AC current and volt meters

On a sunny day (Fri, 08 Jun 2007 01:18:03 GMT) it happened Steve wrote in :

For AC current use a current transformer, bridge rectifier, cap, trimmer top calibate, then your normal panel meters.

Don't forget the burden resistor. Bad things happen when that item is missing.

--
Dave M
MasonDG44 at comcast dot net  (Just substitute the appropriate characters in the 
address)

Life is like a roll of toilet paper; the closer to the end, the faster it goes.

Easy enough. By burden resistor, do you mean connect it across the output (i.e. like a load resistor) so the panel meter doesn't blow?

Thanks, Steve

"Steve"

** You are being fed *crap* advice.

Just use a low value resistor for current metering - not a stupid, expensive current transformer.

Describe your application properly - else I will not help you.

....... Phil

On a sunny day (Fri, 8 Jun 2007 20:07:47 -0400) it happened "DaveM" wrote in :

Absolutely:-) In the old place I once worked the 'burden' resistor would be a wirewound with a tap, that making up the 'trimpot', you just unscrewed the tap and moved it around.. then fixed it at that point.

On a sunny day (Sat, 9 Jun 2007 15:51:29 +1000) it happened "Phil Allison" wrote in :

That depends, if current drop is allowed, if meters are AC or DC, if voltage sense leads can be moved after the shunt, if heat is allowed, if things are still stable with a shunt (Ri supply), etc ..

Or you learn to read.

FIGHT FIGHT FIGHT :-)

"Jan Panteltje"

** Watch out, Steve

This WOG IDIOT is dishing out

really CRAP advice.

....... Phil

My application is for a power supply I'm building. Basic AC supply,

0-30v, 0-5a. I just want to monitor current and voltage using the two panel meters I already have (ICL7106 driven 3.5 digit displays). I actually have a spare current transformer, as well as shunts and low value resistors, so I don't mind playing with either of them. I just didn't know where to begin. I'll probably just start tinkering.

Thanks for the help everyone, Steve

"Steve"

** There is no such thing as a " basic AC supply ".

What on earth are you building and what the heck is it for.

YOU are not making SENSE !!

....... Phil

Ignore Phil... he's off his meds. Use Google to search for "current transformer" and "burden resistor" you'll find more than enough sites that explain the theory and math to get you going. BTW, the current transformer is the easiest way to go, assuming that the transformer has enough turns to give you an output voltage that you can easily rectify, filter and scale to your DVM input. What is the rated current of your transformer? Cheers!!

--
Dave M
MasonDG44 at comcast dot net  (Just substitute the appropriate characters in the 
address)

Life is like a roll of toilet paper; the closer to the end, the faster it goes.

"Dave MORON "

** You are one pig ignorant, stinking ASSHOLE !!!! ** Totally rediciculous advice.

Any demented a Google Monkey can do better with his eyes closed.

...... Phil

If you put the resistive load of the current transformer, mostly, after the rectifier, you can get a more accurate measurement at the cost of adding a tiny bit of distortion to the AC power line.

The output of the current transformer has quite a high impedance. It will swing very quickly past the forwards drop of the bridge.

Is your goal to measure RMS, average(abs(I)) or peak?

400Hz supply to power avionics. Sorry for being unclear. I just want to monitor voltage and current.

Actually, now that I look at it, I don't know. I bought it at the local parts shop for $.99. If I remember correctly, it may just be

200 turns of wire in a nice package. It's marked A15603-M. I may need to purchase a more definitive product.

RMS.

How about the cheap AC panel meters sold on Ebay? I just noticed them. No specs though, such as frequency range. Somehow I doubt a meter that costs $6.99 will perform the same as one that costs $80.00.

"Steve"

** So you are going with the ESP audio amp module - right ?

To monitor output current, use a a 0.022 ohm sense resistor ( ie 5 x 0.1 ohms in parallel ) in the plus or minus DC supply rail - this will pass a half wave version of the AC output current and so give you a half wave rectified voltage signal of 50 mV DC @ 5amps rms directly. The DC supply for the LCD panel meter will have to use its own transformer so it can "float" at the rail voltage.

For AC voltage, go with your original idea of using a " true rms to DC converter" IC - the cheaper AD636JH would be fine. Scale the module's output voltage by 1000:1, to give 30 mV AC input to the IC.

....... Phil

Perhaps a refresher on shunts and multipliers is in order...

AC digital panel meters starts at section 6.0 ->

On a sunny day (Sun, 10 Jun 2007 02:36:34 GMT) it happened Steve wrote in :

Or lookup a very old posting of mine:

This uses an old tape recorder playback head, and an opamp.

In fact if you find some normal E core transformer it is usually possible to slide in one extra turn for primary.

"Jan Panteltje"

** Watch out, Steve

This WOG LUNATIC is dishing out

really FUCKING CRAP advice.

....... Phil