# Does the emonTx Shield need an actual Arduino? **URL:** \ **Category:** emonTx\ **Tags:** 3-phase, arduino, emontx\ **Created:** [14 November 2016 15:35 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198 "2016-11-14T15:35:11Z")\ **Posts on this page:** 20\ **Page:** 6
**Author:** ![pb66](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/pb66/32/27_2.png) [@pb66](https://community.openenergymonitor.org/u/pb66)\ **Post date:** [22 December 2016 17:08 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/102 "2016-12-22T17:08:12Z")
> [@Dave](#): > > Ahh TBH I had bought some smaller CTs from China and I wasn’t expecting to have the “all frills safety” thing and I was going to include one in the jack plug. Are they supplied with a flylead or are they CT’s that you need to add wiring too? If it’s the latter you would be better off putting the TVS or Zeners at the CT to protect in the event of wiring breaks or the jack coming off etc. ---
**Author:** ![fabiopbx](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/fabiopbx/32/1934_2.png) [@fabiopbx](https://community.openenergymonitor.org/u/fabiopbx)\ **Post date:** [22 December 2016 17:09 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/103 "2016-12-22T17:09:41Z")
> [@pb66](#): > > Are they all powered by and measuring the current of the same phase? looking at you previous power factors it looks like you maybe powering or measuring accross phases. same phase for AC-AC readings, CT are on their own phase tho… > [@pb66](#): > > ??? I’m unaware of any issues with redis, tell us more! It kept making the feeds page not load… i saw it was creating 2 feed records into the MySQL db every time i tried to make one new feed and it returned an “unknown” error. it felt like they were out of sync… tho I do not entirely understand how REDIS is used… > [@pb66](#): > > phpfiwa is apparently being phased out and only available for backwards compatibility. How are you averaging ?. Ahh i see, i thought that’s what it did, so… thats out the window… i was only asking cause the charts look very ermm not smooth 😛 ill paste some screens! ![](https://community.openenergymonitor.org/uploads/default/original/2X/c/c11681a906d37802af07c229ff3d945a546a9773.png) ![](https://community.openenergymonitor.org/uploads/default/original/2X/4/48b114e3d1ca22230447be3f3396e84608ed5606.png) ---
**Author:** ![pb66](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/pb66/32/27_2.png) [@pb66](https://community.openenergymonitor.org/u/pb66)\ **Post date:** [22 December 2016 17:18 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/104 "2016-12-22T17:18:41Z")
> [@fabiopbx](#): > > same phase for AC-AC readings, CT are on their own phase tho… I’m still not sure here, are you saying all 3 emonTx’s currently have thier AC:AC adapters connected to the same phase but the CT’s are on the separate 3 phases? That would most likely make more sense of understanding the power factors. > [@fabiopbx](#): > > It kept making the feeds page not load… i saw it was creating 2 feed records into the MySQL db every time i tried to make one new feed and it returned an “unknown” error. it felt like they were out of sync… tho I do not entirely understand how REDIS is used… You’ll have to show us when it happens again. ---
**Author:** ![fabiopbx](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/fabiopbx/32/1934_2.png) [@fabiopbx](https://community.openenergymonitor.org/u/fabiopbx)\ **Post date:** [22 December 2016 17:23 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/105 "2016-12-22T17:23:46Z")
here is latest readings ![](https://community.openenergymonitor.org/uploads/default/original/2X/3/3a6fac35517b53022953081158d99666ad497a58.jpg) > [@pb66](#): > > I’m still not sure here, are you saying all 3 emonTx’s currently have thier AC:AC adapters connected to the same phase but the CT’s are on the separate 3 phases? That would most likely make more sense of understanding the power factors. yes this is currently the case, just testing they all actually worked of course… and still waiting on the installation of the separate socket phases. > [@pb66](#): > > You’ll have to show us when it happens again. I shall enable REDIS again on the config and see what happens… and if it breaks then ill try get more info for you 🙂 ---
**Author:** ![pb66](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/pb66/32/27_2.png) [@pb66](https://community.openenergymonitor.org/u/pb66)\ **Post date:** [22 December 2016 17:27 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/106 "2016-12-22T17:27:24Z")
> [@fabiopbx](#): > > yes this is currently the case, just testing they all actually worked of course… and still waiting on the installation of the separate socket phases. But if you put all the CT’s on the same phase as the AC:AC adapters you could compare them, side by side and confirm they are all working “similarly” rather than “just working” but potentially very different. ---
**Author:** ![fabiopbx](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/fabiopbx/32/1934_2.png) [@fabiopbx](https://community.openenergymonitor.org/u/fabiopbx)\ **Post date:** [22 December 2016 17:27 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/107 "2016-12-22T17:27:56Z")
> [@pb66](#): > > But if you put all the CT’s on the same phase as the AC:AC adapters you could compare them, side by side and confirm they are all working “similarly” rather than “just working” but potentially very different. very true 😃 ON MY WAY! lol ---
