AC power meter hookup

[goldstache]

Found this power meter.
Wanted to implement it post variac to live monitor mains conditions.


The hookup info has me puzzled.


I’m not using a current transformer (CT) for preferred outlet use.
But the diagram has me confused.


I have the output of my variac feeding V+ and V- and after changing the internal voltage referencing, was able to get accurate reading as variac scales.


But for current loading. I’m sorta confused.
20A+ and A- read .5ohm R between em.


Based on terminal block diagram.
Seems the current measurement is sensed rather than serial.
Anybody shed some light on this dim soul?
Thanks.

[shooter]

would appear that way to me.  anything in the "manual" on shunt resistor, or typical current measurements??

But for current loading. I’m sorta confused.20A+ and A- read .5ohm R between em.

guessing you ohmed it without anything connected??

[goldstache]

Thanks for the engagement on this.
Yeah seems as though these modern guys use shunt. So that explains why I got low ohms DCR across my
20A+ and A- terminals.


Ideally you’d want Rshunt in one leg of wall AC (neutral seems to be what’s depicted)


Regarding manual. That’s about all ya get. Denotes how to change shunt reference and range.


The drawing in the manual for unit, depicts outlet source/loading as being parallel???
Live to V+ and 20A+
And neutral to V- and A-
As outlet source/load.


At a loss.


In my mind, would make more “sense” to have
Output of variac (or just full wall 120vac) to
Live V+
Neutral V-


Then live to DUT outlet live.
Then I’m lost.
Neutral source to 20A+/DUT neutral terminal. And A- to same A- terminal.
Then shunt senses?

[goldstache]

I think this would sort it.
Somebody slid me this

[SEL49]

This is not complicated. Look at my simpler annotated drawing and forget about that confusing third option. You must connect the source (variac output) to pins 1 and 2 in order to supply power to operate the meter circuit. The voltage reading on the meter is also derived from pins 1 and 2. The current reading is sensed via pins 4 and 6. The top circuit puts a .5Ω resistor in series with the load and the voltage drop across this resistor represents the current flowing through the load. (Same principle as putting a 1Ω resistor on the cathode of a power tube.) Please note. You must use wire size that is capable of handling the load current to make connections to pins 4 and 6.

The second circuit uses a current sensing transformer (doughnut) to couple a small voltage to pins 4 and 6. This voltage represents the current passing through the doughnut. You simply pass the load wire through the doughnut hole so the actual load current never connects to the small delicate meter. This means you can use very small wires to connect the meter. I highly recommend using the CT method.

If you are willing to spend $16 you can get a PZEM-061 meter from Amazon. It uses a CT and a simple one wire mod will allow the meter to work over the full voltage range of your variac. Look at pages 5 and 6 of this scrapbook pdf to see the simple mod.

PS... Here's a forum discussion about adding a meter to a variac.

[goldstache]

Thanks very much.
Will update once I wire up.


RE: handling
Thanks.
16ga with spades on current, prolly won’t see over 10A peak inrush ever.

[SEL49]

16ga with spades on current, prolly won’t see over 10ma peak inrush ever.

16awg is good, but you should expect to see several amps if the load will be a 50W or 100W guitar amp.

I have assumed that you have a small digital panel meter. Is that correct? What is the model number? Do you have the CT?

[goldstache]

I have a marantz to bias. And idle spec is an AC draw figure.


I already have an Ammeter on my bench variac. Built it 20 years ago. But wanted something with digits.
It’s got its own dedicated 120vac input. Then the terminal strip will be off the variac.


I don't have the CT. Just wanted dedicated outlet for load.


Like a dummy, it was the serial connection to the "load" in the first image of that Manual.
Live to 20A+ then on to load via terminal 6.
My brain was burping trying to figure out how to put the neutral of the load into a serial through DUT connection.


Further confused by the what appears to be parallel connection of the "outlet box" diagram.
I was trying to figure out what was serial to sense the current for this thing to spit it out.


Thanks for assist. Clear to me now.