Forums

little pcb-mount CTs

Started by John Larkin May 4, 2015
On 2015-05-04 3:17 PM, John Larkin wrote:
> > Anybody know of a source for a small (1 amp range) PCB mount current > transformer? Frequency will be around 400 Hz. > > There are switcher current sense CTs, but I don't know if they will > work that low. > > Or maybe I could use a shunt and a voltage-mode (audio) transformer. >
How about this one? Lots of stock. http://www.digikey.com/product-detail/en/CSE187L/237-1103-ND/242546 -- Regards, Joerg http://www.analogconsultants.com/
On Mon, 04 May 2015 16:47:14 -0700, Joerg <news@analogconsultants.com>
wrote:

>On 2015-05-04 3:17 PM, John Larkin wrote: >> >> Anybody know of a source for a small (1 amp range) PCB mount current >> transformer? Frequency will be around 400 Hz. >> >> There are switcher current sense CTs, but I don't know if they will >> work that low. >> >> Or maybe I could use a shunt and a voltage-mode (audio) transformer. >> > >How about this one? Lots of stock. > >http://www.digikey.com/product-detail/en/CSE187L/237-1103-ND/242546
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. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On 2015-05-04 5:00 PM, John Larkin wrote:
> On Mon, 04 May 2015 16:47:14 -0700, Joerg <news@analogconsultants.com> > wrote: > >> On 2015-05-04 3:17 PM, John Larkin wrote: >>> >>> Anybody know of a source for a small (1 amp range) PCB mount current >>> transformer? Frequency will be around 400 Hz. >>> >>> There are switcher current sense CTs, but I don't know if they will >>> work that low. >>> >>> Or maybe I could use a shunt and a voltage-mode (audio) transformer. >>> >> >> How about this one? Lots of stock. >> >> http://www.digikey.com/product-detail/en/CSE187L/237-1103-ND/242546 > > 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. -- Regards, Joerg http://www.analogconsultants.com/
On Mon, 04 May 2015 17:20:14 -0700, Joerg <news@analogconsultants.com>
wrote:

>On 2015-05-04 5:00 PM, John Larkin wrote: >> On Mon, 04 May 2015 16:47:14 -0700, Joerg <news@analogconsultants.com> >> wrote: >> >>> On 2015-05-04 3:17 PM, John Larkin wrote: >>>> >>>> Anybody know of a source for a small (1 amp range) PCB mount current >>>> transformer? Frequency will be around 400 Hz. >>>> >>>> There are switcher current sense CTs, but I don't know if they will >>>> work that low. >>>> >>>> Or maybe I could use a shunt and a voltage-mode (audio) transformer. >>>> >>> >>> How about this one? Lots of stock. >>> >>> http://www.digikey.com/product-detail/en/CSE187L/237-1103-ND/242546 >> >> 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. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On 2015-05-04 5:20 PM, Joerg wrote:
> On 2015-05-04 5:00 PM, John Larkin wrote: >> On Mon, 04 May 2015 16:47:14 -0700, Joerg <news@analogconsultants.com> >> wrote: >> >>> On 2015-05-04 3:17 PM, John Larkin wrote: >>>> >>>> Anybody know of a source for a small (1 amp range) PCB mount current >>>> transformer? Frequency will be around 400 Hz. >>>> >>>> There are switcher current sense CTs, but I don't know if they will >>>> work that low. >>>> >>>> Or maybe I could use a shunt and a voltage-mode (audio) transformer. >>>> >>> >>> How about this one? Lots of stock. >>> >>> http://www.digikey.com/product-detail/en/CSE187L/237-1103-ND/242546 >> >> 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. >
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. -- Regards, Joerg http://www.analogconsultants.com/
Den tirsdag den 5. maj 2015 kl. 02.25.24 UTC+2 skrev John Larkin:
> On Mon, 04 May 2015 17:20:14 -0700, Joerg <news@analogconsultants.com> > wrote: > > >On 2015-05-04 5:00 PM, John Larkin wrote: > >> On Mon, 04 May 2015 16:47:14 -0700, Joerg <news@analogconsultants.com> > >> wrote: > >> > >>> On 2015-05-04 3:17 PM, John Larkin wrote: > >>>> > >>>> Anybody know of a source for a small (1 amp range) PCB mount current > >>>> transformer? Frequency will be around 400 Hz. > >>>> > >>>> There are switcher current sense CTs, but I don't know if they will > >>>> work that low. > >>>> > >>>> Or maybe I could use a shunt and a voltage-mode (audio) transformer. > >>>> > >>> > >>> How about this one? Lots of stock. > >>> > >>> http://www.digikey.com/product-detail/en/CSE187L/237-1103-ND/242546 > >> > >> 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. >
does it need to be transformer? how about an ACS712 ? -Lasse
On Mon, 4 May 2015 17:40:54 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>Den tirsdag den 5. maj 2015 kl. 02.25.24 UTC+2 skrev John Larkin: >> On Mon, 04 May 2015 17:20:14 -0700, Joerg <news@analogconsultants.com> >> wrote: >> >> >On 2015-05-04 5:00 PM, John Larkin wrote: >> >> On Mon, 04 May 2015 16:47:14 -0700, Joerg <news@analogconsultants.com> >> >> wrote: >> >> >> >>> On 2015-05-04 3:17 PM, John Larkin wrote: >> >>>> >> >>>> Anybody know of a source for a small (1 amp range) PCB mount current >> >>>> transformer? Frequency will be around 400 Hz. >> >>>> >> >>>> There are switcher current sense CTs, but I don't know if they will >> >>>> work that low. >> >>>> >> >>>> Or maybe I could use a shunt and a voltage-mode (audio) transformer. >> >>>> >> >>> >> >>> How about this one? Lots of stock. >> >>> >> >>> http://www.digikey.com/product-detail/en/CSE187L/237-1103-ND/242546 >> >> >> >> 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. >> > >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. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Mon, 04 May 2015 17:28:12 -0700, Joerg <news@analogconsultants.com>
wrote:

