Any thoughts on this shield? It does not look like the emontx shield sold on the shop. So I’m wondering if anyone has used this one and how well it works? Seems not to have ac-ac voltage measure?
I’ve never seen a reference to it here, and I suspect it works badly, for the simple reason all you can have with any accuracy is a measurement of current, anything else - apparent power or real power is a “best guess” that relies on assumptions, which might or might not be valid. The apparent power will depend on the system voltage being constant (it isn’t) and the value set accurately in the software (how can you – if it varies continually?) and real power will depend on all that plus the overall power factor of the load you’re measuring, which depends on the load itself, or the combination of loads at the time.
That is exactly the one you can buy from The OEM Shop. If you buy from us, the profit goes towards maintaining this website and providing you with our technical expertise.
I’ve never used one, on paper they should work BUT you must break into the circuit to connect, and bear in mind the input isn’t 30 A rms, it’s ± 30 A d.c. (a little over 20 A rms). The sensitivity has a maximum error of about ±4%, which is worse than the SCT-013-000, but calibration should cope with that. You must study the data sheet for the full details of the ACS712.
Sorry I worded it badly. I meant that the shield I pasted does not look like the one which is sold on the shop. So I was wondering if the shield I pasted is as good as the emontx shield or not
Again, I’ve never used the 5 A one, but the presence of an op-amp and the words “and appropriate compensation, and other functions” gives me cause for concern, because some designs incorporate a filer, which adds a phase shift and completely spoils the ability to accurately measure real power.
Don’t worry about that. Now I know, I can tailor my responses to suit. e.g. If you look on page 5 of the data sheet, it says, in table x30A PERFORMANCE CHARACTERISTICS, the “optimised accuracy range” is -30 A to + 30 A, and the sensitivity (output for a given current) can be between 63 and 69 mV/A. That’s where I got “It’s only good to 20 A rms (= 30 ÷ √2)” and “accuracy is ± 4%”.