AVR-DB: emonTx V4, new hardware in progress

whitecitadel · 2022-11-27T21:48:31.046Z

Robert.Wall:

This seems to suggest a later addition to the original wiring. If the property was built or rewired when appliances weren’t quite so ubiquitous, it’s likely that there were a lot fewer socket outlets provided initially, and rather than rewire the entire house, it was simpler to add another circuit.

You would think so, but no this was all as built, only the solar and EVSE were added later. Have some time at home tomorrow, going to do some investigations and in the mean time compromise what CT I order with the emontx4 for most flexibility.

whitecitadel · 2022-11-28T09:12:46.922Z

Trying not to clog up the thread with my personal situation but general observation for those reading later is that the clamp dimensions are in the shop on the Datasheet.

I have struggled in the past to add any more of the old YHDC clamps to the fuse board, and wondered if my ambitions to monitor as much as possible were a bit lofty.

I would advise anyone to check they have space before ordering, as having looked again this morning I will struggle to get either the multiple lighting circuits through a single CT as I hoped, or to add a lot of 50A size clamps.

It’s really tempting to one day change this board to a double height to allow much better arrangement of the circuits and some on rail modbus style meters, however it’s location in the downstairs WC brings a very high bar for WAF (Wife Acceptance Factor) that aside from the cost likely rules it out!

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It’s a bit busy in there, mildly jealous of Glynn and Tristan’s layouts above with a nice sheet of ply to screw into and plenty of room around for tidy conduit!

Going with monitoring the 3 rings as that is where I’m leaking wastage at night, I know when the oven is on or off and I will try to pull the mic cable for the main supply through the house before ordering the expensive 100A CT later.

NiHa · 2022-11-28T11:09:55.339Z

The new Tx4/Vs/base combo is ideal for for the monitoring I need to do at the CU but I have a few ?s around what to get for the tank location.

It will involve several temperature measures, a CT on the HP’s control/pumps (an Ecodan powered via the outdoor unit), a connection to the Ecodan’s Sika flow meter, and ideally a way of connecting two Grundfos VFS flow meters that are on the solar thermal system but which the solar controller seems to be unable to get the right information from.

I think I need to get a second Tx as it will do most of this, presumably still limited to handling six DS18B20s (?) via an RJ45 breakout, and the Sika to one of the analogue inputs.

Does this Tx also need a voltage sensor for more accurate CT data or will the emonBase use the info from the one at the CU?

The VFS meters need a 5V supply, and create 4 analogue inputs – is it possible that one of the add-on boards could be a suitable base for these? Or a different board powered on the RJ45 chain? (I understand enought to see the possibilities, not enough to work them out unless it is blindingly clear!!)

Also, I tried adding a second Tx to my cart but it just duplicates the energy monitor set, but that’s the only way to get the emonVs so I can’t build it piece by piece. I’ll create a second order for the Tx only.

TrystanLea · 2022-11-28T16:53:16.351Z

@whitecitadel that all sounds good, yes figuring our what can go where is always the challenge, especially with crowded consumer units which is usually the case. Im going to get an electrician to replace mine soon to get more room amongst some other work (battery & solar hopefully… ).

@NiHa It might be worth waiting out a bit for the best solution for the heat pump monitor. I will be documenting at least part of what you need hopefully later this week. It requires custom firmware so a bit of involved on that front, but if you are happy with that it’s fine.

There’s one analog input broken out to the terminal block on the outside of the emonTx4, then there are further analog inputs accessible internally, the CT breakout wont do what you are after so it would require some custom wiring to get more than one analog to work.

NiHa:

Does this Tx also need a voltage sensor for more accurate CT data or will the emonBase use the info from the one at the CU?

Yes it does require a voltage sensor, it’s doing a lot more than multiplying an rms voltage value with current, it’s sampling voltage and current many thousands of times per second in order to calculate real power so there’s no easy way to transmit that from the other emonTx.

NiHa:

The VFS meters need a 5V supply

Unfortunately it’s only 3.3V that is broken out on the emonTx4 (that’s getting changed in the next version). You could get the 5V from the emonVs, from the USB-C output or by connecting up your own cable to the 5V terminal block in the emonVs.

NiHa:

Also, I tried adding a second Tx to my cart but it just duplicates the energy monitor set, but that’s the only way to get the emonVs so I can’t build it piece by piece. I’ll create a second order for the Tx only.

It should be possible to order multiple emonTx’s in the single order with different option sets. You need to add the first to the basket and then start again with the second. I’ve seen a couple of orders come in like that over the last few days so it seems to be working as far as I can tell.

Best of luck with the challenge of working this all out, Il update as soon as I’ve finished the heat pump build documentation discussing the use of the analog input.

