Volt amp meters

[shadylane]

The problem is you have 20% of something that isn't within a narrow tolerance.

That's what I was thinking.
One variable is the resistance of heaters.
I bought three camco 4.5kw elements, that measured 11.9 ohms, 12.9 and 13.8

Another variable is the elements resistance changes with heat.
Then there's voltage drop and powerline fluctuations.

[Steve Broady]

I bought one of these for about 15 USD
D69-2058 AC Digital Voltage and Current Power Frequency Factor Electricity Meter Multi-Function Power Monitor
https://a.aliexpress.com/_mqFtrii
The problem with a lot of these cheap meters is they use the voltage input for the power supply too. I believe the power supply circuit is what the chopped sine wave melts not the metering side. …this guy shows how to separate the voltage input from the power supply:

Inspired by this, I decided to get one and see what I could do. Opening it up, mine turned out to be even easier to modify than the one in the video.

You can see where I cut the trace just to the left of the new wire, between that and the diode.

Preliminary testing has been very basic. I connected the meter to 120V before modifying it, and it read 124V. I did the same after the modification, and it read 0.8V. Touching the voltage sense wire to the incoming wires, the meter read 124V or 0V, depending on which wire I touched. I have not yet tried it on a variable voltage supply, because I’m in the process of rebuilding my controller. But based on the video above, I anticipate that it should now be able to measure voltage well below 80V.

[elbono]

mine turned out to be even easier to kidify than the one in the video.

Most of the video's stuff is so he ends up with three screw terminals to connect wires to from the outside.

I have visions of some hackery to sniff the internal signals in there. Been on other adventures lately though.

The 0.8v is probably "phantom voltage" basically noise. I think you'll get 0 to whatever when you get it fully hooked up.

[tjsc5f]

If you don't mind a little tinkering/DIY, here's a video showing an Arduino project that would get the job done.


The amp clamp he's using is only good for up to 20Amps. Depending on your element, you may need a 30Amp clamp instead, like this one:
https://a.co/d/bVdcXnq

[Yummyrum]

I anticipate that it should now be able to measure voltage well below 80V.

Well done Steve .Any chance of some better pics .
You’ve just pulled off a successful hack on a recent module . If you can make it easy for Joe Distiller to see exactly what you have hacked , it will be very useful

If you don't mind a little tinkering/DIY, here's a video showing an Arduino project that would get the job done.


The amp clamp he's using is only good for up to 20Amps. Depending on your element, you may need a 30Amp clamp instead, like this one:
https://a.co/d/bVdcXnq

tjsc5f

Some great stuff there for the Arduino fans . Piqued my interest . Thankyou Sir .

[Steve Broady]

Well done Steve .Any chance of some better pics .

I’m afraid that all I have is what I’ve already shared. I’ve enlarged the relevant part, and marked with a red X where I cut through the trace. That and the new wire are literally the only modifications I made.

I watched the video linked earlier, and in particular I paid attention to his assessment of how the circuit works. The one I bought was not identical, but I reasoned that the circuit was probably functionally the same. I took the circuit boards out and examined them carefully, finding that it did indeed seem to have power from one terminal immediately dividing into two separate portions, with one going through a series of resistors. It was trivial to cut through the trace ahead of the first resistor on that leg, and to solder a new wire there.

I figured it was also trivial to repair the damage, if I stuffed it up. Because let’s be honest, I was just guessing!

A quick test revealed that everything still worked as expected, within my limited ability to test easily. Crucially, the unit still powered on with the new wire unconnected, so I figured I might have succeeded. Subsequent testing seems to confirm this, so I’m happy. I lack the equipment needed to test it with any real accuracy, but it does at least behave exactly as expected, and read voltages all the way down to zero now.

One word of caution. I chose to pull the wire out of the case where I did because it seemed like the simplest solution in the moment. I didn’t take into account that the whole case had to slide into a fairly tight hole in a case, which did a little damage to the insulation when I tried it. In retrospect, I should have pulled the wire either through the back of the case, or at least through the inset area where the other wires go.

I will also note that, while I didn’t show it, I covered that abysmal solder job with a generous glob of hot glue, as well as adding hot glue around the spot where the wire exited the case as a simple strain relief. If you can’t make it neat, cover up the evidence!

[Yummyrum]

Thanks Steve . I get it now .I have to admit I didn’t watch the whole You-tube that Elbono linked to as in general I loose interest in anything longer than 4-5 min .

The original hack I saw involved adding an external 5volt power supply to feed the meter and I figured that was what you did as well .

But what you dis is way more simpler and makes much more sense .
So you are connecting the Existing voltage connections to the input side of the SSVR ( simply to power the meter) and just ran an extra wire to the output side of the SSVR for voltage measurement .

[Steve Broady]

The original hack I saw involved adding an external 5volt power supply to feed the meter and I figured that was what you did as well .

But what you dis is way more simpler and makes much more sense .

I’m a cheap, lazy bastard. I figured the meter as sold has a perfectly functional power supply built in, so why add another one? Also, why go to the effort of figuring out how to do that, when I had a simple solution presented to me? I bought this meter in part because of that video, hoping the modification would be a simple one.

Let’s not talk about the fact that I bought a new meter in part because I hoped it would be easy to modify. I’m going to argue that I bought it for the wattage and kW/hr displays. Yeah, that’s the reason.

So you are connecting the Existing voltage connections to the input side of the SSVR ( simply to power the meter) and just ran an extra wire to the output side of the SSVR for voltage measurement .

Exactly. The only thing to note is that polarity is now important. The unmodified meter didn’t care about polarity since it’s AC, but now I have to be careful to have the input power and control voltage be the same side of the circuit. Simple enough. Since I run the SSR on the black (hot, in the case of 120V) wire, I just colored the two original terminals black and white. That’s why I chose to add a black wire, as well, though some other color like blue might have made a little more sense if I’d had that at the time. If you connect the voltage meter wire to the opposite side, it’ll just read zero all the time. No harm done.

[shadylane]

Thanks for taking the time to share with us.
It's folks like you that make the forum great.