>On 2015-05-04 5:20 PM, Joerg wrote: >> On 2015-05-04 5:00 PM, John Larkin wrote: >>> On Mon, 04 May 2015 16:47:14 -0700, Joerg <news@analogconsultants.com> >>> wrote: >>> >>>> On 2015-05-04 3:17 PM, John Larkin wrote: >>>>> >>>>> Anybody know of a source for a small (1 amp range) PCB mount current >>>>> transformer? Frequency will be around 400 Hz. >>>>> >>>>> There are switcher current sense CTs, but I don't know if they will >>>>> work that low. >>>>> >>>>> Or maybe I could use a shunt and a voltage-mode (audio) transformer. >>>>> >>>> >>>> How about this one? Lots of stock. >>>> >>>> http://www.digikey.com/product-detail/en/CSE187L/237-1103-ND/242546 >>> >>> 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. >> > >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.
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. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Mon, 04 May 2015 17:25:20 -0700, John Larkin
<jlarkin@highlandtechnology.com> Gave us:

>On Mon, 04 May 2015 17:20:14 -0700, Joerg <news@analogconsultants.com> >wrote: > >>On 2015-05-04 5:00 PM, John Larkin wrote: >>> On Mon, 04 May 2015 16:47:14 -0700, Joerg <news@analogconsultants.com> >>> wrote: >>> >>>> On 2015-05-04 3:17 PM, John Larkin wrote: >>>>> >>>>> Anybody know of a source for a small (1 amp range) PCB mount current >>>>> transformer? Frequency will be around 400 Hz. >>>>> >>>>> There are switcher current sense CTs, but I don't know if they will >>>>> work that low. >>>>> >>>>> Or maybe I could use a shunt and a voltage-mode (audio) transformer. >>>>> >>>> >>>> How about this one? Lots of stock. >>>> >>>> http://www.digikey.com/product-detail/en/CSE187L/237-1103-ND/242546 >>> >>> 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.
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
<langwadt@fonz.dk> Gave us:

> >does it need to be transformer? how about an ACS712 ? > >-Lasse > >
Damn! Looks like you beat me to it! :-)