I was about to order two more EmonTX’s with AC adapters but I found that the shipping increased to 60 Euro’s (an extra 42 Euro’s) just by adding the AC adapters. That’s a lot of CAD$ for two wall warts as it turns out.
Have any north-americans found an AC adapter that can work with an EmonTX (even if I have to change a couple of resistors)?
I found these:
I’ve been unable to find the Ideal Power (or TDC) DA-10-09 anywhere in North America.
Bear in mind that if you’re using those to power the emonTx, the no-load voltage needs to be about the same, viz. 12.0 Volts ±5%. “9 V” refers to the output voltage at full load, it is very lightly loaded by the emonTx. And the regulation is important too, because if the source impedance as seen by the emonTx is too great, there’s going to be a big dent in the wave where it draws its chunk of power on each cycle, spoiling the voltage measurement.
As neither of these parameters are mentioned (nor can be inferred) from the data in that link, caveat emptor.
Yeah, hence the long-shot post in case someone else has made a north american supply work for them.
I’ll probably have to suck it up and accept the exorbitant shipping costs.
The problem is, copper and iron is heavy, and that’s what you’re paying to ship.
I couldn’t find anything on the WWW that looked like the original manufacturer, so it’s going to be hard to find decent information about that device. It’s likely that the parameters will be similar, but that’s an expectation only.
It doesn’t have to be a pre-assembled unit. If you want to do it differently, you could buy an isolating transformer from one of the recognised and reputable component suppliers where you can get all the relevant data, a plastic box for it, fuses and holders for the input and output sides, plugs and leads, and make up your own.
I realize the weight is contributing to shipping. I’m not commenting on https://shop.openenergymonitor.com as they’re just transferring their cost over.
I also realize I could build my own but that wouldn’t benefit other people in North America who might be wanting to install EmonTX’s and not want to pay to ship a bunch of copper/iron across the ocean in onesies or twosies when some other north american company has already done a bulk transfer via ship.
There’s still no data, but there is an email address and a San Francisco PO Box number for returns. It’s worth an email.
ok. I’ll see if they have a datasheet.
The Digikey adapter from my original post does have a datasheet:
Electrical Specifications (@25C)
1. Primary Rating: 120V 60Hz
2. Primary Excitation Current: < 4mA
3. Secondary Rating: 9VAC ± 5%, 1200mA AC
4. Secondary No-Load Rating: <11.6VAC Ref.
5. No Load Power (stand by): <0.21W
6. Average Efficiency: 82.38%. Meets minimum level VI efficiency*
7. Operating Temperature Range: -10 Deg C to +40 Deg C
8. Temperature Rise: 30 Deg C Max at rated load
11.6VAC is within 5% of 12VAC. Nothing about impedance though.
Oh yes there is: You know the internal volt drop (11.6 V - 9 V) at 1.2 A, therefore you can calculate it: 2.17 Ω. That’s somewhat better than our a.c. adapter at 2.7 Ω.
I’m not that smart. I only deal with 1’s and 0’s.
So I deduce that you think that wall wart may be sufficient?
Yes, the Triad Magnetics one looks to be OK from that point of view.
Thanks. I’ll try it out and report back I guess.
Thanks. I went through the datasheets on all of them and none of them have a no-load voltage anywhere near 12v +/-5%. The closest is this one:
GPU480901000WAOO: Jameco Reliapro : 9 VAC 1A AC to AC Wall Adapter Transformer 2.1mm Plug Level VI : Power Supplies & Wall Adapters (11.28VAC +/-5%)
I’ve placed my order for EmonTX’s and I’ll order the Digikey one and throw it on my scope to see what it does under no-load vs. load while powering an EmonTX or two. If it works, then a Digikey part is a great option for north-americans.
What really matters is the voltage as seen by the emonTx given the lowest supply voltage you’ll ever see at the place where the adapter is plugged in, the lowest possible output voltage from the adapter due to its tolerances, and the tolerances of the power supply components within the emonTx and the loading due to any additional optional components (temperature sensors, etc).
If you can tell me what additional components you have, I can work that out for you (but it might not be for a couple of days).
I use the DA-10-09 which works fine. See
I also needed a DC supply for things to be stable.
Nice price. But “This item does not ship to Canada”. It’s like we live in igloos up here.
That’s why I’m asking what additional components have been added. If the voltage available in worst case conditions isn’t enough, the emonTx will reset, or possibly hang, when transmitting as that’s when maximum current is drawn from the a.c. adapter and the a.c. supply’s regulator. It’s like that because operating with power from the a.c. adapter is a delicate balancing act between having enough power to just operate whilst keeping distortion of the a.c. waveform that’s being used for measurement to a minimum.
Running with the operating power coming from a d.c. supply removes that problem - as does having an a.c. adapter with an adequate output voltage.
I only have one temperature sensor that isn’t even plugged in at the moment. I don’t think I need it anyway as I have other temperature/humidity sensors throughout the house. Other than that, I’ll just have 4 CT’s on each emonTX. If I have to run USB for power, I’m ok doing that too if necessary.
On the stability question, Robert kindly solved mine by suggesting the extra 5 volt supply. I had only 4 CTs at the time but about once a month the emonTx would stop and need a reboot. I now have added 5 temp sensors + the 4 CTs and all has been very stable.
I would imagine that Jameco or Digikey would have this same transformer, and maybe ebay. Good luck.
If my simulation is accurate, both the Jameco 9 V 1 A and the Digikey should work with no additional load on the 3.3 V d.c. rail (e.g temperature sensors) on supplies down to below 100 V, so both should be fine.