TrystanLea · 2022-11-28T17:09:57.762Z

It’s been busy day in the office today getting the orders ready for shipping it was hands on deck for the whole team: @Gwil, Bella, @glyn.hudson and myself. The first few caught the post today, lots more to do over the next few days…

It’'s a great feeling getting a new design like this to this point. Thank you to everyone who has ordered and supported us, we really appreciate it!

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borpin · 2022-11-29T10:02:40.664Z

3 posts were split to a new topic: EmonTX4 - use old or new kit

TrystanLea · 2022-11-29T18:56:25.754Z

Latest updates to the documentation:

New structure to provide contained documentation for all the main OpenEnergyMonitor components including legacy hardware: https://docs.openenergymonitor.org
EmonTx4 documentation ‘docs’ part removed from the URL for a cleaner URL: https://docs.openenergymonitor.org/emontx4 Links updated in the shop and on this thread.
emonSD image release page moved into the new documentation site: https://docs.openenergymonitor.org/emonsd/download.html. Alongside documentation for EmonScripts. (UPDATED & includes new emonSD-10Nov22 release which is being shipped with hardware this week)
Emoncms user guide copied over from the guide: https://docs.openenergymonitor.org/emoncms/postingdata.html
A start on moving Learn into this single documentation location to try and provide a more integrated experience https://docs.openenergymonitor.org/electricity-monitoring/ac-power-theory/introduction.html#understanding-ac-power.

We’re going to move this to a https://docs.openenergymonitor.org subdomain. And ultimately redirect guide and learn once we are closer to finishing this process.

TrystanLea · 2022-11-30T11:50:28.242Z

A new documentation page discussing the RFM69 radio packet format on the emonTx4 is now available:
Technical Guide — OpenEnergyMonitor 0.0.1 documentation

I will be added details about temperature sensing, RJ11 and RJ45 pinouts etc to this technical guide page. The intention is to integrate what we used to cover on the wiki on a single page here available directly in the guide.

TrystanLea · 2022-11-30T14:00:54.369Z

The documentation site is now available at https://docs.openenergymonitor.org/. The links above and shop page have been updated.

Robert.Wall · 2022-11-30T14:49:52.720Z

Please can you do a global edit and get MHz right? Please, pretty please?

TrystanLea · 2022-11-30T17:32:26.219Z

I’ve started a new thread here EmonTx4 Documentation specifically for documentation updates.

oliv3r · 2022-12-01T09:43:38.502Z

I have some curious design questions, which may sound critical, but my intend is absolutely not to be rude or anything

Why the need for the separate emonVs? Putting all those electronics in the same housing would make the device simpler and possible cheaper? (I’m currently looking at the https://community.openenergymonitor.org/t/emporia-vue-2-alternate-firmware PCB design and think they solved some issues quite elegantly; I do not own one ). I know for a start-up getting all that compliance and EMC done is a big PITA, but since you are already designing your own PSU, what’s the reason now?

Why the galvanic isolation on the voltage input? The Emporia doesn’t do it; and they are certified to sell world-wide. I can get it in mainland EU, and NA. Are transformers that more accurate then a few big resistors? I think in the end, you still end up with a scaled voltage?

0.333V CT’s seem to be somewhat common. Emporia uses them, I’ve seen them @ $work in our product. But I can’t wrap my head around the sensitivty/accuracy here. 0.333V CT’s would be 666mV across the range, right? But that’s not RMS, so we’ll add about half (napkin style) to get to 999mV or 1V for the CT output. If we VREF is 3v3 that’s a lot of lost resolution? We want to offset the CT’s to make sure they are always positive; e.g. VREF/2. So we would have signals from 1V15 - 2V15.

Looking at Getting the most out of the SAM D21's ADC - Stargirl (Thea) Flowers we actually see however, the the ADC is not so amazing generally. While this speaks of the ATsamd21, I bet that most ADC’s behave more or less the same. What’s interesting to note here, is that the ADC behaves more poorly in the lower half then in the upper half. The emporia seems to account for that by using 1v8 as the offset voltage, bringing that voltage swing to 1v3 - 2v3. Though in reality it’s probably ore like 1v5 - 2v1 looking at https://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcAmWDLMgZgBxmcgCxg4CcS6IShWVApgLRhgBQATiKQGwhbKc9uUEJnjsBEoWC6RhyAOxwWAYwnTZQgoTnRR8fQeSMcUaFkhciOQpfldC3BHdNxWAJQlbP8-rNmFZMGgcX2EYBBYAeTUZcFJ+dXAoFgA3Xn4vPglAkFiYLAKw0wiAd3TJQR5IFjLNInKvaoBzCSyhP2SAexBte2F8ZFJZVDAEQekx7h8hhRdXOSpeFiA for example. Sadly for the atsamd21 at least, the dynamic range of the ADC doesn’t seem to be specified …

Still, I wonder would it not be worth-while to use a CT at 666mV. I’ve been eyeing the https://talema.com/products/az-series-flying-lead-current-transformer/ for example, and the 25 amp model would be good for 16 amps (24 amps RMS) would give 1.5 p2p so 3V0. Of course in this case we’d be in the ‘dirty region’ of the ADC, so we’d need all the tricks on that earlier page, so maybe the talema CT is just a little too much maybe?

