US plug AC adapters

Try here:

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.

Check Jameco Electronics.

Here’s a link to a page with several AC/AC adapters on it.

Prices start at 9.95 USD.

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: (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.


Unfortunately, after going through checkout and everything, after shipping, it works out to $41.46 USD to buy 1. And they’re back ordered until christmas.

Back to the digikey one.

Is that ever a rip-off! shocked

One of the few negatives to living in Canada. Shipping, exchange and import fees.

I have the TDC DA-10-09 at The Ideal sold by OEM is made by TDC, looks identical and has identical specs. The phase shift is virtually identical and the calibration with the Ideal sample I have is within 2.5%.

Price is $15 and shipping to Canada is flat-rate $10.

Not looking to corner the market on AC transformers, it’s just that I don’t think this should be such an ordeal and I would like to offer some relief.

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Thanks! I should really do more reading. I didn’t know about Iotawatt until just now. 14 inputs is more the speed that I needed in the first place!