Mains Current Sensor Idea

[Joe G \(Home\)]

Hi All,

The concept is very simple. I want to detect / measure current in a power
board and if over a certain current switch on another device.

I was thinking of using a current transformer, rectifying it and the
voltage output would be proportional to the current.

say 10mA to 500mA on a 240V AC device ...


What do you suggest.

Joe

 

[MooseFET]

Hi All,

The concept is very simple. I want to detect / measure current in a power
board and if over a certain current switch on another device.

I was thinking of using a current transformer, rectifying it and the
voltage output would be proportional to the current.

say 10mA to 500mA on a 240V AC device ...

What do you suggest.

Yes basically you have the right idea. A transformer feeding a
rectifier and loaded with a resistor will indicate the current nicely.

Don't forget the load the output side. If you don't you get a high
voltage on it and perhaps may destroy it.

I have used a 120V to 6.3V transformer as a current transformer. The
6.3V side was in series with the load and the 120V side was loaded to
make about a volt. It worked well enough for what I wanted YMMV.

 

[Nico Coesel]

Hi All,

The concept is very simple. I want to detect / measure current in a power
board and if over a certain current switch on another device.

I was thinking of using a current transformer, rectifying it and the
voltage output would be proportional to the current.

say 10mA to 500mA on a 240V AC device ...


What do you suggest.

A hall sensor over a PCB trace.

 

[Vladimir Vassilevsky]

How accurate?

An optocoupler. Two optocouplers for the increased dynamic range.

A hall sensor over a PCB trace.

Isn't 10ma too small for the Hall sensor?


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

 

[Nico Coesel]

How accurate?


An optocoupler. Two optocouplers for the increased dynamic range.


Isn't 10ma too small for the Hall sensor?

Perhaps. I thought he was talking about the secondary current in the
current transformer. I guess the OP could make a coil with multiple
windings on the PCB so the Hall sensor sees a higher field strength.

 

[mpm]

Hi All,

The concept is very simple. I want to detect / measure current in a power
board and if over a certain current switch on another device.

I was thinking of using a current transformer, �rectifying it and the
voltage output would be proportional to the current.

say 10mA to 500mA �on a 240V AC �device ...

What do you suggest.

Joe

Notice: Now slightly "Off Topic"

Is it just me, or does anyone else squirm when they hear the words
"Mains" as referred to electric service?

To me, this is never very clear whether someone means the voltage, or
the conductors themselves - and in either case, is it at the service
entrance to the building (or other), or the wall outlet, power cord,
or power terminals of the device in question.?? Or all of the above?

Seems very loosey-goosey terminology to me. Though, generally, I
guess I know what is meant - at least in the way of "don't touch it or
you might get electrocuted". But generally, not much beyond that.

Does NEC use this terminology? I know a lot of other terms used in
NEC, but I'll have to review my copy to see if there actually is a
recognized & accepted definition for "Mains".

 

[mpm]

Not to mention, why is "Mains" plural?

 

[Spehro Pefhany]

yeah, they have a reasonable selection. I wanted one RIGHT NOW, and I
got it.

I use dgikey a lot - mostly from a design-in perspective, rather than
actually purchasing components, which I prefer to do from Farnell
(quicker and I dont have to fill in any stupid "what is this for" crap).

What's that? More export controls BS? Talk about shooting yourself in
the foot..

that being said, I buy from digikey and mouser where necessary. such as,
for example, LEM DCCTs

Cheers
Terry

Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

I think its akin to the "will all terrorists please report to the
security counter for immediate arrest" announcements at airports.

just another irritating layer of hoops for us furrners to jump thru. I
always write the same thing: intended for use in a SMPS, by me.

Well, if they keep up the stupidity, a French company is going to be
making a whole stack of Euros. The US product is half the price, (and
half as good, but good enough), but the Frenchies don't try to dictate
what happens with it once it's sold by them (or by us, or by our
customer).

hao3 jiu3 mei2 jian4

Cheers
Terry

Shenme?

Motivational management term of the day:

"We're facing insurmountable opportunities".

Best regards,
Spehro Pefhany

 

[ehsjr]

Terry Given wrote:
(snip)



Have you checked, lately, for how many different current transformers
are available from Digikey? The variety has multiplied in the last year
or two.

Good to know. Last time I needed a bunch I got them
direct from Toroid Corporation of Maryland, but that's
a while back.

Ed

 

[Rich Grise]

Not to mention, why is "Mains" plural?

Two wires? ;-)

Cheers!
Rich