly what signal the arduino shield was looking for, I could find a “drop in” replacement that is either exact or close and make the nessecary adjustments. Or I can find a cheaper one eBay. I just want to avoid paying over $50 per current sensor if I can.
I suppose it would be helpful that if you listed the current sensors that are compatible and what needs to be changed on the arduino shield to make it all work. Or maybe a step by step instruction on how to adapt to a different type of current sensor?
Or maybe I just missed this information…
Once again, thanks for your help!
Sorry, you misunderstood my question. I was asking why do you think you missed “learn” and the page that Bill pointed you at when you were searching and before you posted your question.
We thought we’d put all the information on that page, so maybe a second read will help.
Ideally, you need is a CT that gives a 50 mA output at whatever the maximum current is that you want to measure (plus a bit, but not too much, to give some headroom). It also needs to have a VA rating (seldom specified) sufficient to give you about 1.6 V at that 50 mA output current.
If you can’t get that exactly, then more or less anything will do the job, but you’ll need to change (or better if possible, add another resistor in parallel with) your burden resistor. So for example, if you choose a CT with a 100 mA secondary, you can add a parallel burden resistor to give the correct voltage across it, but if you have a 20 mA one say, you’ll need to remove the SMT burden and replace it with a higher valued one.
Don’t get a 0.333 V output one. A 1 V output will be better but not ideal as you’re only using ⅔ of the measurement range. And, unless you’re desperate, don’t get one with a 1 A or 5 A output, because you’ll have a high power and hot burden resistor, and that’s far from ideal.
If you’re in any doubt, post a short list of candidates and one of us will take a look.
I have found a couple:
Which one do you think is better?
Thanks for your help.
I think the 200 A SCT-023R (http://www.yhdc.com/en/product/900/) should be fine with the emonPi or Arduino (emonTx Shield?). Having a 50 mA secondary current, it will require no changes. All you will need to do is fit a 3.5 mm stereo jack plug (tip & ring only).
Check the hole size will accommodate your cable, and don’t screw the locating screws too tightly into the insulation. (And don’t wrap a strip of metal around the cable either to protect it unless you insulate it to avoid a single-turn short circuit!)
What size of burden resistor do I need for CT’s that have a 80mA secondary? Or what size do I need to add in parallel?
You need about 1.1 V for your emonPi, or about 1.6 V for an emonTx Shield running at 5 V, at your maximum load. If you say what those are, it’s easy to calculate.
I’ve had good results with the YHDC SCT019-000. They have a turns ratio of 6000 and are rated for 200A (I’m using a few of them in US 200A panels). With a 30ohm burden, the CT will develop 1V(rms) at 200A, which is 2.8V peak to peak.
These are usually available for less than $20 from someone on eBay. itead studio lists them for $15. They are available with and without internal burdens, so look closely at the offering. The iTeads are without. Hole size is 19mm (3/4"). Near as I can tell, these are pretty much the same as Magnelab’s with respect to linearity and phase shift - at much lower cost.
So I did the math and it appears that I need a 22ohm burden resistor.
The CT that I have has 2500 turns. So now I need to know what the burden resistor is on the Arduino Shield so that I can either add a resistor to the CT circuit or of I need to remove the burden resistor and put a new burden resistor in parallel with the 80mA CT.
Thanks for all your help.
The shield has a 33 Ω burden, so adding a 68 Ω in parallel (there are holes for a wire-ended resistor waiting) should give you the correct output (near enough - it’s 1% high but still within the tolerance of the 33 Ω burden fitted).
(That should give you a safe 180 A full scale reading, plus a little extra for headroom and component tolerances.)
Thanks! I have it all hooked up and it works perfectly! Thanks for all your assistance!
Itead page One-stop Online Shop For Smart Home, HMI Display, Airspy, Diy Kits l ITEAD STUDIO
shows zero units in stock. (at the bottom of the page)
and this page:
www.itead.cc/electronic-components/sensor/non-invasive-ac-current-sensor-sct-019-200a-max.html
shows the item as “retired”
Bummer. 15 bucks was a dynamite price!
Both versions are still available on flea-bay though.
I got a half-dozen from Itead a couple months ago. Their old website still lists it but sends you to their new store, which is where you found the “retired” indication. My take is that they have discontinued selling them because the market has driven the price so low it isn’t worth their while. It’s still listed on the YHDC website, and is listed on AliExpress for $7.98 - $11.29 with shipping. Takes awhile, but my experience has been good across the board dealing with China.
Not too shabby. The flea-bay seller has 'em for $11.26 and free shipping, so at least they’re still available at low cost.
I’ve had good luck with Chinese orders too. Haven’t made but a few of them, but they’ve all come through OK.
The 80mA ones that I got off of eBay are working really well. I did have to do a bit of tweaking in the Arduino firmware to get it to be more precise. It’s accurate even down to less than one amp. If you want to know what the numbers I put in the Arduino firmware let me know.
That’s fine. The Arduino input is subject to component tolerances - principally your burden resistors and the ADC reference voltage (the 5 V supply). Any inaccuracy in those, as well as the CT’s own tolerance, will affect the reading. This is the whole point of calibration.