**Author:** ![pb66](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/pb66/32/27_2.png) [@pb66](https://community.openenergymonitor.org/u/pb66)\ **Post date:** [22 December 2016 18:03 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/108 "2016-12-22T18:03:33Z")
5 posts were split to a new topic: [Enabling Redis is causing issues in emonCMS](https://community.openenergymonitor.org/t/enabling-redis-is-causing-issues-in-emoncms/2574) ---
**Author:** ![fabiopbx](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/fabiopbx/32/1934_2.png) [@fabiopbx](https://community.openenergymonitor.org/u/fabiopbx)\ **Post date:** [22 December 2016 17:37 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/109 "2016-12-22T17:37:25Z")
ermm… so CT2 is negative cause its flipped if im not wrong but has a similar PF if we dont count the negative value… CT3 i have no idea… 😮 EDIT: ohh wait that has no Amp reading… ish ![](https://community.openenergymonitor.org/uploads/default/original/2X/4/4529b2ad56348292bb84cb0bf851373b5d6abd57.jpg) EDIT2 - same AC-AC phase, all CTs into same phase ![](https://community.openenergymonitor.org/uploads/default/original/2X/5/5a3cf428bb0c86f37077a40c2d41c72e9add0e90.png) ---
**Author:** ![pb66](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/pb66/32/27_2.png) [@pb66](https://community.openenergymonitor.org/u/pb66)\ **Post date:** [22 December 2016 18:09 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/110 "2016-12-22T18:09:27Z")
> [@fabiopbx](#): > > same AC-AC phase, all CTs into same phase That looks much better power factor wise, but the other values are very inconsistent so it’s difficult to compare, do you have a steady load you can monitor with the 3 CT’s or can you use emonhub or similar so that all 3 nodes results are simultaneously shown. ---
**Author:** ![fabiopbx](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/fabiopbx/32/1934_2.png) [@fabiopbx](https://community.openenergymonitor.org/u/fabiopbx)\ **Post date:** [22 December 2016 18:14 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/111 "2016-12-22T18:14:32Z")
Steady load i dont think i have anything lying around tbh… those are live feeds from the serial output, they should be very simultaneous accounting for my fast screen /dev/ttyUSBX copy paste skills 😄 but from emonhub i can paste too: ![](https://community.openenergymonitor.org/uploads/default/original/2X/0/0a7c6f9c47dd297caa219a0f55bcf7e3d57821c2.png) ---
**Author:** ![pb66](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/pb66/32/27_2.png) [@pb66](https://community.openenergymonitor.org/u/pb66)\ **Post date:** [22 December 2016 18:24 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/112 "2016-12-22T18:24:15Z")
> [@fabiopbx](#): > > those are live feeds from the serial output, they should be very simultaneous accounting for my fast screen /dev/ttyUSBX copy paste skills 😄 > > but from emonhub i can paste too: not to worry, The fact they are all running on 10sec intervals and not synced will result in variation anyway. ---
**Author:** ![fabiopbx](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/fabiopbx/32/1934_2.png) [@fabiopbx](https://community.openenergymonitor.org/u/fabiopbx)\ **Post date:** [22 December 2016 18:25 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/113 "2016-12-22T18:25:33Z")
would sync be a good idea? and how would that be accomplished if so? ---
**Author:** ![pb66](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/pb66/32/27_2.png) [@pb66](https://community.openenergymonitor.org/u/pb66)\ **Post date:** [22 December 2016 19:41 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/114 "2016-12-22T19:41:53Z")
It would be a good idea but it’s not easily accomplished with what we have, emonhub would need to poll for the info or a “trigger signal” would be needed, either way the sketches would also need changing. For the moment the nearest you could get is to power cycle (not reboot) the Pi so that the 3 emonTx’s all start at the same time, it will go out of sync over time but to be honest with the load you have varying so much and a discreet sampling sketch they would need to be absolutely in sync to be directly comparable, hence the “better to test on a constant load”. ---
**Author:** ![Dave](https://community.openenergymonitor.org/letter_avatar_proxy/v4/letter/d/ee7513/32.png) [@Dave](https://community.openenergymonitor.org/u/Dave)\ **Post date:** [22 December 2016 21:22 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/115 "2016-12-22T21:22:46Z")
I use a 2Kw heater and a long phase cable to wrap through the CT a couple of times, it will only vary slightly then as the voltage creeps up and down. Paul, the ones I bought are… > **[DL-CT08CL5 20A/10mA 2000/1 0~120A Micro Current Transformer | eBay](https://www.ebay.co.uk/itm/171907176383?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT)** > > Linear protection current: 0 ~ 120A. Rated output current: 0 ~ 10mA. Rated Input Current: 0 ~ 20A. Zero sequence / drain / remaining capacity detection and monitoring. Regards Dave ---