Another option would be to use an input gain of 2, but that would actually introduce noise too … or use smaller reference voltages I suppose …

Finally, I really dislike clamp CT’s personally. They take up a lot of space, and bring lots of accuracy risks due poor mating of the clamp. Will solid ring coils ever be an option? They tend to be much smaller … For example I really like the MLG-WST-0200 30 amp https://www.measurlogic.com/product/mlg-wst-solid-core-ct-333mv-output/ on paper, but not buyable for mere mortals (afaik an OEM only product) (hence why I was looking at the talema ones, as digikey stocks those …)

Robert.Wall · 2022-12-01T13:37:44.084Z

With every respect, I can’t see Glyn & Trystan changing anything at this late stage.

oliv3r:

Will solid ring coils ever be an option?

Don’t you means cores? Personally, I don’t like people calling split-core c.t’s “clamps” - because they’re not. You clearly don’t understand either the legal ramifications in various countries of installing c.t’s, how c.t’s work with the sensing node, or both, if you need to ask this.

TrystanLea · 2022-12-01T14:11:53.419Z

oliv3r:

I have some curious design questions, which may sound critical, but my intend is absolutely not to be rude or anything

Thanks for the input and questions @oliv3r . As ever we are in a process of continuous development here and we will be considering our next steps again soon once we’re out of the initial delivery stage with the emonTx4.

oliv3r:

If we VREF is 3v3 that’s a lot of lost resolution?

We are using an analog reference at 1.024V in order to get a good match with the 333mV CT sensors. The 333mV CT sensors seem to be the most common size giving us the wider range of options. We are using a precision voltage reference MCP1502 0.1% in order to calibrate the internal analog reference on the AVR-DB.

oliv3r:

Finally, I really dislike clamp CT’s personally. They take up a lot of space, and bring lots of accuracy risks due poor mating of the clamp. Will solid ring coils ever be an option?

I really like the Talema range that you linked (https://talema.com/products/az-series-flying-lead-current-transformer/), we have a number of these in the office for testing.

That said the new range of Echun CT’s that we are stocking have a much more solid ‘mating’ of the cores. Their accuracy is also much better than the YHDC CT’s we were using. Their accuracy is also better at 333mV than higher voltage outputs.

The benefit with split core CT’s is that it’s safer for the user to install them - which is the primary reason we use split core CT sensors.

oliv3r · 2022-12-01T14:47:21.085Z

Robert.Wall:

With every respect, I can’t see Glyn & Trystan changing anything at this late stage.

I don’t think they should. These are just design questions I have on the tx4, which are influencing my purchasing decisions. Also, I think it’s much better to discus these in the open, rather then just go somewhere else, right? In the end, we all learn a little bit from critique generally

Robert.Wall:

Don’t you means cores? Personally, I don’t like people calling split-core c.t’s “clamps” - because they’re not. You clearly don’t understand either the legal ramifications in various countries of installing c.t’s, how c.t’s work with the sensing node, or both, if you need to ask this.

Hah, that’s a sad typo. CT Coils, solid core ring, type to fast, and in your mind it becomes solid coil, oops.

There’s no legal problems atleast in the netherlands, and I doubt in other european countries as far as I know, by installing Solid Core Current Transformer Coils afaik. Obviously, I wouldn’t put them Between the mains and the main shutoff. But after the shutoff, it’s safe and fine. Even installing them before the mains switch, there’s still the ‘sort of switch’ of the meter, and the main fuses.

Obviously, I understand you have to de-energize the whole panel, remove wires, run the wires through the cores, an reconnect things again. Not ideal for installers, not a problem for me, as I don’t mind taking the time. Since I’ve done my own wiring panel, I hope I will figure this out Here’s a pic of the panel as it is now, though I want to change a few things with some remoddeling of the home.
Before:

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Note the rust on those wires, which actually caused some issues obviously

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After:

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The brown/blue wires entering from the bottom right is something I wouldn’t touch of course, including that switch (the main on/off switch). And yes, I had prepared everything for 3 phases, but haven’t had it hooked up yet. I do have 3 phases entering the house, but the meter is single phase.

