little pcb-mount CTs

Triad CSE184L ??

Den tirsdag den 5. maj 2015 kl. 00.17.18 UTC+2 skrev John Larkin:

isn't the difference basically what side the shunt is on?

-Lasse

Sure, but if I use a shunt (like, 0.1 ohms) on the high side, I can use a dinky audio transformer that has any amount of copper resistance, 10s of ohms maybe, to couple the signal down into my ADC.

Nice part, good price. If anybody stocks it!

Thanks

Den tirsdag den 5. maj 2015 kl. 00.52.20 UTC+2 skrev John Larkin:

exactly so it is mostly a matter of what is easiest to find

-Lasse

Any transformer, with a shunt resistance on the secondary, is a current transformer. Why not go with Coilcraft LPR6235 series

Or, do you need some other features (open hole for primary wire, UL listing...)?

How many do you need?

It would be for production, so we'd need a dependable supply. Two distributors who list it show no stock.

The ones with low primary DCRs also have low L/R time constants, so wouldn't work very well at 400 Hz.

How about this one? Lots of stock.

That one is nice. The 500:1 ratio, makes 2 mA RMS out with 1 amp in. That's 100 mV RMS into a 50 ohm burden resistor.

The alternative is to use a 0.1 ohm shunt and a step-up audio transformer. That could give me more voltage for my ADC, but, then, opamps are cheap.

If you never have more than 1A maybe use a larger burden resistor? The datasheet says 4Vrms max on the output which is probably where the core begins to saturate when operated at 50Hz. You'd have to check the bandwidth though.

I won't run much below 300 Hz, so the burden could go up. Maybe I can drive my ADC (0 to 3V) directly.

We're building a 400 Hz power supply, and I thought it would be cute to add output current measurement. I have a spare ARM ADC mux input available. I could sample that pretty fast, 20 KHz maybe, auto-zero, and compute RMS current.

P.S.: Regarding audio transformers I'd avoid those in case this remains in production for many years. I had my comeuppance a few months ago. Needed med-grade audio isolation transformers for the audio range. I thought I'd just order the same ones I did a decade ago but now ran out of. When I looked it was like visiting an old building and discovering that ... it had become a parking lot.

Den tirsdag den 5. maj 2015 kl. 02.25.24 UTC+2 skrev John Larkin:

does it need to be transformer? how about an ACS712 ?

-Lasse

That's interesting. At 180 mV/A I'd get about 500 mV p-p at 1 amp RMS. Zero drift wouldn't matter for AC measurement.

A little gain would still be good, into the crappy noisy ARM ADC. 3x or so maybe.

Price isn't bad, considering how small and simple it is. Much more accurate than the usual Hall gadget. Tempco is mediocre.

I was just testing an ISDN transformer that we have in stock. That would work OK down to 300 Hz, if I keep the voltage reasonable.

Inductors and transformers are *such* a nuisance.

On Mon, 04 May 2015 17:25:20 -0700, John Larkin Gave us:

Go to findchips.com to locate sources.

But try this one ACS-712

Small Hall Effect type by Allegro.

On Mon, 4 May 2015 17:40:54 -0700 (PDT), Lasse Langwadt Christensen Gave us:

Damn! Looks like you beat me to it! :-)