**Author:** ![pb66](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/pb66/32/27_2.png) [@pb66](https://community.openenergymonitor.org/u/pb66)\ **Post date:** [22 December 2016 23:18 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/116 "2016-12-22T23:18:54Z")
> [@Dave](#): > > I use a 2Kw heater and a long phase cable to wrap through the CT a couple of times, it will only vary slightly then as the voltage creeps up and down. That’s the easiest way to test, you can also test at various increments just by adding or removing CT passes. Looking at those CT’s I’m guessing you will be extending the wires, if it were me I, would factor the diodes in at that point rather than putting them in the jack connector, but I don’t think it’s overly important. ---
**Author:** ![Dave](https://community.openenergymonitor.org/letter_avatar_proxy/v4/letter/d/ee7513/32.png) [@Dave](https://community.openenergymonitor.org/u/Dave)\ **Post date:** [23 December 2016 10:22 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/117 "2016-12-23T10:22:57Z")
Yeh I was going to twist decent alarm cable together and solder with heatshrink to extend. I’m hoping these work well as these are a lot smaller than the standard CTs and with 12 CTs in my fuseboard, its cramped to say the least. Regards Dave ---
**Author:** ![Robert.Wall](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/robert.wall/32/38246_2.png) [@Robert.Wall](https://community.openenergymonitor.org/u/Robert.Wall)\ **Post date:** [23 December 2016 13:27 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/118 "2016-12-23T13:27:46Z")
> [@pb66](#): > > Is it a good idea to put a zener diode in for safety if your not using standard CTs? > > I’d prefer Robert to answer that as it is a safety issue, I usually have in the past but not always. putting safety precautions in place is generally speaking always a good idea. A CT is the _dual_ of a voltage transformer. If you short-circuit a (normal) voltage transformer, you get excessive current and it burns out. A current transformer does the opposite: If you open-circuit a current transformer, you get excessive voltage (as it tries to drive the current it generates into a near-infinite impedance) and it flashes over and destroys the insulation. So, as I’ve written may times in the past, a CT can **always** be short-circuited in safety, because then it is delivering zero power. Therefore, there are two things you can do: 1. Short-circuit the CT before you unplug/disconnect it, or 2. Fit a pair of voltage suppressors (or one bidirectional one), or a pair of zener diodes in series, to clip the voltage at some safe value. It’s not likely that a very small CT like the ones we use would kill, but it could easily be very painful, and would certainly destroy any delicate electronics that couldn’t handle the current. {Sorry I’ve been away for a day - I’m back on-line now.} ---
**Author:** ![Robert.Wall](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/robert.wall/32/38246_2.png) [@Robert.Wall](https://community.openenergymonitor.org/u/Robert.Wall)\ **Post date:** [23 December 2016 13:33 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/119 "2016-12-23T13:33:18Z")
> [@fabiopbx](#): > > it seems either my soldering is bad (looks good tbh) or the jacks are faulty… I have seen faulty jacks. The plastic insulation between the components is either squeezed out of position (so a short circuit), or it has not been assembled properly and prevented two metal parts that should be touching from giving a good contact. ---
**Author:** ![Dave](https://community.openenergymonitor.org/letter_avatar_proxy/v4/letter/d/ee7513/32.png) [@Dave](https://community.openenergymonitor.org/u/Dave)\ **Post date:** [23 December 2016 13:35 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/120 "2016-12-23T13:35:32Z")
Thanks Robert, what voltage diodes would you recommend? also you recommend a pair of diodes in series? what benefit do you have using two diodes rather than one? Regards Dave ---
**Author:** ![Robert.Wall](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/robert.wall/32/38246_2.png) [@Robert.Wall](https://community.openenergymonitor.org/u/Robert.Wall)\ **Post date:** [23 December 2016 13:50 UTC](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198/121 "2016-12-23T13:50:24Z")
What voltage do you want? Anything that gives negligible leakage above the working peak that you need for the input should be fine. The YHDC used to be 22 V, the latest are lower. You need two in series because the “reverse” voltage of a zener diode is ≈ 0.7 V, the same as the forward voltage drop of any diode, and you don’t want it clipping at 0.7 V one way and (say) 15 V the other way. (Any diode will show the zener breakdown characteristic in the ‘reverse’ (blocking) direction - but the voltage at which it happens isn’t controlled. So a Zener diode actually works - passes current - in the “reverse” direction compared to an ordinary rectifier diode.) ![](https://community.openenergymonitor.org/uploads/default/original/2X/0/069a980e1644c8a116f754486059c41b9c12aefa.gif) [from: [Semiconductor Primer, semiconductors 101](http://www.mpoweruk.com/semiconductors.htm)] [Previous page](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198.md?page=5) [Next page](https://community.openenergymonitor.org/t/does-the-emontx-shield-need-an-actual-arduino/2198.md?page=7)