I agree that using solid core’s in the US where they have to be placed on the bus-bar/incoming lines, that’s dangerous, as you’d be working on live-wires.

Also, I was thinking of it as an option, not for everyone …

TrystanLea:

We are using an analog reference at 1.024V in order to get a good match with the 333mV CT sensors. The 333mV CT sensors seem to be the most common size giving us the wider range of options. We are using a precision voltage reference MCP1502 0.1% in order to calibrate the internal analog reference on the AVR-DB.

So now my lack of understanding pops by Afaik, as mentioned above, we are ‘raising’ the voltage of the CT coils which are -0.333V ~ +0.333V to half 3v3, via the 1v65 aref, to ensure we don’t have any negative voltages on the adc input, correct? But if 1v65 (or 1v8) is used, then you’d be exceeding your 1v024 reference? What am I missing here conceptually?

TrystanLea:

The benefit with split core CT’s is that it’s safer for the user to install them - which is the primary reason we use split core CT sensors.

I cannot disagree, but then I’d like at least to have the option. Also, again, size I understand in the UK that might be less of an issue, though I’ve seen some posts here where the space was super cramped. The clamps just take considerable more space.

If you start to offer the talema range as option in your store though (after testing); that would be super interesting!

Hope you can at some point also cover my other questions

Thanks, for your thoughts so far!

Robert.Wall · 2022-12-01T14:59:02.853Z

A principal reason for choosing 0.333 V output c.t’s was their ubiquity - both as split-core and ring-core. There’s absolutely no reason why a user cannot use a set of ring-core c.t’s with any emonTx, nor is there any reason to use only a specific 100 A : 50 mA c.t with the emonTx V2 & V3, so long as the correct burden is chosen and the c.t. is not overloaded by the output voltage requirement.

In the UK, the “meter tails” between the suppliers fuse/neutral link and meter, and between the meter and the “consumer unit” (in UK parlance) or if you have one, an isolating switch, are sealed and you incur the ire of the supplier if the seals are broken. This is why split-core c.t’s are necessary for whole-house monitoring. I’ve been recommending some of the Talema range for some time, in appropriate circumstances.

TrystanLea · 2022-12-01T15:06:18.365Z

oliv3r:

Afaik, as mentioned above, we are ‘raising’ the voltage of the CT coils which are -0.333V ~ +0.333V to half 3v3

The bias voltage is very close to 0.512V (half 1.024V aref). Hence we are in the correct range for the 0.333V CT, 0.333V rms x sqrt(2) = 0.470V mid rail to peak and 0.942V peak to peak, does that make sense?

oliv3r · 2022-12-01T18:25:26.912Z

TrystanLea:

The bias voltage is very close to 0.512V (half 1.024V aref). Hence we are in the correct range for the 0.333V CT, 0.333V rms x sqrt(2) = 0.470V mid rail to peak and 0.942V peak to peak, does that make sense?

Is that the correct term yea? Bias voltage? Right, i remember seeing a post in this thread that you where planning to use a precision 1.65V bias voltage, which is of course half of 3v3, so that indeed is my confusion. Using the internal 1024 reference, and calibrating that ‘at the factory’ makes a lot of sense. pro tip; keep a copy of the calibration data in your manufacturing database for future reference

So then, 0.333V over 1024/2 should be pretty good; you avoid the ADC ‘dead zones’ nicely while still being pretty good within range …

TrystanLea · 2022-12-01T20:57:05.873Z

oliv3r:

So then, 0.333V over 1024/2 should be pretty good; you avoid the ADC ‘dead zones’ nicely while still being pretty good within range …

Great

Yes bias is the right term. You may have seen a mention of a 1.8V precision reference? we are actually using this external reference source (MCP1502 chip 0.1% tolerance) with a voltage divider (0.1% tolerance) to give 0.9V (0.2% tolerance). That is then read by the ADC on the AVR-DB to calibrate the internal analog reference. The MCP1502 precision reference chip is included on every board to do this.

Ideally the AVR-DB would accept an external 1.024V precision reference directly but unfortunately the external reference is limited to 1.8V, hence the workaround is to use the internal 1.024V voltage reference of the AVR-DB chip but calibrate it by reading the voltage of an external precision reference.

That’s a great blog by Stargirl Thea, thanks for that!

oliv3r · 2022-12-05T10:19:15.094Z

That adds a considerable amount to your BoM doesn’t it? Is it really needed to use a chip for the longevity of the device, do you expect a lot of drift over the years? I would have figured it’s much cheaper to calibrate it once in the factory store the calibration factory in the eeprom instead.